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Line 8 pcretest commands.
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Line 8 pcretest commands.
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PCRE(3) PCRE(3) | PCRE(3) Library Functions Manual PCRE(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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INTRODUCTION |
INTRODUCTION |
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The PCRE library is a set of functions that implement regular expres- |
The PCRE library is a set of functions that implement regular expres- |
Line 32 INTRODUCTION
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Line 32 INTRODUCTION
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either one or both to be built. The majority of the work to make this |
either one or both to be built. The majority of the work to make this |
possible was done by Zoltan Herczeg. |
possible was done by Zoltan Herczeg. |
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The two libraries contain identical sets of functions, except that the | Starting with release 8.32 it is possible to compile a third separate |
names in the 16-bit library start with pcre16_ instead of pcre_. To | PCRE library that supports 32-bit character strings (including UTF-32 |
avoid over-complication and reduce the documentation maintenance load, | strings). The build process allows any combination of the 8-, 16- and |
most of the documentation describes the 8-bit library, with the differ- | 32-bit libraries. The work to make this possible was done by Christian |
ences for the 16-bit library described separately in the pcre16 page. | Persch. |
References to functions or structures of the form pcre[16]_xxx should | |
be read as meaning "pcre_xxx when using the 8-bit library and | |
pcre16_xxx when using the 16-bit library". | |
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The three libraries contain identical sets of functions, except that |
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the names in the 16-bit library start with pcre16_ instead of pcre_, |
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and the names in the 32-bit library start with pcre32_ instead of |
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pcre_. To avoid over-complication and reduce the documentation mainte- |
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nance load, most of the documentation describes the 8-bit library, with |
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the differences for the 16-bit and 32-bit libraries described sepa- |
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rately in the pcre16 and pcre32 pages. References to functions or |
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structures of the form pcre[16|32]_xxx should be read as meaning |
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"pcre_xxx when using the 8-bit library, pcre16_xxx when using the |
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16-bit library, or pcre32_xxx when using the 32-bit library". |
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The current implementation of PCRE corresponds approximately with Perl |
The current implementation of PCRE corresponds approximately with Perl |
5.12, including support for UTF-8/16 encoded strings and Unicode gen- | 5.12, including support for UTF-8/16/32 encoded strings and Unicode |
eral category properties. However, UTF-8/16 and Unicode support has to | general category properties. However, UTF-8/16/32 and Unicode support |
be explicitly enabled; it is not the default. The Unicode tables corre- | has to be explicitly enabled; it is not the default. The Unicode tables |
spond to Unicode release 6.0.0. | correspond to Unicode release 6.3.0. |
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In addition to the Perl-compatible matching function, PCRE contains an |
In addition to the Perl-compatible matching function, PCRE contains an |
alternative function that matches the same compiled patterns in a dif- |
alternative function that matches the same compiled patterns in a dif- |
Line 73 INTRODUCTION
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Line 81 INTRODUCTION
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client to discover which features are available. The features them- |
client to discover which features are available. The features them- |
selves are described in the pcrebuild page. Documentation about build- |
selves are described in the pcrebuild page. Documentation about build- |
ing PCRE for various operating systems can be found in the README and |
ing PCRE for various operating systems can be found in the README and |
NON-UNIX-USE files in the source distribution. | NON-AUTOTOOLS_BUILD files in the source distribution. |
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The libraries contains a number of undocumented internal functions and |
The libraries contains a number of undocumented internal functions and |
data tables that are used by more than one of the exported external |
data tables that are used by more than one of the exported external |
functions, but which are not intended for use by external callers. |
functions, but which are not intended for use by external callers. |
Their names all begin with "_pcre_" or "_pcre16_", which hopefully will | Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which |
not provoke any name clashes. In some environments, it is possible to | hopefully will not provoke any name clashes. In some environments, it |
control which external symbols are exported when a shared library is | is possible to control which external symbols are exported when a |
built, and in these cases the undocumented symbols are not exported. | shared library is built, and in these cases the undocumented symbols |
| are not exported. |
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SECURITY CONSIDERATIONS |
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If you are using PCRE in a non-UTF application that permits users to |
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supply arbitrary patterns for compilation, you should be aware of a |
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feature that allows users to turn on UTF support from within a pattern, |
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provided that PCRE was built with UTF support. For example, an 8-bit |
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pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, |
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which interprets patterns and subjects as strings of UTF-8 characters |
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instead of individual 8-bit characters. This causes both the pattern |
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and any data against which it is matched to be checked for UTF-8 valid- |
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ity. If the data string is very long, such a check might use suffi- |
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ciently many resources as to cause your application to lose perfor- |
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mance. |
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One way of guarding against this possibility is to use the |
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pcre_fullinfo() function to check the compiled pattern's options for |
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UTF. Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF |
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option at compile time. This causes an compile time error if a pattern |
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contains a UTF-setting sequence. |
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If your application is one that supports UTF, be aware that validity |
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checking can take time. If the same data string is to be matched many |
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times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second |
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and subsequent matches to save redundant checks. |
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Another way that performance can be hit is by running a pattern that |
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has a very large search tree against a string that will never match. |
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Nested unlimited repeats in a pattern are a common example. PCRE pro- |
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vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea- |
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ture in the pcreapi page. |
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USER DOCUMENTATION |
USER DOCUMENTATION |
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The user documentation for PCRE comprises a number of different sec- |
The user documentation for PCRE comprises a number of different sec- |
Line 94 USER DOCUMENTATION
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Line 135 USER DOCUMENTATION
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lows: |
lows: |
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pcre this document |
pcre this document |
pcre16 details of the 16-bit library |
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pcre-config show PCRE installation configuration information |
pcre-config show PCRE installation configuration information |
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pcre16 details of the 16-bit library |
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pcre32 details of the 32-bit library |
pcreapi details of PCRE's native C API |
pcreapi details of PCRE's native C API |
pcrebuild options for building PCRE | pcrebuild building PCRE |
pcrecallout details of the callout feature |
pcrecallout details of the callout feature |
pcrecompat discussion of Perl compatibility |
pcrecompat discussion of Perl compatibility |
pcrecpp details of the C++ wrapper for the 8-bit library |
pcrecpp details of the C++ wrapper for the 8-bit library |
Line 116 USER DOCUMENTATION
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Line 158 USER DOCUMENTATION
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pcrestack discussion of stack usage |
pcrestack discussion of stack usage |
pcresyntax quick syntax reference |
pcresyntax quick syntax reference |
pcretest description of the pcretest testing command |
pcretest description of the pcretest testing command |
pcreunicode discussion of Unicode and UTF-8/16 support | pcreunicode discussion of Unicode and UTF-8/16/32 support |
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In addition, in the "man" and HTML formats, there is a short page for |
In addition, in the "man" and HTML formats, there is a short page for |
each 8-bit C library function, listing its arguments and results. | each C library function, listing its arguments and results. |
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AUTHOR |
AUTHOR |
Line 135 AUTHOR
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Line 177 AUTHOR
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REVISION |
REVISION |
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Last updated: 10 January 2012 | Last updated: 13 May 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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PCRE(3) PCRE(3) | PCRE(3) Library Functions Manual PCRE(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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Line 278 THE PCRE 16-BIT LIBRARY
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Line 321 THE PCRE 16-BIT LIBRARY
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THE HEADER FILE |
THE HEADER FILE |
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There is only one header file, pcre.h. It contains prototypes for all |
There is only one header file, pcre.h. It contains prototypes for all |
the functions in both libraries, as well as definitions of flags, | the functions in all libraries, as well as definitions of flags, struc- |
structures, error codes, etc. | tures, error codes, etc. |
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THE LIBRARY NAME |
THE LIBRARY NAME |
Line 297 STRING TYPES
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Line 340 STRING TYPES
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PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is |
PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is |
defined as "const PCRE_UCHAR16 *". In very many environments, "short |
defined as "const PCRE_UCHAR16 *". In very many environments, "short |
int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16 |
int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16 |
as "short int", but checks that it really is a 16-bit data type. If it | as "unsigned short int", but checks that it really is a 16-bit data |
is not, the build fails with an error message telling the maintainer to | type. If it is not, the build fails with an error message telling the |
modify the definition appropriately. | maintainer to modify the definition appropriately. |
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STRUCTURE TYPES |
STRUCTURE TYPES |
Line 350 STRUCTURE TYPES
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Line 393 STRUCTURE TYPES
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SUBJECT STRING OFFSETS |
SUBJECT STRING OFFSETS |
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The offsets within subject strings that are returned by the matching | The lengths and starting offsets of subject strings must be specified |
functions are in 16-bit units rather than bytes. | in 16-bit data units, and the offsets within subject strings that are |
| returned by the matching functions are in also 16-bit units rather than |
| bytes. |
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NAMED SUBPATTERNS |
NAMED SUBPATTERNS |
Line 372 OPTION NAMES
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Line 417 OPTION NAMES
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For the pcre16_config() function there is an option PCRE_CONFIG_UTF16 |
For the pcre16_config() function there is an option PCRE_CONFIG_UTF16 |
that returns 1 if UTF-16 support is configured, otherwise 0. If this |
that returns 1 if UTF-16 support is configured, otherwise 0. If this |
option is given to pcre_config(), or if the PCRE_CONFIG_UTF8 option is | option is given to pcre_config() or pcre32_config(), or if the |
given to pcre16_config(), the result is the PCRE_ERROR_BADOPTION error. | PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF32 option is given to pcre16_con- |
| fig(), the result is the PCRE_ERROR_BADOPTION error. |
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CHARACTER CODES |
CHARACTER CODES |
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In 16-bit mode, when PCRE_UTF16 is not set, character values are | In 16-bit mode, when PCRE_UTF16 is not set, character values are |
treated in the same way as in 8-bit, non UTF-8 mode, except, of course, |
treated in the same way as in 8-bit, non UTF-8 mode, except, of course, |
that they can range from 0 to 0xffff instead of 0 to 0xff. Character | that they can range from 0 to 0xffff instead of 0 to 0xff. Character |
types for characters less than 0xff can therefore be influenced by the | types for characters less than 0xff can therefore be influenced by the |
locale in the same way as before. Characters greater than 0xff have | locale in the same way as before. Characters greater than 0xff have |
only one case, and no "type" (such as letter or digit). |
only one case, and no "type" (such as letter or digit). |
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In UTF-16 mode, the character code is Unicode, in the range 0 to | In UTF-16 mode, the character code is Unicode, in the range 0 to |
0x10ffff, with the exception of values in the range 0xd800 to 0xdfff | 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff |
because those are "surrogate" values that are used in pairs to encode | because those are "surrogate" values that are used in pairs to encode |
values greater than 0xffff. |
values greater than 0xffff. |
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A UTF-16 string can indicate its endianness by special code knows as a | A UTF-16 string can indicate its endianness by special code knows as a |
byte-order mark (BOM). The PCRE functions do not handle this, expecting |
byte-order mark (BOM). The PCRE functions do not handle this, expecting |
strings to be in host byte order. A utility function called | strings to be in host byte order. A utility function called |
pcre16_utf16_to_host_byte_order() is provided to help with this (see | pcre16_utf16_to_host_byte_order() is provided to help with this (see |
above). |
above). |
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ERROR NAMES |
ERROR NAMES |
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The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre- | The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre- |
spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is | spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is |
given when a compiled pattern is passed to a function that processes | given when a compiled pattern is passed to a function that processes |
patterns in the other mode, for example, if a pattern compiled with | patterns in the other mode, for example, if a pattern compiled with |
pcre_compile() is passed to pcre16_exec(). |
pcre_compile() is passed to pcre16_exec(). |
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There are new error codes whose names begin with PCRE_UTF16_ERR for | There are new error codes whose names begin with PCRE_UTF16_ERR for |
invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for | invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for |
UTF-8 strings that are described in the section entitled "Reason codes | UTF-8 strings that are described in the section entitled "Reason codes |
for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors | for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors |
are: |
are: |
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PCRE_UTF16_ERR1 Missing low surrogate at end of string |
PCRE_UTF16_ERR1 Missing low surrogate at end of string |
PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate |
PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate |
PCRE_UTF16_ERR3 Isolated low surrogate |
PCRE_UTF16_ERR3 Isolated low surrogate |
PCRE_UTF16_ERR4 Invalid character 0xfffe | PCRE_UTF16_ERR4 Non-character |
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ERROR TEXTS |
ERROR TEXTS |
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If there is an error while compiling a pattern, the error text that is | If there is an error while compiling a pattern, the error text that is |
passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit | passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit |
character string, zero-terminated. |
character string, zero-terminated. |
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CALLOUTS |
CALLOUTS |
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The subject and mark fields in the callout block that is passed to a | The subject and mark fields in the callout block that is passed to a |
callout function point to 16-bit vectors. |
callout function point to 16-bit vectors. |
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TESTING |
TESTING |
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The pcretest program continues to operate with 8-bit input and output | The pcretest program continues to operate with 8-bit input and output |
files, but it can be used for testing the 16-bit library. If it is run | files, but it can be used for testing the 16-bit library. If it is run |
with the command line option -16, patterns and subject strings are con- |
with the command line option -16, patterns and subject strings are con- |
verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit |
verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit |
library functions are used instead of the 8-bit ones. Returned 16-bit | library functions are used instead of the 8-bit ones. Returned 16-bit |
strings are converted to 8-bit for output. If the 8-bit library was not | strings are converted to 8-bit for output. If both the 8-bit and the |
compiled, pcretest defaults to 16-bit and the -16 option is ignored. | 32-bit libraries were not compiled, pcretest defaults to 16-bit and the |
| -16 option is ignored. |
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When PCRE is being built, the RunTest script that is called by "make |
When PCRE is being built, the RunTest script that is called by "make |
check" uses the pcretest -C option to discover which of the 8-bit and | check" uses the pcretest -C option to discover which of the 8-bit, |
16-bit libraries has been built, and runs the tests appropriately. | 16-bit and 32-bit libraries has been built, and runs the tests appro- |
| priately. |
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NOT SUPPORTED IN 16-BIT MODE |
NOT SUPPORTED IN 16-BIT MODE |
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Not all the features of the 8-bit library are available with the 16-bit |
Not all the features of the 8-bit library are available with the 16-bit |
library. The C++ and POSIX wrapper functions support only the 8-bit | library. The C++ and POSIX wrapper functions support only the 8-bit |
library, and the pcregrep program is at present 8-bit only. |
library, and the pcregrep program is at present 8-bit only. |
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Line 461 AUTHOR
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Line 509 AUTHOR
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REVISION |
REVISION |
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Last updated: 14 April 2012 | Last updated: 12 May 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
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PCREBUILD(3) PCREBUILD(3) | PCRE(3) Library Functions Manual PCRE(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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#include <pcre.h> |
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PCRE 32-BIT API BASIC FUNCTIONS |
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pcre32 *pcre32_compile(PCRE_SPTR32 pattern, int options, |
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const char **errptr, int *erroffset, |
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const unsigned char *tableptr); |
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pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options, |
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int *errorcodeptr, |
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const unsigned char *tableptr); |
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pcre32_extra *pcre32_study(const pcre32 *code, int options, |
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const char **errptr); |
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void pcre32_free_study(pcre32_extra *extra); |
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int pcre32_exec(const pcre32 *code, const pcre32_extra *extra, |
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PCRE_SPTR32 subject, int length, int startoffset, |
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int options, int *ovector, int ovecsize); |
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int pcre32_dfa_exec(const pcre32 *code, const pcre32_extra *extra, |
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PCRE_SPTR32 subject, int length, int startoffset, |
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int options, int *ovector, int ovecsize, |
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int *workspace, int wscount); |
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PCRE 32-BIT API STRING EXTRACTION FUNCTIONS |
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int pcre32_copy_named_substring(const pcre32 *code, |
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PCRE_SPTR32 subject, int *ovector, |
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int stringcount, PCRE_SPTR32 stringname, |
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PCRE_UCHAR32 *buffer, int buffersize); |
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int pcre32_copy_substring(PCRE_SPTR32 subject, int *ovector, |
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int stringcount, int stringnumber, PCRE_UCHAR32 *buffer, |
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int buffersize); |
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int pcre32_get_named_substring(const pcre32 *code, |
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PCRE_SPTR32 subject, int *ovector, |
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int stringcount, PCRE_SPTR32 stringname, |
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PCRE_SPTR32 *stringptr); |
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int pcre32_get_stringnumber(const pcre32 *code, |
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PCRE_SPTR32 name); |
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int pcre32_get_stringtable_entries(const pcre32 *code, |
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PCRE_SPTR32 name, PCRE_UCHAR32 **first, PCRE_UCHAR32 **last); |
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int pcre32_get_substring(PCRE_SPTR32 subject, int *ovector, |
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int stringcount, int stringnumber, |
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PCRE_SPTR32 *stringptr); |
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int pcre32_get_substring_list(PCRE_SPTR32 subject, |
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int *ovector, int stringcount, PCRE_SPTR32 **listptr); |
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void pcre32_free_substring(PCRE_SPTR32 stringptr); |
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void pcre32_free_substring_list(PCRE_SPTR32 *stringptr); |
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PCRE 32-BIT API AUXILIARY FUNCTIONS |
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pcre32_jit_stack *pcre32_jit_stack_alloc(int startsize, int maxsize); |
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void pcre32_jit_stack_free(pcre32_jit_stack *stack); |
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void pcre32_assign_jit_stack(pcre32_extra *extra, |
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pcre32_jit_callback callback, void *data); |
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const unsigned char *pcre32_maketables(void); |
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int pcre32_fullinfo(const pcre32 *code, const pcre32_extra *extra, |
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int what, void *where); |
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int pcre32_refcount(pcre32 *code, int adjust); |
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int pcre32_config(int what, void *where); |
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const char *pcre32_version(void); |
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int pcre32_pattern_to_host_byte_order(pcre32 *code, |
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pcre32_extra *extra, const unsigned char *tables); |
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PCRE 32-BIT API INDIRECTED FUNCTIONS |
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void *(*pcre32_malloc)(size_t); |
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void (*pcre32_free)(void *); |
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void *(*pcre32_stack_malloc)(size_t); |
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void (*pcre32_stack_free)(void *); |
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int (*pcre32_callout)(pcre32_callout_block *); |
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PCRE 32-BIT API 32-BIT-ONLY FUNCTION |
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int pcre32_utf32_to_host_byte_order(PCRE_UCHAR32 *output, |
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PCRE_SPTR32 input, int length, int *byte_order, |
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int keep_boms); |
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THE PCRE 32-BIT LIBRARY |
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Starting with release 8.32, it is possible to compile a PCRE library |
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that supports 32-bit character strings, including UTF-32 strings, as |
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well as or instead of the original 8-bit library. This work was done by |
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Christian Persch, based on the work done by Zoltan Herczeg for the |
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16-bit library. All three libraries contain identical sets of func- |
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tions, used in exactly the same way. Only the names of the functions |
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and the data types of their arguments and results are different. To |
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avoid over-complication and reduce the documentation maintenance load, |
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most of the PCRE documentation describes the 8-bit library, with only |
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occasional references to the 16-bit and 32-bit libraries. This page |
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describes what is different when you use the 32-bit library. |
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WARNING: A single application can be linked with all or any of the |
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three libraries, but you must take care when processing any particular |
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pattern to use functions from just one library. For example, if you |
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want to study a pattern that was compiled with pcre32_compile(), you |
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must do so with pcre32_study(), not pcre_study(), and you must free the |
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study data with pcre32_free_study(). |
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THE HEADER FILE |
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There is only one header file, pcre.h. It contains prototypes for all |
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the functions in all libraries, as well as definitions of flags, struc- |
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tures, error codes, etc. |
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THE LIBRARY NAME |
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In Unix-like systems, the 32-bit library is called libpcre32, and can |
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normally be accesss by adding -lpcre32 to the command for linking an |
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application that uses PCRE. |
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STRING TYPES |
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In the 8-bit library, strings are passed to PCRE library functions as |
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vectors of bytes with the C type "char *". In the 32-bit library, |
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strings are passed as vectors of unsigned 32-bit quantities. The macro |
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PCRE_UCHAR32 specifies an appropriate data type, and PCRE_SPTR32 is |
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defined as "const PCRE_UCHAR32 *". In very many environments, "unsigned |
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int" is a 32-bit data type. When PCRE is built, it defines PCRE_UCHAR32 |
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as "unsigned int", but checks that it really is a 32-bit data type. If |
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it is not, the build fails with an error message telling the maintainer |
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to modify the definition appropriately. |
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STRUCTURE TYPES |
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The types of the opaque structures that are used for compiled 32-bit |
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patterns and JIT stacks are pcre32 and pcre32_jit_stack respectively. |
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The type of the user-accessible structure that is returned by |
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pcre32_study() is pcre32_extra, and the type of the structure that is |
|
used for passing data to a callout function is pcre32_callout_block. |
|
These structures contain the same fields, with the same names, as their |
|
8-bit counterparts. The only difference is that pointers to character |
|
strings are 32-bit instead of 8-bit types. |
|
|
|
|
|
32-BIT FUNCTIONS |
|
|
|
For every function in the 8-bit library there is a corresponding func- |
|
tion in the 32-bit library with a name that starts with pcre32_ instead |
|
of pcre_. The prototypes are listed above. In addition, there is one |
|
extra function, pcre32_utf32_to_host_byte_order(). This is a utility |
|
function that converts a UTF-32 character string to host byte order if |
|
necessary. The other 32-bit functions expect the strings they are |
|
passed to be in host byte order. |
|
|
|
The input and output arguments of pcre32_utf32_to_host_byte_order() may |
|
point to the same address, that is, conversion in place is supported. |
|
The output buffer must be at least as long as the input. |
|
|
|
The length argument specifies the number of 32-bit data units in the |
|
input string; a negative value specifies a zero-terminated string. |
|
|
|
If byte_order is NULL, it is assumed that the string starts off in host |
|
byte order. This may be changed by byte-order marks (BOMs) anywhere in |
|
the string (commonly as the first character). |
|
|
|
If byte_order is not NULL, a non-zero value of the integer to which it |
|
points means that the input starts off in host byte order, otherwise |
|
the opposite order is assumed. Again, BOMs in the string can change |
|
this. The final byte order is passed back at the end of processing. |
|
|
|
If keep_boms is not zero, byte-order mark characters (0xfeff) are |
|
copied into the output string. Otherwise they are discarded. |
|
|
|
The result of the function is the number of 32-bit units placed into |
|
the output buffer, including the zero terminator if the string was |
|
zero-terminated. |
|
|
|
|
|
SUBJECT STRING OFFSETS |
|
|
|
The lengths and starting offsets of subject strings must be specified |
|
in 32-bit data units, and the offsets within subject strings that are |
|
returned by the matching functions are in also 32-bit units rather than |
|
bytes. |
|
|
|
|
|
NAMED SUBPATTERNS |
|
|
|
The name-to-number translation table that is maintained for named sub- |
|
patterns uses 32-bit characters. The pcre32_get_stringtable_entries() |
|
function returns the length of each entry in the table as the number of |
|
32-bit data units. |
|
|
|
|
|
OPTION NAMES |
|
|
|
There are two new general option names, PCRE_UTF32 and |
|
PCRE_NO_UTF32_CHECK, which correspond to PCRE_UTF8 and |
|
PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options |
|
define the same bits in the options word. There is a discussion about |
|
the validity of UTF-32 strings in the pcreunicode page. |
|
|
|
For the pcre32_config() function there is an option PCRE_CONFIG_UTF32 |
|
that returns 1 if UTF-32 support is configured, otherwise 0. If this |
|
option is given to pcre_config() or pcre16_config(), or if the |
|
PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF16 option is given to pcre32_con- |
|
fig(), the result is the PCRE_ERROR_BADOPTION error. |
|
|
|
|
|
CHARACTER CODES |
|
|
|
In 32-bit mode, when PCRE_UTF32 is not set, character values are |
|
treated in the same way as in 8-bit, non UTF-8 mode, except, of course, |
|
that they can range from 0 to 0x7fffffff instead of 0 to 0xff. Charac- |
|
ter types for characters less than 0xff can therefore be influenced by |
|
the locale in the same way as before. Characters greater than 0xff |
|
have only one case, and no "type" (such as letter or digit). |
|
|
|
In UTF-32 mode, the character code is Unicode, in the range 0 to |
|
0x10ffff, with the exception of values in the range 0xd800 to 0xdfff |
|
because those are "surrogate" values that are ill-formed in UTF-32. |
|
|
|
A UTF-32 string can indicate its endianness by special code knows as a |
|
byte-order mark (BOM). The PCRE functions do not handle this, expecting |
|
strings to be in host byte order. A utility function called |
|
pcre32_utf32_to_host_byte_order() is provided to help with this (see |
|
above). |
|
|
|
|
|
ERROR NAMES |
|
|
|
The error PCRE_ERROR_BADUTF32 corresponds to its 8-bit counterpart. |
|
The error PCRE_ERROR_BADMODE is given when a compiled pattern is passed |
|
to a function that processes patterns in the other mode, for example, |
|
if a pattern compiled with pcre_compile() is passed to pcre32_exec(). |
|
|
|
There are new error codes whose names begin with PCRE_UTF32_ERR for |
|
invalid UTF-32 strings, corresponding to the PCRE_UTF8_ERR codes for |
|
UTF-8 strings that are described in the section entitled "Reason codes |
|
for invalid UTF-8 strings" in the main pcreapi page. The UTF-32 errors |
|
are: |
|
|
|
PCRE_UTF32_ERR1 Surrogate character (range from 0xd800 to 0xdfff) |
|
PCRE_UTF32_ERR2 Non-character |
|
PCRE_UTF32_ERR3 Character > 0x10ffff |
|
|
|
|
|
ERROR TEXTS |
|
|
|
If there is an error while compiling a pattern, the error text that is |
|
passed back by pcre32_compile() or pcre32_compile2() is still an 8-bit |
|
character string, zero-terminated. |
|
|
|
|
|
CALLOUTS |
|
|
|
The subject and mark fields in the callout block that is passed to a |
|
callout function point to 32-bit vectors. |
|
|
|
|
|
TESTING |
|
|
|
The pcretest program continues to operate with 8-bit input and output |
|
files, but it can be used for testing the 32-bit library. If it is run |
|
with the command line option -32, patterns and subject strings are con- |
|
verted from 8-bit to 32-bit before being passed to PCRE, and the 32-bit |
|
library functions are used instead of the 8-bit ones. Returned 32-bit |
|
strings are converted to 8-bit for output. If both the 8-bit and the |
|
16-bit libraries were not compiled, pcretest defaults to 32-bit and the |
|
-32 option is ignored. |
|
|
|
When PCRE is being built, the RunTest script that is called by "make |
|
check" uses the pcretest -C option to discover which of the 8-bit, |
|
16-bit and 32-bit libraries has been built, and runs the tests appro- |
|
priately. |
|
|
|
|
|
NOT SUPPORTED IN 32-BIT MODE |
|
|
|
Not all the features of the 8-bit library are available with the 32-bit |
|
library. The C++ and POSIX wrapper functions support only the 8-bit |
|
library, and the pcregrep program is at present 8-bit only. |
|
|
|
|
|
AUTHOR |
|
|
|
Philip Hazel |
|
University Computing Service |
|
Cambridge CB2 3QH, England. |
|
|
|
|
|
REVISION |
|
|
|
Last updated: 12 May 2013 |
|
Copyright (c) 1997-2013 University of Cambridge. |
|
------------------------------------------------------------------------------ |
|
|
|
|
|
PCREBUILD(3) Library Functions Manual PCREBUILD(3) |
|
|
|
|
|
|
|
NAME |
|
PCRE - Perl-compatible regular expressions |
|
|
|
BUILDING PCRE |
|
|
|
PCRE is distributed with a configure script that can be used to build |
|
the library in Unix-like environments using the applications known as |
|
Autotools. Also in the distribution are files to support building |
|
using CMake instead of configure. The text file README contains general |
|
information about building with Autotools (some of which is repeated |
|
below), and also has some comments about building on various operating |
|
systems. There is a lot more information about building PCRE without |
|
using Autotools (including information about using CMake and building |
|
"by hand") in the text file called NON-AUTOTOOLS-BUILD. You should |
|
consult this file as well as the README file if you are building in a |
|
non-Unix-like environment. |
|
|
|
|
PCRE BUILD-TIME OPTIONS |
PCRE BUILD-TIME OPTIONS |
|
|
This document describes the optional features of PCRE that can be | The rest of this document describes the optional features of PCRE that |
selected when the library is compiled. It assumes use of the configure | can be selected when the library is compiled. It assumes use of the |
script, where the optional features are selected or deselected by pro- | configure script, where the optional features are selected or dese- |
viding options to configure before running the make command. However, | lected by providing options to configure before running the make com- |
the same options can be selected in both Unix-like and non-Unix-like | mand. However, the same options can be selected in both Unix-like and |
environments using the GUI facility of cmake-gui if you are using CMake | non-Unix-like environments using the GUI facility of cmake-gui if you |
instead of configure to build PCRE. | are using CMake instead of configure to build PCRE. |
|
|
There is a lot more information about building PCRE in non-Unix-like | If you are not using Autotools or CMake, option selection can be done |
environments in the file called NON_UNIX_USE, which is part of the PCRE | by editing the config.h file, or by passing parameter settings to the |
distribution. You should consult this file as well as the README file | compiler, as described in NON-AUTOTOOLS-BUILD. |
if you are building in a non-Unix-like environment. | |
|
|
The complete list of options for configure (which includes the standard |
The complete list of options for configure (which includes the standard |
ones such as the selection of the installation directory) can be | ones such as the selection of the installation directory) can be |
obtained by running |
obtained by running |
|
|
./configure --help |
./configure --help |
|
|
The following sections include descriptions of options whose names | The following sections include descriptions of options whos The following sections include descriptions of options whos |
begin with --enable or --disable. These settings specify changes to the |
begin with --enable or --disable. These settings specify changes to the |
defaults for the configure command. Because of the way that configure | defaults for the configure command. Because of the way that configure |
works, --enable and --disable always come in pairs, so the complemen- | works, --enable and --disable always come in pairs, so the complemen- |
tary option always exists as well, but as it specifies the default, it | tary option always exists as well, but as it specifies the default, it |
is not described. |
is not described. |
|
|
|
|
BUILDING 8-BIT and 16-BIT LIBRARIES | BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES |
|
|
By default, a library called libpcre is built, containing functions | By default, a library called libpcre is built, containing functions |
that take string arguments contained in vectors of bytes, either as | that take string arguments contained in vectors of bytes, either as |
single-byte characters, or interpreted as UTF-8 strings. You can also | single-byte characters, or interpreted as UTF-8 strings. You can also |
build a separate library, called libpcre16, in which strings are con- | build a separate library, called libpcre16, in which strings are con- |
tained in vectors of 16-bit data units and interpreted either as sin- | tained in vectors of 16-bit data units and interpreted either as sin- |
gle-unit characters or UTF-16 strings, by adding |
gle-unit characters or UTF-16 strings, by adding |
|
|
--enable-pcre16 |
--enable-pcre16 |
|
|
|
to the configure command. You can also build yet another separate |
|
library, called libpcre32, in which strings are contained in vectors of |
|
32-bit data units and interpreted either as single-unit characters or |
|
UTF-32 strings, by adding |
|
|
|
--enable-pcre32 |
|
|
to the configure command. If you do not want the 8-bit library, add |
to the configure command. If you do not want the 8-bit library, add |
|
|
--disable-pcre8 |
--disable-pcre8 |
|
|
as well. At least one of the two libraries must be built. Note that the | as well. At least one of the three libraries must be built. Note that |
C++ and POSIX wrappers are for the 8-bit library only, and that pcre- | the C++ and POSIX wrappers are for the 8-bit library only, and that |
grep is an 8-bit program. None of these are built if you select only | pcregrep is an 8-bit program. None of these are built if you select |
the 16-bit library. | only the 16-bit or 32-bit libraries. |
|
|
|
|
BUILDING SHARED AND STATIC LIBRARIES |
BUILDING SHARED AND STATIC LIBRARIES |
|
|
The PCRE building process uses libtool to build both shared and static | The Autotools PCRE building process uses libtool to build both shared |
Unix libraries by default. You can suppress one of these by adding one | and static libraries by default. You can suppress one of these by |
of | adding one of |
|
|
--disable-shared |
--disable-shared |
--disable-static |
--disable-static |
Line 547 C++ SUPPORT
|
Line 944 C++ SUPPORT
|
to the configure command. |
to the configure command. |
|
|
|
|
UTF-8 and UTF-16 SUPPORT | UTF-8, UTF-16 AND UTF-32 SUPPORT |
|
|
To build PCRE with support for UTF Unicode character strings, add |
To build PCRE with support for UTF Unicode character strings, add |
|
|
--enable-utf |
--enable-utf |
|
|
to the configure command. This setting applies to both libraries, | to the configure command. This setting applies to all three libraries, |
adding support for UTF-8 to the 8-bit library and support for UTF-16 to | adding support for UTF-8 to the 8-bit library, support for UTF-16 to |
the 16-bit library. There are no separate options for enabling UTF-8 | the 16-bit library, and support for UTF-32 to the to the 32-bit |
and UTF-16 independently because that would allow ridiculous settings | library. There are no separate options for enabling UTF-8, UTF-16 and |
such as requesting UTF-16 support while building only the 8-bit | UTF-32 independently because that would allow ridiculous settings such |
library. It is not possible to build one library with UTF support and | as requesting UTF-16 support while building only the 8-bit library. It |
the other without in the same configuration. (For backwards compatibil- | is not possible to build one library with UTF support and another with- |
ity, --enable-utf8 is a synonym of --enable-utf.) | out in the same configuration. (For backwards compatibility, --enable- |
| utf8 is a synonym of --enable-utf.) |
|
|
Of itself, this setting does not make PCRE treat strings as UTF-8 or | Of itself, this setting does not make PCRE treat strings as UTF-8, |
UTF-16. As well as compiling PCRE with this option, you also have have | UTF-16 or UTF-32. As well as compiling PCRE with this option, you also |
to set the PCRE_UTF8 or PCRE_UTF16 option when you call one of the pat- | have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as |
tern compiling functions. | appropriate) when you call one of the pattern compiling functions. |
|
|
If you set --enable-utf when compiling in an EBCDIC environment, PCRE | If you set --enable-utf when compiling in an EBCDIC environment, PCRE |
expects its input to be either ASCII or UTF-8 (depending on the run- | expects its input to be either ASCII or UTF-8 (depending on the run- |
time option). It is not possible to support both EBCDIC and UTF-8 codes |
time option). It is not possible to support both EBCDIC and UTF-8 codes |
in the same version of the library. Consequently, --enable-utf and | in the same version of the library. Consequently, --enable-utf and |
--enable-ebcdic are mutually exclusive. |
--enable-ebcdic are mutually exclusive. |
|
|
|
|
UNICODE CHARACTER PROPERTY SUPPORT |
UNICODE CHARACTER PROPERTY SUPPORT |
|
|
UTF support allows the libraries to process character codepoints up to | UTF support allows the libraries to process character codepoints up to |
0x10ffff in the strings that they handle. On its own, however, it does | 0x10ffff in the strings that they handle. On its own, however, it does |
not provide any facilities for accessing the properties of such charac- |
not provide any facilities for accessing the properties of such charac- |
ters. If you want to be able to use the pattern escapes \P, \p, and \X, |
ters. If you want to be able to use the pattern escapes \P, \p, and \X, |
which refer to Unicode character properties, you must add |
which refer to Unicode character properties, you must add |
|
|
--enable-unicode-properties |
--enable-unicode-properties |
|
|
to the configure command. This implies UTF support, even if you have | to the configu to the configure command. This implies UTF support, even if you have |
not explicitly requested it. |
not explicitly requested it. |
|
|
Including Unicode property support adds around 30K of tables to the | Including Unicode property support adds around 30K of tables to the |
PCRE library. Only the general category properties such as Lu and Nd | PCRE library. Only the general category properties such as Lu and Nd |
are supported. Details are given in the pcrepattern documentation. |
are supported. Details are given in the pcrepattern documentation. |
|
|
|
|
Line 598 JUST-IN-TIME COMPILER SUPPORT
|
Line 996 JUST-IN-TIME COMPILER SUPPORT
|
|
|
--enable-jit |
--enable-jit |
|
|
This support is available only for certain hardware architectures. If | This support is available only for certain hardware architectures. If |
this option is set for an unsupported architecture, a compile time | this option is set for an unsupported architecture, a compile time |
error occurs. See the pcrejit documentation for a discussion of JIT | error occurs. See the pcrejit documentation for a discussion of JIT |
usage. When JIT support is enabled, pcregrep automatically makes use of |
usage. When JIT support is enabled, pcregrep automatically makes use of |
it, unless you add |
it, unless you add |
|
|
Line 611 JUST-IN-TIME COMPILER SUPPORT
|
Line 1009 JUST-IN-TIME COMPILER SUPPORT
|
|
|
CODE VALUE OF NEWLINE |
CODE VALUE OF NEWLINE |
|
|
By default, PCRE interprets the linefeed (LF) character as indicating | By default, PCRE interprets the linefeed (LF) character as indicating |
the end of a line. This is the normal newline character on Unix-like | the end of a line. This is the normal newline character on Unix-like |
systems. You can compile PCRE to use carriage return (CR) instead, by | systems. You can compile PCRE to use carriage return (CR) instead, by |
adding |
adding |
|
|
--enable-newline-is-cr |
--enable-newline-is-cr |
|
|
to the configure command. There is also a --enable-newline-is-lf | to the configure command. There is also a --enable-newline-is-lf |
option, which explicitly specifies linefeed as the newline character. |
option, which explicitly specifies linefeed as the newline character. |
|
|
Alternatively, you can specify that line endings are to be indicated by |
Alternatively, you can specify that line endings are to be indicated by |
Line 630 CODE VALUE OF NEWLINE
|
Line 1028 CODE VALUE OF NEWLINE
|
|
|
--enable-newline-is-anycrlf |
--enable-newline-is-anycrlf |
|
|
which causes PCRE to recognize any of the three sequences CR, LF, or | which causes PCRE to recognize any of the three sequences CR, LF, or |
CRLF as indicating a line ending. Finally, a fifth option, specified by |
CRLF as indicating a line ending. Finally, a fifth option, specified by |
|
|
--enable-newline-is-any |
--enable-newline-is-any |
|
|
causes PCRE to recognize any Unicode newline sequence. |
causes PCRE to recognize any Unicode newline sequence. |
|
|
Whatever line ending convention is selected when PCRE is built can be | Whatever line ending convention is selected when PCRE is built can be |
overridden when the library functions are called. At build time it is | overridden when the library functions are called. At build time it is |
conventional to use the standard for your operating system. |
conventional to use the standard for your operating system. |
|
|
|
|
WHAT \R MATCHES |
WHAT \R MATCHES |
|
|
By default, the sequence \R in a pattern matches any Unicode newline | By default, the sequence \R in a pattern matches any Unicode newline |
sequence, whatever has been selected as the line ending sequence. If | sequence, whatever has been selected as the line ending sequence. If |
you specify |
you specify |
|
|
--enable-bsr-anycrlf |
--enable-bsr-anycrlf |
|
|
the default is changed so that \R matches only CR, LF, or CRLF. What- | the default is changed so that \R matches only CR, LF, or CRLF. What- |
ever is selected when PCRE is built can be overridden when the library | ever is selected when PCRE is built can be overridden when the library |
functions are called. |
functions are called. |
|
|
|
|
POSIX MALLOC USAGE |
POSIX MALLOC USAGE |
|
|
When the 8-bit library is called through the POSIX interface (see the | When the 8-bit library is called through the POSIX interface (see the |
pcreposix documentation), additional working storage is required for | pcreposix documentation), additional working storage is required for |
holding the pointers to capturing substrings, because PCRE requires | holding the pointers to capturing substrings, because PCRE requires |
three integers per substring, whereas the POSIX interface provides only |
three integers per substring, whereas the POSIX interface provides only |
two. If the number of expected substrings is small, the wrapper func- | two. If the number of expected substrings is small, the wrapper func- |
tion uses space on the stack, because this is faster than using mal- | tion uses space on the stack, because this is faster than using mal- |
loc() for each call. The default threshold above which the stack is no | loc() for each call. The default threshold above which the stack is no |
longer used is 10; it can be changed by adding a setting such as |
longer used is 10; it can be changed by adding a setting such as |
|
|
--with-posix-malloc-threshold=20 |
--with-posix-malloc-threshold=20 |
Line 673 POSIX MALLOC USAGE
|
Line 1071 POSIX MALLOC USAGE
|
|
|
HANDLING VERY LARGE PATTERNS |
HANDLING VERY LARGE PATTERNS |
|
|
Within a compiled pattern, offset values are used to point from one | Within a compiled pattern, offset values are used to point from one |
part to another (for example, from an opening parenthesis to an alter- | part to another (for example, from an opening parenthesis to an alter- |
nation metacharacter). By default, two-byte values are used for these | nation metacharacter). By default, in the 8-bit and 16-bit libraries, |
offsets, leading to a maximum size for a compiled pattern of around | two-byte values are used for these offsets, leading to a maximum size |
64K. This is sufficient to handle all but the most gigantic patterns. | for a compiled pattern of around 64K. This is sufficient to handle all |
Nevertheless, some people do want to process truly enormous patterns, | but the most gigantic patterns. Nevertheless, some people do want to |
so it is possible to compile PCRE to use three-byte or four-byte off- | process truly enormous patterns, so it is possible to compile PCRE to |
sets by adding a setting such as | use three-byte or four-byte offsets by adding a setting such as |
|
|
--with-link-size=3 |
--with-link-size=3 |
|
|
to the configure command. The value given must be 2, 3, or 4. For the | to the configure command. The value given must be 2, 3, or 4. For the |
16-bit library, a value of 3 is rounded up to 4. Using longer offsets | 16-bit library, a value of 3 is rounded up to 4. In these libraries, |
slows down the operation of PCRE because it has to load additional data | using longer offsets slows down the operation of PCRE because it has to |
when handling them. | load additional data when handling them. For the 32-bit library the |
| value is always 4 and cannot be overridden; the value of --with-link- |
| size is ignored. |
|
|
|
|
AVOIDING EXCESSIVE STACK USAGE |
AVOIDING EXCESSIVE STACK USAGE |
|
|
When matching with the pcre_exec() function, PCRE implements backtrack- |
When matching with the pcre_exec() function, PCRE implements backtrack- |
ing by making recursive calls to an internal function called match(). | ing by making recursive calls to an internal function called match(). |
In environments where the size of the stack is limited, this can se- | In environments where the size of the stack is limited, this can se- |
verely limit PCRE's operation. (The Unix environment does not usually | verely limit PCRE's operation. (The Unix environment does not usually |
suffer from this problem, but it may sometimes be necessary to increase |
suffer from this problem, but it may sometimes be necessary to increase |
the maximum stack size. There is a discussion in the pcrestack docu- | the maximum stack size. There is a discussion in the pcrestack docu- |
mentation.) An alternative approach to recursion that uses memory from | mentation.) An alternative approach to recursion that uses memory from |
the heap to remember data, instead of using recursive function calls, | the heap to remember data, instead of using recursive function calls, |
has been implemented to work round the problem of limited stack size. | has been implemented to work round the problem of limited stack size. |
If you want to build a version of PCRE that works this way, add |
If you want to build a version of PCRE that works this way, add |
|
|
--disable-stack-for-recursion |
--disable-stack-for-recursion |
|
|
to the configure command. With this configuration, PCRE will use the | to the configure command. With this configuration, PCRE will use the |
pcre_stack_malloc and pcre_stack_free variables to call memory manage- | pcre_stack_malloc and pcre_stack_free variables to call memory manage- |
ment functions. By default these point to malloc() and free(), but you | ment functions. By default these point to malloc() and free(), but you |
can replace the pointers so that your own functions are used instead. |
can replace the pointers so that your own functions are used instead. |
|
|
Separate functions are provided rather than using pcre_malloc and | Separate functions are provided rather than using pcre_malloc and |
pcre_free because the usage is very predictable: the block sizes | pcre_free because the usage is very predictable: the block sizes |
requested are always the same, and the blocks are always freed in | requested are always the same, and the blocks are always freed in |
reverse order. A calling program might be able to implement optimized | reverse order. A calling program might be able to implement optimized |
functions that perform better than malloc() and free(). PCRE runs | functions that perform better than malloc() and free(). PCRE runs |
noticeably more slowly when built in this way. This option affects only |
noticeably more slowly when built in this way. This option affects only |
the pcre_exec() function; it is not relevant for pcre_dfa_exec(). |
the pcre_exec() function; it is not relevant for pcre_dfa_exec(). |
|
|
|
|
LIMITING PCRE RESOURCE USAGE |
LIMITING PCRE RESOURCE USAGE |
|
|
Internally, PCRE has a function called match(), which it calls repeat- | Internally, PCRE has a function called match(), which it calls repeat- |
edly (sometimes recursively) when matching a pattern with the | edly (sometimes recursively) when matching a pattern with the |
pcre_exec() function. By controlling the maximum number of times this | pcre_exec() function. By controlling the maximum number of times this |
function may be called during a single matching operation, a limit can | function may be called during a single matching operation, a limit can |
be placed on the resources used by a single call to pcre_exec(). The | be placed on the resources used by a single call to pcre_exec(). The |
limit can be changed at run time, as described in the pcreapi documen- | limit can be changed at run time, as described in the pcreapi documen- |
tation. The default is 10 million, but this can be changed by adding a | tation. The default is 10 million, but this can be changed by adding a |
setting such as |
setting such as |
|
|
--with-match-limit=500000 |
--with-match-limit=500000 |
|
|
to the configure command. This setting has no effect on the | to the configure command. This setting has no effect on the |
pcre_dfa_exec() matching function. |
pcre_dfa_exec() matching function. |
|
|
In some environments it is desirable to limit the depth of recursive | In some environments it is desirable to limit In some environments it is desirable to limit the depth of recursive |
calls of match() more strictly than the total number of calls, in order |
calls of match() more strictly than the total number of calls, in order |
to restrict the maximum amount of stack (or heap, if --disable-stack- | to restrict the maximum amount of stack (or heap, if --disable-stack- |
for-recursion is specified) that is used. A second limit controls this; |
for-recursion is specified) that is used. A second limit controls this; |
it defaults to the value that is set for --with-match-limit, which | it defaults to the value that is set for --with-match-limit, which |
imposes no additional constraints. However, you can set a lower limit | imposes no additional constraints. However, you can set a lower limit |
by adding, for example, |
by adding, for example, |
|
|
--with-match-limit-recursion=10000 |
--with-match-limit-recursion=10000 |
|
|
to the configure command. This value can also be overridden at run | to the configure command. This valu to the configure command. This valu |
time. |
time. |
|
|
|
|
CREATING CHARACTER TABLES AT BUILD TIME |
CREATING CHARACTER TABLES AT BUILD TIME |
|
|
PCRE uses fixed tables for processing characters whose code values are | PCRE uses fixed tables for processing characters whose code values are |
less than 256. By default, PCRE is built with a set of tables that are | less than 256. By default, PCRE is built with a set of tables that are |
distributed in the file pcre_chartables.c.dist. These tables are for | distributed in the file pcre_chartables.c.dist. These tables are for |
ASCII codes only. If you add |
ASCII codes only. If you add |
|
|
--enable-rebuild-chartables |
--enable-rebuild-chartables |
|
|
to the configure command, the distributed tables are no longer used. | to the configure command, the distributed tables are no longer used. |
Instead, a program called dftables is compiled and run. This outputs | Instead, a program called dftables is compiled and run. This outputs |
the source for new set of tables, created in the default locale of your |
the source for new set of tables, created in the default locale of your |
C run-time system. (This method of replacing the tables does not work | C run-time system. (This method of replacing the tables does not work |
if you are cross compiling, because dftables is run on the local host. | if you are cross compiling, because dftables is run on the local host. |
If you need to create alternative tables when cross compiling, you will |
If you need to create alternative tables when cross compiling, you will |
have to do so "by hand".) |
have to do so "by hand".) |
|
|
|
|
USING EBCDIC CODE |
USING EBCDIC CODE |
|
|
PCRE assumes by default that it will run in an environment where the | PCRE assumes by default that it will run in an environment where the |
character code is ASCII (or Unicode, which is a superset of ASCII). | character code is ASCII (or Unicode, which is a superset of ASCII). |
This is the case for most computer operating systems. PCRE can, how- | This is the case for most computer operating systems. PCRE can, how- |
ever, be compiled to run in an EBCDIC environment by adding |
ever, be compiled to run in an EBCDIC environment by adding |
|
|
--enable-ebcdic |
--enable-ebcdic |
|
|
to the configure command. This setting implies --enable-rebuild-charta- |
to the configure command. This setting implies --enable-rebuild-charta- |
bles. You should only use it if you know that you are in an EBCDIC | bles. You should only use it if you know that you are in an EBCDIC |
environment (for example, an IBM mainframe operating system). The | environment (for example, an IBM mainframe operating system). The |
--enable-ebcdic option is incompatible with --enable-utf. |
--enable-ebcdic option is incompatible with --enable-utf. |
|
|
|
The EBCDIC character that corresponds to an ASCII LF is assumed to have |
|
the value 0x15 by default. However, in some EBCDIC environments, 0x25 |
|
is used. In such an environment you should use |
|
|
|
--enable-ebcdic-nl25 |
|
|
|
as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR |
|
has the same value as in ASCII, namely, 0x0d. Whichever of 0x15 and |
|
0x25 is not chosen as LF is made to correspond to the Unicode NEL char- |
|
acter (which, in Unicode, is 0x85). |
|
|
|
The options that select newline behaviour, such as --enable-newline-is- |
|
cr, and equivalent run-time options, refer to these character values in |
|
an EBCDIC environment. |
|
|
|
|
PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT |
PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT |
|
|
By default, pcregrep reads all files as plain text. You can build it so |
By default, pcregrep reads all files as plain text. You can build it so |
Line 843 PCRETEST OPTION FOR LIBREADLINE SUPPORT
|
Line 1258 PCRETEST OPTION FOR LIBREADLINE SUPPORT
|
immediately before the configure command. |
immediately before the configure command. |
|
|
|
|
|
DEBUGGING WITH VALGRIND SUPPORT |
|
|
|
By adding the |
|
|
|
--enable-valgrind |
|
|
|
option to to the configure command, PCRE will use valgrind annotations |
|
to mark certain memory regions as unaddressable. This allows it to |
|
detect invalid memory accesses, and is mostly useful for debugging PCRE |
|
itself. |
|
|
|
|
|
CODE COVERAGE REPORTING |
|
|
|
If your C compiler is gcc, you can build a version of PCRE that can |
|
generate a code coverage report for its test suite. To enable this, you |
|
must install lcov version 1.6 or above. Then specify |
|
|
|
--enable-coverage |
|
|
|
to the configure command and build PCRE in the usual way. |
|
|
|
Note that using ccache (a caching C compiler) is incompatible with code |
|
coverage reporting. If you have configured ccache to run automatically |
|
on your system, you must set the environment variable |
|
|
|
CCACHE_DISABLE=1 |
|
|
|
before running make to build PCRE, so that ccache is not used. |
|
|
|
When --enable-coverage is used, the following addition targets are |
|
added to the Makefile: |
|
|
|
make coverage |
|
|
|
This creates a fresh coverage report for the PCRE test suite. It is |
|
equivalent to running "make coverage-reset", "make coverage-baseline", |
|
"make check", and then "make coverage-report". |
|
|
|
make coverage-reset |
|
|
|
This zeroes the coverage counters, but does nothing else. |
|
|
|
make coverage-baseline |
|
|
|
This captures baseline coverage information. |
|
|
|
make coverage-report |
|
|
|
This creates the coverage report. |
|
|
|
make coverage-clean-report |
|
|
|
This removes the generated coverage report without cleaning the cover- |
|
age data itself. |
|
|
|
make coverage-clean-data |
|
|
|
This removes the captured coverage data without removing the coverage |
|
files created at compile time (*.gcno). |
|
|
|
make coverage-clean |
|
|
|
This cleans all coverage data including the generated coverage report. |
|
For more information about code coverage, see the gcov and lcov docu- |
|
mentation. |
|
|
|
|
SEE ALSO |
SEE ALSO |
|
|
pcreapi(3), pcre16, pcre_config(3). | pcreapi(3), pcre16, pcre32, pcre_config(3). |
|
|
|
|
AUTHOR |
AUTHOR |
Line 857 AUTHOR
|
Line 1340 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 07 January 2012 | Last updated: 12 May 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREMATCHING(3) PCREMATCHING(3) | PCREMATCHING(3) Library Functions Manual PCREMATCHING(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
PCRE MATCHING ALGORITHMS |
PCRE MATCHING ALGORITHMS |
|
|
This document describes the two different algorithms that are available |
This document describes the two different algorithms that are available |
in PCRE for matching a compiled regular expression against a given sub- |
in PCRE for matching a compiled regular expression against a given sub- |
ject string. The "standard" algorithm is the one provided by the |
ject string. The "standard" algorithm is the one provided by the |
pcre_exec() and pcre16_exec() functions. These work in the same was as | pcre_exec(), pcre16_exec() and pcre32_exec() functions. These work in |
Perl's matching function, and provide a Perl-compatible matching opera- | the same as as Perl's matching function, and provide a Perl-compatible |
tion. The just-in-time (JIT) optimization that is described in the | matching operation. The just-in-time (JIT) optimization that is |
pcrejit documentation is compatible with these functions. | described in the pcrejit documentation is compatible with these func- |
| tions. |
|
|
An alternative algorithm is provided by the pcre_dfa_exec() and | An alternative algorithm is provided by the pcre_dfa_exec(), |
pcre16_dfa_exec() functions; they operate in a different way, and are | pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a |
not Perl-compatible. This alternative has advantages and disadvantages | different way, and are not Perl-compatible. This alternative has advan- |
compared with the standard algorithm, and these are described below. | tages and disadvantages compared with the standard algorithm, and these |
| are described below. |
|
|
When there is only one possible way in which a given subject string can |
When there is only one possible way in which a given subject string can |
match a pattern, the two algorithms give the same answer. A difference |
match a pattern, the two algorithms give the same answer. A difference |
Line 972 THE ALTERNATIVE MATCHING ALGORITHM
|
Line 1457 THE ALTERNATIVE MATCHING ALGORITHM
|
at the fifth character of the subject. The algorithm does not automati- |
at the fifth character of the subject. The algorithm does not automati- |
cally move on to find matches that start at later positions. |
cally move on to find matches that start at later positions. |
|
|
|
PCRE's "auto-possessification" optimization usually applies to charac- |
|
ter repeats at the end of a pattern (as well as internally). For exam- |
|
ple, the pattern "a\d+" is compiled as if it were "a\d++" because there |
|
is no point even considering the possibility of backtracking into the |
|
repeated digits. For DFA matching, this means that only one possible |
|
match is found. If you really do want multiple matches in such cases, |
|
either use an ungreedy repeat ("a\d+?") or set the PCRE_NO_AUTO_POSSESS |
|
option when compiling. |
|
|
There are a number of features of PCRE regular expressions that are not |
There are a number of features of PCRE regular expressions that are not |
supported by the alternative matching algorithm. They are as follows: |
supported by the alternative matching algorithm. They are as follows: |
|
|
1. Because the algorithm finds all possible matches, the greedy or | 1. Because the algorithm finds all possible matches, the greedy or |
ungreedy nature of repetition quantifiers is not relevant. Greedy and | ungreedy nature of repetition quantifiers is not relevant. Greedy and |
ungreedy quantifiers are treated in exactly the same way. However, pos- |
ungreedy quantifiers are treated in exactly the same way. However, pos- |
sessive quantifiers can make a difference when what follows could also | sessive quantifiers can make a difference when what follows could also |
match what is quantified, for example in a pattern like this: |
match what is quantified, for example in a pattern like this: |
|
|
^a++\w! |
^a++\w! |
|
|
This pattern matches "aaab!" but not "aaa!", which would be matched by | This pattern matches "aaab!" but not "aaa!", which would be matched by |
a non-possessive quantifier. Similarly, if an atomic group is present, | a non-possessive quantifier. Similarly, if an atomic group is present, |
it is matched as if it were a standalone pattern at the current point, | it is matched as if it were a standalone pattern at the current point, |
and the longest match is then "locked in" for the rest of the overall | and the longest match is then "locked in" for the rest of the overall |
pattern. |
pattern. |
|
|
2. When dealing with multiple paths through the tree simultaneously, it |
2. When dealing with multiple paths through the tree simultaneously, it |
is not straightforward to keep track of captured substrings for the | is not straightforward to keep track of captured substrings for the |
different matching possibilities, and PCRE's implementation of this | different matching possibilities, and PCRE's implementation of this |
algorithm does not attempt to do this. This means that no captured sub- |
algorithm does not attempt to do this. This means that no captured sub- |
strings are available. |
strings are available. |
|
|
3. Because no substrings are captured, back references within the pat- | 3. Because no substrings are captured, back references within the pat- |
tern are not supported, and cause errors if encountered. |
tern are not supported, and cause errors if encountered. |
|
|
4. For the same reason, conditional expressions that use a backrefer- | 4. For the same reason, conditional expressions that use a backrefer- |
ence as the condition or test for a specific group recursion are not | ence as the condition or test for a specific group recursion are not |
supported. |
supported. |
|
|
5. Because many paths through the tree may be active, the \K escape | 5. Because many paths through the tree may be active, the \K escape |
sequence, which resets the start of the match when encountered (but may |
sequence, which resets the start of the match when encountered (but may |
be on some paths and not on others), is not supported. It causes an | be on some paths and not on others), is not supported. It causes an |
error if encountered. |
error if encountered. |
|
|
6. Callouts are supported, but the value of the capture_top field is | 6. Callouts are supported, but the value of the capture_t 6. Callouts are supported, but the value of the capture_t |
always 1, and the value of the capture_last field is always -1. |
always 1, and the value of the capture_last field is always -1. |
|
|
7. The \C escape sequence, which (in the standard algorithm) always | 7. The \C escape sequence, which (in the standard algorithm) always |
matches a single data unit, even in UTF-8 or UTF-16 modes, is not sup- | matches a single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is |
ported in these modes, because the alternative algorithm moves through | not supported in these modes, because the alternative algorithm moves |
the subject string one character (not data unit) at a time, for all | through the subject string one character (not data unit) at a time, for |
active paths through the tree. | all active paths through the tree. |
|
|
8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) | 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) |
are not supported. (*FAIL) is supported, and behaves like a failing | are not supported. (*FAIL) is supported, and behaves like a failing |
negative assertion. |
negative assertion. |
|
|
|
|
ADVANTAGES OF THE ALTERNATIVE ALGORITHM |
ADVANTAGES OF THE ALTERNATIVE ALGORITHM |
|
|
Using the alternative matching algorithm provides the following advan- | Using the alternative matching algorithm provides the following advan- |
tages: |
tages: |
|
|
1. All possible matches (at a single point in the subject) are automat- |
1. All possible matches (at a single point in the subject) are automat- |
ically found, and in particular, the longest match is found. To find | ically found, and in particular, the longest match is found. To find |
more than one match using the standard algorithm, you have to do kludgy |
more than one match using the standard algorithm, you have to do kludgy |
things with callouts. |
things with callouts. |
|
|
2. Because the alternative algorithm scans the subject string just | 2. Because the alternative algorithm scans the subject string just |
once, and never needs to backtrack (except for lookbehinds), it is pos- |
once, and never needs to backtrack (except for lookbehinds), it is pos- |
sible to pass very long subject strings to the matching function in | sible to pass very long subject strings to the matching function in |
several pieces, checking for partial matching each time. Although it is |
several pieces, checking for partial matching each time. Although it is |
possible to do multi-segment matching using the standard algorithm by | possible to do multi-segment matching using the standard algorithm by |
retaining partially matched substrings, it is more complicated. The | retaining partially matched substrings, it is more complicated. The |
pcrepartial documentation gives details of partial matching and dis- | pcrepartial documentation gives details of partial matching and dis- |
cusses multi-segment matching. |
cusses multi-segment matching. |
|
|
|
|
Line 1045 DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
|
Line 1539 DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
|
|
|
The alternative algorithm suffers from a number of disadvantages: |
The alternative algorithm suffers from a number of disadvantages: |
|
|
1. It is substantially slower than the standard algorithm. This is | 1. It is substantially slower than the standard algorithm. This is |
partly because it has to search for all possible matches, but is also | partly because it has to search for all possible matches, but is also |
because it is less susceptible to optimization. |
because it is less susceptible to optimization. |
|
|
2. Capturing parentheses and back references are not supported. |
2. Capturing parentheses and back references are not supported. |
Line 1064 AUTHOR
|
Line 1558 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 08 January 2012 | Last updated: 12 November 2013 |
Copyright (c) 1997-2012 University of Cambridge. |
Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREAPI(3) PCREAPI(3) | PCREAPI(3) Library Functions Manual PCREAPI(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
Line 1140 PCRE NATIVE API STRING EXTRACTION FUNCTIONS
|
Line 1635 PCRE NATIVE API STRING EXTRACTION FUNCTIONS
|
|
|
PCRE NATIVE API AUXILIARY FUNCTIONS |
PCRE NATIVE API AUXILIARY FUNCTIONS |
|
|
|
int pcre_jit_exec(const pcre *code, const pcre_extra *extra, |
|
const char *subject, int length, int startoffset, |
|
int options, int *ovector, int ovecsize, |
|
pcre_jit_stack *jstack); |
|
|
pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize); |
pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize); |
|
|
void pcre_jit_stack_free(pcre_jit_stack *stack); |
void pcre_jit_stack_free(pcre_jit_stack *stack); |
Line 1175 PCRE NATIVE API INDIRECTED FUNCTIONS
|
Line 1675 PCRE NATIVE API INDIRECTED FUNCTIONS
|
int (*pcre_callout)(pcre_callout_block *); |
int (*pcre_callout)(pcre_callout_block *); |
|
|
|
|
PCRE 8-BIT AND 16-BIT LIBRARIES | PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES |
|
|
From release 8.30, PCRE can be compiled as a library for handling | As well as support for 8-bit character strings, PCRE also supports |
16-bit character strings as well as, or instead of, the original | 16-bit strings (from release 8.30) and 32-bit strings (from release |
library that handles 8-bit character strings. To avoid too much compli- | 8.32), by means of two additional libraries. They can be built as well |
cation, this document describes the 8-bit versions of the functions, | as, or instead of, the 8-bit library. To avoid too much complication, |
with only occasional references to the 16-bit library. | this document describes the 8-bit versions of the functions, with only |
| occasional references to the 16-bit and 32-bit libraries. |
|
|
The 16-bit functions operate in the same way as their 8-bit counter- | The 16-bit and 32-bit functions operate in the same way as their 8-bit |
parts; they just use different data types for their arguments and | counterparts; they just use different data types for their arguments |
results, and their names start with pcre16_ instead of pcre_. For every | and results, and their names start with pcre16_ or pcre32_ instead of |
option that has UTF8 in its name (for example, PCRE_UTF8), there is a | pcre_. For every option that has UTF8 in its name (for example, |
corresponding 16-bit name with UTF8 replaced by UTF16. This facility is | PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8 |
in fact just cosmetic; the 16-bit option names define the same bit val- | replaced by UTF16 or UTF32, respectively. This facility is in fact just |
| cosmetic; the 16-bit and 32-bit option names define the same bit val- |
ues. |
ues. |
|
|
References to bytes and UTF-8 in this document should be read as refer- |
References to bytes and UTF-8 in this document should be read as refer- |
ences to 16-bit data quantities and UTF-16 when using the 16-bit | ences to 16-bit data units and UTF-16 when using the 16-bit library, or |
library, unless specified otherwise. More details of the specific dif- | 32-bit data units and UTF-32 when using the 32-bit library, unless |
ferences for the 16-bit library are given in the pcre16 page. | specified otherwise. More details of the specific differences for the |
| 16-bit and 32-bit libraries are given in the pcre16 and pcre32 pages. |
|
|
|
|
PCRE API OVERVIEW |
PCRE API OVERVIEW |
|
|
PCRE has its own native API, which is described in this document. There |
PCRE has its own native API, which is described in this document. There |
are also some wrapper functions (for the 8-bit library only) that cor- | are also some wrapper functions (for the 8-bit library only) that cor- |
respond to the POSIX regular expression API, but they do not give | respond to the POSIX regular expression API, but they do not give |
access to all the functionality. They are described in the pcreposix | access to all the functionality. They are described in the pcreposix |
documentation. Both of these APIs define a set of C function calls. A | documentation. Both of these APIs define a set of C function calls. A |
C++ wrapper (again for the 8-bit library only) is also distributed with |
C++ wrapper (again for the 8-bit library only) is also distributed with |
PCRE. It is documented in the pcrecpp page. |
PCRE. It is documented in the pcrecpp page. |
|
|
The native API C function prototypes are defined in the header file | The native API C function prototypes are defined in the header file |
pcre.h, and on Unix-like systems the (8-bit) library itself is called | pcre.h, and on Unix-like systems the (8-bit) library itself is called |
libpcre. It can normally be accessed by adding -lpcre to the command | libpcre. It can normally be accessed by adding -lpcre to the command |
for linking an application that uses PCRE. The header file defines the | for linking an application that uses PCRE. The header file defines the |
macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release |
macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release |
numbers for the library. Applications can use these to include support | numbers for the library. Applications can use these to include support |
for different releases of PCRE. |
for different releases of PCRE. |
|
|
In a Windows environment, if you want to statically link an application |
In a Windows environment, if you want to statically link an application |
program against a non-dll pcre.a file, you must define PCRE_STATIC | program against a non-dll pcre.a file, you must define PCRE_STATIC |
before including pcre.h or pcrecpp.h, because otherwise the pcre_mal- | before including pcre.h or pcrecpp.h, because otherwise the pcre_mal- |
loc() and pcre_free() exported functions will be declared |
loc() and pcre_free() exported functions will be declared |
__declspec(dllimport), with unwanted results. |
__declspec(dllimport), with unwanted results. |
|
|
The functions pcre_compile(), pcre_compile2(), pcre_study(), and | The functions pcre_compile(), pcre_compile2(), pcre_study(), and |
pcre_exec() are used for compiling and matching regular expressions in | pcre_exec() are used for compiling and matching regular expressions in |
a Perl-compatible manner. A sample program that demonstrates the sim- | a Perl-compatible manner. A sample program that demonstrates the sim- |
plest way of using them is provided in the file called pcredemo.c in | plest way of using them is provided in the file called pcredemo.c in |
the PCRE source distribution. A listing of this program is given in the |
the PCRE source distribution. A listing of this program is given in the |
pcredemo documentation, and the pcresample documentation describes how | pcredemo documentation, and the pcresample documentation describes how |
to compile and run it. |
to compile and run it. |
|
|
Just-in-time compiler support is an optional feature of PCRE that can | Just-in-time compiler support is an optional feature of PCRE that can |
be built in appropriate hardware environments. It greatly speeds up the |
be built in appropriate hardware environments. It greatly speeds up the |
matching performance of many patterns. Simple programs can easily | matching performance of many patterns. Simple programs can easily |
request that it be used if available, by setting an option that is | request that it be used if available, by setting an option that is |
ignored when it is not relevant. More complicated programs might need | ignored when it is not relevant. More complicated programs might need |
to make use of the functions pcre_jit_stack_alloc(), | to make use of the functions pcre_jit_stack_alloc(), |
pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control | pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control |
the JIT code's memory usage. These functions are discussed in the | the JIT code's memory usage. |
pcrejit documentation. | |
|
|
|
From release 8.32 there is also a direct interface for JIT execution, |
|
which gives improved performance. The JIT-specific functions are dis- |
|
cussed in the pcrejit documentation. |
|
|
A second matching function, pcre_dfa_exec(), which is not Perl-compati- |
A second matching function, pcre_dfa_exec(), which is not Perl-compati- |
ble, is also provided. This uses a different algorithm for the match- |
ble, is also provided. This uses a different algorithm for the match- |
ing. The alternative algorithm finds all possible matches (at a given |
ing. The alternative algorithm finds all possible matches (at a given |
Line 1384 CHECKING BUILD-TIME OPTIONS
|
Line 1890 CHECKING BUILD-TIME OPTIONS
|
PCRE_CONFIG_UTF8 |
PCRE_CONFIG_UTF8 |
|
|
The output is an integer that is set to one if UTF-8 support is avail- |
The output is an integer that is set to one if UTF-8 support is avail- |
able; otherwise it is set to zero. If this option is given to the | able; otherwise it is set to zero. This value should normally be given |
16-bit version of this function, pcre16_config(), the result is | to the 8-bit version of this function, pcre_config(). If it is given to |
| the 16-bit or 32-bit version of this function, the result is |
PCRE_ERROR_BADOPTION. |
PCRE_ERROR_BADOPTION. |
|
|
PCRE_CONFIG_UTF16 |
PCRE_CONFIG_UTF16 |
|
|
The output is an integer that is set to one if UTF-16 support is avail- |
The output is an integer that is set to one if UTF-16 support is avail- |
able; otherwise it is set to zero. This value should normally be given | able; otherwise it is set to zero. This value should normally be given |
to the 16-bit version of this function, pcre16_config(). If it is given |
to the 16-bit version of this function, pcre16_config(). If it is given |
to the 8-bit version of this function, the result is PCRE_ERROR_BADOP- | to the 8-bit or 32-bit version of this function, the result is to the 8-bit or 32-bit version of this function, the result is |
TION. | PCRE_ERROR_BADOPTION. |
|
|
|
PCRE_CONFIG_UTF32 |
|
|
|
The output is an integer that is set to one if UTF-32 support is avail- |
|
able; otherwise it is set to zero. This value should normally be given |
|
to the 32-bit version of this function, pcre32_config(). If it is given |
|
to the 8-bit or 16-bit version of this function, the result is |
|
PCRE_ERROR_BADOPTION. |
|
|
PCRE_CONFIG_UNICODE_PROPERTIES |
PCRE_CONFIG_UNICODE_PROPERTIES |
|
|
The output is an integer that is set to one if support for Unicode | The output is an integer that is set to one if support for Unicode |
character properties is available; otherwise it is set to zero. |
character properties is available; otherwise it is set to zero. |
|
|
PCRE_CONFIG_JIT |
PCRE_CONFIG_JIT |
Line 1408 CHECKING BUILD-TIME OPTIONS
|
Line 1923 CHECKING BUILD-TIME OPTIONS
|
|
|
PCRE_CONFIG_JITTARGET |
PCRE_CONFIG_JITTARGET |
|
|
The output is a pointer to a zero-terminated "const char *" string. If | The output is a pointer to a zero-terminated "const char *" string. If |
JIT support is available, the string contains the name of the architec- |
JIT support is available, the string contains the name of the architec- |
ture for which the JIT compiler is configured, for example "x86 32bit | ture for which the JIT compiler is configured, for example "x86 32bit |
(little endian + unaligned)". If JIT support is not available, the | (little endian + unaligned)". If JIT support is not available, the |
result is NULL. |
result is NULL. |
|
|
PCRE_CONFIG_NEWLINE |
PCRE_CONFIG_NEWLINE |
|
|
The output is an integer whose value specifies the default character | The output is an integer whose value specifies the default character |
sequence that is recognized as meaning "newline". The four values that | sequence that is recognized as meaning "newline". The values that are |
are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, | supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338 |
and -1 for ANY. Though they are derived from ASCII, the same values | for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR, |
are returned in EBCDIC environments. The default should normally corre- | ANYCRLF, and ANY yield the same values. However, the value for LF is |
| normally 21, though some EBCDIC environments use 37. The corresponding |
| values for CRLF are 3349 and 3365. The default should normally corre- |
spond to the standard sequence for your operating system. |
spond to the standard sequence for your operating system. |
|
|
PCRE_CONFIG_BSR |
PCRE_CONFIG_BSR |
|
|
The output is an integer whose value indicates what character sequences |
The output is an integer whose value indicates what character sequences |
the \R escape sequence matches by default. A value of 0 means that \R | the \R escape sequence matches by default. A value of 0 means that \R |
matches any Unicode line ending sequence; a value of 1 means that \R | matches any Unicode line ending sequence; a value of 1 means that \R |
matches only CR, LF, or CRLF. The default can be overridden when a pat- |
matches only CR, LF, or CRLF. The default can be overridden when a pat- |
tern is compiled or matched. |
tern is compiled or matched. |
|
|
PCRE_CONFIG_LINK_SIZE |
PCRE_CONFIG_LINK_SIZE |
|
|
The output is an integer that contains the number of bytes used for | The output is an integer that contains the number of byt The output is an integer that contains the number of byt |
internal linkage in compiled regular expressions. For the 8-bit |
internal linkage in compiled regular expressions. For the 8-bit |
library, the value can be 2, 3, or 4. For the 16-bit library, the value |
library, the value can be 2, 3, or 4. For the 16-bit library, the value |
is either 2 or 4 and is still a number of bytes. The default value of 2 | is either 2 or 4 and is still a number of bytes. For the 32-bit |
is sufficient for all but the most massive patterns, since it allows | library, the value is either 2 or 4 and is still a number of bytes. The |
the compiled pattern to be up to 64K in size. Larger values allow | default value of 2 is sufficient for all but the most massive patterns, |
larger regular expressions to be compiled, at the expense of slower | since it allows the compiled pattern to be up to 64K in size. Larger |
matching. | values allow larger regular expressions to be compiled, at the expense |
| of slower matching. |
|
|
PCRE_CONFIG_POSIX_MALLOC_THRESHOLD |
PCRE_CONFIG_POSIX_MALLOC_THRESHOLD |
|
|
Line 1448 CHECKING BUILD-TIME OPTIONS
|
Line 1966 CHECKING BUILD-TIME OPTIONS
|
POSIX interface uses malloc() for output vectors. Further details are |
POSIX interface uses malloc() for output vectors. Further details are |
given in the pcreposix documentation. |
given in the pcreposix documentation. |
|
|
|
PCRE_CONFIG_PARENS_LIMIT |
|
|
|
The output is a long integer that gives the maximum depth of nesting of |
|
parentheses (of any kind) in a pattern. This limit is imposed to cap |
|
the amount of system stack used when a pattern is compiled. It is spec- |
|
ified when PCRE is built; the default is 250. |
|
|
PCRE_CONFIG_MATCH_LIMIT |
PCRE_CONFIG_MATCH_LIMIT |
|
|
The output is a long integer that gives the default limit for the num- | The output is a long integer that gives the default limit for the num- |
ber of internal matching function calls in a pcre_exec() execution. | ber of internal matching function calls in a pcre_exec() execution. |
Further details are given with pcre_exec() below. |
Further details are given with pcre_exec() below. |
|
|
PCRE_CONFIG_MATCH_LIMIT_RECURSION |
PCRE_CONFIG_MATCH_LIMIT_RECURSION |
|
|
The output is a long integer that gives the default limit for the depth |
The output is a long integer that gives the default limit for the depth |
of recursion when calling the internal matching function in a | of recursion when calling the internal matching function in a |
pcre_exec() execution. Further details are given with pcre_exec() | pcre_exec() execution. Further details are given with pcre_exec() |
below. |
below. |
|
|
PCRE_CONFIG_STACKRECURSE |
PCRE_CONFIG_STACKRECURSE |
|
|
The output is an integer that is set to one if internal recursion when | The output is an integer that is set to one if internal recursion when |
running pcre_exec() is implemented by recursive function calls that use |
running pcre_exec() is implemented by recursive function calls that use |
the stack to remember their state. This is the usual way that PCRE is | the stack to remember their state. This is the usual way th the stack to remember their state. This is the usual way that PCRE is |
compiled. The output is zero if PCRE was compiled to use blocks of data |
compiled. The output is zero if PCRE was compiled to use blocks of data |
on the heap instead of recursive function calls. In this case, | on the heap instead of recursive function calls. In this case, |
pcre_stack_malloc and pcre_stack_free are called to manage memory | pcre_stack_malloc and pcre_stack_free are called to manage memory |
blocks on the heap, thus avoiding the use of the stack. |
blocks on the heap, thus avoiding the use of the stack. |
|
|
|
|
Line 1485 COMPILING A PATTERN
|
Line 2010 COMPILING A PATTERN
|
|
|
Either of the functions pcre_compile() or pcre_compile2() can be called |
Either of the functions pcre_compile() or pcre_compile2() can be called |
to compile a pattern into an internal form. The only difference between |
to compile a pattern into an internal form. The only difference between |
the two interfaces is that pcre_compile2() has an additional argument, | the two interfaces is that pcre_compile2() has an additional argument, |
errorcodeptr, via which a numerical error code can be returned. To | errorcodeptr, via which a numerical error code can be returned. To |
avoid too much repetition, we refer just to pcre_compile() below, but | avoid too much repetition, we refer just to pcre_compile() below, but |
the information applies equally to pcre_compile2(). |
the information applies equally to pcre_compile2(). |
|
|
The pattern is a C string terminated by a binary zero, and is passed in |
The pattern is a C string terminated by a binary zero, and is passed in |
the pattern argument. A pointer to a single block of memory that is | the pattern argument. A pointer to a single block of memory that is |
obtained via pcre_malloc is returned. This contains the compiled code | obtained via pcre_malloc is returned. This contains the compiled code |
and related data. The pcre type is defined for the returned block; this |
and related data. The pcre type is defined for the returned block; this |
is a typedef for a structure whose contents are not externally defined. |
is a typedef for a structure whose contents are not externally defined. |
It is up to the caller to free the memory (via pcre_free) when it is no |
It is up to the caller to free the memory (via pcre_free) when it is no |
longer required. |
longer required. |
|
|
Although the compiled code of a PCRE regex is relocatable, that is, it | Although the compiled code of a PCRE regex is relocatable, that is, it |
does not depend on memory location, the complete pcre data block is not |
does not depend on memory location, the complete pcre data block is not |
fully relocatable, because it may contain a copy of the tableptr argu- | fully relocatable, because it may contain a copy of the tableptr argu- |
ment, which is an address (see below). |
ment, which is an address (see below). |
|
|
The options argument contains various bit settings that affect the com- |
The options argument contains various bit settings that affect the com- |
pilation. It should be zero if no options are required. The available | pilation. It should be zero if no options are required. The available |
options are described below. Some of them (in particular, those that | options are described below. Some of them (in particular, those that |
are compatible with Perl, but some others as well) can also be set and | are compatible with Perl, but some others as well) can also be set and |
unset from within the pattern (see the detailed description in the | unset from within the pattern (see the detailed description in the |
pcrepattern documentation). For those options that can be different in | pcrepattern documentation). For those options that can be different in |
different parts of the pattern, the contents of the options argument | different parts of the pattern, the contents of the options argument |
specifies their settings at the start of compilation and execution. The |
specifies their settings at the start of compilation and execution. The |
PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and | PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and |
PCRE_NO_START_OPTIMIZE options can be set at the time of matching as | PCRE_NO_START_OPTIMIZE options can be set at the time of matching as |
well as at compile time. |
well as at compile time. |
|
|
If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise, |
If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise, |
if compilation of a pattern fails, pcre_compile() returns NULL, and | if compilation of a pattern fails, pcre_compile() returns NULL, and |
sets the variable pointed to by errptr to point to a textual error mes- |
sets the variable pointed to by errptr to point to a textual error mes- |
sage. This is a static string that is part of the library. You must not |
sage. This is a static string that is part of the library. You must not |
try to free it. Normally, the offset from the start of the pattern to | try to free it. Normally, the offset from the start of the pattern to |
the byte that was being processed when the error was discovered is | the data unit that was being processed when the error was discovered is |
placed in the variable pointed to by erroffset, which must not be NULL | placed in the variable pointed to by erroffset, which must not be NULL |
(if it is, an immediate error is given). However, for an invalid UTF-8 | (if it is, an immediate error is given). However, for an invalid UTF-8 |
string, the offset is that of the first byte of the failing character. | or UTF-16 string, the offset is that of the first data unit of the |
| failing character. |
|
|
Some errors are not detected until the whole pattern has been scanned; |
Some errors are not detected until the whole pattern has been scanned; |
in these cases, the offset passed back is the length of the pattern. |
in these cases, the offset passed back is the length of the pattern. |
Note that the offset is in bytes, not characters, even in UTF-8 mode. | Note that the offset is in data units, not characters, even in a UTF |
It may sometimes point into the middle of a UTF-8 character. | mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char- |
| acter. |
|
|
If pcre_compile2() is used instead of pcre_compile(), and the error- | If pcre_compile2() is used instead of pcre_compile(), and the error- |
codeptr argument is not NULL, a non-zero error code number is returned | codeptr argument is not NULL, a non-zero error code number is returned |
via this argument in the event of an error. This is in addition to the | via this argument in the event of an error. This is in addition to the |
textual error message. Error codes and messages are listed below. |
textual error message. Error codes and messages are listed below. |
|
|
If the final argument, tableptr, is NULL, PCRE uses a default set of | If the final argument, tableptr, is NULL, PCRE uses a default set of |
character tables that are built when PCRE is compiled, using the | character tables that are built when PCRE is compiled, using the |
default C locale. Otherwise, tableptr must be an address that is the | default C locale. Otherwise, tableptr must be an address that is the |
result of a call to pcre_maketables(). This value is stored with the | result of a call to pcre_maketables(). This value is stored with the |
compiled pattern, and used again by pcre_exec(), unless another table | compiled pattern, and used again by pcre_exec() and pcre_dfa_exec() |
pointer is passed to it. For more discussion, see the section on locale | when the pattern is matched. For more discussion, see the section on |
support below. | locale support below. |
|
|
This code fragment shows a typical straightforward call to pcre_com- | This code fragment shows a typical straightforward call to pcre_com- |
pile(): |
pile(): |
|
|
pcre *re; |
pcre *re; |
Line 1556 COMPILING A PATTERN
|
Line 2083 COMPILING A PATTERN
|
&erroffset, /* for error offset */ |
&erroffset, /* for error offset */ |
NULL); /* use default character tables */ |
NULL); /* use default character tables */ |
|
|
The following names for option bits are defined in the pcre.h header | The following names for option bits are defined in the pcre.h header |
file: |
file: |
|
|
PCRE_ANCHORED |
PCRE_ANCHORED |
|
|
If this bit is set, the pattern is forced to be "anchored", that is, it |
If this bit is set, the pattern is forced to be "anchored", that is, it |
is constrained to match only at the first matching point in the string | is constrained to match only at the first matching point in the string |
that is being searched (the "subject string"). This effect can also be | that is being searched (the "subject string"). This effect can also be |
achieved by appropriate constructs in the pattern itself, which is the | achieved by appropriate constructs in the pattern itself, which is the |
only way to do it in Perl. |
only way to do it in Perl. |
|
|
PCRE_AUTO_CALLOUT |
PCRE_AUTO_CALLOUT |
|
|
If this bit is set, pcre_compile() automatically inserts callout items, |
If this bit is set, pcre_compile() automatically inserts callout items, |
all with number 255, before each pattern item. For discussion of the | all with number 255, before each pattern item. For discussion of the |
callout facility, see the pcrecallout documentation. |
callout facility, see the pcrecallout documentation. |
|
|
PCRE_BSR_ANYCRLF |
PCRE_BSR_ANYCRLF |
PCRE_BSR_UNICODE |
PCRE_BSR_UNICODE |
|
|
These options (which are mutually exclusive) control what the \R escape |
These options (which are mutually exclusive) control what the \R escape |
sequence matches. The choice is either to match only CR, LF, or CRLF, | sequence matches. The choice is either to match only CR, LF, or CRLF, |
or to match any Unicode newline sequence. The default is specified when |
or to match any Unicode newline sequence. The default is specified when |
PCRE is built. It can be overridden from within the pattern, or by set- |
PCRE is built. It can be overridden from within the pattern, or by set- |
ting an option when a compiled pattern is matched. |
ting an option when a compiled pattern is matched. |
|
|
PCRE_CASELESS |
PCRE_CASELESS |
|
|
If this bit is set, letters in the pattern match both upper and lower | If this bit is set, letters in the pattern match both upper and lower |
case letters. It is equivalent to Perl's /i option, and it can be | case letters. It is equivalent to Perl's /i option, and it can be |
changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE | changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE |
always understands the concept of case for characters whose values are | always understands the concept of case for characters whose values are |
less than 128, so caseless matching is always possible. For characters | less than 128, so caseless matching is always possible. For characters |
with higher values, the concept of case is supported if PCRE is com- | with higher values, the concept of case is supported if PCRE is com- |
piled with Unicode property support, but not otherwise. If you want to | piled with Unicode property support, but not otherwise. If you want to |
use caseless matching for characters 128 and above, you must ensure | use caseless matching for characters 128 and above, you must ensure |
that PCRE is compiled with Unicode property support as well as with | that PCRE is compiled with Unicode property support as well as with |
UTF-8 support. |
UTF-8 support. |
|
|
PCRE_DOLLAR_ENDONLY |
PCRE_DOLLAR_ENDONLY |
|
|
If this bit is set, a dollar metacharacter in the pattern matches only | If this bit is set, a dollar metacharacter in the pattern matches only |
at the end of the subject string. Without this option, a dollar also | at the end of the subject string. Without this option, a dollar also |
matches immediately before a newline at the end of the string (but not | matches immediately before a newline at the end of the string (but not |
before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored | before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored |
if PCRE_MULTILINE is set. There is no equivalent to this option in | if PCRE_MULTILINE is set. There is no equivalent to this option in |
Perl, and no way to set it within a pattern. |
Perl, and no way to set it within a pattern. |
|
|
PCRE_DOTALL |
PCRE_DOTALL |
|
|
If this bit is set, a dot metacharacter in the pattern matches a char- | If this bit is set, a dot metacharacter in the pattern matches a char- |
acter of any value, including one that indicates a newline. However, it |
acter of any value, including one that indicates a newline. However, it |
only ever matches one character, even if newlines are coded as CRLF. | only ever matches one character, even if newlines are coded as CRLF. |
Without this option, a dot does not match when the current position is | Without this option, a dot does not match when the current position is |
at a newline. This option is equivalent to Perl's /s option, and it can |
at a newline. This option is equivalent to Perl's /s option, and it can |
be changed within a pattern by a (?s) option setting. A negative class | be changed within a pattern by a (?s) option setting. A negative class |
such as [^a] always matches newline characters, independent of the set- |
such as [^a] always matches newline characters, independent of the set- |
ting of this option. |
ting of this option. |
|
|
PCRE_DUPNAMES |
PCRE_DUPNAMES |
|
|
If this bit is set, names used to identify capturing subpatterns need | If this bit is set, names used to identify capturing subpatterns need |
not be unique. This can be helpful for certain types of pattern when it |
not be unique. This can be helpful for certain types of pattern when it |
is known that only one instance of the named subpattern can ever be | is known that only one instance of the named subpattern can ever be |
matched. There are more details of named subpatterns below; see also | matched. There are more details of named subpatterns below; see also |
the pcrepattern documentation. |
the pcrepattern documentation. |
|
|
PCRE_EXTENDED |
PCRE_EXTENDED |
|
|
If this bit is set, white space data characters in the pattern are | If this bit is set, most white space characters in the pattern are |
totally ignored except when escaped or inside a character class. White | totally ignored except when escaped or inside a character class. How- |
space does not include the VT character (code 11). In addition, charac- | ever, white space is not allowed within sequences such as (?> that |
ters between an unescaped # outside a character class and the next new- | introduce various parenthesized subpatterns, nor within a numerical |
line, inclusive, are also ignored. This is equivalent to Perl's /x | quantifier such as {1,3}. However, ignorable white space is permitted |
option, and it can be changed within a pattern by a (?x) option set- | between an item and a following quantifier and between a quantifier and |
ting. | a following + that indicates possessiveness. |
|
|
Which characters are interpreted as newlines is controlled by the | White space did not used to include the VT character (code 11), because |
options passed to pcre_compile() or by a special sequence at the start | Perl did not treat this character as white space. However, Perl changed |
of the pattern, as described in the section entitled "Newline conven- | at release 5.18, so PCRE followed at release 8.34, and VT is now |
| treated as white space. |
| |
| PCRE_EXTENDED also causes characters between an unescaped # outside a |
| character class and the next newline, inclusive, to be ignored. |
| PCRE_EXTENDED is equivalent to Perl's /x option, and it can be changed |
| within a pattern by a (?x) option setting. |
| |
| Which characters are interpreted as newlines is controlled by the |
| options passed to pcre_compile() or by a special sequence at the start |
| of the pattern, as described in the section entitled "Newline conven- |
tions" in the pcrepattern documentation. Note that the end of this type |
tions" in the pcrepattern documentation. Note that the end of this type |
of comment is a literal newline sequence in the pattern; escape | of comment is a literal newline sequence in the pattern; escape |
sequences that happen to represent a newline do not count. |
sequences that happen to represent a newline do not count. |
|
|
This option makes it possible to include comments inside complicated | This option makes it possible to include comments inside complicated |
patterns. Note, however, that this applies only to data characters. | patterns. Note, however, that this applies only to data characters. |
White space characters may never appear within special character | White space characters may never appear within special character |
sequences in a pattern, for example within the sequence (?( that intro- |
sequences in a pattern, for example within the sequence (?( that intro- |
duces a conditional subpattern. |
duces a conditional subpattern. |
|
|
PCRE_EXTRA |
PCRE_EXTRA |
|
|
This option was invented in order to turn on additional functionality | This option was invented in order to turn on additional functionality |
of PCRE that is incompatible with Perl, but it is currently of very | of PCRE that is incompatible with Perl, but it is currently of very |
little use. When set, any backslash in a pattern that is followed by a | little use. When set, any backslash in a pattern that is followed by a |
letter that has no special meaning causes an error, thus reserving | letter that has no special meaning causes an error, thus reserving |
these combinations for future expansion. By default, as in Perl, a | these combinations for future expansion. By default, as in Perl, a |
backslash followed by a letter with no special meaning is treated as a | backslash followed by a letter with no special meaning is treated as a |
literal. (Perl can, however, be persuaded to give an error for this, by |
literal. (Perl can, however, be persuaded to give an error for this, by |
running it with the -w option.) There are at present no other features | running it with the -w option.) There are at present no other features |
controlled by this option. It can also be set by a (?X) option setting | controlled by this option. It can also be set by a (?X) option setting |
within a pattern. |
within a pattern. |
|
|
PCRE_FIRSTLINE |
PCRE_FIRSTLINE |
|
|
If this option is set, an unanchored pattern is required to match | If this option is set, an unanchored pattern is required to match |
before or at the first newline in the subject string, though the | before or at the first newline in the subject string, though the |
matched text may continue over the newline. |
matched text may continue over the newline. |
|
|
PCRE_JAVASCRIPT_COMPAT |
PCRE_JAVASCRIPT_COMPAT |
|
|
If this option is set, PCRE's behaviour is changed in some ways so that |
If this option is set, PCRE's behaviour is changed in some ways so that |
it is compatible with JavaScript rather than Perl. The changes are as | it is compatible with JavaScript rather than Perl. The changes are as |
follows: |
follows: |
|
|
(1) A lone closing square bracket in a pattern causes a compile-time | (1) A lone closing square bracket in a pattern causes a compile-time |
error, because this is illegal in JavaScript (by default it is treated | error, because this is illegal in JavaScript (by default it is treated |
as a data character). Thus, the pattern AB]CD becomes illegal when this |
as a data character). Thus, the pattern AB]CD becomes illegal when this |
option is set. |
option is set. |
|
|
(2) At run time, a back reference to an unset subpattern group matches | (2) At run time, a back reference to an unset subpattern group matches |
an empty string (by default this causes the current matching alterna- | an empty string (by default this causes the current matching alterna- |
tive to fail). A pattern such as (\1)(a) succeeds when this option is | tive to fail). A pattern such as (\1)(a) succeeds when this option is |
set (assuming it can find an "a" in the subject), whereas it fails by | set (assuming it can find an "a" in the subject), whereas it fails by |
default, for Perl compatibility. |
default, for Perl compatibility. |
|
|
(3) \U matches an upper case "U" character; by default \U causes a com- |
(3) \U matches an upper case "U" character; by default \U causes a com- |
pile time error (Perl uses \U to upper case subsequent characters). |
pile time error (Perl uses \U to upper case subsequent characters). |
|
|
(4) \u matches a lower case "u" character unless it is followed by four |
(4) \u matches a lower case "u" character unless it is followed by four |
hexadecimal digits, in which case the hexadecimal number defines the | hexadecimal digits, in which case the hexadecimal number defines the |
code point to match. By default, \u causes a compile time error (Perl | code point to match. By default, \u causes a compile time error (Perl |
uses it to upper case the following character). |
uses it to upper case the following character). |
|
|
(5) \x matches a lower case "x" character unless it is followed by two | (5) \x matches a lower case "x" character unless it is followed by two |
hexadecimal digits, in which case the hexadecimal number defines the | hexadecimal digits, in which case the hexadecimal number defines the |
code point to match. By default, as in Perl, a hexadecimal number is | code point to match. By default, as in Perl, a hexadecimal number is |
always expected after \x, but it may have zero, one, or two digits (so, |
always expected after \x, but it may have zero, one, or two digits (so, |
for example, \xz matches a binary zero character followed by z). |
for example, \xz matches a binary zero character followed by z). |
|
|
PCRE_MULTILINE |
PCRE_MULTILINE |
|
|
By default, PCRE treats the subject string as consisting of a single | By default, for the purposes of matching "start of line" and "end of |
line of characters (even if it actually contains newlines). The "start | line", PCRE treats the subject string as consisting of a single line of |
of line" metacharacter (^) matches only at the start of the string, | characters, even if it actually contains newlines. The "start of line" |
while the "end of line" metacharacter ($) matches only at the end of | metacharacter (^) matches only at the start of the string, and the "end |
the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY | of line" metacharacter ($) matches only at the end of the string, or |
is set). This is the same as Perl. | before a terminating newline (except when PCRE_DOLLAR_ENDONLY is set). |
| Note, however, that unless PCRE_DOTALL is set, the "any character" |
| metacharacter (.) does not match at a newline. This behaviour (for ^, |
| $, and dot) is the same as Perl. |
|
|
When PCRE_MULTILINE it is set, the "start of line" and "end of line" |
When PCRE_MULTILINE it is set, the "start of line" and "end of line" |
constructs match immediately following or immediately before internal |
constructs match immediately following or immediately before internal |
Line 1713 COMPILING A PATTERN
|
Line 2253 COMPILING A PATTERN
|
lines in a subject string, or no occurrences of ^ or $ in a pattern, |
lines in a subject string, or no occurrences of ^ or $ in a pattern, |
setting PCRE_MULTILINE has no effect. |
setting PCRE_MULTILINE has no effect. |
|
|
|
PCRE_NEVER_UTF |
|
|
|
This option locks out interpretation of the pattern as UTF-8 (or UTF-16 |
|
or UTF-32 in the 16-bit and 32-bit libraries). In particular, it pre- |
|
vents the creator of the pattern from switching to UTF interpretation |
|
by starting the pattern with (*UTF). This may be useful in applications |
|
that process patterns from external sources. The combination of |
|
PCRE_UTF8 and PCRE_NEVER_UTF also causes an error. |
|
|
PCRE_NEWLINE_CR |
PCRE_NEWLINE_CR |
PCRE_NEWLINE_LF |
PCRE_NEWLINE_LF |
PCRE_NEWLINE_CRLF |
PCRE_NEWLINE_CRLF |
PCRE_NEWLINE_ANYCRLF |
PCRE_NEWLINE_ANYCRLF |
PCRE_NEWLINE_ANY |
PCRE_NEWLINE_ANY |
|
|
These options override the default newline definition that was chosen | These options override the default newline definition that was chosen |
when PCRE was built. Setting the first or the second specifies that a | when PCRE was built. Setting the first or the second specifies that a |
newline is indicated by a single character (CR or LF, respectively). | newline is indicated by a single character (CR or LF, respectively). |
Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the | Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the |
two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies | two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies |
that any of the three preceding sequences should be recognized. Setting |
that any of the three preceding sequences should be recognized. Setting |
PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be | PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be |
recognized. The Unicode newline sequences are the three just mentioned, | recognized. |
plus the single characters VT (vertical tab, U+000B), FF (form feed, | |
U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS | |
(paragraph separator, U+2029). For the 8-bit library, the last two are | |
recognized only in UTF-8 mode. | |
|
|
|
In an ASCII/Unicode environment, the Unicode newline sequences are the |
|
three just mentioned, plus the single characters VT (vertical tab, |
|
U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line sep- |
|
arator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit |
|
library, the last two are recognized only in UTF-8 mode. |
|
|
|
When PCRE is compiled to run in an EBCDIC (mainframe) environment, the |
|
code for CR is 0x0d, the same as ASCII. However, the character code for |
|
LF is normally 0x15, though in some EBCDIC environments 0x25 is used. |
|
Whichever of these is not LF is made to correspond to Unicode's NEL |
|
character. EBCDIC codes are all less than 256. For more details, see |
|
the pcrebuild documentation. |
|
|
The newline setting in the options word uses three bits that are |
The newline setting in the options word uses three bits that are |
treated as a number, giving eight possibilities. Currently only six are |
treated as a number, giving eight possibilities. Currently only six are |
used (default plus the five values above). This means that if you set |
used (default plus the five values above). This means that if you set |
Line 1758 COMPILING A PATTERN
|
Line 2316 COMPILING A PATTERN
|
be used for capturing (and they acquire numbers in the usual way). |
be used for capturing (and they acquire numbers in the usual way). |
There is no equivalent of this option in Perl. |
There is no equivalent of this option in Perl. |
|
|
NO_START_OPTIMIZE | PCRE_NO_AUTO_POSSESS |
|
|
|
If this option is set, it disables "auto-possessification". This is an |
|
optimization that, for example, turns a+b into a++b in order to avoid |
|
backtracks into a+ that can never be successful. However, if callouts |
|
are in use, auto-possessification means that some of them are never |
|
taken. You can set this option if you want the matching functions to do |
|
a full unoptimized search and run all the callouts, but it is mainly |
|
provided for testing purposes. |
|
|
|
PCRE_NO_START_OPTIMIZE |
|
|
This is an option that acts at matching time; that is, it is really an |
This is an option that acts at matching time; that is, it is really an |
option for pcre_exec() or pcre_dfa_exec(). If it is set at compile |
option for pcre_exec() or pcre_dfa_exec(). If it is set at compile |
time, it is remembered with the compiled pattern and assumed at match- |
time, it is remembered with the compiled pattern and assumed at match- |
ing time. For details see the discussion of PCRE_NO_START_OPTIMIZE | ing time. This is necessary if you want to use JIT execution, because |
below. | the JIT compiler needs to know whether or not this option is set. For |
| details see the discussion of PCRE_NO_START_OPTIMIZE below. |
|
|
PCRE_UCP |
PCRE_UCP |
|
|
This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W, | This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W, |
\w, and some of the POSIX character classes. By default, only ASCII | \w, and some of the POSIX character classes. By default, only ASCII |
characters are recognized, but if PCRE_UCP is set, Unicode properties | characters are recognized, but if PCRE_UCP is set, Unicode properties |
are used instead to classify characters. More details are given in the | are used instead to classify characters. More details are given in the |
section on generic character types in the pcrepattern page. If you set | section on generic character types in the pcrepattern page. If you set |
PCRE_UCP, matching one of the items it affects takes much longer. The | PCRE_UCP, matching one of the items it affects takes much longer. The |
option is available only if PCRE has been compiled with Unicode prop- | option is available only if PCRE has been compiled with Unicode prop- |
erty support. |
erty support. |
|
|
PCRE_UNGREEDY |
PCRE_UNGREEDY |
|
|
This option inverts the "greediness" of the quantifiers so that they | This option inverts the "greediness" of the quantifiers so that they |
are not greedy by default, but become greedy if followed by "?". It is | are not greedy by default, but become greedy if followed by "?". It is |
not compatible with Perl. It can also be set by a (?U) option setting | not compatible with Perl. It can also be set by a (?U) option setting |
within the pattern. |
within the pattern. |
|
|
PCRE_UTF8 |
PCRE_UTF8 |
|
|
This option causes PCRE to regard both the pattern and the subject as | This option causes PCRE to regard both the pattern and the subject as |
strings of UTF-8 characters instead of single-byte strings. However, it |
strings of UTF-8 characters instead of single-byte strings. However, it |
is available only when PCRE is built to include UTF support. If not, | is available only when PCRE is built to include UTF support. If not, |
the use of this option provokes an error. Details of how this option | the use of this option provokes an error. Details of how this option |
changes the behaviour of PCRE are given in the pcreunicode page. |
changes the behaviour of PCRE are given in the pcreunicode page. |
|
|
PCRE_NO_UTF8_CHECK |
PCRE_NO_UTF8_CHECK |
|
|
When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is |
When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is |
automatically checked. There is a discussion about the validity of | automatically checked. There is a discussion about the validity of |
UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is | UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is |
found, pcre_compile() returns an error. If you already know that your | found, pcre_compile() returns an error. If you already know that your |
pattern is valid, and you want to skip this check for performance rea- | pattern is valid, and you want to skip this check for performance rea- |
sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the | sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the |
effect of passing an invalid UTF-8 string as a pattern is undefined. It |
effect of passing an invalid UTF-8 string as a pattern is undefined. It |
may cause your program to crash. Note that this option can also be | may cause your program to crash or loop. Note that this option can also |
passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity | be passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity |
checking of subject strings. | checking of subject strings only. If the same string is being matched |
| many times, the option can be safely set for the second and subsequent |
| matchings to improve performance. |
|
|
|
|
COMPILATION ERROR CODES |
COMPILATION ERROR CODES |
|
|
The following table lists the error codes than may be returned by | The following table lists the error codes than may be returned by |
pcre_compile2(), along with the error messages that may be returned by | pcre_compile2(), along with the error messages that may be returned by |
both compiling functions. Note that error messages are always 8-bit | both compiling functions. Note that error messages are always 8-bit |
ASCII strings, even in 16-bit mode. As PCRE has developed, some error | ASCII strings, even in 16-bit or 32-bit mode. As PCRE has developed, |
codes have fallen out of use. To avoid confusion, they have not been | some error codes have fallen out of use. To avoid confusion, they have |
re-used. | not been re-used. |
|
|
0 no error |
0 no error |
1 \ at end of pattern |
1 \ at end of pattern |
Line 1849 COMPILATION ERROR CODES
|
Line 2420 COMPILATION ERROR CODES
|
31 POSIX collating elements are not supported |
31 POSIX collating elements are not supported |
32 this version of PCRE is compiled without UTF support |
32 this version of PCRE is compiled without UTF support |
33 [this code is not in use] |
33 [this code is not in use] |
34 character value in \x{...} sequence is too large | 34 character value in \x{} or \o{} is too large |
35 invalid condition (?(0) |
35 invalid condition (?(0) |
36 \C not allowed in lookbehind assertion |
36 \C not allowed in lookbehind assertion |
37 PCRE does not support \L, \l, \N{name}, \U, or \u |
37 PCRE does not support \L, \l, \N{name}, \U, or \u |
Line 1877 COMPILATION ERROR CODES
|
Line 2448 COMPILATION ERROR CODES
|
name/number or by a plain number |
name/number or by a plain number |
58 a numbered reference must not be zero |
58 a numbered reference must not be zero |
59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT) |
59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT) |
60 (*VERB) not recognized | 60 (*VERB) not recognized or malformed |
61 number is too big |
61 number is too big |
62 subpattern name expected |
62 subpattern name expected |
63 digit expected after (?+ |
63 digit expected after (?+ |
Line 1896 COMPILATION ERROR CODES
|
Line 2467 COMPILATION ERROR CODES
|
74 invalid UTF-16 string (specifically UTF-16) |
74 invalid UTF-16 string (specifically UTF-16) |
75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN) |
75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN) |
76 character value in \u.... sequence is too large |
76 character value in \u.... sequence is too large |
|
77 invalid UTF-32 string (specifically UTF-32) |
|
78 setting UTF is disabled by the application |
|
79 non-hex character in \x{} (closing brace missing?) |
|
80 non-octal character in \o{} (closing brace missing?) |
|
81 missing opening brace after \o |
|
82 parentheses are too deeply nested |
|
83 invalid range in character class |
|
|
The numbers 32 and 10000 in errors 48 and 49 are defaults; different | The numbers 32 and 10000 in errors 48 and 49 are defaults The numbers 32 and 10000 in errors 48 and 49 are defaults |
values may be used if the limits were changed when PCRE was built. |
values may be used if the limits were changed when PCRE was built. |
|
|
|
|
STUDYING A PATTERN |
STUDYING A PATTERN |
|
|
pcre_extra *pcre_study(const pcre *code, int options | pcre_extra *pcre_study(const pcre *code, int options, |
const char **errptr); |
const char **errptr); |
|
|
If a compiled pattern is going to be used several times, it is worth | If a compiled pattern is going to be used several times, it is worth |
spending more time analyzing it in order to speed up the time taken for |
spending more time analyzing it in order to speed up the time taken for |
matching. The function pcre_study() takes a pointer to a compiled pat- | matching. The function pcre_study() takes a pointer to a compiled pat- |
tern as its first argument. If studying the pattern produces additional |
tern as its first argument. If studying the pattern produces additional |
information that will help speed up matching, pcre_study() returns a | information that will help speed up matching, pcre_study() returns a |
pointer to a pcre_extra block, in which the study_data field points to | pointer to a pcre_extra block, in which the study_data field points to |
the results of the study. |
the results of the study. |
|
|
The returned value from pcre_study() can be passed directly to |
The returned value from pcre_study() can be passed directly to |
pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con- | pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con- |
tains other fields that can be set by the caller before the block is | tains other fields that can be set by the caller before the block is |
passed; these are described below in the section on matching a pattern. |
passed; these are described below in the section on matching a pattern. |
|
|
If studying the pattern does not produce any useful information, | If studying the pattern does not produce any useful information, |
pcre_study() returns NULL. In that circumstance, if the calling program | pcre_study() returns NULL by default. In that circumstance, if the |
wants to pass any of the other fields to pcre_exec() or | calling program wants to pass any of the other fields to pcre_exec() or |
pcre_dfa_exec(), it must set up its own pcre_extra block. | pcre_dfa_exec(), it must set up its own pcre_extra block. However, if |
| pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it |
| returns a pcre_extra block even if studying did not find any additional |
| information. It may still return NULL, however, if an error occurs in |
| pcre_study(). |
|
|
The second argument of pcre_study() contains option bits. There are | The second argument of pcre_study() contains option bits. There are |
three options: | three further options in addition to PCRE_STUDY_EXTRA_NEEDED: |
|
|
PCRE_STUDY_JIT_COMPILE |
PCRE_STUDY_JIT_COMPILE |
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE |
PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE |
|
|
If any of these are set, and the just-in-time compiler is available, | If any of these are set, and the just-in-time compiler is available, |
the pattern is further compiled into machine code that executes much | the pattern is further compiled into machine code that executes much |
faster than the pcre_exec() interpretive matching function. If the | faster than the pcre_exec() interpretive matching function. If the |
just-in-time compiler is not available, these options are ignored. All | just-in-time compiler is not available, these options are ignored. All |
other bits in the options argument must be zero. | undefined bits in the options argument must be zero. |
|
|
JIT compilation is a heavyweight optimization. It can take some time | JIT compilation is a heavyweight optimization. It can take some time |
for patterns to be analyzed, and for one-off matches and simple pat- | for patterns to be analyzed, and for one-off matches and simple pat- |
terns the benefit of faster execution might be offset by a much slower | terns the benefit of faster execution might be offset by a much slower |
study time. Not all patterns can be optimized by the JIT compiler. For |
study time. Not all patterns can be optimized by the JIT compiler. For |
those that cannot be handled, matching automatically falls back to the | those that cannot be handled, matching automatically falls back to the |
pcre_exec() interpreter. For more details, see the pcrejit documenta- | pcre_exec() interpreter. For more details, see the pcrejit documenta- |
tion. |
tion. |
|
|
The third argument for pcre_study() is a pointer for an error message. | The third argument for pcre_study() is a pointer for an error message. |
If studying succeeds (even if no data is returned), the variable it | If studying succeeds (even if no data is returned), the variable it |
points to is set to NULL. Otherwise it is set to point to a textual | points to is set to NULL. Otherwise it is set to point to a textual |
error message. This is a static string that is part of the library. You |
error message. This is a static string that is part of the library. You |
must not try to free it. You should test the error pointer for NULL | must not try to free it. You should test the error pointer for NULL |
after calling pcre_study(), to be sure that it has run successfully. |
after calling pcre_study(), to be sure that it has run successfully. |
|
|
When you are finished with a pattern, you can free the memory used for | When you are finished with a pattern, you can free the memory used for |
the study data by calling pcre_free_study(). This function was added to |
the study data by calling pcre_free_study(). This function was added to |
the API for release 8.20. For earlier versions, the memory could be | the API for release 8.20. For earlier versions, the memory could be |
freed with pcre_free(), just like the pattern itself. This will still | freed with pcre_free(), just like the pattern itself. This will still |
work in cases where JIT optimization is not used, but it is advisable | work in cases where JIT optimization is not used, but it is advisable |
to change to the new function when convenient. |
to change to the new function when convenient. |
|
|
This is a typical way in which pcre_study() is used (except that in a | This is a typical way in which pcre_study() is used (except that in a |
real application there should be tests for errors): |
real application there should be tests for errors): |
|
|
int rc; |
int rc; |
Line 1979 STUDYING A PATTERN
|
Line 2561 STUDYING A PATTERN
|
Studying a pattern does two things: first, a lower bound for the length |
Studying a pattern does two things: first, a lower bound for the length |
of subject string that is needed to match the pattern is computed. This |
of subject string that is needed to match the pattern is computed. This |
does not mean that there are any strings of that length that match, but |
does not mean that there are any strings of that length that match, but |
it does guarantee that no shorter strings match. The value is used by | it does guarantee that no shorter strings match. The value is used to |
pcre_exec() and pcre_dfa_exec() to avoid wasting time by trying to | avoid wasting time by trying to match strings that are shorter than the |
match strings that are shorter than the lower bound. You can find out | lower bound. You can find out the value in a calling program via the |
the value in a calling program via the pcre_fullinfo() function. | |
|
|
Studying a pattern is also useful for non-anchored patterns that do not |
Studying a pattern is also useful for non-anchored patterns that do not |
have a single fixed starting character. A bitmap of possible starting | have a single fixed starting character. A bitmap of possible starting |
bytes is created. This speeds up finding a position in the subject at | bytes is created. This speeds up finding a position in the subject at |
which to start matching. (In 16-bit mode, the bitmap is used for 16-bit |
which to start matching. (In 16-bit mode, the bitmap is used for 16-bit |
|
values less than 256. In 32-bit mode, the bitmap is used for 32-bit |
values less than 256.) |
values less than 256.) |
|
|
These two optimizations apply to both pcre_exec() and pcre_dfa_exec(), |
These two optimizations apply to both pcre_exec() and pcre_dfa_exec(), |
and the information is also used by the JIT compiler. The optimiza- |
and the information is also used by the JIT compiler. The optimiza- |
tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option when | tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option. |
calling pcre_exec() or pcre_dfa_exec(), but if this is done, JIT execu- | You might want to do this if your pattern contains callouts or (*MARK) |
tion is also disabled. You might want to do this if your pattern con- | and you want to make use of these facilities in cases where matching |
tains callouts or (*MARK) and you want to make use of these facilities | fails. |
in cases where matching fails. See the discussion of | |
PCRE_NO_START_OPTIMIZE below. | |
|
|
|
PCRE_NO_START_OPTIMIZE can be specified at either compile time or exe- |
|
cution time. However, if PCRE_NO_START_OPTIMIZE is passed to |
|
pcre_exec(), (that is, after any JIT compilation has happened) JIT exe- |
|
cution is disabled. For JIT execution to work with PCRE_NO_START_OPTI- |
|
MIZE, the option must be set at compile time. |
|
|
|
There is a longer discussion of PCRE_NO_START_OPTIMIZE below. |
|
|
|
|
LOCALE SUPPORT |
LOCALE SUPPORT |
|
|
PCRE handles caseless matching, and determines whether characters are |
PCRE handles caseless matching, and determines whether characters are |
letters, digits, or whatever, by reference to a set of tables, indexed |
letters, digits, or whatever, by reference to a set of tables, indexed |
by character value. When running in UTF-8 mode, this applies only to | by character code point. When running in UTF-8 mode, or in the 16- or |
characters with codes less than 128. By default, higher-valued codes | 32-bit libraries, this applies only to characters with code points less |
never match escapes such as \w or \d, but they can be tested with \p if | than 256. By default, higher-valued code points never match escapes |
PCRE is built with Unicode character property support. Alternatively, | such as \w or \d. However, if PCRE is built with Unicode property sup- |
the PCRE_UCP option can be set at compile time; this causes \w and | port, all characters can be tested with \p and \P, or, alternatively, |
friends to use Unicode property support instead of built-in tables. The | the PCRE_UCP option can be set when a pattern is compiled; this causes |
use of locales with Unicode is discouraged. If you are handling charac- | \w and friends to use Unicode property support instead of the built-in |
ters with codes greater than 128, you should either use UTF-8 and Uni- | tables. |
code, or use locales, but not try to mix the two. | |
|
|
PCRE contains an internal set of tables that are used when the final | The use of locales with Unicode is discouraged. If you are handling |
argument of pcre_compile() is NULL. These are sufficient for many | characters with code points greater than 128, you should either use |
| Unicode support, or use locales, but not try to mix the two. |
| |
| PCRE contains an internal set of tables that are used when the final |
| argument of pcre_compile() is NULL. These are sufficient for many |
applications. Normally, the internal tables recognize only ASCII char- |
applications. Normally, the internal tables recognize only ASCII char- |
acters. However, when PCRE is built, it is possible to cause the inter- |
acters. However, when PCRE is built, it is possible to cause the inter- |
nal tables to be rebuilt in the default "C" locale of the local system, |
nal tables to be rebuilt in the default "C" locale of the local system, |
which may cause them to be different. |
which may cause them to be different. |
|
|
The internal tables can always be overridden by tables supplied by the | The internal tables can always be overridden by tables supplied by the |
application that calls PCRE. These may be created in a different locale |
application that calls PCRE. These may be created in a different locale |
from the default. As more and more applications change to using Uni- | from the default. As more and more applications change to using Uni- |
code, the need for this locale support is expected to die away. |
code, the need for this locale support is expected to die away. |
|
|
External tables are built by calling the pcre_maketables() function, | External tables are built by calling the pcre_maketables() function, |
which has no arguments, in the relevant locale. The result can then be | which has no arguments, in the relevant locale. The result can then be |
passed to pcre_compile() or pcre_exec() as often as necessary. For | passed to pcre_compile() as often as necessary. For example, to build |
example, to build and use tables that are appropriate for the French | and use tables that are appropriate for the French locale (where |
locale (where accented characters with values greater than 128 are | accented characters with values greater than 128 are treated as let- |
treated as letters), the following code could be used: | ters), the following code could be used: |
|
|
setlocale(LC_CTYPE, "fr_FR"); |
setlocale(LC_CTYPE, "fr_FR"); |
tables = pcre_maketables(); |
tables = pcre_maketables(); |
re = pcre_compile(..., tables); |
re = pcre_compile(..., tables); |
|
|
The locale name "fr_FR" is used on Linux and other Unix-like systems; | The locale name "fr_FR" is used on Linux and other Unix-like systems; |
if you are using Windows, the name for the French locale is "french". |
if you are using Windows, the name for the French locale is "french". |
|
|
When pcre_maketables() runs, the tables are built in memory that is | When pcre_maketables() runs, the tables are built in memory that is |
obtained via pcre_malloc. It is the caller's responsibility to ensure | obtained via pcre_malloc. It is the caller's responsibility to ensure |
that the memory containing the tables remains available for as long as | that the memory containing the tables remains available for as long as |
it is needed. |
it is needed. |
|
|
The pointer that is passed to pcre_compile() is saved with the compiled |
The pointer that is passed to pcre_compile() is saved with the compiled |
pattern, and the same tables are used via this pointer by pcre_study() | pattern, and the same tables are used via this pointer by pcre_study() |
and normally also by pcre_exec(). Thus, by default, for any single pat- | and also by pcre_exec() and pcre_dfa_exec(). Thus, for any single pat- |
tern, compilation, studying and matching all happen in the same locale, |
tern, compilation, studying and matching all happen in the same locale, |
but different patterns can be compiled in different locales. | but different patterns can be processed in different locales. |
|
|
It is possible to pass a table pointer or NULL (indicating the use of | It is possible to pass a table pointer or NULL (indicating the use of |
the internal tables) to pcre_exec(). Although not intended for this | the internal tables) to pcre_exec() or pcre_dfa_exec() (see the discus- |
purpose, this facility could be used to match a pattern in a different | sion below in the section on matching a pattern). This facility is pro- |
locale from the one in which it was compiled. Passing table pointers at | vided for use with pre-compiled patterns that have been saved and |
run time is discussed below in the section on matching a pattern. | reloaded. Character tables are not saved with patterns, so if a non- |
| standard table was used at compile time, it must be provided again when |
| the reloaded pattern is matched. Attempting to use this facility to |
| match a pattern in a different locale from the one in which it was com- |
| piled is likely to lead to anomalous (usually incorrect) results. |
|
|
|
|
INFORMATION ABOUT A PATTERN |
INFORMATION ABOUT A PATTERN |
Line 2063 INFORMATION ABOUT A PATTERN
|
Line 2659 INFORMATION ABOUT A PATTERN
|
int pcre_fullinfo(const pcre *code, const pcre_extra *extra, |
int pcre_fullinfo(const pcre *code, const pcre_extra *extra, |
int what, void *where); |
int what, void *where); |
|
|
The pcre_fullinfo() function returns information about a compiled pat- | The pcre_fullinfo() function returns information about a compiled pat- |
tern. It replaces the pcre_info() function, which was removed from the | tern. It replaces the pcre_info() function, which was removed from the |
library at version 8.30, after more than 10 years of obsolescence. |
library at version 8.30, after more than 10 years of obsolescence. |
|
|
The first argument for pcre_fullinfo() is a pointer to the compiled | The first argument for pcre_fullinfo() is a pointer to the compiled |
pattern. The second argument is the result of pcre_study(), or NULL if | pattern. The second argument is the result of pcre_study(), or NULL if |
the pattern was not studied. The third argument specifies which piece | the pattern was not studied. The third argument specifies which piece |
of information is required, and the fourth argument is a pointer to a | of information is required, and the fourth argument is a pointer to a |
variable to receive the data. The yield of the function is zero for | variable to receive the data. The yield of the function is zero for |
success, or one of the following negative numbers: |
success, or one of the following negative numbers: |
|
|
PCRE_ERROR_NULL the argument code was NULL |
PCRE_ERROR_NULL the argument code was NULL |
Line 2080 INFORMATION ABOUT A PATTERN
|
Line 2676 INFORMATION ABOUT A PATTERN
|
PCRE_ERROR_BADENDIANNESS the pattern was compiled with different |
PCRE_ERROR_BADENDIANNESS the pattern was compiled with different |
endianness |
endianness |
PCRE_ERROR_BADOPTION the value of what was invalid |
PCRE_ERROR_BADOPTION the value of what was invalid |
|
PCRE_ERROR_UNSET the requested field is not set |
|
|
The "magic number" is placed at the start of each compiled pattern as | The "magic number" is placed at the start of each compiled pattern as |
an simple check against passing an arbitrary memory pointer. The endi- | an simple check against passing an arbitrary memory pointer. The endi- |
anness error can occur if a compiled pattern is saved and reloaded on a |
anness error can occur if a compiled pattern is saved and reloaded on a |
different host. Here is a typical call of pcre_fullinfo(), to obtain | different host. Here is a typical call of pcre_fullinfo(), to obtain |
the length of the compiled pattern: |
the length of the compiled pattern: |
|
|
int rc; |
int rc; |
Line 2095 INFORMATION ABOUT A PATTERN
|
Line 2692 INFORMATION ABOUT A PATTERN
|
PCRE_INFO_SIZE, /* what is required */ |
PCRE_INFO_SIZE, /* what is required */ |
&length); /* where to put the data */ |
&length); /* where to put the data */ |
|
|
The possible values for the third argument are defined in pcre.h, and | The possible values for the third argument are defined The possible values for the third argument are defined in pcre.h, and |
are as follows: |
are as follows: |
|
|
PCRE_INFO_BACKREFMAX |
PCRE_INFO_BACKREFMAX |
|
|
Return the number of the highest back reference in the pattern. The | Return the number of the highest back reference in the pattern. The |
fourth argument should point to an int variable. Zero is returned if | fourth argument should point to an int variable. Zero is returned if |
there are no back references. |
there are no back references. |
|
|
PCRE_INFO_CAPTURECOUNT |
PCRE_INFO_CAPTURECOUNT |
|
|
Return the number of capturing subpatterns in the pattern. The fourth | Return the number of capturing subpatterns in the pattern. The fourth |
argument should point to an int variable. |
argument should point to an int variable. |
|
|
PCRE_INFO_DEFAULT_TABLES |
PCRE_INFO_DEFAULT_TABLES |
|
|
Return a pointer to the internal default character tables within PCRE. | Return a pointer to the internal default character tables within PCRE. |
The fourth argument should point to an unsigned char * variable. This | The fourth argument should point to an unsigned char * variable. This |
information call is provided for internal use by the pcre_study() func- |
information call is provided for internal use by the pcre_study() func- |
tion. External callers can cause PCRE to use its internal tables by | tion. External callers can cause PCRE to use its internal tables by |
passing a NULL table pointer. |
passing a NULL table pointer. |
|
|
PCRE_INFO_FIRSTBYTE |
PCRE_INFO_FIRSTBYTE |
|
|
Return information about the first data unit of any matched string, for |
Return information about the first data unit of any matched string, for |
a non-anchored pattern. (The name of this option refers to the 8-bit | a non-anchored pattern. (The name of this option refers to the 8-bit |
library, where data units are bytes.) The fourth argument should point | library, where data units are bytes.) The fourth argument should point |
to an int variable. |
to an int variable. |
|
|
If there is a fixed first value, for example, the letter "c" from a | If there is a fixed first value, for example, the letter "c" from a |
pattern such as (cat|cow|coyote), its value is returned. In the 8-bit | pattern such as (cat|cow|coyote), its value is returned. In the 8-bit |
library, the value is always less than 256; in the 16-bit library the | library, the value is always less than 256. In the 16-bit library the |
value can be up to 0xffff. | value can be up to 0xffff. In the 32-bit library the value can be up to |
| 0x10ffff. |
|
|
If there is no fixed first value, and if either |
If there is no fixed first value, and if either |
|
|
Line 2141 INFORMATION ABOUT A PATTERN
|
Line 2739 INFORMATION ABOUT A PATTERN
|
of a subject string or after any newline within the string. Otherwise |
of a subject string or after any newline within the string. Otherwise |
-2 is returned. For anchored patterns, -2 is returned. |
-2 is returned. For anchored patterns, -2 is returned. |
|
|
|
Since for the 32-bit library using the non-UTF-32 mode, this function |
|
is unable to return the full 32-bit range of the character, this value |
|
is deprecated; instead the PCRE_INFO_FIRSTCHARACTERFLAGS and |
|
PCRE_INFO_FIRSTCHARACTER values should be used. |
|
|
PCRE_INFO_FIRSTTABLE |
PCRE_INFO_FIRSTTABLE |
|
|
If the pattern was studied, and this resulted in the construction of a | If the pattern was studied, and this resulted in the construction of a |
256-bit table indicating a fixed set of values for the first data unit | 256-bit table indicating a fixed set of values for the first data unit |
in any matching string, a pointer to the table is returned. Otherwise | in any matching string, a pointer to the table is returned. Otherwise |
NULL is returned. The fourth argument should point to an unsigned char | NULL is returned. The fourth argument should point to an unsigned char |
* variable. |
* variable. |
|
|
PCRE_INFO_HASCRORLF |
PCRE_INFO_HASCRORLF |
|
|
Return 1 if the pattern contains any explicit matches for CR or LF | Return 1 if the pattern contains any explicit matches for CR or LF |
characters, otherwise 0. The fourth argument should point to an int | characters, otherwise 0. The fourth argument should point to an int |
variable. An explicit match is either a literal CR or LF character, or | variable. An explicit match is either a literal CR or LF character, or |
\r or \n. |
\r or \n. |
|
|
PCRE_INFO_JCHANGED |
PCRE_INFO_JCHANGED |
|
|
Return 1 if the (?J) or (?-J) option setting is used in the pattern, | Return 1 if the (?J) or (?-J) option setting is used in the pattern, |
otherwise 0. The fourth argument should point to an int variable. (?J) | otherwise 0. The fourth argument should point to an int variable. (?J) |
and (?-J) set and unset the local PCRE_DUPNAMES option, respectively. |
and (?-J) set and unset the local PCRE_DUPNAMES option, respectively. |
|
|
PCRE_INFO_JIT |
PCRE_INFO_JIT |
|
|
Return 1 if the pattern was studied with one of the JIT options, and | Return 1 if the pattern was studied with one of the JIT options, and |
just-in-time compiling was successful. The fourth argument should point |
just-in-time compiling was successful. The fourth argument should point |
to an int variable. A return value of 0 means that JIT support is not | to an int variable. A return value of 0 means that JIT support is not |
available in this version of PCRE, or that the pattern was not studied | available in this version of PCRE, or that the pattern was not studied |
with a JIT option, or that the JIT compiler could not handle this par- | with a JIT option, or that the JIT compiler could not handle this par- |
ticular pattern. See the pcrejit documentation for details of what can | ticular pattern. See the pcrejit documentation for details of what can |
and cannot be handled. |
and cannot be handled. |
|
|
PCRE_INFO_JITSIZE |
PCRE_INFO_JITSIZE |
|
|
If the pattern was successfully studied with a JIT option, return the | If the pattern was successfully studied with a JIT option, return the |
size of the JIT compiled code, otherwise return zero. The fourth argu- | size of the JIT compiled code, otherwise return zero. The fourth argu- |
ment should point to a size_t variable. |
ment should point to a size_t variable. |
|
|
PCRE_INFO_LASTLITERAL |
PCRE_INFO_LASTLITERAL |
|
|
Return the value of the rightmost literal data unit that must exist in | Return the value of the rightmost literal data unit that must exist in |
any matched string, other than at its start, if such a value has been | any matched string, other than at its start, if such a value has been |
recorded. The fourth argument should point to an int variable. If there |
recorded. The fourth argument should point to an int variable. If there |
is no such value, -1 is returned. For anchored patterns, a last literal |
is no such value, -1 is returned. For anchored patterns, a last literal |
value is recorded only if it follows something of variable length. For | value is recorded only if it follows something of variable length. For |
example, for the pattern /^a\d+z\d+/ the returned value is "z", but for |
example, for the pattern /^a\d+z\d+/ the returned value is "z", but for |
/^a\dz\d/ the returned value is -1. |
/^a\dz\d/ the returned value is -1. |
|
|
|
Since for the 32-bit library using the non-UTF-32 mode, this function |
|
is unable to return the full 32-bit range of characters, this value is |
|
deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and |
|
PCRE_INFO_REQUIREDCHAR values should be used. |
|
|
|
PCRE_INFO_MATCH_EMPTY |
|
|
|
Return 1 if the pattern can match an empty string, otherwise 0. The |
|
fourth argument should point to an int variable. |
|
|
|
PCRE_INFO_MATCHLIMIT |
|
|
|
If the pattern set a match limit by including an item of the form |
|
(*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth |
|
argument should point to an unsigned 32-bit integer. If no such value |
|
has been set, the call to pcre_fullinfo() returns the error |
|
PCRE_ERROR_UNSET. |
|
|
PCRE_INFO_MAXLOOKBEHIND |
PCRE_INFO_MAXLOOKBEHIND |
|
|
Return the number of characters (NB not bytes) in the longest lookbe- | Return the number of characters (NB not data units) in the longest |
hind assertion in the pattern. Note that the simple assertions \b and | lookbehind assertion in the pattern. This information is useful when |
\B require a one-character lookbehind. This information is useful when | doing multi-segment matching using the partial matching facilities. |
doing multi-segment matching using the partial matching facilities. | Note that the simple assertions \b and \B require a one-character look- |
| behind. \A also registers a one-character lookbehind, though it does |
| not actually inspect the previous character. This is to ensure that at |
| least one character from the old segment is retained when a new segment |
| is processed. Otherwise, if there are no lookbehinds in the pattern, \A |
| might match incorrectly at the start of a new segment. |
|
|
PCRE_INFO_MINLENGTH |
PCRE_INFO_MINLENGTH |
|
|
If the pattern was studied and a minimum length for matching subject |
If the pattern was studied and a minimum length for matching subject |
strings was computed, its value is returned. Otherwise the returned |
strings was computed, its value is returned. Otherwise the returned |
value is -1. The value is a number of characters, which in UTF-8 mode | value is -1. The value is a number of characters, which in UTF mode may |
may be different from the number of bytes. The fourth argument should | be different from the number of data units. The fourth argument should |
point to an int variable. A non-negative value is a lower bound to the |
point to an int variable. A non-negative value is a lower bound to the |
length of any matching string. There may not be any strings of that |
length of any matching string. There may not be any strings of that |
length that do actually match, but every string that does match is at |
length that do actually match, but every string that does match is at |
Line 2228 INFORMATION ABOUT A PATTERN
|
Line 2854 INFORMATION ABOUT A PATTERN
|
the 8-bit library, where the first two bytes of each entry are the num- |
the 8-bit library, where the first two bytes of each entry are the num- |
ber of the capturing parenthesis, most significant byte first. In the |
ber of the capturing parenthesis, most significant byte first. In the |
16-bit library, the pointer points to 16-bit data units, the first of |
16-bit library, the pointer points to 16-bit data units, the first of |
which contains the parenthesis number. The rest of the entry is the | which contains the parenthesis number. In the 32-bit library, the |
corresponding name, zero terminated. | pointer points to 32-bit data units, the first of which contains the |
| parenthesis number. The rest of the entry is the corresponding name, |
| zero terminated. |
|
|
The names are in alphabetical order. Duplicate names may appear if (?| | The names are in alphabetical order. If (?| is used to create multiple |
is used to create multiple groups with the same number, as described in | groups with the same number, as described in the section on duplicate |
the section on duplicate subpattern numbers in the pcrepattern page. | subpattern numbers in the pcrepattern page, the groups may be given the |
Duplicate names for subpatterns with different numbers are permitted | same name, but there is only one entry in the table. Different names |
only if PCRE_DUPNAMES is set. In all cases of duplicate names, they | for groups of the same number are not permitted. Duplicate names for |
appear in the table in the order in which they were found in the pat- | subpatterns with different numbers are permitted, but only if PCRE_DUP- |
tern. In the absence of (?| this is the order of increasing number; | NAMES is set. They appear in the table in the order in which they were |
when (?| is used this is not necessarily the case because later subpat- | found in the pattern. In the absence of (?| this is the order of |
terns may have lower numbers. | increasing number; when (?| is used this is not necessarily the case |
| because later subpatterns may have lower numbers. |
|
|
As a simple example of the name/number table, consider the following | As a simple example of the name/number tab As a simple example of the name/number table, consider the following |
pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is |
pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is |
set, so white space - including newlines - is ignored): |
set, so white space - including newlines - is ignored): |
|
|
(?<date> (?<year>(\d\d)?\d\d) - |
(?<date> (?<year>(\d\d)?\d\d) - |
(?<month>\d\d) - (?<day>\d\d) ) |
(?<month>\d\d) - (?<day>\d\d) ) |
|
|
There are four named subpatterns, so the table has four entries, and | There are four named subpatterns, so the table has four entries, and |
each entry in the table is eight bytes long. The table is as follows, | each entry in the table is eight bytes long. The table is as follows, |
with non-printing bytes shows in hexadecimal, and undefined bytes shown |
with non-printing bytes shows in hexadecimal, and undefined bytes shown |
as ??: |
as ??: |
|
|
Line 2258 INFORMATION ABOUT A PATTERN
|
Line 2887 INFORMATION ABOUT A PATTERN
|
00 04 m o n t h 00 |
00 04 m o n t h 00 |
00 02 y e a r 00 ?? |
00 02 y e a r 00 ?? |
|
|
When writing code to extract data from named subpatterns using the | When writing code to extract data from named subpatterns using the |
name-to-number map, remember that the length of the entries is likely | name-to-number map, remember that the length of the entries is likely |
to be different for each compiled pattern. |
to be different for each compiled pattern. |
|
|
PCRE_INFO_OKPARTIAL |
PCRE_INFO_OKPARTIAL |
|
|
Return 1 if the pattern can be used for partial matching with | Return 1 if the pattern can be used for partial matching with |
pcre_exec(), otherwise 0. The fourth argument should point to an int | pcre_exec(), otherwise 0. The fourth argument should point to an int |
variable. From release 8.00, this always returns 1, because the | variable. From release 8.00, this always returns 1, because the |
restrictions that previously applied to partial matching have been | restrictions that previously applied to partial matching have been |
lifted. The pcrepartial documentation gives details of partial match- | lifted. The pcrepartial documentation gives details of partial match- |
ing. |
ing. |
|
|
PCRE_INFO_OPTIONS |
PCRE_INFO_OPTIONS |
|
|
Return a copy of the options with which the pattern was compiled. The | Return a copy of the options with which the pattern was compiled. The |
fourth argument should point to an unsigned long int variable. These | fourth argument should point to an unsigned long int variable. These |
option bits are those specified in the call to pcre_compile(), modified |
option bits are those specified in the call to pcre_compile(), modified |
by any top-level option settings at the start of the pattern itself. In |
by any top-level option settings at the start of the pattern itself. In |
other words, they are the options that will be in force when matching | other words, they are the options that will be in force when matching |
starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with | starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with |
the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE, | the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE, |
and PCRE_EXTENDED. |
and PCRE_EXTENDED. |
|
|
A pattern is automatically anchored by PCRE if all of its top-level | A pattern is automatically anchored by PCRE if all of its top-level |
alternatives begin with one of the following: |
alternatives begin with one of the following: |
|
|
^ unless PCRE_MULTILINE is set |
^ unless PCRE_MULTILINE is set |
Line 2294 INFORMATION ABOUT A PATTERN
|
Line 2923 INFORMATION ABOUT A PATTERN
|
For such patterns, the PCRE_ANCHORED bit is set in the options returned |
For such patterns, the PCRE_ANCHORED bit is set in the options returned |
by pcre_fullinfo(). |
by pcre_fullinfo(). |
|
|
|
PCRE_INFO_RECURSIONLIMIT |
|
|
|
If the pattern set a recursion limit by including an item of the form |
|
(*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth |
|
argument should point to an unsigned 32-bit integer. If no such value |
|
has been set, the call to pcre_fullinfo() returns the error |
|
PCRE_ERROR_UNSET. |
|
|
PCRE_INFO_SIZE |
PCRE_INFO_SIZE |
|
|
Return the size of the compiled pattern in bytes (for both libraries). | Return the size of the compiled pattern in bytes (for all three |
The fourth argument should point to a size_t variable. This value does | libraries). The fourth argument should point to a size_t variable. This |
not include the size of the pcre structure that is returned by | value does not include the size of the pcre structure that is returned |
pcre_compile(). The value that is passed as the argument to pcre_mal- | by pcre_compile(). The value that is passed as the argument to |
loc() when pcre_compile() is getting memory in which to place the com- | pcre_malloc() when pcre_compile() is getting memory in which to place |
piled data is the value returned by this option plus the size of the | the compiled data is the value returned by this option plus the size of |
pcre structure. Studying a compiled pattern, with or without JIT, does | the pcre structure. Studying a compiled pattern, with or without JIT, |
not alter the value returned by this option. | does not alter the value returned by this option. |
|
|
PCRE_INFO_STUDYSIZE |
PCRE_INFO_STUDYSIZE |
|
|
Return the size in bytes of the data block pointed to by the study_data | Return the size in bytes (for all three libraries) of the data block |
field in a pcre_extra block. If pcre_extra is NULL, or there is no | pointed to by the study_data field in a pcre_extra block. If pcre_extra |
study data, zero is returned. The fourth argument should point to a | is NULL, or there is no study data, zero is returned. The fourth argu- |
size_t variable. The study_data field is set by pcre_study() to record | ment should point to a size_t variable. The study_data field is set by |
information that will speed up matching (see the section entitled | pcre_study() to record information that will speed up matching (see the |
"Studying a pattern" above). The format of the study_data block is pri- | section entitled "Studying a pattern" above). The format of the |
vate, but its length is made available via this option so that it can | study_data block is private, but its length is made available via this |
be saved and restored (see the pcreprecompile documentation for | option so that it can be saved and restored (see the pcreprecompile |
details). | documentation for details). |
|
|
|
PCRE_INFO_FIRSTCHARACTERFLAGS |
|
|
|
Return information about the first data unit of any matched string, for |
|
a non-anchored pattern. The fourth argument should point to an int |
|
variable. |
|
|
|
If there is a fixed first value, for example, the letter "c" from a |
|
pattern such as (cat|cow|coyote), 1 is returned, and the character |
|
value can be retrieved using PCRE_INFO_FIRSTCHARACTER. |
|
|
|
If there is no fixed first value, and if either |
|
|
|
(a) the pattern was compiled with the PCRE_MULTILINE option, and every |
|
branch starts with "^", or |
|
|
|
(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not |
|
set (if it were set, the pattern would be anchored), |
|
|
|
2 is returned, indicating that the pattern matches only at the start of |
|
a subject string or after any newline within the string. Otherwise 0 is |
|
returned. For anchored patterns, 0 is returned. |
|
|
|
PCRE_INFO_FIRSTCHARACTER |
|
|
|
Return the fixed first character value in the situation where |
|
PCRE_INFO_FIRSTCHARACTERFLAGS returns 1; otherwise return 0. The fourth |
|
argument should point to an uint_t variable. |
|
|
|
In the 8-bit library, the value is always less than 256. In the 16-bit |
|
library the value can be up to 0xffff. In the 32-bit library in UTF-32 |
|
mode the value can be up to 0x10ffff, and up to 0xffffffff when not |
|
using UTF-32 mode. |
|
|
|
PCRE_INFO_REQUIREDCHARFLAGS |
|
|
|
Returns 1 if there is a rightmost literal data unit that must exist in |
|
any matched string, other than at its start. The fourth argument should |
|
point to an int variable. If there is no such value, 0 is returned. If |
|
returning 1, the character value itself can be retrieved using |
|
PCRE_INFO_REQUIREDCHAR. |
|
|
|
For anchored patterns, a last literal value is recorded only if it fol- |
|
lows something of variable length. For example, for the pattern |
|
/^a\d+z\d+/ the returned value 1 (with "z" returned from |
|
PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0. |
|
|
|
PCRE_INFO_REQUIREDCHAR |
|
|
|
Return the value of the rightmost literal data unit that must exist in |
|
any matched string, other than at its start, if such a value has been |
|
recorded. The fourth argument should point to an uint32_t variable. If |
|
there is no such value, 0 is returned. |
|
|
|
|
REFERENCE COUNTS |
REFERENCE COUNTS |
|
|
int pcre_refcount(pcre *code, int adjust); |
int pcre_refcount(pcre *code, int adjust); |
Line 2398 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3088 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
In the 16-bit version of this structure, the mark field has type |
In the 16-bit version of this structure, the mark field has type |
"PCRE_UCHAR16 **". |
"PCRE_UCHAR16 **". |
|
|
The flags field is used to specify which of the other fields are set. | In the 32-bit version of this structure, the mark field has type |
| "PCRE_UCHAR32 **". |
| |
| The flags field is used to specify which of the other fields are set. |
The flag bits are: |
The flag bits are: |
|
|
PCRE_EXTRA_CALLOUT_DATA |
PCRE_EXTRA_CALLOUT_DATA |
Line 2409 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3102 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_EXTRA_STUDY_DATA |
PCRE_EXTRA_STUDY_DATA |
PCRE_EXTRA_TABLES |
PCRE_EXTRA_TABLES |
|
|
Other flag bits should be set to zero. The study_data field and some- | Other flag bits should be set to zero. The study_data field and some- |
times the executable_jit field are set in the pcre_extra block that is | times the executable_jit field are set in the pcre_extra block that is |
returned by pcre_study(), together with the appropriate flag bits. You | returned by pcre_study(), together with the appropriate flag bits. You |
should not set these yourself, but you may add to the block by setting | should not set these yourself, but you may add to the block by setting |
other fields and their corresponding flag bits. |
other fields and their corresponding flag bits. |
|
|
The match_limit field provides a means of preventing PCRE from using up |
The match_limit field provides a means of preventing PCRE from using up |
a vast amount of resources when running patterns that are not going to | a vast amount of resources when running patterns that are not going to |
match, but which have a very large number of possibilities in their | match, but which have a very large number of possibilities in their |
search trees. The classic example is a pattern that uses nested unlim- | search trees. The classic example is a pattern that uses nested unlim- |
ited repeats. |
ited repeats. |
|
|
Internally, pcre_exec() uses a function called match(), which it calls | Internally, pcre_exec() uses a function called match(), which it calls |
repeatedly (sometimes recursively). The limit set by match_limit is | repeatedly (sometimes recursively). The limit set by match_limit is |
imposed on the number of times this function is called during a match, | imposed on the number of times this function is called during a match, |
which has the effect of limiting the amount of backtracking that can | which has the effect of limiting the amount of backtracking that can |
take place. For patterns that are not anchored, the count restarts from |
take place. For patterns that are not anchored, the count restarts from |
zero for each position in the subject string. |
zero for each position in the subject string. |
|
|
When pcre_exec() is called with a pattern that was successfully studied |
When pcre_exec() is called with a pattern that was successfully studied |
with a JIT option, the way that the matching is executed is entirely | with a JIT option, the way that the matching is executed is entirely |
different. However, there is still the possibility of runaway matching |
different. However, there is still the possibility of runaway matching |
that goes on for a very long time, and so the match_limit value is also |
that goes on for a very long time, and so the match_limit value is also |
used in this case (but in a different way) to limit how long the match- |
used in this case (but in a different way) to limit how long the match- |
ing can continue. |
ing can continue. |
|
|
The default value for the limit can be set when PCRE is built; the | The default value for the limit can be set when PCRE is built; the |
default default is 10 million, which handles all but the most extreme | default default is 10 million, which handles all but the most extreme |
cases. You can override the default by suppling pcre_exec() with a | cases. You can override the default by suppling pcre_exec() with a |
pcre_extra block in which match_limit is set, and | pcre_extra block in which match_limit is set, and |
PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is | PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is |
exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT. |
exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT. |
|
|
|
A value for the match limit may also be supplied by an item at the |
|
start of a pattern of the form |
|
|
|
(*LIMIT_MATCH=d) |
|
|
|
where d is a decimal number. However, such a setting is ignored unless |
|
d is less than the limit set by the caller of pcre_exec() or, if no |
|
such limit is set, less than the default. |
|
|
The match_limit_recursion field is similar to match_limit, but instead |
The match_limit_recursion field is similar to match_limit, but instead |
of limiting the total number of times that match() is called, it limits |
of limiting the total number of times that match() is called, it limits |
the depth of recursion. The recursion depth is a smaller number than |
the depth of recursion. The recursion depth is a smaller number than |
Line 2461 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3163 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the |
PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the |
limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT. |
limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT. |
|
|
The callout_data field is used in conjunction with the "callout" fea- | A value for the recursion limit may also be supplied by an item at the |
| start of a pattern of the form |
| |
| (*LIMIT_RECURSION=d) |
| |
| where d is a decimal number. However, such a setting is ignored unless |
| d is less than the limit set by the caller of pcre_exec() or, if no |
| such limit is set, less than the default. |
| |
| The callout_data field is used in conjunction with the "callout" fea- |
ture, and is described in the pcrecallout documentation. |
ture, and is described in the pcrecallout documentation. |
|
|
The tables field is used to pass a character tables pointer to | The tables field is provided for use with patterns that have been pre- |
pcre_exec(); this overrides the value that is stored with the compiled | compiled using custom character tables, saved to disc or elsewhere, and |
pattern. A non-NULL value is stored with the compiled pattern only if | then reloaded, because the tables that were used to compile a pattern |
custom tables were supplied to pcre_compile() via its tableptr argu- | are not saved with it. See the pcreprecompile documentation for a dis- |
ment. If NULL is passed to pcre_exec() using this mechanism, it forces | cussion of saving compiled patterns for later use. If NULL is passed |
PCRE's internal tables to be used. This facility is helpful when re- | using this mechanism, it forces PCRE's internal tables to be used. |
using patterns that have been saved after compiling with an external | |
set of tables, because the external tables might be at a different | |
address when pcre_exec() is called. See the pcreprecompile documenta- | |
tion for a discussion of saving compiled patterns for later use. | |
|
|
If PCRE_EXTRA_MARK is set in the flags field, the mark field must be | Warning: The tables that pcre_exec() uses must be the same as those |
set to point to a suitable variable. If the pattern contains any back- | that were used when the pattern was compiled. If this is not the case, |
tracking control verbs such as (*MARK:NAME), and the execution ends up | the behaviour of pcre_exec() is undefined. Therefore, when a pattern is |
with a name to pass back, a pointer to the name string (zero termi- | compiled and matched in the same process, this field should never be |
nated) is placed in the variable pointed to by the mark field. The | set. In this (the most common) case, the correct table pointer is auto- |
names are within the compiled pattern; if you wish to retain such a | matically passed with the compiled pattern from pcre_compile() to |
name you must copy it before freeing the memory of a compiled pattern. | pcre_exec(). |
If there is no name to pass back, the variable pointed to by the mark | |
field is set to NULL. For details of the backtracking control verbs, | If PCRE_EXTRA_MARK is set in the flags field, the mark field must be |
| set to point to a suitable variable. If the pattern contains any back- |
| tracking control verbs such as (*MARK:NAME), and the execution ends up |
| with a name to pass back, a pointer to the name string (zero termi- |
| nated) is placed in the variable pointed to by the mark field. The |
| names are within the compiled pattern; if you wish to retain such a |
| name you must copy it before freeing the memory of a compiled pattern. |
| If there is no name to pass back, the variable pointed to by the mark |
| field is set to NULL. For details of the backtracking control verbs, |
see the section entitled "Backtracking control" in the pcrepattern doc- |
see the section entitled "Backtracking control" in the pcrepattern doc- |
umentation. |
umentation. |
|
|
Option bits for pcre_exec() |
Option bits for pcre_exec() |
|
|
The unused bits of the options argument for pcre_exec() must be zero. | The unused bits of the options argument for pcre_exec() must be zero. |
The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx, | The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx, |
PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, | PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, |
PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and | PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and |
PCRE_PARTIAL_SOFT. |
PCRE_PARTIAL_SOFT. |
|
|
If the pattern was successfully studied with one of the just-in-time | If the pattern was successfully studied with one of the just-in-time |
(JIT) compile options, the only supported options for JIT execution are |
(JIT) compile options, the only supported options for JIT execution are |
PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, | PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, |
PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an | PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an |
unsupported option is used, JIT execution is disabled and the normal | unsupported option is used, JIT execution is disabled and the normal |
interpretive code in pcre_exec() is run. |
interpretive code in pcre_exec() is run. |
|
|
PCRE_ANCHORED |
PCRE_ANCHORED |
|
|
The PCRE_ANCHORED option limits pcre_exec() to matching at the first | The PCRE_ANCHORED option limits pcre_exec() to matching at the first |
matching position. If a pattern was compiled with PCRE_ANCHORED, or | matching position. If a pattern was compiled with PCRE_ANCHORED, or |
turned out to be anchored by virtue of its contents, it cannot be made | turned out to be anchored by virtue of its contents, it cannot be made |
unachored at matching time. |
unachored at matching time. |
|
|
PCRE_BSR_ANYCRLF |
PCRE_BSR_ANYCRLF |
PCRE_BSR_UNICODE |
PCRE_BSR_UNICODE |
|
|
These options (which are mutually exclusive) control what the \R escape |
These options (which are mutually exclusive) control what the \R escape |
sequence matches. The choice is either to match only CR, LF, or CRLF, | sequence matches. The choice is either to match only CR, LF, or CRLF, |
or to match any Unicode newline sequence. These options override the | or to match any Unicode newline sequence. These options override the |
choice that was made or defaulted when the pattern was compiled. |
choice that was made or defaulted when the pattern was compiled. |
|
|
PCRE_NEWLINE_CR |
PCRE_NEWLINE_CR |
Line 2523 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3238 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_NEWLINE_ANYCRLF |
PCRE_NEWLINE_ANYCRLF |
PCRE_NEWLINE_ANY |
PCRE_NEWLINE_ANY |
|
|
These options override the newline definition that was chosen or | These options override the newline definition that was chosen or |
defaulted when the pattern was compiled. For details, see the descrip- | defaulted when the pattern was compiled. For details, see the descrip- |
tion of pcre_compile() above. During matching, the newline choice | tion of pcre_compile() above. During matching, the newline choice |
affects the behaviour of the dot, circumflex, and dollar metacharac- | affects the behaviour of the dot, circumflex, and dollar metacharac- |
ters. It may also alter the way the match position is advanced after a | ters. It may also alter the way the match position is advanced after a |
match failure for an unanchored pattern. |
match failure for an unanchored pattern. |
|
|
When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is | When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is |
set, and a match attempt for an unanchored pattern fails when the cur- | set, and a match attempt for an unanchored pattern fails when the cur- |
rent position is at a CRLF sequence, and the pattern contains no | rent position is at a CRLF sequence, and the pattern contains no |
explicit matches for CR or LF characters, the match position is | explicit matches for CR or LF characters, the match position is |
advanced by two characters instead of one, in other words, to after the |
advanced by two characters instead of one, in other words, to after the |
CRLF. |
CRLF. |
|
|
The above rule is a compromise that makes the most common cases work as |
The above rule is a compromise that makes the most common cases work as |
expected. For example, if the pattern is .+A (and the PCRE_DOTALL | expected. For example, if the pattern is .+A (and the PCRE_DOTALL |
option is not set), it does not match the string "\r\nA" because, after |
option is not set), it does not match the string "\r\nA" because, after |
failing at the start, it skips both the CR and the LF before retrying. | failing at the start, it skips both the CR and the LF before retrying. |
However, the pattern [\r\n]A does match that string, because it con- | However, the pattern [\r\n]A does match that string, because it con- |
tains an explicit CR or LF reference, and so advances only by one char- |
tains an explicit CR or LF reference, and so advances only by one char- |
acter after the first failure. |
acter after the first failure. |
|
|
An explicit match for CR of LF is either a literal appearance of one of |
An explicit match for CR of LF is either a literal appearance of one of |
those characters, or one of the \r or \n escape sequences. Implicit | those characters, or one of the \r or \n escape sequences. Implicit |
matches such as [^X] do not count, nor does \s (which includes CR and | matches such as [^X] do not count, nor does \s (which includes CR and |
LF in the characters that it matches). |
LF in the characters that it matches). |
|
|
Notwithstanding the above, anomalous effects may still occur when CRLF | Notwithstanding the above, anomalous effects may still occur when CRLF |
is a valid newline sequence and explicit \r or \n escapes appear in the |
is a valid newline sequence and explicit \r or \n escapes appear in the |
pattern. |
pattern. |
|
|
PCRE_NOTBOL |
PCRE_NOTBOL |
|
|
This option specifies that first character of the subject string is not |
This option specifies that first character of the subject string is not |
the beginning of a line, so the circumflex metacharacter should not | the beginning of a line, so the circumflex metacharacter should not |
match before it. Setting this without PCRE_MULTILINE (at compile time) | match before it. Setting this without PCRE_MULTILINE (at compile time) |
causes circumflex never to match. This option affects only the behav- | causes circumflex never to match. This option affects only the behav- |
iour of the circumflex metacharacter. It does not affect \A. |
iour of the circumflex metacharacter. It does not affect \A. |
|
|
PCRE_NOTEOL |
PCRE_NOTEOL |
|
|
This option specifies that the end of the subject string is not the end |
This option specifies that the end of the subject string is not the end |
of a line, so the dollar metacharacter should not match it nor (except | of a line, so the dollar metacharacter should not match it nor (except |
in multiline mode) a newline immediately before it. Setting this with- | in multiline mode) a newline immediately before it. Setting this with- |
out PCRE_MULTILINE (at compile time) causes dollar never to match. This |
out PCRE_MULTILINE (at compile time) causes dollar never to match. This |
option affects only the behaviour of the dollar metacharacter. It does | option affects only the behaviour of the dollar metacharacter. It does |
not affect \Z or \z. |
not affect \Z or \z. |
|
|
PCRE_NOTEMPTY |
PCRE_NOTEMPTY |
|
|
An empty string is not considered to be a valid match if this option is |
An empty string is not considered to be a valid match if this option is |
set. If there are alternatives in the pattern, they are tried. If all | set. If there are alternatives in the pattern, they are tried. If all |
the alternatives match the empty string, the entire match fails. For | the alternatives match the empty string, the entire match fails. For |
example, if the pattern |
example, if the pattern |
|
|
a?b? |
a?b? |
|
|
is applied to a string not beginning with "a" or "b", it matches an | is applied to a string not beginning with "a" or "b", it matches an |
empty string at the start of the subject. With PCRE_NOTEMPTY set, this | empty string at the start of the subject. With PCRE_NOTEMPTY set, this |
match is not valid, so PCRE searches further into the string for occur- |
match is not valid, so PCRE searches further into the string for occur- |
rences of "a" or "b". |
rences of "a" or "b". |
|
|
PCRE_NOTEMPTY_ATSTART |
PCRE_NOTEMPTY_ATSTART |
|
|
This is like PCRE_NOTEMPTY, except that an empty string match that is | This is like PCRE_NOTEMPTY, except that an empty string match that is |
not at the start of the subject is permitted. If the pattern is | not at the start of the subject is permitted. If the pattern is |
anchored, such a match can occur only if the pattern contains \K. |
anchored, such a match can occur only if the pattern contains \K. |
|
|
Perl has no direct equivalent of PCRE_NOTEMPTY or | Perl has no direct equivalent of PCRE_NOTEMPTY or |
PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern | PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern |
match of the empty string within its split() function, and when using | match of the empty string within its split() function, and when using |
the /g modifier. It is possible to emulate Perl's behaviour after | the /g modifier. It is possible to emulate Perl's behaviour after |
matching a null string by first trying the match again at the same off- |
matching a null string by first trying the match again at the same off- |
set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that | set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that |
fails, by advancing the starting offset (see below) and trying an ordi- |
fails, by advancing the starting offset (see below) and trying an ordi- |
nary match again. There is some code that demonstrates how to do this | nary match again. There is some code that demonstrates how to do this |
in the pcredemo sample program. In the most general case, you have to | in the pcredemo sample program. In the most general case, you have to |
check to see if the newline convention recognizes CRLF as a newline, | check to see if the newline convention recognizes CRLF as a newline, |
and if so, and the current character is CR followed by LF, advance the | and if so, and the current character is CR followed by LF, advance the |
starting offset by two characters instead of one. |
starting offset by two characters instead of one. |
|
|
PCRE_NO_START_OPTIMIZE |
PCRE_NO_START_OPTIMIZE |
|
|
There are a number of optimizations that pcre_exec() uses at the start | There are a number of optimizations that pcre_exec() uses at the start |
of a match, in order to speed up the process. For example, if it is | of a match, in order to speed up the process. For example, if it is |
known that an unanchored match must start with a specific character, it |
known that an unanchored match must start with a specific character, it |
searches the subject for that character, and fails immediately if it | searches the subject for that character, and fails immediately if it |
cannot find it, without actually running the main matching function. | cannot find it, without actually running the main matching function. |
This means that a special item such as (*COMMIT) at the start of a pat- |
This means that a special item such as (*COMMIT) at the start of a pat- |
tern is not considered until after a suitable starting point for the | tern is not considered until after a suitable starting point for the |
match has been found. When callouts or (*MARK) items are in use, these | match has been found. Also, when callouts or (*MARK) items are in use, |
"start-up" optimizations can cause them to be skipped if the pattern is | these "start-up" optimizations can cause them to be skipped if the pat- |
never actually used. The start-up optimizations are in effect a pre- | tern is never actually used. The start-up optimizations are in effect a |
scan of the subject that takes place before the pattern is run. | pre-scan of the subject that takes place before the pattern is run. |
|
|
The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, | The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, |
possibly causing performance to suffer, but ensuring that in cases | possibly causing performance to suffer, but ensuring that in cases |
where the result is "no match", the callouts do occur, and that items | where the result is "no match", the callouts do occur, and that items |
such as (*COMMIT) and (*MARK) are considered at every possible starting |
such as (*COMMIT) and (*MARK) are considered at every possible starting |
position in the subject string. If PCRE_NO_START_OPTIMIZE is set at | position in the subject string. If PCRE_NO_START_OPTIMIZE is set at |
compile time, it cannot be unset at matching time. The use of | compile time, it cannot be unset at matching time. The use of |
PCRE_NO_START_OPTIMIZE disables JIT execution; when it is set, matching | PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to |
is always done using interpretively. | pcre_exec()) disables JIT execution; in this situation, matching is |
| always done using interpretively. |
|
|
Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching |
Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching |
operation. Consider the pattern |
operation. Consider the pattern |
Line 2681 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3397 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
points to the start of a character (or the end of the subject). When |
points to the start of a character (or the end of the subject). When |
PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a |
PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a |
subject or an invalid value of startoffset is undefined. Your program |
subject or an invalid value of startoffset is undefined. Your program |
may crash. | may crash or loop. |
|
|
PCRE_PARTIAL_HARD |
PCRE_PARTIAL_HARD |
PCRE_PARTIAL_SOFT |
PCRE_PARTIAL_SOFT |
Line 2711 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3427 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
The string to be matched by pcre_exec() |
The string to be matched by pcre_exec() |
|
|
The subject string is passed to pcre_exec() as a pointer in subject, a |
The subject string is passed to pcre_exec() as a pointer in subject, a |
length in bytes in length, and a starting byte offset in startoffset. | length in length, and a starting offset in startoffset. The units for |
If this is negative or greater than the length of the subject, | length and startoffset are bytes for the 8-bit library, 16-bit data |
| items for the 16-bit library, and 32-bit data items for the 32-bit |
| library. |
| |
| If startoffset is negative or greater than the length of the subject, |
pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is |
pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is |
zero, the search for a match starts at the beginning of the subject, |
zero, the search for a match starts at the beginning of the subject, |
and this is by far the most common case. In UTF-8 mode, the byte offset | and this is by far the most common case. In UTF-8 or UTF-16 mode, the |
must point to the start of a UTF-8 character (or the end of the sub- | offset must point to the start of a character, or the end of the sub- |
ject). Unlike the pattern string, the subject may contain binary zero | ject (in UTF-32 mode, one data unit equals one character, so all off- |
bytes. | sets are valid). Unlike the pattern string, the subject may contain |
| binary zeroes. |
|
|
A non-zero starting offset is useful when searching for another match | A non-zero starting offset is useful when searching for another match |
in the same subject by calling pcre_exec() again after a previous suc- | in the same subject by calling pcre_exec() again after a previous suc- |
cess. Setting startoffset differs from just passing over a shortened | cess. Setting startoffset differs from just passing over a shortened |
string and setting PCRE_NOTBOL in the case of a pattern that begins | string and setting PCRE_NOTBOL in the case of a pattern that begins |
with any kind of lookbehind. For example, consider the pattern |
with any kind of lookbehind. For example, consider the pattern |
|
|
\Biss\B |
\Biss\B |
|
|
which finds occurrences of "iss" in the middle of words. (\B matches | which finds occurrences of "iss" in the middle of words. (\B matches |
only if the current position in the subject is not a word boundary.) | only if the current position in the subject is not a word boundary.) |
When applied to the string "Mississipi" the first call to pcre_exec() | When applied to the string "Mississipi" the first call to pcre_exec() |
finds the first occurrence. If pcre_exec() is called again with just | finds the first occurrence. If pcre_exec() is called again with just |
the remainder of the subject, namely "issipi", it does not match, | the remainder of the subject, namely "issipi", it does not match, |
because \B is always false at the start of the subject, which is deemed |
because \B is always false at the start of the subject, which is deemed |
to be a word boundary. However, if pcre_exec() is passed the entire | to be a w to be a word boundary. However, if pcre_exec() is passed the entire |
string again, but with startoffset set to 4, it finds the second occur- |
string again, but with startoffset set to 4, it finds the second occur- |
rence of "iss" because it is able to look behind the starting point to | rence of "iss" because it is able to look behind the starting point to |
discover that it is preceded by a letter. |
discover that it is preceded by a letter. |
|
|
Finding all the matches in a subject is tricky when the pattern can | Finding all the matches in a subject is tricky when the pattern can |
match an empty string. It is possible to emulate Perl's /g behaviour by |
match an empty string. It is possible to emulate Perl's /g behaviour by |
first trying the match again at the same offset, with the | first trying the match again at the same offset, with the |
PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that | PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that |
fails, advancing the starting offset and trying an ordinary match | fails, advancing the starting offset and trying an ordinary match |
again. There is some code that demonstrates how to do this in the pcre- |
again. There is some code that demonstrates how to do this in the pcre- |
demo sample program. In the most general case, you have to check to see |
demo sample program. In the most general case, you have to check to see |
if the newline convention recognizes CRLF as a newline, and if so, and | if the newline convention recognizes CRLF as a newline, and if so, and |
the current character is CR followed by LF, advance the starting offset |
the current character is CR followed by LF, advance the starting offset |
by two characters instead of one. |
by two characters instead of one. |
|
|
If a non-zero starting offset is passed when the pattern is anchored, | If a non-zero starting offset is passed when the pattern is anchored, |
one attempt to match at the given offset is made. This can only succeed |
one attempt to match at the given offset is made. This can only succeed |
if the pattern does not require the match to be at the start of the | if the pattern d if the pattern d |
subject. |
subject. |
|
|
How pcre_exec() returns captured substrings |
How pcre_exec() returns captured substrings |
|
|
In general, a pattern matches a certain portion of the subject, and in | In general, a pattern matches a certain portion of the subject, and in |
addition, further substrings from the subject may be picked out by | addition, further substrings from the subject may be picked out by |
parts of the pattern. Following the usage in Jeffrey Friedl's book, | parts of the pattern. Following the usage in Jeffrey Friedl's book, |
this is called "capturing" in what follows, and the phrase "capturing | this is called "capturing" in what follows, and the phrase "capturing |
subpattern" is used for a fragment of a pattern that picks out a sub- | subpattern" is used for a fragment of a pattern that picks out a sub- |
string. PCRE supports several other kinds of parenthesized subpattern | string. PCRE supports several other kinds of parenthesized subpattern |
that do not cause substrings to be captured. |
that do not cause substrings to be captured. |
|
|
Captured substrings are returned to the caller via a vector of integers |
Captured substrings are returned to the caller via a vector of integers |
whose address is passed in ovector. The number of elements in the vec- | whose address is passed in ovector. The number of elements in the vec- |
tor is passed in ovecsize, which must be a non-negative number. Note: | tor is passed in ovecsize, which must be a non-negative number. Note: |
this argument is NOT the size of ovector in bytes. |
this argument is NOT the size of ovector in bytes. |
|
|
The first two-thirds of the vector is used to pass back captured sub- | The first two-thirds of the vector is used to pass back captured sub- |
strings, each substring using a pair of integers. The remaining third | strings, each substring using a pair of integers. The remaining third |
of the vector is used as workspace by pcre_exec() while matching cap- | of the vector is used as workspace by pcre_exec() while matching cap- |
turing subpatterns, and is not available for passing back information. | turing subpatterns, and is not available for passing back information. |
The number passed in ovecsize should always be a multiple of three. If | The number passed in ovecsize should always be a multiple of three. If |
it is not, it is rounded down. |
it is not, it is rounded down. |
|
|
When a match is successful, information about captured substrings is | When a match is successful, information about captured substrings is |
returned in pairs of integers, starting at the beginning of ovector, | returned in pairs of integers, starting at the beginning of ovector, |
and continuing up to two-thirds of its length at the most. The first | and continuing up to two-thirds of its length at the most. The first |
element of each pair is set to the byte offset of the first character | element of each pair is set to the offset of the first character in a |
in a substring, and the second is set to the byte offset of the first | substring, and the second is set to the offset of the first character |
character after the end of a substring. Note: these values are always | after the end of a substring. These values are always data unit off- |
byte offsets, even in UTF-8 mode. They are not character counts. | sets, even in UTF mode. They are byte offsets in the 8-bit library, |
| 16-bit data item offsets in the 16-bit library, and 32-bit data item |
| offsets in the 32-bit library. Note: they are not character counts. |
|
|
The first pair of integers, ovector[0] and ovector[1], identify the | The first pair of integers, ovector[0] and ovector[1], identify the |
portion of the subject string matched by the entire pattern. The next | portion of the subject string matched by the entire pattern. The next |
pair is used for the first capturing subpattern, and so on. The value | pair is used for the first capturing subpattern, and so on. The value |
returned by pcre_exec() is one more than the highest numbered pair that |
returned by pcre_exec() is one more than the highest numbered pair that |
has been set. For example, if two substrings have been captured, the | has been set. For example, if two substrings have been captured, the |
returned value is 3. If there are no capturing subpatterns, the return | returned value is 3. If there are no capturing subpatterns, the return |
value from a successful match is 1, indicating that just the first pair |
value from a successful match is 1, indicating that just the first pair |
of offsets has been set. |
of offsets has been set. |
|
|
If a capturing subpattern is matched repeatedly, it is the last portion |
If a capturing subpattern is matched repeatedly, it is the last portion |
of the string that it matched that is returned. |
of the string that it matched that is returned. |
|
|
If the vector is too small to hold all the captured substring offsets, | If the vector is too small to hold all the captured substring offsets, |
it is used as far as possible (up to two-thirds of its length), and the |
it is used as far as possible (up to two-thirds of its length), and the |
function returns a value of zero. If neither the actual string matched | function returns a value of zero. If neither the actual string matched |
nor any captured substrings are of interest, pcre_exec() may be called | nor any captured substrings are of interest, pcre_exec() may be called |
with ovector passed as NULL and ovecsize as zero. However, if the pat- | with ovector passed as NULL and ovecsize as zero. However, if the pat- |
tern contains back references and the ovector is not big enough to | tern contains back references and the ovector is not big enough to |
remember the related substrings, PCRE has to get additional memory for | remember the related substrings, PCRE has to get additional memory for |
use during matching. Thus it is usually advisable to supply an ovector | use during matching. Thus it is usually advisable to supply an ovector |
of reasonable size. |
of reasonable size. |
|
|
There are some cases where zero is returned (indicating vector over- | There are some cases where zero is returned (indicating vector over- |
flow) when in fact the vector is exactly the right size for the final | flow) when in fact the vector is exactly the right size for the final |
match. For example, consider the pattern |
match. For example, consider the pattern |
|
|
(a)(?:(b)c|bd) |
(a)(?:(b)c|bd) |
|
|
If a vector of 6 elements (allowing for only 1 captured substring) is | If a vector of 6 elements (allowing for only 1 captured substring) is |
given with subject string "abd", pcre_exec() will try to set the second |
given with subject string "abd", pcre_exec() will try to set the second |
captured string, thereby recording a vector overflow, before failing to |
captured string, thereby recording a vector overflow, before failing to |
match "c" and backing up to try the second alternative. The zero | match "c" and backing up to try the second alternative. The zero |
return, however, does correctly indicate that the maximum number of | return, however, does correctly indicate that the maximum number of |
slots (namely 2) have been filled. In similar cases where there is tem- |
slots (namely 2) have been filled. In similar cases where there is tem- |
porary overflow, but the final number of used slots is actually less | porary overflow, but the final number of used slots is actually less |
than the maximum, a non-zero value is returned. |
than the maximum, a non-zero value is returned. |
|
|
The pcre_fullinfo() function can be used to find out how many capturing |
The pcre_fullinfo() function can be used to find out how many capturing |
subpatterns there are in a compiled pattern. The smallest size for | subpatterns there are in a compiled pattern. The smallest size for |
ovector that will allow for n captured substrings, in addition to the | ovector that will allow for n captured substrings, in addition to the |
offsets of the substring matched by the whole pattern, is (n+1)*3. |
offsets of the substring matched by the whole pattern, is (n+1)*3. |
|
|
It is possible for capturing subpattern number n+1 to match some part | It is possible for capturing subpattern number n+1 to match some part |
of the subject when subpattern n has not been used at all. For example, |
of the subject when subpattern n has not been used at all. For example, |
if the string "abc" is matched against the pattern (a|(z))(bc) the | if the string "abc" is matched against the pattern (a|(z))(bc) the |
return from the function is 4, and subpatterns 1 and 3 are matched, but |
return from the function is 4, and subpatterns 1 and 3 are matched, but |
2 is not. When this happens, both values in the offset pairs corre- | 2 is not. When this happens, both values in the offset pairs corre- |
sponding to unused subpatterns are set to -1. |
sponding to unused subpatterns are set to -1. |
|
|
Offset values that correspond to unused subpatterns at the end of the | Offset values that correspond to unused subpatterns at the end of the |
expression are also set to -1. For example, if the string "abc" is | expression are also set to -1. For example, if the string "abc" is |
matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not | matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not |
matched. The return from the function is 2, because the highest used | matched. The return from the function is 2, because the highest used |
capturing subpattern number is 1, and the offsets for for the second | capturing subpattern number is 1, and the offsets for for the second |
and third capturing subpatterns (assuming the vector is large enough, | and third capturing subpatterns (assuming the vector is large enough, |
of course) are set to -1. |
of course) are set to -1. |
|
|
Note: Elements in the first two-thirds of ovector that do not corre- | Note: Elements in the first two-thirds of ovector that do not corre- |
spond to capturing parentheses in the pattern are never changed. That | spond to capturing parentheses in the pattern are never changed. That |
is, if a pattern contains n capturing parentheses, no more than ovec- | is, if a pattern contains n capturing parentheses, no more than ovec- |
tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in | tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in |
the first two-thirds) retain whatever values they previously had. |
the first two-thirds) retain whatever values they previously had. |
|
|
Some convenience functions are provided for extracting the captured | Some convenience functions are provided for extracting the captured |
substrings as separate strings. These are described below. |
substrings as separate strings. These are described below. |
|
|
Error return values from pcre_exec() |
Error return values from pcre_exec() |
|
|
If pcre_exec() fails, it returns a negative number. The following are | If pcre_exec() fails, it returns a negative number. The following are |
defined in the header file: |
defined in the header file: |
|
|
PCRE_ERROR_NOMATCH (-1) |
PCRE_ERROR_NOMATCH (-1) |
Line 2862 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3585 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
|
|
PCRE_ERROR_NULL (-2) |
PCRE_ERROR_NULL (-2) |
|
|
Either code or subject was passed as NULL, or ovector was NULL and | Either code or subject was passed as NULL, or ovector was NULL and |
ovecsize was not zero. |
ovecsize was not zero. |
|
|
PCRE_ERROR_BADOPTION (-3) |
PCRE_ERROR_BADOPTION (-3) |
Line 2871 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3594 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
|
|
PCRE_ERROR_BADMAGIC (-4) |
PCRE_ERROR_BADMAGIC (-4) |
|
|
PCRE stores a 4-byte "magic number" at the start of the compiled code, | PCRE stores a 4-byte "magic number" at the start of the compiled code, |
to catch the case when it is passed a junk pointer and to detect when a |
to catch the case when it is passed a junk pointer and to detect when a |
pattern that was compiled in an environment of one endianness is run in |
pattern that was compiled in an environment of one endianness is run in |
an environment with the other endianness. This is the error that PCRE | an environment with the other endianness. This is the err an environment with the other endianness. This is the error that PCRE |
gives when the magic number is not present. |
gives when the magic number is not present. |
|
|
PCRE_ERROR_UNKNOWN_OPCODE (-5) |
PCRE_ERROR_UNKNOWN_OPCODE (-5) |
|
|
While running the pattern match, an unknown item was encountered in the |
While running the pattern match, an unknown item was encountered in the |
compiled pattern. This error could be caused by a bug in PCRE or by | compiled pattern. This error could be caused by a bug in PCRE or by |
overwriting of the compiled pattern. |
overwriting of the compiled pattern. |
|
|
PCRE_ERROR_NOMEMORY (-6) |
PCRE_ERROR_NOMEMORY (-6) |
|
|
If a pattern contains back references, but the ovector that is passed | If a pattern contains back references, but the ovector that is passed |
to pcre_exec() is not big enough to remember the referenced substrings, |
to pcre_exec() is not big enough to remember the referenced substrings, |
PCRE gets a block of memory at the start of matching to use for this | PCRE gets a block of memory at the start of matching to use for this |
purpose. If the call via pcre_malloc() fails, this error is given. The | purpose. If the call via pcre_malloc() fails, this error is given. The |
memory is automatically freed at the end of matching. |
memory is automatically freed at the end of matching. |
|
|
This error is also given if pcre_stack_malloc() fails in pcre_exec(). | This error is also given if pcre_stack_malloc() fails in pcre_exec(). |
This can happen only when PCRE has been compiled with --disable-stack- | This can happen only when PCRE has been compiled with --disable-stack- |
for-recursion. |
for-recursion. |
|
|
PCRE_ERROR_NOSUBSTRING (-7) |
PCRE_ERROR_NOSUBSTRING (-7) |
|
|
This error is used by the pcre_copy_substring(), pcre_get_substring(), | This error is used by the pcre_copy_substring(), pcre_get_substring(), |
and pcre_get_substring_list() functions (see below). It is never |
and pcre_get_substring_list() functions (see below). It is never |
returned by pcre_exec(). |
returned by pcre_exec(). |
|
|
PCRE_ERROR_MATCHLIMIT (-8) |
PCRE_ERROR_MATCHLIMIT (-8) |
|
|
The backtracking limit, as specified by the match_limit field in a | The backtracking limit, as specified by the match_limit field in a |
pcre_extra structure (or defaulted) was reached. See the description | pcre_extra structure (or defaulted) was reached. See the description |
above. |
above. |
|
|
PCRE_ERROR_CALLOUT (-9) |
PCRE_ERROR_CALLOUT (-9) |
|
|
This error is never generated by pcre_exec() itself. It is provided for |
This error is never generated by pcre_exec() itself. It is provided for |
use by callout functions that want to yield a distinctive error code. | use by callout functions that want to yield a distinctive error code. |
See the pcrecallout documentation for details. |
See the pcrecallout documentation for details. |
|
|
PCRE_ERROR_BADUTF8 (-10) |
PCRE_ERROR_BADUTF8 (-10) |
|
|
A string that contains an invalid UTF-8 byte sequence was passed as a | A string that contains an invalid UTF-8 byte sequence was passed as a |
subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of | subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of |
the output vector (ovecsize) is at least 2, the byte offset to the | the output vector (ovecsize) is at least 2, the byte offset to the |
start of the the invalid UTF-8 character is placed in the first ele- | start of the the invalid UTF-8 character is placed in the first ele- |
ment, and a reason code is placed in the second element. The reason | ment, and a reason code is placed in the second element. The reason |
codes are listed in the following section. For backward compatibility, |
codes are listed in the following section. For backward compatibility, |
if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char- | if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char- |
acter at the end of the subject (reason codes 1 to 5), | acter at the end of the subject (reason codes 1 to 5), |
PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8. |
PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8. |
|
|
PCRE_ERROR_BADUTF8_OFFSET (-11) |
PCRE_ERROR_BADUTF8_OFFSET (-11) |
|
|
The UTF-8 byte sequence that was passed as a subject was checked and | The UTF-8 byte sequence that was passed as a subject was checked and |
found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the | found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the |
value of startoffset did not point to the beginning of a UTF-8 charac- | value of startoffset did not point to the beginning of a UTF-8 charac- |
ter or the end of the subject. |
ter or the end of the subject. |
|
|
PCRE_ERROR_PARTIAL (-12) |
PCRE_ERROR_PARTIAL (-12) |
|
|
The subject string did not match, but it did match partially. See the | The subject string did not match, but it did match partiall The subject string did not match, but it did match partially. See the |
pcrepartial documentation for details of partial matching. |
pcrepartial documentation for details of partial matching. |
|
|
PCRE_ERROR_BADPARTIAL (-13) |
PCRE_ERROR_BADPARTIAL (-13) |
|
|
This code is no longer in use. It was formerly returned when the | This code is no longer in use. It was formerly returned when the |
PCRE_PARTIAL option was used with a compiled pattern containing items | PCRE_PARTIAL option was used with a compiled pattern containing items |
that were not supported for partial matching. From release 8.00 | that were not supported for partial matching. From release 8.00 |
onwards, there are no restrictions on partial matching. |
onwards, there are no restrictions on partial matching. |
|
|
PCRE_ERROR_INTERNAL (-14) |
PCRE_ERROR_INTERNAL (-14) |
|
|
An unexpected internal error has occurred. This error could be caused | An unexpected internal error has occurred. This error could be caused |
by a bug in PCRE or by overwriting of the compiled pattern. |
by a bug in PCRE or by overwriting of the compiled pattern. |
|
|
PCRE_ERROR_BADCOUNT (-15) |
PCRE_ERROR_BADCOUNT (-15) |
Line 2956 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3679 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_ERROR_RECURSIONLIMIT (-21) |
PCRE_ERROR_RECURSIONLIMIT (-21) |
|
|
The internal recursion limit, as specified by the match_limit_recursion |
The internal recursion limit, as specified by the match_limit_recursion |
field in a pcre_extra structure (or defaulted) was reached. See the | field in a pcre_extra structure (or defaulted) was reached. See the |
description above. |
description above. |
|
|
PCRE_ERROR_BADNEWLINE (-23) |
PCRE_ERROR_BADNEWLINE (-23) |
Line 2970 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3693 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
|
|
PCRE_ERROR_SHORTUTF8 (-25) |
PCRE_ERROR_SHORTUTF8 (-25) |
|
|
This error is returned instead of PCRE_ERROR_BADUTF8 when the subject | This error is returned instead of PCRE_ERROR_BADUTF8 when the subject |
string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD | string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD |
option is set. Information about the failure is returned as for | option is set. Information about the failure is returned as for |
PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but | PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but |
this special error code for PCRE_PARTIAL_HARD precedes the implementa- | this special error code for PCRE_PARTIAL_HARD precedes the implementa- |
tion of returned information; it is retained for backwards compatibil- | tion of returned information; it is retained for backwards compatibil- |
ity. |
ity. |
|
|
PCRE_ERROR_RECURSELOOP (-26) |
PCRE_ERROR_RECURSELOOP (-26) |
|
|
This error is returned when pcre_exec() detects a recursion loop within |
This error is returned when pcre_exec() detects a recursion loop within |
the pattern. Specifically, it means that either the whole pattern or a | the pattern. Specifically, it means that either the whole pattern or a |
subpattern has been called recursively for the second time at the same | subpattern has been called recursively for the second time at the same |
position in the subject string. Some simple patterns that might do this |
position in the subject string. Some simple patterns that might do this |
are detected and faulted at compile time, but more complicated cases, | are detected and faulted at compile time, but more complicate are detected and faulted at compile time, but more complicate |
in particular mutual recursions between two different subpatterns, can- |
in particular mutual recursions between two different subpatterns, can- |
not be detected until run time. |
not be detected until run time. |
|
|
PCRE_ERROR_JIT_STACKLIMIT (-27) |
PCRE_ERROR_JIT_STACKLIMIT (-27) |
|
|
This error is returned when a pattern that was successfully studied | This error is returned when a pattern that was successfully studied |
using a JIT compile option is being matched, but the memory available | using a JIT compile option is being matched, but the memory available |
for the just-in-time processing stack is not large enough. See the | for the just-in-time processing stack is not large enough. See the |
pcrejit documentation for more details. |
pcrejit documentation for more details. |
|
|
PCRE_ERROR_BADMODE (-28) |
PCRE_ERROR_BADMODE (-28) |
|
|
This error is given if a pattern that was compiled by the 8-bit library |
This error is given if a pattern that was compiled by the 8-bit library |
is passed to a 16-bit library function, or vice versa. | is passed to a 16-bit or 32-bit library function, or vice versa. |
|
|
PCRE_ERROR_BADENDIANNESS (-29) |
PCRE_ERROR_BADENDIANNESS (-29) |
|
|
This error is given if a pattern that was compiled and saved is | This error is given if a pattern that was compiled and saved is |
reloaded on a host with different endianness. The utility function | reloaded on a host with different endianness. The utility function |
pcre_pattern_to_host_byte_order() can be used to convert such a pattern |
pcre_pattern_to_host_byte_order() can be used to convert such a pattern |
so that it runs on the new host. |
so that it runs on the new host. |
|
|
Error numbers -16 to -20, -22, and -30 are not used by pcre_exec(). | PCRE_ERROR_JIT_BADOPTION |
|
|
|
This error is returned when a pattern that was successfully studied |
|
using a JIT compile option is being matched, but the matching mode |
|
(partial or complete match) does not correspond to any JIT compilation |
|
mode. When the JIT fast path function is used, this error may be also |
|
given for invalid options. See the pcrejit documentation for more |
|
details. |
|
|
|
PCRE_ERROR_BADLENGTH (-32) |
|
|
|
This error is given if pcre_exec() is called with a negative value for |
|
the length argument. |
|
|
|
Error numbers -16 to -20, -22, and 30 are not used by pcre_exec(). |
|
|
Reason codes for invalid UTF-8 strings |
Reason codes for invalid UTF-8 strings |
|
|
This section applies only to the 8-bit library. The corresponding | This section applies only to the 8-bit library. The corresponding |
information for the 16-bit library is given in the pcre16 page. | information for the 16-bit and 32-bit libraries is given in the pcre16 |
| and pcre32 pages. |
|
|
When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT- |
When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT- |
UTF8, and the size of the output vector (ovecsize) is at least 2, the |
UTF8, and the size of the output vector (ovecsize) is at least 2, the |
Line 3083 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3821 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
The first byte of a character has the value 0xfe or 0xff. These values |
The first byte of a character has the value 0xfe or 0xff. These values |
can never occur in a valid UTF-8 string. |
can never occur in a valid UTF-8 string. |
|
|
|
PCRE_UTF8_ERR22 |
|
|
|
This error code was formerly used when the presence of a so-called |
|
"non-character" caused an error. Unicode corrigendum #9 makes it clear |
|
that such characters should not cause a string to be rejected, and so |
|
this code is no longer in use and is never returned. |
|
|
|
|
EXTRACTING CAPTURED SUBSTRINGS BY NUMBER |
EXTRACTING CAPTURED SUBSTRINGS BY NUMBER |
|
|
int pcre_copy_substring(const char *subject, int *ovector, |
int pcre_copy_substring(const char *subject, int *ovector, |
Line 3097 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
|
Line 3842 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
|
int pcre_get_substring_list(const char *subject, |
int pcre_get_substring_list(const char *subject, |
int *ovector, int stringcount, const char ***listptr); |
int *ovector, int stringcount, const char ***listptr); |
|
|
Captured substrings can be accessed directly by using the offsets | Captured substrings can be accessed directly by using the offsets |
returned by pcre_exec() in ovector. For convenience, the functions | returned by pcre_exec() in ovector. For convenience, the functions |
pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub- |
pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub- |
string_list() are provided for extracting captured substrings as new, | string_list() are provided for extracting captured substrings as new, |
separate, zero-terminated strings. These functions identify substrings | separate, zero-terminated strings. These functions identify substrings |
by number. The next section describes functions for extracting named | by number. The next section describes functions for extracting named |
substrings. |
substrings. |
|
|
A substring that contains a binary zero is correctly extracted and has | A substring that contains a binary zero is correctly extracted and has |
a further zero added on the end, but the result is not, of course, a C | a further zero added on the end, but the result is not, of course, a C |
string. However, you can process such a string by referring to the | string. However, you can process such a string by referring to the |
length that is returned by pcre_copy_substring() and pcre_get_sub- | length that is returned by pcre_copy_substring() and pcre_get_sub- |
string(). Unfortunately, the interface to pcre_get_substring_list() is |
string(). Unfortunately, the interface to pcre_get_substring_list() is |
not adequate for handling strings containing binary zeros, because the | not adequate for handling strings containing binary zeros, because the |
end of the final string is not independently indicated. |
end of the final string is not independently indicated. |
|
|
The first three arguments are the same for all three of these func- | The first three arguments are the same for all three of these func- |
tions: subject is the subject string that has just been successfully | tions: subject is the subject string that has just been successfully |
matched, ovector is a pointer to the vector of integer offsets that was |
matched, ovector is a pointer to the vector of integer offsets that was |
passed to pcre_exec(), and stringcount is the number of substrings that |
passed to pcre_exec(), and stringcount is the number of substrings that |
were captured by the match, including the substring that matched the | were captured by the match, including the substring that matched the |
entire regular expression. This is the value returned by pcre_exec() if |
entire regular expression. This is the value returned by pcre_exec() if |
it is greater than zero. If pcre_exec() returned zero, indicating that | it is greater than zero. If pcre_exec() returned zero, indicating that |
it ran out of space in ovector, the value passed as stringcount should | it ran out of space in ovector, the value passed as stringcount should |
be the number of elements in the vector divided by three. |
be the number of elements in the vector divided by three. |
|
|
The functions pcre_copy_substring() and pcre_get_substring() extract a | The functions pcre_copy_substring() and pcre_get_substring() extract a |
single substring, whose number is given as stringnumber. A value of | single substring, whose number is given as stringnumber. A value of |
zero extracts the substring that matched the entire pattern, whereas | zero extracts the substring that matched the entire pattern, whereas |
higher values extract the captured substrings. For pcre_copy_sub- | higher values extract the captured substrings. For pcre_copy_sub- |
string(), the string is placed in buffer, whose length is given by | string(), the string is placed in buffer, whose length is given by |
buffersize, while for pcre_get_substring() a new block of memory is | buffersize, while for pcre_get_substring() a new block of memory is |
obtained via pcre_malloc, and its address is returned via stringptr. | obtained via pcre_malloc, and its address is returned via stringptr. |
The yield of the function is the length of the string, not including | The yield of the function is the length of the string, not including |
the terminating zero, or one of these error codes: |
the terminating zero, or one of these error codes: |
|
|
PCRE_ERROR_NOMEMORY (-6) |
PCRE_ERROR_NOMEMORY (-6) |
|
|
The buffer was too small for pcre_copy_substring(), or the attempt to | The buffer was too small for pcre_copy_substring(), or t The buffer was too small for pcre_copy_substring(), or the attempt to |
get memory failed for pcre_get_substring(). |
get memory failed for pcre_get_substring(). |
|
|
PCRE_ERROR_NOSUBSTRING (-7) |
PCRE_ERROR_NOSUBSTRING (-7) |
|
|
There is no substring whose number is stringnumber. |
There is no substring whose number is stringnumber. |
|
|
The pcre_get_substring_list() function extracts all available sub- | The pcre_get_substring_list() function extracts all available sub- |
strings and builds a list of pointers to them. All this is done in a | strings and builds a list of pointers to them. All this is done in a |
single block of memory that is obtained via pcre_malloc. The address of |
single block of memory that is obtained via pcre_malloc. The address of |
the memory block is returned via listptr, which is also the start of | the memory block is returned via listptr, which is also the start of |
the list of string pointers. The end of the list is marked by a NULL | the list of string pointers. The end of the list is marked by a NULL |
pointer. The yield of the function is zero if all went well, or the | pointer. The yield of the function is zero if all went well, or the |
error code |
error code |
|
|
PCRE_ERROR_NOMEMORY (-6) |
PCRE_ERROR_NOMEMORY (-6) |
|
|
if the attempt to get the memory block failed. |
if the attempt to get the memory block failed. |
|
|
When any of these functions encounter a substring that is unset, which | When any of these functions encounter a substring that is unset, which |
can happen when capturing subpattern number n+1 matches some part of | can happen when capturing subpattern number n+1 matches some part of |
the subject, but subpattern n has not been used at all, they return an | the subject, but subpattern n has not been used at all, they return an |
empty string. This can be distinguished from a genuine zero-length sub- |
empty string. This can be distinguished from a genuine zero-length sub- |
string by inspecting the appropriate offset in ovector, which is nega- | string by inspecting the appropriate offset in ovector, which is nega- |
tive for unset substrings. |
tive for unset substrings. |
|
|
The two convenience functions pcre_free_substring() and pcre_free_sub- | The two convenience functions pcre_free_substring() and pcre_free_sub- |
string_list() can be used to free the memory returned by a previous | string_list() can be used to free the memory returned by a previous |
call of pcre_get_substring() or pcre_get_substring_list(), respec- |
call of pcre_get_substring() or pcre_get_substring_list(), respec- |
tively. They do nothing more than call the function pointed to by | tively. They do nothing more than call the function pointed to by |
pcre_free, which of course could be called directly from a C program. | pcre_free, which of course could be called directly from a C program. |
However, PCRE is used in some situations where it is linked via a spe- | However, PCRE is used in some situations where it is linked via a spe- |
cial interface to another programming language that cannot use | cial interface to another programming language that cannot use |
pcre_free directly; it is for these cases that the functions are pro- | pcre_free directly; it is for these cases that the functions are pro- |
vided. |
vided. |
|
|
|
|
Line 3187 EXTRACTING CAPTURED SUBSTRINGS BY NAME
|
Line 3932 EXTRACTING CAPTURED SUBSTRINGS BY NAME
|
int stringcount, const char *stringname, |
int stringcount, const char *stringname, |
const char **stringptr); |
const char **stringptr); |
|
|
To extract a substring by name, you first have to find associated num- | To extract a substring by name, you first have to find associated num- |
ber. For example, for this pattern |
ber. For example, for this pattern |
|
|
(a+)b(?<xxx>\d+)... |
(a+)b(?<xxx>\d+)... |
Line 3196 EXTRACTING CAPTURED SUBSTRINGS BY NAME
|
Line 3941 EXTRACTING CAPTURED SUBSTRINGS BY NAME
|
be unique (PCRE_DUPNAMES was not set), you can find the number from the |
be unique (PCRE_DUPNAMES was not set), you can find the number from the |
name by calling pcre_get_stringnumber(). The first argument is the com- |
name by calling pcre_get_stringnumber(). The first argument is the com- |
piled pattern, and the second is the name. The yield of the function is |
piled pattern, and the second is the name. The yield of the function is |
the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no | the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no |
subpattern of that name. |
subpattern of that name. |
|
|
Given the number, you can extract the substring directly, or use one of |
Given the number, you can extract the substring directly, or use one of |
the functions described in the previous section. For convenience, there |
the functions described in the previous section. For convenience, there |
are also two functions that do the whole job. |
are also two functions that do the whole job. |
|
|
Most of the arguments of pcre_copy_named_substring() and | Most of the arguments of pcre_copy_named_substring() and |
pcre_get_named_substring() are the same as those for the similarly | pcre_get_named_substring() are the same as those for the similarly |
named functions that extract by number. As these are described in the | named functions that extract by number. As these are described in the |
previous section, they are not re-described here. There are just two | previous section, they are not re-described here. There are just two |
differences: |
differences: |
|
|
First, instead of a substring number, a substring name is given. Sec- | First, instead of a substring number, a substring name is given. Sec- |
ond, there is an extra argument, given at the start, which is a pointer |
ond, there is an extra argument, given at the start, which is a pointer |
to the compiled pattern. This is needed in order to gain access to the | to the compiled pattern. This is needed in order to gain access to the |
name-to-number translation table. |
name-to-number translation table. |
|
|
These functions call pcre_get_stringnumber(), and if it succeeds, they | These functions call pcre_get_stringnumber(), and if it succeeds, they |
then call pcre_copy_substring() or pcre_get_substring(), as appropri- | then call pcre_copy_substring() or pcre_get_substring(), as appropri- |
ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the | ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the |
behaviour may not be what you want (see the next section). |
behaviour may not be what you want (see the next section). |
|
|
Warning: If the pattern uses the (?| feature to set up multiple subpat- |
Warning: If the pattern uses the (?| feature to set up multiple subpat- |
terns with the same number, as described in the section on duplicate | terns with the same number, as described in the section on duplicate |
subpattern numbers in the pcrepattern page, you cannot use names to | subpattern numbers in the pcrepattern page, you cannot use names to |
distinguish the different subpatterns, because names are not included | distinguish the different subpatterns, because names are not included |
in the compiled code. The matching process uses only numbers. For this | in the compiled code. The matching process uses only numbers. For this |
reason, the use of different names for subpatterns of the same number | reason, the use of different names for subpatterns of the same number |
causes an error at compile time. |
causes an error at compile time. |
|
|
|
|
Line 3233 DUPLICATE SUBPATTERN NAMES
|
Line 3978 DUPLICATE SUBPATTERN NAMES
|
int pcre_get_stringtable_entries(const pcre *code, |
int pcre_get_stringtable_entries(const pcre *code, |
const char *name, char **first, char **last); |
const char *name, char **first, char **last); |
|
|
When a pattern is compiled with the PCRE_DUPNAMES option, names for | When a pattern is compiled with the PCRE_DUPNAMES option, names for |
subpatterns are not required to be unique. (Duplicate names are always | subpatterns are not required to be unique. (Duplicate names are always |
allowed for subpatterns with the same number, created by using the (?| | allowed for subpatterns with the same number, created by using the (?| |
feature. Indeed, if such subpatterns are named, they are required to | feature. Indeed, if such subpatterns are named, they are required to |
use the same names.) |
use the same names.) |
|
|
Normally, patterns with duplicate names are such that in any one match, |
Normally, patterns with duplicate names are such that in any one match, |
only one of the named subpatterns participates. An example is shown in | only one of the named subpatterns participates. An example is shown in |
the pcrepattern documentation. |
the pcrepattern documentation. |
|
|
When duplicates are present, pcre_copy_named_substring() and | When duplicates are present, pcre_copy_named_substring() and |
pcre_get_named_substring() return the first substring corresponding to | pcre_get_named_substring() return the first substring corresponding to |
the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING | the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING |
(-7) is returned; no data is returned. The pcre_get_stringnumber() | (-7) is returned; no data is returned. The pcre_get_stringnumber() |
function returns one of the numbers that are associated with the name, | function returns one of the numbers that are associated with the name, |
but it is not defined which it is. |
but it is not defined which it is. |
|
|
If you want to get full details of all captured substrings for a given | If you want to get full details of all captured substrings for a given |
name, you must use the pcre_get_stringtable_entries() function. The | name, you must use the pcre_get_stringtable_entries() function. The |
first argument is the compiled pattern, and the second is the name. The |
first argument is the compiled pattern, and the second is the name. The |
third and fourth are pointers to variables which are updated by the | third and fourth are pointers to variables which are updated by the |
function. After it has run, they point to the first and last entries in |
function. After it has run, they point to the first and last entries in |
the name-to-number table for the given name. The function itself | the name-to-number table for the given name. The function itself |
returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if | returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if |
there are none. The format of the table is described above in the sec- | there are none. The format of the table is described above in the sec- |
tion entitled Information about a pattern above. Given all the rele- | tion entitled Information about a pattern above. Given all the rele- |
vant entries for the name, you can extract each of their numbers, and | vant entries for the name, you can extract each of their numbers, and |
hence the captured data, if any. |
hence the captured data, if any. |
|
|
|
|
FINDING ALL POSSIBLE MATCHES |
FINDING ALL POSSIBLE MATCHES |
|
|
The traditional matching function uses a similar algorithm to Perl, | The traditional matching function uses a similar algorithm to Perl, |
which stops when it finds the first match, starting at a given point in |
which stops when it finds the first match, starting at a given point in |
the subject. If you want to find all possible matches, or the longest | the subject. If you want to find all possible matches, or the longest |
possible match, consider using the alternative matching function (see | possible match, consider using the alternative matching function (see |
below) instead. If you cannot use the alternative function, but still | below) instead. If you cannot use the alternative function, but still |
need to find all possible matches, you can kludge it up by making use | need to find all possible matches, you can kludge it up by making use |
of the callout facility, which is described in the pcrecallout documen- |
of the callout facility, which is described in the pcrecallout documen- |
tation. |
tation. |
|
|
What you have to do is to insert a callout right at the end of the pat- |
What you have to do is to insert a callout right at the end of the pat- |
tern. When your callout function is called, extract and save the cur- | tern. When your callout function is called, extract and save the cur- |
rent matched substring. Then return 1, which forces pcre_exec() to | rent matched substring. Then return 1, which forces pcre_exec() to |
backtrack and try other alternatives. Ultimately, when it runs out of | backtrack and try other alternatives. Ultimately, when it runs out of |
matches, pcre_exec() will yield PCRE_ERROR_NOMATCH. |
matches, pcre_exec() will yield PCRE_ERROR_NOMATCH. |
|
|
|
|
OBTAINING AN ESTIMATE OF STACK USAGE |
OBTAINING AN ESTIMATE OF STACK USAGE |
|
|
Matching certain patterns using pcre_exec() can use a lot of process | Matching certain patterns using pcre_exec() can use a lot of process |
stack, which in certain environments can be rather limited in size. | stack, which in certain environments can be rather limited in size. |
Some users find it helpful to have an estimate of the amount of stack | Some users find it helpful to have an estimate of the amount of stack |
that is used by pcre_exec(), to help them set recursion limits, as | that is used by pcre_exec(), to help them set recursion limits, as |
described in the pcrestack documentation. The estimate that is output | described in the pcrestack documentation. The estimate that is output |
by pcretest when called with the -m and -C options is obtained by call- |
by pcretest when called with the -m and -C options is obtained by call- |
ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its | ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its |
first five arguments. |
first five arguments. |
|
|
Normally, if its first argument is NULL, pcre_exec() immediately | Normally, if its first argument is NULL, pcre_exec() immediately |
returns the negative error code PCRE_ERROR_NULL, but with this special | returns the negative error code PCRE_ERROR_NULL, but with this special |
combination of arguments, it returns instead a negative number whose | combination of arguments, it returns instead a negative number whose |
absolute value is the approximate stack frame size in bytes. (A nega- | absolute value is the approximate stack frame size in bytes. (A nega- |
tive number is used so that it is clear that no match has happened.) | tive number is used so that it is clear that no match has happened.) |
The value is approximate because in some cases, recursive calls to | The value is approximate because in some cases, recursive calls to |
pcre_exec() occur when there are one or two additional variables on the |
pcre_exec() occur when there are one or two additional variables on the |
stack. |
stack. |
|
|
If PCRE has been compiled to use the heap instead of the stack for | If PCRE has been compiled to use the heap instead of the stack for |
recursion, the value returned is the size of each block that is | recursion, the value returned is the size of each block that is |
obtained from the heap. |
obtained from the heap. |
|
|
|
|
Line 3313 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
Line 4058 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
int options, int *ovector, int ovecsize, |
int options, int *ovector, int ovecsize, |
int *workspace, int wscount); |
int *workspace, int wscount); |
|
|
The function pcre_dfa_exec() is called to match a subject string | The function pcre_dfa_exec() is called to match a subject string |
against a compiled pattern, using a matching algorithm that scans the | against a compiled pattern, using a matching algorithm that scans the |
subject string just once, and does not backtrack. This has different | subject string just once, and does not backtrack. This has different |
characteristics to the normal algorithm, and is not compatible with | characteristics to the normal algorithm, and is not compatible with |
Perl. Some of the features of PCRE patterns are not supported. Never- | Perl. Some of the features of PCRE patterns are not supported. Never- |
theless, there are times when this kind of matching can be useful. For | theless, there are times when this kind of matching can be useful. For |
a discussion of the two matching algorithms, and a list of features | a discussion of the two matching algorithms, and a list of features |
that pcre_dfa_exec() does not support, see the pcrematching documenta- | that pcre_dfa_exec() does not support, see the pcrematching documenta- |
tion. |
tion. |
|
|
The arguments for the pcre_dfa_exec() function are the same as for | The arguments for the pcre_dfa_exec() fun The arguments for the pcre_dfa_exec() fun |
pcre_exec(), plus two extras. The ovector argument is used in a differ- |
pcre_exec(), plus two extras. The ovector argument is used in a differ- |
ent way, and this is described below. The other common arguments are | ent way, and this is described below. The other common arguments are |
used in the same way as for pcre_exec(), so their description is not | used in the same way as for pcre_exec(), so their description is not |
repeated here. |
repeated here. |
|
|
The two additional arguments provide workspace for the function. The | The two additional arguments provide workspace for the function. The |
workspace vector should contain at least 20 elements. It is used for | workspace vector should contain at least 20 elements. It is used for |
keeping track of multiple paths through the pattern tree. More |
keeping track of multiple paths through the pattern tree. More |
workspace will be needed for patterns and subjects where there are a | workspace will be needed for patterns and subjects where there are a |
lot of potential matches. |
lot of potential matches. |
|
|
Here is an example of a simple call to pcre_dfa_exec(): |
Here is an example of a simple call to pcre_dfa_exec(): |
Line 3354 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
Line 4099 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
|
|
Option bits for pcre_dfa_exec() |
Option bits for pcre_dfa_exec() |
|
|
The unused bits of the options argument for pcre_dfa_exec() must be | The unused bits of the options argument for pcre_dfa_exec() must be |
zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW- | zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW- |
LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, |
LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, |
PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, | PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, |
PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR- | PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR- |
TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last | TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last |
four of these are exactly the same as for pcre_exec(), so their | four of these are exactly the same as for pcre_exec(), so their |
description is not repeated here. |
description is not repeated here. |
|
|
PCRE_PARTIAL_HARD |
PCRE_PARTIAL_HARD |
PCRE_PARTIAL_SOFT |
PCRE_PARTIAL_SOFT |
|
|
These have the same general effect as they do for pcre_exec(), but the | These have the same general effect as they do for pcre_exec(), but the |
details are slightly different. When PCRE_PARTIAL_HARD is set for | details are slightly different. When PCRE_PARTIAL_HARD is set for |
pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub- | pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub- |
ject is reached and there is still at least one matching possibility | ject is reached and there is still at least one matching possibility |
that requires additional characters. This happens even if some complete |
that requires additional characters. This happens even if some complete |
matches have also been found. When PCRE_PARTIAL_SOFT is set, the return |
matches have also been found. When PCRE_PARTIAL_SOFT is set, the return |
code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end |
code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end |
of the subject is reached, there have been no complete matches, but | of the subject is reached, there have been no complete matches, but |
there is still at least one matching possibility. The portion of the | there is still at least one matching possibility. The portion of the |
string that was inspected when the longest partial match was found is | string that was inspected when the longest partial match was found is |
set as the first matching string in both cases. There is a more | set as the first matching string in both cases. There is a more |
detailed discussion of partial and multi-segment matching, with exam- | detailed discussion of partial and multi-segment matching, with exam- |
ples, in the pcrepartial documentation. |
ples, in the pcrepartial documentation. |
|
|
PCRE_DFA_SHORTEST |
PCRE_DFA_SHORTEST |
|
|
Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to | Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to |
stop as soon as it has found one match. Because of the way the alterna- |
stop as soon as it has found one match. Because of the way the alterna- |
tive algorithm works, this is necessarily the shortest possible match | tive algorithm works, this is necessarily the shortest possible match |
at the first possible matching point in the subject string. |
at the first possible matching point in the subject string. |
|
|
PCRE_DFA_RESTART |
PCRE_DFA_RESTART |
|
|
When pcre_dfa_exec() returns a partial match, it is possible to call it |
When pcre_dfa_exec() returns a partial match, it is possible to call it |
again, with additional subject characters, and have it continue with | again, with additional subject characters, and have it continue with |
the same match. The PCRE_DFA_RESTART option requests this action; when | the same match. The PCRE_DFA_RESTART option requests this action; when |
it is set, the workspace and wscount options must reference the same | it is set, the workspace and wscount options must reference the same |
vector as before because data about the match so far is left in them | vector as before because data about the match so far is left in them |
after a partial match. There is more discussion of this facility in the |
after a partial match. There is more discussion of this facility in the |
pcrepartial documentation. |
pcrepartial documentation. |
|
|
Successful returns from pcre_dfa_exec() |
Successful returns from pcre_dfa_exec() |
|
|
When pcre_dfa_exec() succeeds, it may have matched more than one sub- | When pcre_dfa_exec() succeeds, it may have matched more than one sub- |
string in the subject. Note, however, that all the matches from one run |
string in the subject. Note, however, that all the matches from one run |
of the function start at the same point in the subject. The shorter | of the function start at the same point in the subject. The shorter |
matches are all initial substrings of the longer matches. For example, | matches are all initial substrings of the longer matches. For example, |
if the pattern |
if the pattern |
|
|
<.*> |
<.*> |
Line 3417 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
Line 4162 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
<something> <something else> |
<something> <something else> |
<something> <something else> <something further> |
<something> <something else> <something further> |
|
|
On success, the yield of the function is a number greater than zero, | On success, the yield of the function is a number greater than zero, |
which is the number of matched substrings. The substrings themselves | which is the number of matched substrings. The substrings themselves |
are returned in ovector. Each string uses two elements; the first is | are returned in ovector. Each string uses two elements; the first is |
the offset to the start, and the second is the offset to the end. In | the offset to the start, and the second is the offset to the end. In |
fact, all the strings have the same start offset. (Space could have | fact, all the strings have the same start offset. (Space could have |
been saved by giving this only once, but it was decided to retain some | been saved by giving this only once, but it was decided to retain some |
compatibility with the way pcre_exec() returns data, even though the | compatibility with the way pcre_exec() returns data, even though the |
meaning of the strings is different.) |
meaning of the strings is different.) |
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The strings are returned in reverse order of length; that is, the long- |
The strings are returned in reverse order of length; that is, the long- |
est matching string is given first. If there were too many matches to | est matching string is given first. If there were too many matches to |
fit into ovector, the yield of the function is zero, and the vector is | fit into ovector, the yield of the function is zero, and the vector is |
filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() | filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() |
can use the entire ovector for returning matched strings. |
can use the entire ovector for returning matched strings. |
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NOTE: PCRE's "auto-possessification" optimization usually applies to |
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character repeats at the end of a pattern (as well as internally). For |
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example, the pattern "a\d+" is compiled as if it were "a\d++" because |
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there is no point even considering the possibility of backtracking into |
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the repeated digits. For DFA matching, this means that only one possi- |
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ble match is found. If you really do want multiple matches in such |
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cases, either use an ungreedy repeat ("a\d+?") or set the |
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PCRE_NO_AUTO_POSSESS option when compiling. |
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Error returns from pcre_dfa_exec() |
Error returns from pcre_dfa_exec() |
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The pcre_dfa_exec() function returns a negative number when it fails. |
The pcre_dfa_exec() function returns a negative number when it fails. |
Line 3480 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
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Line 4234 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
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SEE ALSO |
SEE ALSO |
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pcre16(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematch- | pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), |
ing(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcresample(3), | pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre- |
pcrestack(3). | sample(3), pcrestack(3). |
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AUTHOR |
AUTHOR |
Line 3494 AUTHOR
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Line 4248 AUTHOR
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REVISION |
REVISION |
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Last updated: 17 June 2012 | Last updated: 12 November 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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PCRECALLOUT(3) PCRECALLOUT(3) | PCRECALLOUT(3) Library Functions Manual PCRECALLOUT(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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SYNOPSIS |
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PCRE CALLOUTS | #include <pcre.h> |
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int (*pcre_callout)(pcre_callout_block *); |
int (*pcre_callout)(pcre_callout_block *); |
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int (*pcre16_callout)(pcre16_callout_block *); |
int (*pcre16_callout)(pcre16_callout_block *); |
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int (*pcre32_callout)(pcre32_callout_block *); |
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DESCRIPTION |
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PCRE provides a feature called "callout", which is a means of temporar- |
PCRE provides a feature called "callout", which is a means of temporar- |
ily passing control to the caller of PCRE in the middle of pattern |
ily passing control to the caller of PCRE in the middle of pattern |
matching. The caller of PCRE provides an external function by putting |
matching. The caller of PCRE provides an external function by putting |
its entry point in the global variable pcre_callout (pcre16_callout for |
its entry point in the global variable pcre_callout (pcre16_callout for |
the 16-bit library). By default, this variable contains NULL, which | the 16-bit library, pcre32_callout for the 32-bit library). By default, |
disables all calling out. | this variable contains NULL, which disables all calling out. |
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Within a regular expression, (?C) indicates the points at which the |
Within a regular expression, (?C) indicates the points at which the |
external function is to be called. Different callout points can be |
external function is to be called. Different callout points can be |
Line 3539 PCRE CALLOUTS
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Line 4300 PCRE CALLOUTS
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(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) |
(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) |
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Notice that there is a callout before and after each parenthesis and |
Notice that there is a callout before and after each parenthesis and |
alternation bar. Automatic callouts can be used for tracking the | alternation bar. If the pattern contains a conditional group whose con- |
progress of pattern matching. The pcretest command has an option that | dition is an assertion, an automatic callout is inserted immediately |
sets automatic callouts; when it is used, the output indicates how the | before the condition. Such a callout may also be inserted explicitly, |
pattern is matched. This is useful information when you are trying to | for example: |
optimize the performance of a particular pattern. | |
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The use of callouts in a pattern makes it ineligible for optimization | (?(?C9)(?=a)ab|de) |
by the just-in-time compiler. Studying such a pattern with the | |
PCRE_STUDY_JIT_COMPILE option always fails. | |
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This applies only to assertion conditions (because they are themselves |
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independent groups). |
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Automatic callouts can be used for tracking the progress of pattern |
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matching. The pcretest program has a pattern qualifier (/C) that sets |
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automatic callouts; when it is used, the output indicates how the pat- |
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tern is being matched. This is useful information when you are trying |
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to optimize the performance of a particular pattern. |
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MISSING CALLOUTS |
MISSING CALLOUTS |
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You should be aware that, because of optimizations in the way PCRE | You should be aware that, because of optimizations in the way PCRE com- |
matches patterns by default, callouts sometimes do not happen. For | piles and matches patterns, callouts sometimes do not happen exactly as |
example, if the pattern is | you might expect. |
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At compile time, PCRE "auto-possessifies" repeated items when it knows |
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that what follows cannot be part of the repeat. For example, a+[bc] is |
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compiled as if it were a++[bc]. The pcretest output when this pattern |
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is anchored and then applied with automatic callouts to the string |
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"aaaa" is: |
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--->aaaa |
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+0 ^ ^ |
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+1 ^ a+ |
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+3 ^ ^ [bc] |
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No match |
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This indicates that when matching [bc] fails, there is no backtracking |
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into a+ and therefore the callouts that would be taken for the back- |
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tracks do not occur. You can disable the auto-possessify feature by |
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passing PCRE_NO_AUTO_POSSESS to pcre_compile(), or starting the pattern |
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with (*NO_AUTO_POSSESS). If this is done in pcretest (using the /O |
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qualifier), the output changes to this: |
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--->aaaa |
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+0 ^ ^ |
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+1 ^ a+ |
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+3 ^ ^ [bc] |
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+3 ^ ^ [bc] |
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+3 ^ ^ [bc] |
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+3 ^^ [bc] |
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No match |
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This time, when matching [bc] fails, the matcher backtracks into a+ and |
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tries again, repeatedly, until a+ itself fails. |
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Other optimizations that provide fast "no match" results also affect |
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callouts. For example, if the pattern is |
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ab(?C4)cd |
ab(?C4)cd |
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PCRE knows that any matching string must contain the letter "d". If the |
PCRE knows that any matching string must contain the letter "d". If the |
subject string is "abyz", the lack of "d" means that matching doesn't | subject string is "abyz", the lack of "d" means that matching doesn't |
ever start, and the callout is never reached. However, with "abyd", | ever start, and the callout is never reached. However, with "abyd", |
though the result is still no match, the callout is obeyed. |
though the result is still no match, the callout is obeyed. |
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If the pattern is studied, PCRE knows the minimum length of a matching | If the pattern is studied, PCRE knows the minimum length of a matching |
string, and will immediately give a "no match" return without actually | string, and will immediately give a "no match" return without actually |
running a match if the subject is not long enough, or, for unanchored | running a match if the subject is not long enough, or, for unanchored |
patterns, if it has been scanned far enough. |
patterns, if it has been scanned far enough. |
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You can disable these optimizations by passing the PCRE_NO_START_OPTI- | You can disable these optimizations by passing the PCRE_NO_START_OPTI- |
MIZE option to the matching function, or by starting the pattern with | MIZE option to the matching function, or by starting the pattern with |
(*NO_START_OPT). This slows down the matching process, but does ensure | (*NO_START_OPT). This slows down the matching process, but does ensure |
that callouts such as the example above are obeyed. |
that callouts such as the example above are obeyed. |
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THE CALLOUT INTERFACE |
THE CALLOUT INTERFACE |
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During matching, when PCRE reaches a callout point, the external func- | During matching, when PCRE reaches a callout point, the external func- |
tion defined by pcre_callout or pcre16_callout is called (if it is | tion defined by pcre_callout or pcre[16|32]_callout is called (if it is |
set). This applies to both normal and DFA matching. The only argument | set). This applies to both normal and DFA matching. The only argument |
to the callout function is a pointer to a pcre_callout or pcre16_call- | to the callout function is a pointer to a pcre_callout or |
out block. These structures contains the following fields: | pcre[16|32]_callout block. These structures contains the following |
| fields: |
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int version; |
int version; |
int callout_number; |
int callout_number; |
int *offset_vector; |
int *offset_vector; |
const char *subject; (8-bit version) |
const char *subject; (8-bit version) |
PCRE_SPTR16 subject; (16-bit version) |
PCRE_SPTR16 subject; (16-bit version) |
|
PCRE_SPTR32 subject; (32-bit version) |
int subject_length; |
int subject_length; |
int start_match; |
int start_match; |
int current_position; |
int current_position; |
Line 3597 THE CALLOUT INTERFACE
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Line 4400 THE CALLOUT INTERFACE
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int next_item_length; |
int next_item_length; |
const unsigned char *mark; (8-bit version) |
const unsigned char *mark; (8-bit version) |
const PCRE_UCHAR16 *mark; (16-bit version) |
const PCRE_UCHAR16 *mark; (16-bit version) |
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const PCRE_UCHAR32 *mark; (32-bit version) |
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The version field is an integer containing the version number of the |
The version field is an integer containing the version number of the |
block format. The initial version was 0; the current version is 2. The |
block format. The initial version was 0; the current version is 2. The |
Line 3609 THE CALLOUT INTERFACE
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Line 4413 THE CALLOUT INTERFACE
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The offset_vector field is a pointer to the vector of offsets that was |
The offset_vector field is a pointer to the vector of offsets that was |
passed by the caller to the matching function. When pcre_exec() or |
passed by the caller to the matching function. When pcre_exec() or |
pcre16_exec() is used, the contents can be inspected, in order to | pcre[16|32]_exec() is used, the contents can be inspected, in order to |
extract substrings that have been matched so far, in the same way as |
extract substrings that have been matched so far, in the same way as |
for extracting substrings after a match has completed. For the DFA |
for extracting substrings after a match has completed. For the DFA |
matching functions, this field is not useful. |
matching functions, this field is not useful. |
Line 3627 THE CALLOUT INTERFACE
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Line 4431 THE CALLOUT INTERFACE
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The current_position field contains the offset within the subject of |
The current_position field contains the offset within the subject of |
the current match pointer. |
the current match pointer. |
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When the pcre_exec() or pcre16_exec() is used, the capture_top field | When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top |
contains one more than the number of the highest numbered captured sub- | field contains one more than the number of the highest numbered cap- |
string so far. If no substrings have been captured, the value of cap- | tured substring so far. If no substrings have been captured, the value |
ture_top is one. This is always the case when the DFA functions are | of capture_top is one. This is always the case when the DFA functions |
used, because they do not support captured substrings. | are used, because they do not support captured substrings. |
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The capture_last field contains the number of the most recently cap- |
The capture_last field contains the number of the most recently cap- |
tured substring. If no substrings have been captured, its value is -1. | tured substring. However, when a recursion exits, the value reverts to |
This is always the case for the DFA matching functions. | what it was outside the recursion, as do the values of all captured |
| substrings. If no substrings have been captured, the value of cap- |
| ture_last is -1. This is always the case for the DFA matching func- |
| tions. |
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The callout_data field contains a value that is passed to a matching | The callout_data field contains a value that is passed to a matching |
function specifically so that it can be passed back in callouts. It is | function specifically so that it can be passed back in callouts. It is |
passed in the callout_data field of a pcre_extra or pcre16_extra data | passed in the callout_data field of a pcre_extra or pcre[16|32]_extra |
structure. If no such data was passed, the value of callout_data in a | data structure. If no such data was passed, the value of callout_data |
callout block is NULL. There is a description of the pcre_extra struc- | in a callout block is NULL. There is a description of the pcre_extra |
ture in the pcreapi documentation. | structure in the pcreapi documentation. |
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The pattern_position field is present from version 1 of the callout | The pattern_position field is present from version 1 of the callout |
structure. It contains the offset to the next item to be matched in the |
structure. It contains the offset to the next item to be matched in the |
pattern string. |
pattern string. |
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The next_item_length field is present from version 1 of the callout | The next_item_length field is present from version 1 of the callout |
structure. It contains the length of the next item to be matched in the |
structure. It contains the length of the next item to be matched in the |
pattern string. When the callout immediately precedes an alternation | pattern string. When the callout immediately precedes an alternation |
bar, a closing parenthesis, or the end of the pattern, the length is | bar, a closing parenthesis, or the end of the pattern, the length is |
zero. When the callout precedes an opening parenthesis, the length is | zero. When the callout precedes an opening parenthesis, the length is |
that of the entire subpattern. |
that of the entire subpattern. |
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The pattern_position and next_item_length fields are intended to help | The pattern_position and next_item_length fields are intended to help |
in distinguishing between different automatic callouts, which all have | in distinguishing between different automatic callouts, which all have |
the same callout number. However, they are set for all callouts. |
the same callout number. However, they are set for all callouts. |
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The mark field is present from version 2 of the callout structure. In | The mark field is present from version 2 of the callout structure. In |
callouts from pcre_exec() or pcre16_exec() it contains a pointer to the | callouts from pcre_exec() or pcre[16|32]_exec() it contains a pointer |
zero-terminated name of the most recently passed (*MARK), (*PRUNE), or | to the zero-terminated name of the most recently passed (*MARK), |
(*THEN) item in the match, or NULL if no such items have been passed. | (*PRUNE), or (*THEN) item in the match, or NULL if no such items have |
Instances of (*PRUNE) or (*THEN) without a name do not obliterate a | been passed. Instances of (*PRUNE) or (*THEN) without a name do not |
previous (*MARK). In callouts from the DFA matching functions this | obliterate a previous (*MARK). In callouts from the DFA matching func- |
field always contains NULL. | tions this field always contains NULL. |
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RETURN VALUES |
RETURN VALUES |
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The external callout function returns an integer to PCRE. If the value | The external callout function returns an integer to PCRE. If the value |
is zero, matching proceeds as normal. If the value is greater than | is zero, matching proceeds as normal. If the value is greater than |
zero, matching fails at the current point, but the testing of other | zero, matching fails at the current point, but the testing of other |
matching possibilities goes ahead, just as if a lookahead assertion had |
matching possibilities goes ahead, just as if a lookahead assertion had |
failed. If the value is less than zero, the match is abandoned, the | failed. If the value is less than zero, the match is abandoned, the |
matching function returns the negative value. |
matching function returns the negative value. |
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Negative values should normally be chosen from the set of | Negative values should normally be chosen from the set of |
PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan- |
PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan- |
dard "no match" failure. The error number PCRE_ERROR_CALLOUT is | dard "no match" failure. The error number PCRE_ERROR_CALLOUT is |
reserved for use by callout functions; it will never be used by PCRE | reserved for use by callout functions; it will never be used by PCRE |
itself. |
itself. |
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Line 3693 AUTHOR
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Line 4500 AUTHOR
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REVISION |
REVISION |
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Last updated: 08 Janurary 2012 | Last updated: 12 November 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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PCRECOMPAT(3) PCRECOMPAT(3) | PCRECOMPAT(3) Library Functions Manual PCRECOMPAT(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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DIFFERENCES BETWEEN PCRE AND PERL |
DIFFERENCES BETWEEN PCRE AND PERL |
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This document describes the differences in the ways that PCRE and Perl |
This document describes the differences in the ways that PCRE and Perl |
Line 3723 DIFFERENCES BETWEEN PCRE AND PERL
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Line 4530 DIFFERENCES BETWEEN PCRE AND PERL
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3. Capturing subpatterns that occur inside negative lookahead asser- |
3. Capturing subpatterns that occur inside negative lookahead asser- |
tions are counted, but their entries in the offsets vector are never |
tions are counted, but their entries in the offsets vector are never |
set. Perl sets its numerical variables from any such patterns that are | set. Perl sometimes (but not always) sets its numerical variables from |
matched before the assertion fails to match something (thereby succeed- | inside negative assertions. |
ing), but only if the negative lookahead assertion contains just one | |
branch. | |
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4. Though binary zero characters are supported in the subject string, |
4. Though binary zero characters are supported in the subject string, |
they are not allowed in a pattern string because it is passed as a nor- |
they are not allowed in a pattern string because it is passed as a nor- |
Line 3752 DIFFERENCES BETWEEN PCRE AND PERL
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Line 4557 DIFFERENCES BETWEEN PCRE AND PERL
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tion of Unicode characters, there is no need to implement the somewhat |
tion of Unicode characters, there is no need to implement the somewhat |
messy concept of surrogates." |
messy concept of surrogates." |
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7. PCRE implements a simpler version of \X than Perl, which changed to | 7. PCRE does support the \Q...\E escape for quoting substrings. Charac- |
make \X match what Unicode calls an "extended grapheme cluster". This | ters in between are treated as literals. This is slightly different |
is more complicated than an extended Unicode sequence, which is what | from Perl in that $ and @ are also handled as literals inside the |
PCRE matches. | quotes. In Perl, they cause variable interpolation (but of course PCRE |
| |
8. PCRE does support the \Q...\E escape for quoting substrings. Charac- | |
ters in between are treated as literals. This is slightly different | |
from Perl in that $ and @ are also handled as literals inside the | |
quotes. In Perl, they cause variable interpolation (but of course PCRE | |
does not have variables). Note the following examples: |
does not have variables). Note the following examples: |
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Pattern PCRE matches Perl matches |
Pattern PCRE matches Perl matches |
Line 3770 DIFFERENCES BETWEEN PCRE AND PERL
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Line 4570 DIFFERENCES BETWEEN PCRE AND PERL
|
\Qabc\$xyz\E abc\$xyz abc\$xyz |
\Qabc\$xyz\E abc\$xyz abc\$xyz |
\Qabc\E\$\Qxyz\E abc$xyz abc$xyz |
\Qabc\E\$\Qxyz\E abc$xyz abc$xyz |
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The \Q...\E sequence is recognized both inside and outside character | The \Q...\E sequence is recognized both inside and outside character |
classes. |
classes. |
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9. Fairly obviously, PCRE does not support the (?{code}) and (??{code}) | 8. Fairly obviously, PCRE does not support the (?{code}) and (??{code}) |
constructions. However, there is support for recursive patterns. This | constructions. However, there is support for recursive patterns. This |
is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE | is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE |
"callout" feature allows an external function to be called during pat- | "callout" feature allows an external function to be called during pat- |
tern matching. See the pcrecallout documentation for details. |
tern matching. See the pcrecallout documentation for details. |
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10. Subpatterns that are called as subroutines (whether or not recur- | 9. Subpatterns that are called as subroutines (whether or not recur- |
sively) are always treated as atomic groups in PCRE. This is like | sively) are always treated as atomic groups in PCRE. This is like |
Python, but unlike Perl. Captured values that are set outside a sub- | Python, but unlike Perl. Captured values that are set outside a sub- |
routine call can be reference from inside in PCRE, but not in Perl. | routine call can be reference from inside in PCRE, but not in Perl. |
There is a discussion that explains these differences in more detail in |
There is a discussion that explains these differences in more detail in |
the section on recursion differences from Perl in the pcrepattern page. |
the section on recursion differences from Perl in the pcrepattern page. |
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11. If any of the backtracking control verbs are used in an assertion | 10. If any of the backtracking control verbs are used in a subpattern |
or in a subpattern that is called as a subroutine (whether or not | that is called as a subroutine (whether or not recursively), their |
recursively), their effect is confined to that subpattern; it does not | effect is confined to that subpattern; it does not extend to the sur- |
extend to the surrounding pattern. This is not always the case in Perl. | rounding pattern. This is not always the case in Perl. In particular, |
In particular, if (*THEN) is present in a group that is called as a | if (*THEN) is present in a group that is called as a subroutine, its |
subroutine, its action is limited to that group, even if the group does | action is limited to that group, even if the group does not contain any |
not contain any | characters. There is one exception to this: the name | | characters. Note that such subpatterns are processed as anchored at |
from a *(MARK), (*PRUNE), or (*THEN) that is encountered in a success- | the point where they are tested. |
ful positive assertion is passed back when a match succeeds (compare | |
capturing parentheses in assertions). Note that such subpatterns are | |
processed as anchored at the point where they are tested. | |
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12. There are some differences that are concerned with the settings of | 11. If a pattern contains more than one backtracking control verb, the |
captured strings when part of a pattern is repeated. For example, | first one that is backtracked onto acts. For example, in the pattern |
matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2 | A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure |
| in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases |
| it is the same as PCRE, but there are examples where it differs. |
| |
| 12. Most backtracking verbs in assertions have their normal actions. |
| They are not confined to the assertion. |
| |
| 13. There are some differences that are concerned with the settings of |
| captured strings when part of a pattern is repeated. For example, |
| matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2 |
unset, but in PCRE it is set to "b". |
unset, but in PCRE it is set to "b". |
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|
13. PCRE's handling of duplicate subpattern numbers and duplicate sub- | 14. PCRE's handling of duplicate subpattern numbers and duplicate sub- |
pattern names is not as general as Perl's. This is a consequence of the |
pattern names is not as general as Perl's. This is a consequence of the |
fact the PCRE works internally just with numbers, using an external ta- |
fact the PCRE works internally just with numbers, using an external ta- |
ble to translate between numbers and names. In particular, a pattern | ble to translate between numbers and names. In particular, a pattern |
such as (?|(?<a>A)|(?<b)B), where the two capturing parentheses have | such as (?|(?<a>A)|(?<b)B), where the two capturing parentheses have |
the same number but different names, is not supported, and causes an | the same number but different names, is not supported, and causes an |
error at compile time. If it were allowed, it would not be possible to | error at compile time. If it were allowed, it would not be possible to |
distinguish which parentheses matched, because both names map to cap- | distinguish which parentheses matched, because both names map to cap- |
turing subpattern number 1. To avoid this confusing situation, an error |
turing subpattern number 1. To avoid this confusing situation, an error |
is given at compile time. |
is given at compile time. |
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|
14. Perl recognizes comments in some places that PCRE does not, for | 15. Perl recognizes comments in some places that PCRE does not, for |
example, between the ( and ? at the start of a subpattern. If the /x | example, between the ( and ? at the start of a subpattern. If the /x |
modifier is set, Perl allows white space between ( and ? but PCRE never | modifier is set, Perl allows white space between ( and ? (though cur- |
does, even if the PCRE_EXTENDED option is set. | rent Perls warn that this is deprecated) but PCRE never does, even if |
| the PCRE_EXTENDED option is set. |
|
|
15. PCRE provides some extensions to the Perl regular expression facil- | 16. Perl, when in warning mode, gives warnings for character classes |
| such as [A-\d] or [a-[:digit:]]. It then treats the hyphens as liter- |
| als. PCRE has no warning features, so it gives an error in these cases |
| because they are almost certainly user mistakes. |
| |
| 17. In PCRE, the upper/lower case character properties Lu and Ll are |
| not affected when case-independent matching is specified. For example, |
| \p{Lu} always matches an upper case letter. I think Perl has changed in |
| this respect; in the release at the time of writing (5.16), \p{Lu} and |
| \p{Ll} match all letters, regardless of case, when case independence is |
| specified. |
| |
| 18. PCRE provides some extensions to the Perl regular expression facil- |
ities. Perl 5.10 includes new features that are not in earlier ver- |
ities. Perl 5.10 includes new features that are not in earlier ver- |
sions of Perl, some of which (such as named parentheses) have been in |
sions of Perl, some of which (such as named parentheses) have been in |
PCRE for some time. This list is with respect to Perl 5.10: |
PCRE for some time. This list is with respect to Perl 5.10: |
Line 3858 DIFFERENCES BETWEEN PCRE AND PERL
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Line 4677 DIFFERENCES BETWEEN PCRE AND PERL
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even on different hosts that have the other endianness. However, this |
even on different hosts that have the other endianness. However, this |
does not apply to optimized data created by the just-in-time compiler. |
does not apply to optimized data created by the just-in-time compiler. |
|
|
(k) The alternative matching functions (pcre_dfa_exec() and | (k) The alternative matching functions (pcre_dfa_exec(), |
pcre16_dfa_exec()) match in a different way and are not Perl-compati- | pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and |
ble. | are not Perl-compatible. |
|
|
(l) PCRE recognizes some special sequences such as (*CR) at the start |
(l) PCRE recognizes some special sequences such as (*CR) at the start |
of a pattern that set overall options that cannot be changed within the |
of a pattern that set overall options that cannot be changed within the |
Line 3876 AUTHOR
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Line 4695 AUTHOR
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|
REVISION |
REVISION |
|
|
Last updated: 01 June 2012 | Last updated: 10 November 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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PCREPATTERN(3) PCREPATTERN(3) | PCREPATTERN(3) Library Functions Manual PCREPATTERN(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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PCRE REGULAR EXPRESSION DETAILS |
PCRE REGULAR EXPRESSION DETAILS |
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The syntax and semantics of the regular expressions that are supported |
The syntax and semantics of the regular expressions that are supported |
Line 3905 PCRE REGULAR EXPRESSION DETAILS
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Line 4724 PCRE REGULAR EXPRESSION DETAILS
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great detail. This description of PCRE's regular expressions is |
great detail. This description of PCRE's regular expressions is |
intended as reference material. |
intended as reference material. |
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|
This document discusses the patterns that are supported by PCRE when |
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one its main matching functions, pcre_exec() (8-bit) or |
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pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has alternative |
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matching functions, pcre_dfa_exec() and pcre[16|32_dfa_exec(), which |
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match using a different algorithm that is not Perl-compatible. Some of |
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the features discussed below are not available when DFA matching is |
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used. The advantages and disadvantages of the alternative functions, |
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and how they differ from the normal functions, are discussed in the |
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pcrematching page. |
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SPECIAL START-OF-PATTERN ITEMS |
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A number of options that can be passed to pcre_compile() can also be |
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set by special items at the start of a pattern. These are not Perl-com- |
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patible, but are provided to make these options accessible to pattern |
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writers who are not able to change the program that processes the pat- |
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tern. Any number of these items may appear, but they must all be |
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together right at the start of the pattern string, and the letters must |
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be in upper case. |
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UTF support |
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|
The original operation of PCRE was on strings of one-byte characters. |
The original operation of PCRE was on strings of one-byte characters. |
However, there is now also support for UTF-8 strings in the original |
However, there is now also support for UTF-8 strings in the original |
library, and a second library that supports 16-bit and UTF-16 character | library, an extra library that supports 16-bit and UTF-16 character |
| strings, and a third library that supports 32-bit and UTF-32 character |
strings. To use these features, PCRE must be built to include appropri- |
strings. To use these features, PCRE must be built to include appropri- |
ate support. When using UTF strings you must either call the compiling | ate support. When using UTF strings you must either call the compiling |
function with the PCRE_UTF8 or PCRE_UTF16 option, or the pattern must | function with the PCRE_UTF8, PCRE_UTF16, or PCRE_UTF32 option, or the |
start with one of these special sequences: | pattern must start with one of these special sequences: |
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(*UTF8) |
(*UTF8) |
(*UTF16) |
(*UTF16) |
|
(*UTF32) |
|
(*UTF) |
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|
Starting a pattern with such a sequence is equivalent to setting the | (*UTF) is a generic sequence that can be used with any of the |
relevant option. This feature is not Perl-compatible. How setting a UTF | libraries. Starting a pattern with such a sequence is equivalent to |
mode affects pattern matching is mentioned in several places below. | setting the relevant option. How setting a UTF mode affects pattern |
There is also a summary of features in the pcreunicode page. | matching is mentioned in several places below. There is also a summary |
| of features in the pcreunicode page. |
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|
Another special sequence that may appear at the start of a pattern or | Some applications that allow their users to supply patterns may wish to |
in combination with (*UTF8) or (*UTF16) is: | restrict them to non-UTF data for security reasons. If the |
| PCRE_NEVER_UTF option is set at compile time, (*UTF) etc. are not |
| allowed, and their appearance causes an error. |
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(*UCP) | Unicode property support |
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|
This has the same effect as setting the PCRE_UCP option: it causes | Another special sequence that may appear at the start of a pattern is |
sequences such as \d and \w to use Unicode properties to determine | (*UCP). This has the same effect as setting the PCRE_UCP option: it |
character types, instead of recognizing only characters with codes less | causes sequences such as \d and \w to use Unicode properties to deter- |
than 128 via a lookup table. | mine character types, instead of recognizing only characters with codes |
| less than 128 via a lookup table. |
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|
If a pattern starts with (*NO_START_OPT), it has the same effect as | Disabling auto-possessification |
setting the PCRE_NO_START_OPTIMIZE option either at compile or matching | |
time. There are also some more of these special sequences that are con- | |
cerned with the handling of newlines; they are described below. | |
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|
The remainder of this document discusses the patterns that are sup- | If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as |
ported by PCRE when one its main matching functions, pcre_exec() | setting the PCRE_NO_AUTO_POSSESS option at compile time. This stops |
(8-bit) or pcre16_exec() (16-bit), is used. PCRE also has alternative | PCRE from making quantifiers possessive when what follows cannot match |
matching functions, pcre_dfa_exec() and pcre16_dfa_exec(), which match | the repeated item. For example, by default a+b is treated as a++b. For |
using a different algorithm that is not Perl-compatible. Some of the | more details, see the pcreapi documentation. |
features discussed below are not available when DFA matching is used. | |
The advantages and disadvantages of the alternative functions, and how | |
they differ from the normal functions, are discussed in the pcrematch- | |
ing page. | |
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Disabling start-up optimizations |
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|
NEWLINE CONVENTIONS | If a pattern starts with (*NO_START_OPT), it has the same effect as |
| setting the PCRE_NO_START_OPTIMIZE option either at compile or matching |
| time. This disables several optimizations for quickly reaching "no |
| match" results. For more details, see the pcreapi documentation. |
|
|
PCRE supports five different conventions for indicating line breaks in | Newline conventions |
strings: a single CR (carriage return) character, a single LF (line- | |
| PCRE supports five different conventions for indicating line breaks in |
| strings: a single CR (carriage return) character, a single LF (line- |
feed) character, the two-character sequence CRLF, any of the three pre- |
feed) character, the two-character sequence CRLF, any of the three pre- |
ceding, or any Unicode newline sequence. The pcreapi page has further | ceding, or any Unicode newline sequence. The pcreapi page has further |
discussion about newlines, and shows how to set the newline convention | discussion about newlines, and shows how to set the newline convention |
in the options arguments for the compiling and matching functions. |
in the options arguments for the compiling and matching functions. |
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|
It is also possible to specify a newline convention by starting a pat- | It is also possible to specify a newline convention by starting a pat- |
tern string with one of the following five sequences: |
tern string with one of the following five sequences: |
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|
(*CR) carriage return |
(*CR) carriage return |
Line 3966 NEWLINE CONVENTIONS
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Line 4814 NEWLINE CONVENTIONS
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(*ANY) all Unicode newline sequences |
(*ANY) all Unicode newline sequences |
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These override the default and the options given to the compiling func- |
These override the default and the options given to the compiling func- |
tion. For example, on a Unix system where LF is the default newline | tion. For example, on a Unix system where LF is the default newline |
sequence, the pattern |
sequence, the pattern |
|
|
(*CR)a.b |
(*CR)a.b |
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|
changes the convention to CR. That pattern matches "a\nb" because LF is |
changes the convention to CR. That pattern matches "a\nb" because LF is |
no longer a newline. Note that these special settings, which are not | no longer a newline. If more than one of these settings is present, the |
Perl-compatible, are recognized only at the very start of a pattern, | last one is used. |
and that they must be in upper case. If more than one of them is | |
present, the last one is used. | |
|
|
The newline convention affects the interpretation of the dot metachar- | The newline convention affects where the circumflex and dollar asser- |
acter when PCRE_DOTALL is not set, and also the behaviour of \N. How- | tions are true. It also affects the interpretation of the dot metachar- |
ever, it does not affect what the \R escape sequence matches. By | acter when PCRE_DOTALL is not set, and the behaviour of \N. However, it |
default, this is any Unicode newline sequence, for Perl compatibility. | does not affect what the \R escape sequence matches. By default, this |
However, this can be changed; see the description of \R in the section | is any Unicode newline sequence, for Perl compatibility. However, this |
entitled "Newline sequences" below. A change of \R setting can be com- | can be changed; see the description of \R in the section entitled "New- |
bined with a change of newline convention. | line sequences" below. A change of \R setting can be combined with a |
| change of newline convention. |
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Setting match and recursion limits |
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The caller of pcre_exec() can set a limit on the number of times the |
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internal match() function is called and on the maximum depth of recur- |
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sive calls. These facilities are provided to catch runaway matches that |
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are provoked by patterns with huge matching trees (a typical example is |
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a pattern with nested unlimited repeats) and to avoid running out of |
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system stack by too much recursion. When one of these limits is |
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reached, pcre_exec() gives an error return. The limits can also be set |
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by items at the start of the pattern of the form |
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(*LIMIT_MATCH=d) |
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(*LIMIT_RECURSION=d) |
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where d is any number of decimal digits. However, the value of the set- |
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ting must be less than the value set (or defaulted) by the caller of |
|
pcre_exec() for it to have any effect. In other words, the pattern |
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writer can lower the limits set by the programmer, but not raise them. |
|
If there is more than one setting of one of these limits, the lower |
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value is used. |
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EBCDIC CHARACTER CODES |
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PCRE can be compiled to run in an environment that uses EBCDIC as its |
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character code rather than ASCII or Unicode (typically a mainframe sys- |
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tem). In the sections below, character code values are ASCII or Uni- |
|
code; in an EBCDIC environment these characters may have different code |
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values, and there are no code points greater than 255. |
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CHARACTERS AND METACHARACTERS |
CHARACTERS AND METACHARACTERS |
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A regular expression is a pattern that is matched against a subject |
A regular expression is a pattern that is matched against a subject |
Line 4062 BACKSLASH
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Line 4939 BACKSLASH
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after a backslash. All other characters (in particular, those whose |
after a backslash. All other characters (in particular, those whose |
codepoints are greater than 127) are treated as literals. |
codepoints are greater than 127) are treated as literals. |
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|
If a pattern is compiled with the PCRE_EXTENDED option, white space in | If a pattern is compiled with the PCRE_EXTENDED option, most white |
the pattern (other than in a character class) and characters between a | space in the pattern (other than in a character class), and characters |
# outside a character class and the next newline are ignored. An escap- | between a # outside a character class and the next newline, inclusive, |
ing backslash can be used to include a white space or # character as | are ignored. An escaping backslash can be used to include a white space |
part of the pattern. | or # character as part of the pattern. |
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|
If you want to remove the special meaning from a sequence of charac- |
If you want to remove the special meaning from a sequence of charac- |
ters, you can do so by putting them between \Q and \E. This is differ- |
ters, you can do so by putting them between \Q and \E. This is differ- |
Line 4104 BACKSLASH
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Line 4981 BACKSLASH
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\n linefeed (hex 0A) |
\n linefeed (hex 0A) |
\r carriage return (hex 0D) |
\r carriage return (hex 0D) |
\t tab (hex 09) |
\t tab (hex 09) |
|
\0dd character with octal code 0dd |
\ddd character with octal code ddd, or back reference |
\ddd character with octal code ddd, or back reference |
|
\o{ddd..} character with octal code ddd.. |
\xhh character with hex code hh |
\xhh character with hex code hh |
\x{hhh..} character with hex code hhh.. (non-JavaScript mode) |
\x{hhh..} character with hex code hhh.. (non-JavaScript mode) |
\uhhhh character with hex code hhhh (JavaScript mode only) |
\uhhhh character with hex code hhhh (JavaScript mode only) |
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The precise effect of \cx is as follows: if x is a lower case letter, | The precise effect of \cx on ASCII characters is as follows: if x is a |
it is converted to upper case. Then bit 6 of the character (hex 40) is | lower case letter, it is converted to upper case. Then bit 6 of the |
inverted. Thus \cz becomes hex 1A (z is 7A), but \c{ becomes hex 3B ({ | character (hex 40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A |
is 7B), while \c; becomes hex 7B (; is 3B). If the byte following \c | (A is 41, Z is 5A), but \c{ becomes hex 3B ({ is 7B), and \c; becomes |
has a value greater than 127, a compile-time error occurs. This locks | hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c |
out non-ASCII characters in all modes. (When PCRE is compiled in EBCDIC | has a value greater than 127, a compile-time error occurs. This locks |
mode, all byte values are valid. A lower case letter is converted to | out non-ASCII characters in all modes. |
upper case, and then the 0xc0 bits are flipped.) | |
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|
By default, after \x, from zero to two hexadecimal digits are read | The \c facility was designed for use with ASCII characters, but with |
(letters can be in upper or lower case). Any number of hexadecimal dig- | the extension to Unicode it is even less useful than it once was. It |
its may appear between \x{ and }, but the character code is constrained | is, however, recognized when PCRE is compiled in EBCDIC mode, where |
as follows: | data items are always bytes. In this mode, all values are valid after |
| \c. If the next character is a lower case letter, it is converted to |
| upper case. Then the 0xc0 bits of the byte are inverted. Thus \cA |
| becomes hex 01, as in ASCII (A is C1), but because the EBCDIC letters |
| are disjoint, \cZ becomes hex 29 (Z is E9), and other characters also |
| generate different values. |
|
|
8-bit non-UTF mode less than 0x100 | After \0 up to two further octal digits are read. If there are fewer |
8-bit UTF-8 mode less than 0x10ffff and a valid codepoint | than two digits, just those that are present are used. Thus the |
16-bit non-UTF mode less than 0x10000 | |
16-bit UTF-16 mode less than 0x10ffff and a valid codepoint | |
| |
Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- | |
called "surrogate" codepoints). | |
| |
If characters other than hexadecimal digits appear between \x{ and }, | |
or if there is no terminating }, this form of escape is not recognized. | |
Instead, the initial \x will be interpreted as a basic hexadecimal | |
escape, with no following digits, giving a character whose value is | |
zero. | |
| |
If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x | |
is as just described only when it is followed by two hexadecimal dig- | |
its. Otherwise, it matches a literal "x" character. In JavaScript | |
mode, support for code points greater than 256 is provided by \u, which | |
must be followed by four hexadecimal digits; otherwise it matches a | |
literal "u" character. Character codes specified by \u in JavaScript | |
mode are constrained in the same was as those specified by \x in non- | |
JavaScript mode. | |
| |
Characters whose value is less than 256 can be defined by either of the | |
two syntaxes for \x (or by \u in JavaScript mode). There is no differ- | |
ence in the way they are handled. For example, \xdc is exactly the same | |
as \x{dc} (or \u00dc in JavaScript mode). | |
| |
After \0 up to two further octal digits are read. If there are fewer | |
than two digits, just those that are present are used. Thus the | |
sequence \0\x\07 specifies two binary zeros followed by a BEL character |
sequence \0\x\07 specifies two binary zeros followed by a BEL character |
(code value 7). Make sure you supply two digits after the initial zero | (code value 7). Make sure you supply two digits after the initial zero |
if the pattern character that follows is itself an octal digit. |
if the pattern character that follows is itself an octal digit. |
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|
|
The escape \o must be followed by a sequence of octal digits, enclosed |
|
in braces. An error occurs if this is not the case. This escape is a |
|
recent addition to Perl; it provides way of specifying character code |
|
points as octal numbers greater than 0777, and it also allows octal |
|
numbers and back references to be unambiguously specified. |
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|
For greater clarity and unambiguity, it is best to avoid following \ by |
|
a digit greater than zero. Instead, use \o{} or \x{} to specify charac- |
|
ter numbers, and \g{} to specify back references. The following para- |
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graphs describe the old, ambiguous syntax. |
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|
The handling of a backslash followed by a digit other than 0 is compli- |
The handling of a backslash followed by a digit other than 0 is compli- |
cated. Outside a character class, PCRE reads it and any following dig- | cated, and Perl has changed in recent releases, causing PCRE also to |
its as a decimal number. If the number is less than 10, or if there | change. Outside a character class, PCRE reads the digit and any follow- |
have been at least that many previous capturing left parentheses in the | ing digits as a decimal number. If the number is less than 8, or if |
expression, the entire sequence is taken as a back reference. A | there have been at least that many previous capturing left parentheses |
description of how this works is given later, following the discussion | in the expression, the entire sequence is taken as a back reference. A |
| description of how this works is given later, following the discussion |
of parenthesized subpatterns. |
of parenthesized subpatterns. |
|
|
Inside a character class, or if the decimal number is greater than 9 | Inside a character class, or if the decimal number following \ is |
and there have not been that many capturing subpatterns, PCRE re-reads | greater than 7 and there have not been that many capturing subpatterns, |
up to three octal digits following the backslash, and uses them to gen- | PCRE handles \8 and \9 as the literal characters "8" and "9", and oth- |
erate a data character. Any subsequent digits stand for themselves. The | erwise re-reads up to three octal digits following the backslash, using |
value of the character is constrained in the same way as characters | them to generate a data character. Any subsequent digits stand for |
specified in hexadecimal. For example: | themselves. For example: |
|
|
\040 is another way of writing a space | \040 is another way of writing an ASCII space |
\40 is the same, provided there are fewer than 40 |
\40 is the same, provided there are fewer than 40 |
previous capturing subpatterns |
previous capturing subpatterns |
\7 is always a back reference |
\7 is always a back reference |
Line 4184 BACKSLASH
|
Line 5051 BACKSLASH
|
character with octal code 113 |
character with octal code 113 |
\377 might be a back reference, otherwise |
\377 might be a back reference, otherwise |
the value 255 (decimal) |
the value 255 (decimal) |
\81 is either a back reference, or a binary zero | \81 is either a back reference, or the two |
followed by the two characters "8" and "1" | characters "8" and "1" |
|
|
Note that octal values of 100 or greater must not be introduced by a | Note that octal values of 100 or greater that are specified using this |
leading zero, because no more than three octal digits are ever read. | syntax must not be introduced by a leading zero, because no more than |
| three octal digits are ever read. |
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|
By default, after \x that is not followed by {, from zero to two hexa- |
|
decimal digits are read (letters can be in upper or lower case). Any |
|
number of hexadecimal digits may appear between \x{ and }. If a charac- |
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ter other than a hexadecimal digit appears between \x{ and }, or if |
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there is no terminating }, an error occurs. |
|
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|
If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x |
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is as just described only when it is followed by two hexadecimal dig- |
|
its. Otherwise, it matches a literal "x" character. In JavaScript |
|
mode, support for code points greater than 256 is provided by \u, which |
|
must be followed by four hexadecimal digits; otherwise it matches a |
|
literal "u" character. |
|
|
|
Characters whose value is less than 256 can be defined by either of the |
|
two syntaxes for \x (or by \u in JavaScript mode). There is no differ- |
|
ence in the way they are handled. For example, \xdc is exactly the same |
|
as \x{dc} (or \u00dc in JavaScript mode). |
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Constraints on character values |
|
|
|
Characters that are specified using octal or hexadecimal numbers are |
|
limited to certain values, as follows: |
|
|
|
8-bit non-UTF mode less than 0x100 |
|
8-bit UTF-8 mode less than 0x10ffff and a valid codepoint |
|
16-bit non-UTF mode less than 0x10000 |
|
16-bit UTF-16 mode less than 0x10ffff and a valid codepoint |
|
32-bit non-UTF mode less than 0x100000000 |
|
32-bit UTF-32 mode less than 0x10ffff and a valid codepoint |
|
|
|
Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- |
|
called "surrogate" codepoints), and 0xffef. |
|
|
|
Escape sequences in character classes |
|
|
All the sequences that define a single character value can be used both |
All the sequences that define a single character value can be used both |
inside and outside character classes. In addition, inside a character |
inside and outside character classes. In addition, inside a character |
class, \b is interpreted as the backspace character (hex 08). |
class, \b is interpreted as the backspace character (hex 08). |
Line 4253 BACKSLASH
|
Line 5156 BACKSLASH
|
the subject string, all of them fail, because there is no character to |
the subject string, all of them fail, because there is no character to |
match. |
match. |
|
|
For compatibility with Perl, \s does not match the VT character (code | For compatibility with Perl, \s did not used to match the VT character |
11). This makes it different from the the POSIX "space" class. The \s | (code 11), which made it different from the the POSIX "space" class. |
characters are HT (9), LF (10), FF (12), CR (13), and space (32). If | However, Perl added VT at release 5.18, and PCRE followed suit at |
"use locale;" is included in a Perl script, \s may match the VT charac- | release 8.34. The default \s characters are now HT (9), LF (10), VT |
ter. In PCRE, it never does. | (11), FF (12), CR (13), and space (32), which are defined as white |
| space in the "C" locale. This list may vary if locale-specific matching |
| is taking place. For example, in some locales the "non-breaking space" |
| character (\xA0) is recognized as white space, and in others the VT |
| character is not. |
|
|
A "word" character is an underscore or any character that is a letter |
A "word" character is an underscore or any character that is a letter |
or digit. By default, the definition of letters and digits is con- |
or digit. By default, the definition of letters and digits is con- |
trolled by PCRE's low-valued character tables, and may vary if locale- |
trolled by PCRE's low-valued character tables, and may vary if locale- |
specific matching is taking place (see "Locale support" in the pcreapi |
specific matching is taking place (see "Locale support" in the pcreapi |
page). For example, in a French locale such as "fr_FR" in Unix-like |
page). For example, in a French locale such as "fr_FR" in Unix-like |
systems, or "french" in Windows, some character codes greater than 128 | systems, or "french" in Windows, some character codes greater than 127 |
are used for accented letters, and these are then matched by \w. The |
are used for accented letters, and these are then matched by \w. The |
use of locales with Unicode is discouraged. |
use of locales with Unicode is discouraged. |
|
|
By default, in a UTF mode, characters with values greater than 128 | By default, characters whose code points are greater than 127 never |
never match \d, \s, or \w, and always match \D, \S, and \W. These | match \d, \s, or \w, and always match \D, \S, and \W, although this may |
sequences retain their original meanings from before UTF support was | vary for characters in the range 128-255 when locale-specific matching |
available, mainly for efficiency reasons. However, if PCRE is compiled | is happening. These escape sequences retain their original meanings |
with Unicode property support, and the PCRE_UCP option is set, the be- | from before Unicode support was available, mainly for efficiency rea- |
haviour is changed so that Unicode properties are used to determine | sons. If PCRE is compiled with Unicode property support, and the |
character types, as follows: | PCRE_UCP option is set, the behaviour is changed so that Unicode prop- |
| erties are used to determine character types, as follows: |
|
|
\d any character that \p{Nd} matches (decimal digit) | \d any character that matches \p{Nd} (decimal digit) |
\s any character that \p{Z} matches, plus HT, LF, FF, CR | \s any character that matches \p{Z} or \h or \v |
\w any character that \p{L} or \p{N} matches, plus underscore | \w any character that matches \p{L} or \p{N}, plus underscore |
|
|
The upper case escapes match the inverse sets of characters. Note that | The upper case escapes match the inverse sets of characters. Note that |
\d matches only decimal digits, whereas \w matches any Unicode digit, | \d matches only decimal digits, whereas \w matches any Unicode digit, |
as well as any Unicode letter, and underscore. Note also that PCRE_UCP | as well as any Unicode letter, and underscore. Note also that PCRE_UCP |
affects \b, and \B because they are defined in terms of \w and \W. | affects \b, and \B because they are defined in terms of \w and \W. |
Matching these sequences is noticeably slower when PCRE_UCP is set. |
Matching these sequences is noticeably slower when PCRE_UCP is set. |
|
|
The sequences \h, \H, \v, and \V are features that were added to Perl | The sequences \h, \H, \v, and \V are features that were added to Perl |
at release 5.10. In contrast to the other sequences, which match only | at release 5.10. In contrast to the other sequences, which match only |
ASCII characters by default, these always match certain high-valued | ASCII characters by default, these always match certain high-valued |
codepoints, whether or not PCRE_UCP is set. The horizontal space char- | code points, whether or not PCRE_UCP is set. The horizontal space char- |
acters are: |
acters are: |
|
|
U+0009 Horizontal tab | U+0009 Horizontal tab (HT) |
U+0020 Space |
U+0020 Space |
U+00A0 Non-break space |
U+00A0 Non-break space |
U+1680 Ogham space mark |
U+1680 Ogham space mark |
Line 4314 BACKSLASH
|
Line 5222 BACKSLASH
|
|
|
The vertical space characters are: |
The vertical space characters are: |
|
|
U+000A Linefeed | U+000A Linefeed (LF) |
U+000B Vertical tab | U+000B Vertical tab (VT) |
U+000C Form feed | U+000C Form feed (FF) |
U+000D Carriage return | U+000D Carriage return (CR) |
U+0085 Next line | U+0085 Next line (NEL) |
U+2028 Line separator |
U+2028 Line separator |
U+2029 Paragraph separator |
U+2029 Paragraph separator |
|
|
Line 4327 BACKSLASH
|
Line 5235 BACKSLASH
|
|
|
Newline sequences |
Newline sequences |
|
|
Outside a character class, by default, the escape sequence \R matches | Outside a character class, by default, the escape sequence \R matches |
any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent | any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent |
to the following: |
to the following: |
|
|
(?>\r\n|\n|\x0b|\f|\r|\x85) |
(?>\r\n|\n|\x0b|\f|\r|\x85) |
|
|
This is an example of an "atomic group", details of which are given | This is an example of an "atomic group", details of which are given |
below. This particular group matches either the two-character sequence |
below. This particular group matches either the two-character sequence |
CR followed by LF, or one of the single characters LF (linefeed, | CR followed by LF, or one of the single characters LF (linefeed, |
U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car- | U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car- |
riage return, U+000D), or NEL (next line, U+0085). The two-character | riage return, U+000D), or NEL (next line, U+0085). The two-character |
sequence is treated as a single unit that cannot be split. |
sequence is treated as a single unit that cannot be split. |
|
|
In other modes, two additional characters whose codepoints are greater | In other modes, two additional characters whose codepoints are greater |
than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa- |
than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa- |
rator, U+2029). Unicode character property support is not needed for | rator, U+2029). Unicode character property support is not needed for |
these characters to be recognized. |
these characters to be recognized. |
|
|
It is possible to restrict \R to match only CR, LF, or CRLF (instead of |
It is possible to restrict \R to match only CR, LF, or CRLF (instead of |
the complete set of Unicode line endings) by setting the option | the complete set of Unicode line endings) by setting the option |
PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched. |
PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched. |
(BSR is an abbrevation for "backslash R".) This can be made the default |
(BSR is an abbrevation for "backslash R".) This can be made the default |
when PCRE is built; if this is the case, the other behaviour can be | when PCRE is built; if this is the case, the other behaviour can be |
requested via the PCRE_BSR_UNICODE option. It is also possible to | requested via the PCRE_BSR_UNICODE option. It is also possible to |
specify these settings by starting a pattern string with one of the | specify these settings by starting a pattern string with one of the |
following sequences: |
following sequences: |
|
|
(*BSR_ANYCRLF) CR, LF, or CRLF only |
(*BSR_ANYCRLF) CR, LF, or CRLF only |
(*BSR_UNICODE) any Unicode newline sequence |
(*BSR_UNICODE) any Unicode newline sequence |
|
|
These override the default and the options given to the compiling func- |
These override the default and the options given to the compiling func- |
tion, but they can themselves be overridden by options given to a | tion, but they can themselves be overridden by options given to a |
matching function. Note that these special settings, which are not | matching function. Note that these special settings, which are not |
Perl-compatible, are recognized only at the very start of a pattern, | Perl-compatible, are recognized only at the very start of a pattern, |
and that they must be in upper case. If more than one of them is | and that they must be in upper case. If more than one of them is |
present, the last one is used. They can be combined with a change of | present, the last one is used. They can be combined with a change of |
newline convention; for example, a pattern can start with: |
newline convention; for example, a pattern can start with: |
|
|
(*ANY)(*BSR_ANYCRLF) |
(*ANY)(*BSR_ANYCRLF) |
|
|
They can also be combined with the (*UTF8), (*UTF16), or (*UCP) special | They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF) |
sequences. Inside a character class, \R is treated as an unrecognized | or (*UCP) special sequences. Inside a character class, \R is treated as |
escape sequence, and so matches the letter "R" by default, but causes | an unrecognized escape sequence, and so matches the letter "R" by |
an error if PCRE_EXTRA is set. | default, but causes an error if PCRE_EXTRA is set. |
|
|
Unicode character properties |
Unicode character properties |
|
|
When PCRE is built with Unicode character property support, three addi- |
When PCRE is built with Unicode character property support, three addi- |
tional escape sequences that match characters with specific properties | tional escape sequences that match characters with specific properties |
are available. When in 8-bit non-UTF-8 mode, these sequences are of | are available. When in 8-bit non-UTF-8 mode, these sequences are of |
course limited to testing characters whose codepoints are less than | course limited to testing characters whose codepoints are less than |
256, but they do work in this mode. The extra escape sequences are: |
256, but they do work in this mode. The extra escape sequences are: |
|
|
\p{xx} a character with the xx property |
\p{xx} a character with the xx property |
\P{xx} a character without the xx property |
\P{xx} a character without the xx property |
\X an extended Unicode sequence | \X a Unicode extended grapheme cluster |
|
|
The property names represented by xx above are limited to the Unicode | The property names represented by xx above are limited to the Unicode |
script names, the general category properties, "Any", which matches any |
script names, the general category properties, "Any", which matches any |
character (including newline), and some special PCRE properties | character (including newline), and some special PCRE properties |
(described in the next section). Other Perl properties such as "InMu- | (described in the next section). Other Perl properties such as "InMu- |
sicalSymbols" are not currently supported by PCRE. Note that \P{Any} | sicalSymbols" are not currently supported by PCRE. Note that \P{Any} |
does not match any characters, so always causes a match failure. |
does not match any characters, so always causes a match failure. |
|
|
Sets of Unicode characters are defined as belonging to certain scripts. |
Sets of Unicode characters are defined as belonging to certain scripts. |
A character from one of these sets can be matched using a script name. | A character from one of these sets can be matched using a script name. |
For example: |
For example: |
|
|
\p{Greek} |
\p{Greek} |
\P{Han} |
\P{Han} |
|
|
Those that are not part of an identified script are lumped together as | Those that are not part of an identified script are lumped together as |
"Common". The current list of scripts is: |
"Common". The current list of scripts is: |
|
|
Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo, | Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo, |
Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma, | Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma, |
Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, | Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, |
Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, | Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, |
Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira- | Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira- |
gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- | gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- |
tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, | tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, |
Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, | Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, |
Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive, |
Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive, |
Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko, | Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko, |
Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic, | Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic, |
Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari- | Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari- |
tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese, | tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese, |
Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, | Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, |
Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, | Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, |
Yi. |
Yi. |
|
|
Each character has exactly one Unicode general category property, spec- |
Each character has exactly one Unicode general category property, spec- |
ified by a two-letter abbreviation. For compatibility with Perl, nega- | ified by a two-letter abbreviation. For compatibility with Perl, nega- |
tion can be specified by including a circumflex between the opening | tion can be specified by including a circumflex between the opening |
brace and the property name. For example, \p{^Lu} is the same as | brace and the property name. For example, \p{^Lu} is the same as |
\P{Lu}. |
\P{Lu}. |
|
|
If only one letter is specified with \p or \P, it includes all the gen- |
If only one letter is specified with \p or \P, it includes all the gen- |
eral category properties that start with that letter. In this case, in | eral category properties that start with that letter. In this case, in |
the absence of negation, the curly brackets in the escape sequence are | the absence of negation, the curly brackets in the escape sequence are |
optional; these two examples have the same effect: |
optional; these two examples have the same effect: |
|
|
\p{L} |
\p{L} |
Line 4478 BACKSLASH
|
Line 5386 BACKSLASH
|
Zp Paragraph separator |
Zp Paragraph separator |
Zs Space separator |
Zs Space separator |
|
|
The special property L& is also supported: it matches a character that | The special property L& is also supported: it matches a character that |
has the Lu, Ll, or Lt property, in other words, a letter that is not | has the Lu, Ll, or Lt property, in other words, a letter that is not |
classified as a modifier or "other". |
classified as a modifier or "other". |
|
|
The Cs (Surrogate) property applies only to characters in the range | The Cs (Surrogate) property applies only to characters in the range |
U+D800 to U+DFFF. Such characters are not valid in Unicode strings and | U+D800 to U+DFFF. Such characters are not valid in Unicode strings and |
so cannot be tested by PCRE, unless UTF validity checking has been | so cannot be tested by PCRE, unless UTF validity checking has been |
turned off (see the discussion of PCRE_NO_UTF8_CHECK and | turned off (see the discussion of PCRE_NO_UTF8_CHECK, |
PCRE_NO_UTF16_CHECK in the pcreapi page). Perl does not support the Cs | PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_CHECK in the pcreapi page). Perl |
property. | does not support the Cs property. |
|
|
The long synonyms for property names that Perl supports (such as | The long synonyms for property names that Perl supports (such as |
\p{Letter}) are not supported by PCRE, nor is it permitted to prefix | \p{Letter}) are not supported by PCRE, nor is it permitted to prefix |
any of these properties with "Is". |
any of these properties with "Is". |
|
|
No character that is in the Unicode table has the Cn (unassigned) prop- |
No character that is in the Unicode table has the Cn (unassigned) prop- |
erty. Instead, this property is assumed for any code point that is not |
erty. Instead, this property is assumed for any code point that is not |
in the Unicode table. |
in the Unicode table. |
|
|
Specifying caseless matching does not affect these escape sequences. | Specifying caseless matching does not affect these escape sequences. |
For example, \p{Lu} always matches only upper case letters. | For example, \p{Lu} always matches only upper case letters. This is |
| different from the behaviour of current versions of Perl. |
|
|
The \X escape matches any number of Unicode characters that form an | Matching characters by Unicode property is not fast, because PCRE has |
extended Unicode sequence. \X is equivalent to | to do a multistage table lookup in order to find a character's prop- |
| erty. That is why the traditional escape sequences such as \d and \w do |
| not use Unicode properties in PCRE by default, though you can make them |
| do so by setting the PCRE_UCP option or by starting the pattern with |
| (*UCP). |
|
|
|
Extended grapheme clusters |
|
|
|
The \X escape matches any number of Unicode characters that form an |
|
"extended grapheme cluster", and treats the sequence as an atomic group |
|
(see below). Up to and including release 8.31, PCRE matched an ear- |
|
lier, simpler definition that was equivalent to |
|
|
(?>\PM\pM*) |
(?>\PM\pM*) |
|
|
That is, it matches a character without the "mark" property, followed | That is, it matched a character without the "mark" property, followed |
by zero or more characters with the "mark" property, and treats the | by zero or more characters with the "mark" property. Characters with |
sequence as an atomic group (see below). Characters with the "mark" | the "mark" property are typically non-spacing accents that affect the |
property are typically accents that affect the preceding character. | preceding character. |
None of them have codepoints less than 256, so in 8-bit non-UTF-8 mode | |
\X matches any one character. | |
|
|
Note that recent versions of Perl have changed \X to match what Unicode | This simple definition was extended in Unicode to include more compli- |
calls an "extended grapheme cluster", which has a more complicated def- | cated kinds of composite character by giving each character a grapheme |
inition. | breaking property, and creating rules that use these properties to |
| define the boundaries of extended grapheme clusters. In releases of |
| PCRE later than 8.31, \X matches one of these clusters. |
|
|
Matching characters by Unicode property is not fast, because PCRE has | \X always matches at least one character. Then it decides whether to |
to search a structure that contains data for over fifteen thousand | add additional characters according to the following rules for ending a |
characters. That is why the traditional escape sequences such as \d and | cluster: |
\w do not use Unicode properties in PCRE by default, though you can | |
make them do so by setting the PCRE_UCP option or by starting the pat- | |
tern with (*UCP). | |
|
|
|
1. End at the end of the subject string. |
|
|
|
2. Do not end between CR and LF; otherwise end after any control char- |
|
acter. |
|
|
|
3. Do not break Hangul (a Korean script) syllable sequences. Hangul |
|
characters are of five types: L, V, T, LV, and LVT. An L character may |
|
be followed by an L, V, LV, or LVT character; an LV or V character may |
|
be followed by a V or T character; an LVT or T character may be follwed |
|
only by a T character. |
|
|
|
4. Do not end before extending characters or spacing marks. Characters |
|
with the "mark" property always have the "extend" grapheme breaking |
|
property. |
|
|
|
5. Do not end after prepend characters. |
|
|
|
6. Otherwise, end the cluster. |
|
|
PCRE's additional properties |
PCRE's additional properties |
|
|
As well as the standard Unicode properties described in the previous | As well as the standard Unicode properties described above, PCRE sup- |
section, PCRE supports four more that make it possible to convert tra- | ports four more that make it possible to convert traditional escape |
ditional escape sequences such as \w and \s and POSIX character classes | sequences such as \w and \s to use Unicode properties. PCRE uses these |
to use Unicode properties. PCRE uses these non-standard, non-Perl prop- | non-standard, non-Perl properties internally when PCRE_UCP is set. How- |
erties internally when PCRE_UCP is set. They are: | ever, they may also be used explicitly. These properties are: |
|
|
Xan Any alphanumeric character |
Xan Any alphanumeric character |
Xps Any POSIX space character |
Xps Any POSIX space character |
Xsp Any Perl space character |
Xsp Any Perl space character |
Xwd Any Perl "word" character |
Xwd Any Perl "word" character |
|
|
Xan matches characters that have either the L (letter) or the N (num- | Xan matches characters that have either the L (letter) or the N (num- |
ber) property. Xps matches the characters tab, linefeed, vertical tab, | ber) property. Xps matches the characters tab, linefeed, vertical tab, |
form feed, or carriage return, and any other character that has the Z | form feed, or carriage return, and any other character that has the Z |
(separator) property. Xsp is the same as Xps, except that vertical tab | (separator) property. Xsp is the same as Xps; it used to exclude ver- |
is excluded. Xwd matches the same characters as Xan, plus underscore. | tical tab, for Perl compatibility, but Perl changed, and so PCRE fol- |
| lowed at release 8.34. Xwd matches the same characters as Xan, plus |
| underscore. |
|
|
|
There is another non-standard property, Xuc, which matches any charac- |
|
ter that can be represented by a Universal Character Name in C++ and |
|
other programming languages. These are the characters $, @, ` (grave |
|
accent), and all characters with Unicode code points greater than or |
|
equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that |
|
most base (ASCII) characters are excluded. (Universal Character Names |
|
are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit. |
|
Note that the Xuc property does not match these sequences but the char- |
|
acters that they represent.) |
|
|
Resetting the match start |
Resetting the match start |
|
|
The escape sequence \K causes any previously matched characters not to | The escape sequence \K causes any previously matched characters not to |
be included in the final matched sequence. For example, the pattern: |
be included in the final matched sequence. For example, the pattern: |
|
|
foo\Kbar |
foo\Kbar |
|
|
matches "foobar", but reports that it has matched "bar". This feature | matches "foobar", but reports that it has matched "bar". This feature |
is similar to a lookbehind assertion (described below). However, in | is similar to a lookbehind assertion (described below). However, in |
this case, the part of the subject before the real match does not have | this case, the part of the subject before the real match does not have |
to be of fixed length, as lookbehind assertions do. The use of \K does | to be of fixed length, as lookbehind assertions do. The use of \K does |
not interfere with the setting of captured substrings. For example, | not interfere with the setting of captured substrings. For example, |
when the pattern |
when the pattern |
|
|
(foo)\Kbar |
(foo)\Kbar |
|
|
matches "foobar", the first substring is still set to "foo". |
matches "foobar", the first substring is still set to "foo". |
|
|
Perl documents that the use of \K within assertions is "not well | Perl documents that the use of \K within assertions is "not well |
defined". In PCRE, \K is acted upon when it occurs inside positive | defined". In PCRE, \K is acted upon when it occurs inside positive |
assertions, but is ignored in negative assertions. |
assertions, but is ignored in negative assertions. |
|
|
Simple assertions |
Simple assertions |
|
|
The final use of backslash is for certain simple assertions. An asser- | The final use of backslash is for certain simple assertions. An asser- |
tion specifies a condition that has to be met at a particular point in | tion specifies a condition that has to be met at a particular point in |
a match, without consuming any characters from the subject string. The | a match, without consuming any characters from the subject string. The |
use of subpatterns for more complicated assertions is described below. | use of subpatterns for more complicated assertions is described below. |
The backslashed assertions are: |
The backslashed assertions are: |
|
|
\b matches at a word boundary |
\b matches at a word boundary |
Line 4580 BACKSLASH
|
Line 5528 BACKSLASH
|
\z matches only at the end of the subject |
\z matches only at the end of the subject |
\G matches at the first matching position in the subject |
\G matches at the first matching position in the subject |
|
|
Inside a character class, \b has a different meaning; it matches the | Inside a character class, \b has a different meaning; it matches the |
backspace character. If any other of these assertions appears in a | backspace character. If any other of these assertions appears in a |
character class, by default it matches the corresponding literal char- | character class, by default it matches the corresponding literal char- |
acter (for example, \B matches the letter B). However, if the |
acter (for example, \B matches the letter B). However, if the |
PCRE_EXTRA option is set, an "invalid escape sequence" error is gener- | PCRE_EXTRA option is set, an "invalid escape sequence" error is gener- |
ated instead. |
ated instead. |
|
|
A word boundary is a position in the subject string where the current | A word boundary is a position in the subject string where the current |
character and the previous character do not both match \w or \W (i.e. | character and the previous character do not both match \w or \W (i.e. |
one matches \w and the other matches \W), or the start or end of the | one matches \w and the other matches \W), or the start or end of the |
string if the first or last character matches \w, respectively. In a | string if the first or last character matches \w, respectively. In a |
UTF mode, the meanings of \w and \W can be changed by setting the | UTF mode, the meanings of \w and \W can be changed by setting the |
PCRE_UCP option. When this is done, it also affects \b and \B. Neither | PCRE_UCP option. When this is done, it also affects \b and \B. Neither |
PCRE nor Perl has a separate "start of word" or "end of word" metase- | PCRE nor Perl has a separate "start of word" or "end of word" metase- |
quence. However, whatever follows \b normally determines which it is. | quence. However, whatever follows \b normally determines which it is. |
For example, the fragment \ba matches "a" at the start of a word. |
For example, the fragment \ba matches "a" at the start of a word. |
|
|
The \A, \Z, and \z assertions differ from the traditional circumflex | The \A, \Z, and \z assertions differ from the traditional circumflex |
and dollar (described in the next section) in that they only ever match |
and dollar (described in the next section) in that they only ever match |
at the very start and end of the subject string, whatever options are | at the very start and end of the subject string, whatever options are |
set. Thus, they are independent of multiline mode. These three asser- | set. Thus, they are independent of multiline mode. These three asser- |
tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which |
tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which |
affect only the behaviour of the circumflex and dollar metacharacters. | affect only the behaviour of the circumflex and dollar metacharacters. |
However, if the startoffset argument of pcre_exec() is non-zero, indi- | However, if the startoffset argument of pcre_exec() is non-zero, indi- |
cating that matching is to start at a point other than the beginning of |
cating that matching is to start at a point other than the beginning of |
the subject, \A can never match. The difference between \Z and \z is | the subject, \A can never match. The difference between \Z and \z is |
that \Z matches before a newline at the end of the string as well as at |
that \Z matches before a newline at the end of the string as well as at |
the very end, whereas \z matches only at the end. |
the very end, whereas \z matches only at the end. |
|
|
The \G assertion is true only when the current matching position is at | The \G assertion is true only when the current matching position is at |
the start point of the match, as specified by the startoffset argument | the start point of the match, as specified by the startoffset argument |
of pcre_exec(). It differs from \A when the value of startoffset is | of pcre_exec(). It differs from \A when the value of startoffset is |
non-zero. By calling pcre_exec() multiple times with appropriate argu- | non-zero. By calling pcre_exec() multiple times with appropriate argu- |
ments, you can mimic Perl's /g option, and it is in this kind of imple- |
ments, you can mimic Perl's /g option, and it is in this kind of imple- |
mentation where \G can be useful. |
mentation where \G can be useful. |
|
|
Note, however, that PCRE's interpretation of \G, as the start of the | Note, however, that PCRE's interpretation of \G, as the start of the |
current match, is subtly different from Perl's, which defines it as the |
current match, is subtly different from Perl's, which defines it as the |
end of the previous match. In Perl, these can be different when the | end of the previous match. In Perl, these can be different when the |
previously matched string was empty. Because PCRE does just one match | previously matched string was empty. Because PCRE does just one match |
at a time, it cannot reproduce this behaviour. |
at a time, it cannot reproduce this behaviour. |
|
|
If all the alternatives of a pattern begin with \G, the expression is | If all the alternatives of a pattern begin with \G, t If all the alternatives of a pattern begin with \G, the expression is |
anchored to the starting match position, and the "anchored" flag is set |
anchored to the starting match position, and the "anchored" flag is set |
in the compiled regular expression. |
in the compiled regular expression. |
|
|
|
|
CIRCUMFLEX AND DOLLAR |
CIRCUMFLEX AND DOLLAR |
|
|
|
The circumflex and dollar metacharacters are zero-width assertions. |
|
That is, they test for a particular condition being true without con- |
|
suming any characters from the subject string. |
|
|
Outside a character class, in the default matching mode, the circumflex |
Outside a character class, in the default matching mode, the circumflex |
character is an assertion that is true only if the current matching | character is an assertion that is true only if the current matching |
point is at the start of the subject string. If the startoffset argu- | point is at the start of the subject string. If the startoffset argu- |
ment of pcre_exec() is non-zero, circumflex can never match if the | ment of pcre_exec() is non-zero, circumflex can never match if the |
PCRE_MULTILINE option is unset. Inside a character class, circumflex | PCRE_MULTILINE option is unset. Inside a character class, circumflex |
has an entirely different meaning (see below). |
has an entirely different meaning (see below). |
|
|
Circumflex need not be the first character of the pattern if a number | Circumflex need not be the first character of the pattern if a number |
of alternatives are involved, but it should be the first thing in each | of alternatives are involved, but it should be the first thing in each |
alternative in which it appears if the pattern is ever to match that | alternative in which it appears if the pattern is ever to match that |
branch. If all possible alternatives start with a circumflex, that is, | branch. If all possible alternatives start with a circumflex, that is, |
if the pattern is constrained to match only at the start of the sub- | if the pattern is constrained to match only at the start of the sub- |
ject, it is said to be an "anchored" pattern. (There are also other | ject, it is said to be an "anchored" pattern. (There are also other |
constructs that can cause a pattern to be anchored.) |
constructs that can cause a pattern to be anchored.) |
|
|
A dollar character is an assertion that is true only if the current | The dollar character is an assertion that is true only if the current |
matching point is at the end of the subject string, or immediately | matching point is at the end of the subject string, or immediately |
before a newline at the end of the string (by default). Dollar need not | before a newline at the end of the string (by default). Note, however, |
be the last character of the pattern if a number of alternatives are | that it does not actually match the newline. Dollar need not be the |
involved, but it should be the last item in any branch in which it | last character of the pattern if a number of alternatives are involved, |
appears. Dollar has no special meaning in a character class. | but it should be the last item in any branch in which it appears. Dol- |
| lar has no special meaning in a character class. |
|
|
The meaning of dollar can be changed so that it matches only at the |
The meaning of dollar can be changed so that it matches only at the |
very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at |
very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at |
Line 4710 MATCHING A SINGLE DATA UNIT
|
Line 5663 MATCHING A SINGLE DATA UNIT
|
|
|
Outside a character class, the escape sequence \C matches any one data |
Outside a character class, the escape sequence \C matches any one data |
unit, whether or not a UTF mode is set. In the 8-bit library, one data |
unit, whether or not a UTF mode is set. In the 8-bit library, one data |
unit is one byte; in the 16-bit library it is a 16-bit unit. Unlike a | unit is one byte; in the 16-bit library it is a 16-bit unit; in the |
dot, \C always matches line-ending characters. The feature is provided | 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches |
in Perl in order to match individual bytes in UTF-8 mode, but it is | line-ending characters. The feature is provided in Perl in order to |
unclear how it can usefully be used. Because \C breaks up characters | match individual bytes in UTF-8 mode, but it is unclear how it can use- |
into individual data units, matching one unit with \C in a UTF mode | fully be used. Because \C breaks up characters into individual data |
means that the rest of the string may start with a malformed UTF char- | units, matching one unit with \C in a UTF mode means that the rest of |
acter. This has undefined results, because PCRE assumes that it is | the string may start with a malformed UTF character. This has undefined |
dealing with valid UTF strings (and by default it checks this at the | results, because PCRE assumes that it is dealing with valid UTF strings |
start of processing unless the PCRE_NO_UTF8_CHECK or | (and by default it checks this at the start of processing unless the |
PCRE_NO_UTF16_CHECK option is used). | PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_CHECK option |
| is used). |
|
|
PCRE does not allow \C to appear in lookbehind assertions (described | PCRE does not allow \C to appear in lookbehind assertions (described |
below) in a UTF mode, because this would make it impossible to calcu- | below) in a UTF mode, because this would make it impossible to calcu- |
late the length of the lookbehind. |
late the length of the lookbehind. |
|
|
In general, the \C escape sequence is best avoided. However, one way of |
In general, the \C escape sequence is best avoided. However, one way of |
using it that avoids the problem of malformed UTF characters is to use | using it that avoids the problem of malformed UTF characters is to use |
a lookahead to check the length of the next character, as in this pat- | a lookahead to check the length of the next character, as in this pat- |
tern, which could be used with a UTF-8 string (ignore white space and | tern, which could be used with a UTF-8 string (ignore white space and |
line breaks): |
line breaks): |
|
|
(?| (?=[\x00-\x7f])(\C) | |
(?| (?=[\x00-\x7f])(\C) | |
Line 4736 MATCHING A SINGLE DATA UNIT
|
Line 5690 MATCHING A SINGLE DATA UNIT
|
(?=[\x{800}-\x{ffff}])(\C)(\C)(\C) | |
(?=[\x{800}-\x{ffff}])(\C)(\C)(\C) | |
(?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C)) |
(?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C)) |
|
|
A group that starts with (?| resets the capturing parentheses numbers | A group that starts with (?| resets the capturing parentheses numbers |
in each alternative (see "Duplicate Subpattern Numbers" below). The | in each alternative (see "Duplicate Subpattern Numbers" below). The |
assertions at the start of each branch check the next UTF-8 character | assertions at the start of each branch check the next UTF-8 character |
for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The | for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The |
character's individual bytes are then captured by the appropriate num- | character's individual bytes are then captured by the appropriate num- |
ber of groups. |
ber of groups. |
|
|
|
|
Line 4750 SQUARE BRACKETS AND CHARACTER CLASSES
|
Line 5704 SQUARE BRACKETS AND CHARACTER CLASSES
|
closing square bracket. A closing square bracket on its own is not spe- |
closing square bracket. A closing square bracket on its own is not spe- |
cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set, |
cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set, |
a lone closing square bracket causes a compile-time error. If a closing |
a lone closing square bracket causes a compile-time error. If a closing |
square bracket is required as a member of the class, it should be the | square bracket is required as a member of the class, it should be the |
first data character in the class (after an initial circumflex, if | first data character in the class (after an initial circumflex, if |
present) or escaped with a backslash. |
present) or escaped with a backslash. |
|
|
A character class matches a single character in the subject. In a UTF | A character class matches a single character in the subject. In a UTF |
mode, the character may be more than one data unit long. A matched | mode, the character may be more than one data unit long. A matched |
character must be in the set of characters defined by the class, unless |
character must be in the set of characters defined by the class, unless |
the first character in the class definition is a circumflex, in which | the first character in the class definition is a circumflex, in which |
case the subject character must not be in the set defined by the class. |
case the subject character must not be in the set defined by the class. |
If a circumflex is actually required as a member of the class, ensure | If a circumflex is actually required as a member of the class If a circumflex is actually required as a member of the class |
it is not the first character, or escape it with a backslash. |
it is not the first character, or escape it with a backslash. |
|
|
For example, the character class [aeiou] matches any lower case vowel, | For example, the character class [aeiou] matches any lower case vowel, |
while [^aeiou] matches any character that is not a lower case vowel. | while [^aeiou] matches any character that is not a lower case vowel. |
Note that a circumflex is just a convenient notation for specifying the |
Note that a circumflex is just a convenient notation for specifying the |
characters that are in the class by enumerating those that are not. A | characters that are in the class by enumerating those that are not. A |
class that starts with a circumflex is not an assertion; it still con- | class that starts with a circumflex is not an assertion; it still con- |
sumes a character from the subject string, and therefore it fails if | sumes a character from the subject string, and therefore it fails if |
the current pointer is at the end of the string. |
the current pointer is at the end of the string. |
|
|
In UTF-8 (UTF-16) mode, characters with values greater than 255 | In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255 |
(0xffff) can be included in a class as a literal string of data units, | (0xffff) can be included in a class as a literal string of data units, |
or by using the \x{ escaping mechanism. |
or by using the \x{ escaping mechanism. |
|
|
When caseless matching is set, any letters in a class represent both | When caseless matching is set, any letters in a class represent both |
their upper case and lower case versions, so for example, a caseless | their upper case and lower case versions, so for example, a caseless |
[aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not | [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not |
match "A", whereas a caseful version would. In a UTF mode, PCRE always | match "A", whereas a caseful version would. In a UTF mode, PCRE always |
understands the concept of case for characters whose values are less | understands the concept of case for characters whose values are less |
than 128, so caseless matching is always possible. For characters with | than 128, so caseless matching is always possible. For characters with |
higher values, the concept of case is supported if PCRE is compiled | higher values, the concept of case is supported if PCRE is compiled |
with Unicode property support, but not otherwise. If you want to use | with Unicode property support, but not otherwise. If you want to use |
caseless matching in a UTF mode for characters 128 and above, you must | caseless matching in a UTF mode for characters 128 and above, you must |
ensure that PCRE is compiled with Unicode property support as well as | ensure that PCRE is compiled with Unicode property support as well as |
with UTF support. |
with UTF support. |
|
|
Characters that might indicate line breaks are never treated in any | Characters that might indicate line breaks are never treated in any |
special way when matching character classes, whatever line-ending | special way when matching character classes, whatever line-ending |
sequence is in use, and whatever setting of the PCRE_DOTALL and | sequence is in use, and whatever setting of the PCRE_DOTALL and |
PCRE_MULTILINE options is used. A class such as [^a] always matches one |
PCRE_MULTILINE options is used. A class such as [^a] always matches one |
of these characters. |
of these characters. |
|
|
The minus (hyphen) character can be used to specify a range of charac- | The minus (hyphen) character can be used to specify a range of charac- |
ters in a character class. For example, [d-m] matches any letter | ters in a character class. For example, [d-m] matches any letter |
between d and m, inclusive. If a minus character is required in a | between d and m, inclusive. If a minus character is required in a |
class, it must be escaped with a backslash or appear in a position | class, it must be escaped with a backslash or appear in a position |
where it cannot be interpreted as indicating a range, typically as the | where it cannot be interpreted as indicating a range, typically as the |
first or last character in the class. | first or last character in the class, or immediately after a range. For |
| example, [b-d-z] matches letters in the range b to d, a hyphen charac- |
| ter, or z. |
|
|
It is not possible to have the literal character "]" as the end charac- |
It is not possible to have the literal character "]" as the end charac- |
ter of a range. A pattern such as [W-]46] is interpreted as a class of | ter of a range. A pattern such as [W-]46] is interpreted as a class of |
two characters ("W" and "-") followed by a literal string "46]", so it | two characters ("W" and "-") followed by a literal string "46]", so it |
would match "W46]" or "-46]". However, if the "]" is escaped with a | would match "W46]" or "-46]". However, if the "]" is escaped with a |
backslash it is interpreted as the end of range, so [W-\]46] is inter- | backslash it is interpreted as the end of range, so [W-\]46] is inter- |
preted as a class containing a range followed by two other characters. | preted as a class containing a range followed by two other characters. |
The octal or hexadecimal representation of "]" can also be used to end | The octal or hexadecimal representation of "]" can also be used to end |
a range. |
a range. |
|
|
|
An error is generated if a POSIX character class (see below) or an |
|
escape sequence other than one that defines a single character appears |
|
at a point where a range ending character is expected. For example, |
|
[z-\xff] is valid, but [A-\d] and [A-[:digit:]] are not. |
|
|
Ranges operate in the collating sequence of character values. They can |
Ranges operate in the collating sequence of character values. They can |
also be used for characters specified numerically, for example |
also be used for characters specified numerically, for example |
[\000-\037]. Ranges can include any characters that are valid for the |
[\000-\037]. Ranges can include any characters that are valid for the |
Line 4844 SQUARE BRACKETS AND CHARACTER CLASSES
|
Line 5805 SQUARE BRACKETS AND CHARACTER CLASSES
|
The only metacharacters that are recognized in character classes are |
The only metacharacters that are recognized in character classes are |
backslash, hyphen (only where it can be interpreted as specifying a |
backslash, hyphen (only where it can be interpreted as specifying a |
range), circumflex (only at the start), opening square bracket (only |
range), circumflex (only at the start), opening square bracket (only |
when it can be interpreted as introducing a POSIX class name - see the | when it can be interpreted as introducing a POSIX class name, or for a |
next section), and the terminating closing square bracket. However, | special compatibility feature - see the next two sections), and the |
escaping other non-alphanumeric characters does no harm. | terminating closing square bracket. However, escaping other non- |
| alphanumeric characters does no harm. |
|
|
|
|
POSIX CHARACTER CLASSES |
POSIX CHARACTER CLASSES |
|
|
Perl supports the POSIX notation for character classes. This uses names |
Perl supports the POSIX notation for character classes. This uses names |
enclosed by [: and :] within the enclosing square brackets. PCRE also | enclosed by [: and :] within the enclosing square brackets. PCRE also |
supports this notation. For example, |
supports this notation. For example, |
|
|
[01[:alpha:]%] |
[01[:alpha:]%] |
Line 4870 POSIX CHARACTER CLASSES
|
Line 5832 POSIX CHARACTER CLASSES
|
lower lower case letters |
lower lower case letters |
print printing characters, including space |
print printing characters, including space |
punct printing characters, excluding letters and digits and space |
punct printing characters, excluding letters and digits and space |
space white space (not quite the same as \s) | space white space (the same as \s from PCRE 8.34) |
upper upper case letters |
upper upper case letters |
word "word" characters (same as \w) |
word "word" characters (same as \w) |
xdigit hexadecimal digits |
xdigit hexadecimal digits |
|
|
The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), | The default "space" characters are HT (9), LF (10), VT (11), FF (12), |
and space (32). Notice that this list includes the VT character (code | CR (13), and space (32). If locale-specific matching is taking place, |
11). This makes "space" different to \s, which does not include VT (for | the list of space characters may be different; there may be fewer or |
Perl compatibility). | more of them. "Space" used to be different to \s, which did not include |
| VT, for Perl compatibility. However, Perl changed at release 5.18, and |
| PCRE followed at release 8.34. "Space" and \s now match the same set |
| of characters. |
|
|
The name "word" is a Perl extension, and "blank" is a GNU extension |
The name "word" is a Perl extension, and "blank" is a GNU extension |
from Perl 5.8. Another Perl extension is negation, which is indicated |
from Perl 5.8. Another Perl extension is negation, which is indicated |
Line 4890 POSIX CHARACTER CLASSES
|
Line 5855 POSIX CHARACTER CLASSES
|
POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but |
POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but |
these are not supported, and an error is given if they are encountered. |
these are not supported, and an error is given if they are encountered. |
|
|
By default, in UTF modes, characters with values greater than 128 do | By default, characters with values greater than 128 do not match any of |
not match any of the POSIX character classes. However, if the PCRE_UCP | the POSIX character classes. However, if the PCRE_UCP option is passed |
option is passed to pcre_compile(), some of the classes are changed so | to pcre_compile(), some of the classes are changed so that Unicode |
that Unicode character properties are used. This is achieved by replac- | character properties are used. This is achieved by replacing certain |
ing the POSIX classes by other sequences, as follows: | POSIX classes by other sequences, as follows: |
|
|
[:alnum:] becomes \p{Xan} |
[:alnum:] becomes \p{Xan} |
[:alpha:] becomes \p{L} |
[:alpha:] becomes \p{L} |
Line 4905 POSIX CHARACTER CLASSES
|
Line 5870 POSIX CHARACTER CLASSES
|
[:upper:] becomes \p{Lu} |
[:upper:] becomes \p{Lu} |
[:word:] becomes \p{Xwd} |
[:word:] becomes \p{Xwd} |
|
|
Negated versions, such as [:^alpha:] use \P instead of \p. The other | Negated versions, such as [:^alpha:] use \P instead of \p. Three other |
POSIX classes are unchanged, and match only characters with code points | POSIX classes are handled specially in UCP mode: |
less than 128. | |
|
|
|
[:graph:] This matches characters that have glyphs that mark the page |
|
when printed. In Unicode property terms, it matches all char- |
|
acters with the L, M, N, P, S, or Cf properties, except for: |
|
|
|
U+061C Arabic Letter Mark |
|
U+180E Mongolian Vowel Separator |
|
U+2066 - U+2069 Various "isolate"s |
|
|
|
|
|
[:print:] This matches the same characters as [:graph:] plus space |
|
characters that are not controls, that is, characters with |
|
the Zs property. |
|
|
|
[:punct:] This matches all characters that have the Unicode P (punctua- |
|
tion) property, plus those characters whose code points are |
|
less than 128 that have the S (Symbol) property. |
|
|
|
The other POSIX classes are unchanged, and match only characters with |
|
code points less than 128. |
|
|
|
|
|
COMPATIBILITY FEATURE FOR WORD BOUNDARIES |
|
|
|
In the POSIX.2 compliant library that was included in 4.4BSD Unix, the |
|
ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word" |
|
and "end of word". PCRE treats these items as follows: |
|
|
|
[[:<:]] is converted to \b(?=\w) |
|
[[:>:]] is converted to \b(?<=\w) |
|
|
|
Only these exact character sequences are recognized. A sequence such as |
|
[a[:<:]b] provokes error for an unrecognized POSIX class name. This |
|
support is not compatible with Perl. It is provided to help migrations |
|
from other environments, and is best not used in any new patterns. Note |
|
that \b matches at the start and the end of a word (see "Simple asser- |
|
tions" above), and in a Perl-style pattern the preceding or following |
|
character normally shows which is wanted, without the need for the |
|
assertions that are used above in order to give exactly the POSIX be- |
|
haviour. |
|
|
|
|
VERTICAL BAR |
VERTICAL BAR |
|
|
Vertical bar characters are used to separate alternative patterns. For |
Vertical bar characters are used to separate alternative patterns. For |
Line 4978 INTERNAL OPTION SETTING
|
Line 5982 INTERNAL OPTION SETTING
|
some cases the pattern can contain special leading sequences such as |
some cases the pattern can contain special leading sequences such as |
(*CRLF) to override what the application has set or what has been |
(*CRLF) to override what the application has set or what has been |
defaulted. Details are given in the section entitled "Newline |
defaulted. Details are given in the section entitled "Newline |
sequences" above. There are also the (*UTF8), (*UTF16), and (*UCP) | sequences" above. There are also the (*UTF8), (*UTF16),(*UTF32), and |
leading sequences that can be used to set UTF and Unicode property | (*UCP) leading sequences that can be used to set UTF and Unicode prop- |
modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16, and | erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16, |
the PCRE_UCP options, respectively. | PCRE_UTF32 and the PCRE_UCP options, respectively. The (*UTF) sequence |
| is a generic version that can be used with any of the libraries. How- |
| ever, the application can set the PCRE_NEVER_UTF option, which locks |
| out the use of the (*UTF) sequences. |
|
|
|
|
SUBPATTERNS |
SUBPATTERNS |
Line 4993 SUBPATTERNS
|
Line 6000 SUBPATTERNS
|
|
|
cat(aract|erpillar|) |
cat(aract|erpillar|) |
|
|
matches "cataract", "caterpillar", or "cat". Without the parentheses, | matches "cataract", "caterpillar", or "cat". Without the parentheses, |
it would match "cataract", "erpillar" or an empty string. |
it would match "cataract", "erpillar" or an empty string. |
|
|
2. It sets up the subpattern as a capturing subpattern. This means | 2. It sets up the subpattern as a capturing subpattern. This means |
that, when the whole pattern matches, that portion of the subject | that, when the whole pattern matches, that portion of the subject |
string that matched the subpattern is passed back to the caller via the |
string that matched the subpattern is passed back to the caller via the |
ovector argument of the matching function. (This applies only to the | ovector argument of the matching function. (This applies only to the |
traditional matching functions; the DFA matching functions do not sup- | traditional matching functions; the DFA matching functions do not sup- |
port capturing.) |
port capturing.) |
|
|
Opening parentheses are counted from left to right (starting from 1) to |
Opening parentheses are counted from left to right (starting from 1) to |
obtain numbers for the capturing subpatterns. For example, if the | obtain numbers for the capturing subpatterns. For example, if the |
string "the red king" is matched against the pattern |
string "the red king" is matched against the pattern |
|
|
the ((red|white) (king|queen)) |
the ((red|white) (king|queen)) |
Line 5012 SUBPATTERNS
|
Line 6019 SUBPATTERNS
|
the captured substrings are "red king", "red", and "king", and are num- |
the captured substrings are "red king", "red", and "king", and are num- |
bered 1, 2, and 3, respectively. |
bered 1, 2, and 3, respectively. |
|
|
The fact that plain parentheses fulfil two functions is not always | The fact that plain parentheses fulfil two functions is not always |
helpful. There are often times when a grouping subpattern is required | helpful. There are often times when a grouping subpattern is required |
without a capturing requirement. If an opening parenthesis is followed | without a capturing requirement. If an opening parenthesis is followed |
by a question mark and a colon, the subpattern does not do any captur- | by a question mark and a colon, the subpattern does not do any captur- |
ing, and is not counted when computing the number of any subsequent | ing, and is not counted when computing the number of any subsequent |
capturing subpatterns. For example, if the string "the white queen" is | capturing subpatterns. For example, if the string "the white queen" is |
matched against the pattern |
matched against the pattern |
|
|
the ((?:red|white) (king|queen)) |
the ((?:red|white) (king|queen)) |
Line 5025 SUBPATTERNS
|
Line 6032 SUBPATTERNS
|
the captured substrings are "white queen" and "queen", and are numbered |
the captured substrings are "white queen" and "queen", and are numbered |
1 and 2. The maximum number of capturing subpatterns is 65535. |
1 and 2. The maximum number of capturing subpatterns is 65535. |
|
|
As a convenient shorthand, if any option settings are required at the | As a convenient shorthand, if any option settings are required at the |
start of a non-capturing subpattern, the option letters may appear | start of a non-capturing subpattern, the option letters may appear |
between the "?" and the ":". Thus the two patterns |
between the "?" and the ":". Thus the two patterns |
|
|
(?i:saturday|sunday) |
(?i:saturday|sunday) |
(?:(?i)saturday|sunday) |
(?:(?i)saturday|sunday) |
|
|
match exactly the same set of strings. Because alternative branches are |
match exactly the same set of strings. Because alternative branches are |
tried from left to right, and options are not reset until the end of | tried from left to right, and options are not reset until the end of |
the subpattern is reached, an option setting in one branch does affect | the subpattern is reached, an option setting in one branch does affect |
subsequent branches, so the above patterns match "SUNDAY" as well as | subsequent branches, so the above patterns match "SUNDAY" as well as |
"Saturday". |
"Saturday". |
|
|
|
|
DUPLICATE SUBPATTERN NUMBERS |
DUPLICATE SUBPATTERN NUMBERS |
|
|
Perl 5.10 introduced a feature whereby each alternative in a subpattern |
Perl 5.10 introduced a feature whereby each alternative in a subpattern |
uses the same numbers for its capturing parentheses. Such a subpattern | uses the same numbers for its capturing parentheses. Such a subpattern |
starts with (?| and is itself a non-capturing subpattern. For example, | starts with (?| and is itself a non-capturing subpattern. For example, |
consider this pattern: |
consider this pattern: |
|
|
(?|(Sat)ur|(Sun))day |
(?|(Sat)ur|(Sun))day |
|
|
Because the two alternatives are inside a (?| group, both sets of cap- | Because the two alternatives are inside a (?| group, both sets of cap- |
turing parentheses are numbered one. Thus, when the pattern matches, | turing parentheses are numbered one. Thus, when the pattern matches, |
you can look at captured substring number one, whichever alternative | you can look at captured substring number one, whichever alternative |
matched. This construct is useful when you want to capture part, but | matched. This construct is useful when you want to capture part, but |
not all, of one of a number of alternatives. Inside a (?| group, paren- |
not all, of one of a number of alternatives. Inside a (?| group, paren- |
theses are numbered as usual, but the number is reset at the start of | theses are numbered as usual, but the number is reset at the start of |
each branch. The numbers of any capturing parentheses that follow the | each branch. The numbers of any capturing parentheses that follow the |
subpattern start after the highest number used in any branch. The fol- | subpattern start after the highest number used in any branch. The fol- |
lowing example is taken from the Perl documentation. The numbers under- |
lowing example is taken from the Perl documentation. The numbers under- |
neath show in which buffer the captured content will be stored. |
neath show in which buffer the captured content will be stored. |
|
|
Line 5063 DUPLICATE SUBPATTERN NUMBERS
|
Line 6070 DUPLICATE SUBPATTERN NUMBERS
|
/ ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x |
/ ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x |
# 1 2 2 3 2 3 4 |
# 1 2 2 3 2 3 4 |
|
|
A back reference to a numbered subpattern uses the most recent value | A back reference to a numbered subpattern uses the most recent value |
that is set for that number by any subpattern. The following pattern | that is set for that number by any subpattern. The following pattern |
matches "abcabc" or "defdef": |
matches "abcabc" or "defdef": |
|
|
/(?|(abc)|(def))\1/ |
/(?|(abc)|(def))\1/ |
|
|
In contrast, a subroutine call to a numbered subpattern always refers | In contrast, a subroutine call to a numbered subpattern always refers |
to the first one in the pattern with the given number. The following | to the first one in the pattern with the given number. The following |
pattern matches "abcabc" or "defabc": |
pattern matches "abcabc" or "defabc": |
|
|
/(?|(abc)|(def))(?1)/ |
/(?|(abc)|(def))(?1)/ |
|
|
If a condition test for a subpattern's having matched refers to a non- | If a condition test for a subpattern's having matched refers to a non- |
unique number, the test is true if any of the subpatterns of that num- | unique number, the test is true if any of the subpatterns of that num- |
ber have matched. |
ber have matched. |
|
|
An alternative approach to using this "branch reset" feature is to use | An alternative approach to using this "branch reset" feature is to use |
duplicate named subpatterns, as described in the next section. |
duplicate named subpatterns, as described in the next section. |
|
|
|
|
NAMED SUBPATTERNS |
NAMED SUBPATTERNS |
|
|
Identifying capturing parentheses by number is simple, but it can be | Identifying capturing parentheses by number is simple, but it can be |
very hard to keep track of the numbers in complicated regular expres- | very hard to keep track of the numbers in complicated regular expres- |
sions. Furthermore, if an expression is modified, the numbers may | sions. Furthermore, if an expression is modified, the numbers may |
change. To help with this difficulty, PCRE supports the naming of sub- | change. To help with this difficulty, PCRE supports the naming of sub- |
patterns. This feature was not added to Perl until release 5.10. Python |
patterns. This feature was not added to Perl until release 5.10. Python |
had the feature earlier, and PCRE introduced it at release 4.0, using | had the feature earlier, and PCRE introduced it at release 4.0, using |
the Python syntax. PCRE now supports both the Perl and the Python syn- | the Python syntax. PCRE now supports both the Perl and the Python syn- |
tax. Perl allows identically numbered subpatterns to have different | tax. Perl allows identically numbered subpatterns to have different |
names, but PCRE does not. |
names, but PCRE does not. |
|
|
In PCRE, a subpattern can be named in one of three ways: (?<name>...) | In PCRE, a subpattern can be named in one of three ways: (?<name>...) |
or (?'name'...) as in Perl, or (?P<name>...) as in Python. References | or (?'name'...) as in Perl, or (?P<name>...) as in Python. References |
to capturing parentheses from other parts of the pattern, such as back | to capturing parentheses from other parts of the pattern, such as back |
references, recursion, and conditions, can be made by name as well as | references, recursion, and conditions, can be made by name as well as |
by number. |
by number. |
|
|
Names consist of up to 32 alphanumeric characters and underscores. | Names consist of up to 32 alphanumeric characters and underscores, but |
Named capturing parentheses are still allocated numbers as well as | must start with a non-digit. Named capturing parentheses are still |
names, exactly as if the names were not present. The PCRE API provides | allocated numbers as well as names, exactly as if the names were not |
function calls for extracting the name-to-number translation table from | present. The PCRE API provides function calls for extracting the name- |
a compiled pattern. There is also a convenience function for extracting | to-number translation table from a compiled pattern. There is also a |
a captured substring by name. | convenience function for extracting a captured substring by name. |
|
|
By default, a name must be unique within a pattern, but it is possible | By default, a name must be unique within a pattern, but it is possible |
to relax this constraint by setting the PCRE_DUPNAMES option at compile |
to relax this constraint by setting the PCRE_DUPNAMES option at compile |
time. (Duplicate names are also always permitted for subpatterns with | time. (Duplicate names are also always permitted for subpatterns with |
the same number, set up as described in the previous section.) Dupli- | the same number, set up as described in the previous section.) Dupli- |
cate names can be useful for patterns where only one instance of the | cate names can be useful for patterns where only one instance of the |
named parentheses can match. Suppose you want to match the name of a | named parentheses can match. Suppose you want to match the name of a |
weekday, either as a 3-letter abbreviation or as the full name, and in | weekday, either as a 3-letter abbreviation or as the full name, and in |
both cases you want to extract the abbreviation. This pattern (ignoring |
both cases you want to extract the abbreviation. This pattern (ignoring |
the line breaks) does the job: |
the line breaks) does the job: |
|
|
Line 5124 NAMED SUBPATTERNS
|
Line 6131 NAMED SUBPATTERNS
|
(?<DN>Thu)(?:rsday)?| |
(?<DN>Thu)(?:rsday)?| |
(?<DN>Sat)(?:urday)? |
(?<DN>Sat)(?:urday)? |
|
|
There are five capturing substrings, but only one is ever set after a | There are five capturing substrings, but only one is ever set after a |
match. (An alternative way of solving this problem is to use a "branch |
match. (An alternative way of solving this problem is to use a "branch |
reset" subpattern, as described in the previous section.) |
reset" subpattern, as described in the previous section.) |
|
|
The convenience function for extracting the data by name returns the | The convenience function for extracting the data by name returns the |
substring for the first (and in this example, the only) subpattern of | substring for the first (and in this example, the only) subpattern of |
that name that matched. This saves searching to find which numbered | that name that matched. This saves searching to find which numbered |
subpattern it was. |
subpattern it was. |
|
|
If you make a back reference to a non-unique named subpattern from | If you make a back reference to a non-unique named subpattern from |
elsewhere in the pattern, the one that corresponds to the first occur- | elsewhere in the pattern, the subpatterns to which the name refers are |
rence of the name is used. In the absence of duplicate numbers (see the | checked in the order in which they appear in the overall pattern. The |
previous section) this is the one with the lowest number. If you use a | first one that is set is used for the reference. For example, this pat- |
named reference in a condition test (see the section about conditions | tern matches both "foofoo" and "barbar" but not "foobar" or "barfoo": |
below), either to check whether a subpattern has matched, or to check | |
for recursion, all subpatterns with the same name are tested. If the | |
condition is true for any one of them, the overall condition is true. | |
This is the same behaviour as testing by number. For further details of | |
the interfaces for handling named subpatterns, see the pcreapi documen- | |
tation. | |
|
|
|
(?:(?<n>foo)|(?<n>bar))\k<n> |
|
|
|
|
|
If you make a subroutine call to a non-unique named subpattern, the one |
|
that corresponds to the first occurrence of the name is used. In the |
|
absence of duplicate numbers (see the previous section) this is the one |
|
with the lowest number. |
|
|
|
If you use a named reference in a condition test (see the section about |
|
conditions below), either to check whether a subpattern has matched, or |
|
to check for recursion, all subpatterns with the same name are tested. |
|
If the condition is true for any one of them, the overall condition is |
|
true. This is the same behaviour as testing by number. For further |
|
details of the interfaces for handling named subpatterns, see the |
|
pcreapi documentation. |
|
|
Warning: You cannot use different names to distinguish between two sub- |
Warning: You cannot use different names to distinguish between two sub- |
patterns with the same number because PCRE uses only the numbers when |
patterns with the same number because PCRE uses only the numbers when |
matching. For this reason, an error is given at compile time if differ- |
matching. For this reason, an error is given at compile time if differ- |
ent names are given to subpatterns with the same number. However, you |
ent names are given to subpatterns with the same number. However, you |
can give the same name to subpatterns with the same number, even when | can always give the same name to subpatterns with the same number, even |
PCRE_DUPNAMES is not set. | when PCRE_DUPNAMES is not set. |
|
|
|
|
REPETITION |
REPETITION |
Line 5196 REPETITION
|
Line 6213 REPETITION
|
In UTF modes, quantifiers apply to characters rather than to individual |
In UTF modes, quantifiers apply to characters rather than to individual |
data units. Thus, for example, \x{100}{2} matches two characters, each |
data units. Thus, for example, \x{100}{2} matches two characters, each |
of which is represented by a two-byte sequence in a UTF-8 string. Simi- |
of which is represented by a two-byte sequence in a UTF-8 string. Simi- |
larly, \X{3} matches three Unicode extended sequences, each of which | larly, \X{3} matches three Unicode extended grapheme clusters, each of |
may be several data units long (and they may be of different lengths). | which may be several data units long (and they may be of different |
| lengths). |
|
|
The quantifier {0} is permitted, causing the expression to behave as if |
The quantifier {0} is permitted, causing the expression to behave as if |
the previous item and the quantifier were not present. This may be use- |
the previous item and the quantifier were not present. This may be use- |
ful for subpatterns that are referenced as subroutines from elsewhere | ful for subpatterns that are referenced as subroutin ful for subpatterns that are referenced as subroutines from elsewhere |
in the pattern (but see also the section entitled "Defining subpatterns |
in the pattern (but see also the section entitled "Defining subpatterns |
for use by reference only" below). Items other than subpatterns that | for use by reference only" below). Items other than subpattern for use by reference only" below). Items other than subpattern |
have a {0} quantifier are omitted from the compiled pattern. |
have a {0} quantifier are omitted from the compiled pattern. |
|
|
For convenience, the three most common quantifiers have single-charac- | For convenience, the three most common quantifiers have single-charac- |
ter abbreviations: |
ter abbreviations: |
|
|
* is equivalent to {0,} |
* is equivalent to {0,} |
+ is equivalent to {1,} |
+ is equivalent to {1,} |
? is equivalent to {0,1} |
? is equivalent to {0,1} |
|
|
It is possible to construct infinite loops by following a subpattern | It is possible to construct infinite loops It is possible to construct infinite loops by following a subpattern |
that can match no characters with a quantifier that has no upper limit, |
that can match no characters with a quantifier that has no upper limit, |
for example: |
for example: |
|
|
(a?)* |
(a?)* |
|
|
Earlier versions of Perl and PCRE used to give an error at compile time |
Earlier versions of Perl and PCRE used to give an error at compile time |
for such patterns. However, because there are cases where this can be | for such patterns. However, because there are cases where this can be |
useful, such patterns are now accepted, but if any repetition of the | useful, such patterns are now accepted, but if any repetition of the |
subpattern does in fact match no characters, the loop is forcibly bro- | subpattern does in fact match no characters, the loop is forcibly bro- |
ken. |
ken. |
|
|
By default, the quantifiers are "greedy", that is, they match as much | By default, the quantifiers are "greedy", that is, they match as much |
as possible (up to the maximum number of permitted times), without | as possible (up to the maximum number of permitted times), without |
causing the rest of the pattern to fail. The classic example of where | causing the rest of the pattern to fail. The classic example of where |
this gives problems is in trying to match comments in C programs. These |
this gives problems is in trying to match comments in C programs. These |
appear between /* and */ and within the comment, individual * and / | appear between /* and */ and within the comment, individual * and / |
characters may appear. An attempt to match C comments by applying the | characters may appear. An attempt to match C comments by applying the |
pattern |
pattern |
|
|
/\*.*\*/ |
/\*.*\*/ |
Line 5239 REPETITION
|
Line 6257 REPETITION
|
|
|
/* first comment */ not comment /* second comment */ |
/* first comment */ not comment /* second comment */ |
|
|
fails, because it matches the entire string owing to the greediness of | fails, because it matches the entire string owing to the greediness of |
the .* item. |
the .* item. |
|
|
However, if a quantifier is followed by a question mark, it ceases to | However, if a quantifier is followed by a question mark, it ceases to |
be greedy, and instead matches the minimum number of times possible, so |
be greedy, and instead matches the minimum number of times possible, so |
the pattern |
the pattern |
|
|
/\*.*?\*/ |
/\*.*?\*/ |
|
|
does the right thing with the C comments. The meaning of the various | does the right thing with the C comments. The meaning of the various |
quantifiers is not otherwise changed, just the preferred number of | quantifiers is not otherwise changed, just the preferred number of |
matches. Do not confuse this use of question mark with its use as a | matches. Do not confuse this use of question mark with its use as a |
quantifier in its own right. Because it has two uses, it can sometimes | quantifier in its own right. Because it has two uses, it can sometimes |
appear doubled, as in |
appear doubled, as in |
|
|
\d??\d |
\d??\d |
Line 5259 REPETITION
|
Line 6277 REPETITION
|
which matches one digit by preference, but can match two if that is the |
which matches one digit by preference, but can match two if that is the |
only way the rest of the pattern matches. |
only way the rest of the pattern matches. |
|
|
If the PCRE_UNGREEDY option is set (an option that is not available in | If the PCRE_UNGREEDY option is set (an option that is not available in |
Perl), the quantifiers are not greedy by default, but individual ones | Perl), the quantifiers are not greedy by default, but individual ones |
can be made greedy by following them with a question mark. In other | can be made greedy by following them with a question mark. In other |
words, it inverts the default behaviour. |
words, it inverts the default behaviour. |
|
|
When a parenthesized subpattern is quantified with a minimum repeat | When a parenthesized subpattern is quantified with a minimum repeat |
count that is greater than 1 or with a limited maximum, more memory is | count that is greater than 1 or with a limited maximum, more memory is |
required for the compiled pattern, in proportion to the size of the | required for the compiled pattern, in proportion to the size of the |
minimum or maximum. |
minimum or maximum. |
|
|
If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv- |
If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv- |
alent to Perl's /s) is set, thus allowing the dot to match newlines, | alent to Perl's /s) is set, thus allowing the dot to match newlines, |
the pattern is implicitly anchored, because whatever follows will be | the pattern is implicitly anchored, because whatever follows will be |
tried against every character position in the subject string, so there | tried against every character position in the subject string, so there |
is no point in retrying the overall match at any position after the | is no point in retrying the overall match at any position after the |
first. PCRE normally treats such a pattern as though it were preceded | first. PCRE normally treats such a pattern as though it were preceded |
by \A. |
by \A. |
|
|
In cases where it is known that the subject string contains no new- | In cases where it is known that the subject string contains no new- |
lines, it is worth setting PCRE_DOTALL in order to obtain this opti- | lines, it is worth setting PCRE_DOTALL in order to obtain this opti- |
mization, or alternatively using ^ to indicate anchoring explicitly. |
mization, or alternatively using ^ to indicate anchoring explicitly. |
|
|
However, there is one situation where the optimization cannot be used. | However, there are some cases where the optimization cannot be used. |
When .* is inside capturing parentheses that are the subject of a back |
When .* is inside capturing parentheses that are the subject of a back |
reference elsewhere in the pattern, a match at the start may fail where |
reference elsewhere in the pattern, a match at the start may fail where |
a later one succeeds. Consider, for example: |
a later one succeeds. Consider, for example: |
|
|
(.*)abc\1 |
(.*)abc\1 |
|
|
If the subject is "xyz123abc123" the match point is the fourth charac- | If the subject is "xyz123abc123" the match point is the fourth charac- |
ter. For this reason, such a pattern is not implicitly anchored. |
ter. For this reason, such a pattern is not implicitly anchored. |
|
|
|
Another case where implicit anchoring is not applied is when the lead- |
|
ing .* is inside an atomic group. Once again, a match at the start may |
|
fail where a later one succeeds. Consider this pattern: |
|
|
|
(?>.*?a)b |
|
|
|
It matches "ab" in the subject "aab". The use of the backtracking con- |
|
trol verbs (*PRUNE) and (*SKIP) also disable this optimization. |
|
|
When a capturing subpattern is repeated, the value captured is the sub- |
When a capturing subpattern is repeated, the value captured is the sub- |
string that matched the final iteration. For example, after |
string that matched the final iteration. For example, after |
|
|
Line 5545 ASSERTIONS
|
Line 6572 ASSERTIONS
|
tion contains capturing subpatterns within it, these are counted for |
tion contains capturing subpatterns within it, these are counted for |
the purposes of numbering the capturing subpatterns in the whole pat- |
the purposes of numbering the capturing subpatterns in the whole pat- |
tern. However, substring capturing is carried out only for positive |
tern. However, substring capturing is carried out only for positive |
assertions, because it does not make sense for negative assertions. | assertions. (Perl sometimes, but not always, does do capturing in nega- |
| tive assertions.) |
|
|
For compatibility with Perl, assertion subpatterns may be repeated; | For compatibility with Perl, assertion subpatterns may be repeated; |
though it makes no sense to assert the same thing several times, the | though it makes no sense to assert the same thing several times, the |
side effect of capturing parentheses may occasionally be useful. In | side effect of capturing parentheses may occasionally be useful. In |
practice, there only three cases: |
practice, there only three cases: |
|
|
(1) If the quantifier is {0}, the assertion is never obeyed during | (1) If the quantifier is {0}, the assertion is never obeyed during |
matching. However, it may contain internal capturing parenthesized | matching. However, it may contain internal capturing parenthesized |
groups that are called from elsewhere via the subroutine mechanism. |
groups that are called from elsewhere via the subroutine mechanism. |
|
|
(2) If quantifier is {0,n} where n is greater than zero, it is treated | (2) If quantifier is {0,n} where n is greater than zero, it is treated |
as if it were {0,1}. At run time, the rest of the pattern match is | as if it were {0,1}. At run time, the rest of the pattern match is |
tried with and without the assertion, the order depending on the greed- |
tried with and without the assertion, the order depending on the greed- |
iness of the quantifier. |
iness of the quantifier. |
|
|
(3) If the minimum repetition is greater than zero, the quantifier is | (3) If the minimum repetition is greater than zero, the quantifier is |
ignored. The assertion is obeyed just once when encountered during | ignored. The assertion is obeyed just once when encountered during |
matching. |
matching. |
|
|
Lookahead assertions |
Lookahead assertions |
Line 5572 ASSERTIONS
|
Line 6600 ASSERTIONS
|
|
|
\w+(?=;) |
\w+(?=;) |
|
|
matches a word followed by a semicolon, but does not include the semi- | matches a word followed by a semicolon, but does not include the semi- |
colon in the match, and |
colon in the match, and |
|
|
foo(?!bar) |
foo(?!bar) |
|
|
matches any occurrence of "foo" that is not followed by "bar". Note | matches any occurrence of "foo" that is not followed by "bar". Note |
that the apparently similar pattern |
that the apparently similar pattern |
|
|
(?!foo)bar |
(?!foo)bar |
|
|
does not find an occurrence of "bar" that is preceded by something | does not find an occurrence of "bar" that is preceded by something |
other than "foo"; it finds any occurrence of "bar" whatsoever, because | other than "foo"; it finds any occurrence of "bar" whatsoever, because |
the assertion (?!foo) is always true when the next three characters are |
the assertion (?!foo) is always true when the next three characters are |
"bar". A lookbehind assertion is needed to achieve the other effect. |
"bar". A lookbehind assertion is needed to achieve the other effect. |
|
|
If you want to force a matching failure at some point in a pattern, the |
If you want to force a matching failure at some point in a pattern, the |
most convenient way to do it is with (?!) because an empty string | most convenient way to do it is with (?!) because an empty string |
always matches, so an assertion that requires there not to be an empty | always matches, so an assertion that requires there not to be an empty |
string must always fail. The backtracking control verb (*FAIL) or (*F) |
string must always fail. The backtracking control verb (*FAIL) or (*F) |
is a synonym for (?!). |
is a synonym for (?!). |
|
|
Lookbehind assertions |
Lookbehind assertions |
|
|
Lookbehind assertions start with (?<= for positive assertions and (?<! | Lookbehind assertions start with (?<= for positive assertions and (?<! |
for negative assertions. For example, |
for negative assertions. For example, |
|
|
(?<!foo)bar |
(?<!foo)bar |
|
|
does find an occurrence of "bar" that is not preceded by "foo". The | does find an occurrence of "bar" that is not preceded by "foo". The |
contents of a lookbehind assertion are restricted such that all the | contents of a lookbehind assertion are restricted such that all the |
strings it matches must have a fixed length. However, if there are sev- |
strings it matches must have a fixed length. However, if there are sev- |
eral top-level alternatives, they do not all have to have the same | eral top-level alternatives, they do not all have to have the same |
fixed length. Thus |
fixed length. Thus |
|
|
(?<=bullock|donkey) |
(?<=bullock|donkey) |
Line 5612 ASSERTIONS
|
Line 6640 ASSERTIONS
|
|
|
(?<!dogs?|cats?) |
(?<!dogs?|cats?) |
|
|
causes an error at compile time. Branches that match different length | causes an error at compile time. Branches that match different length |
strings are permitted only at the top level of a lookbehind assertion. | strings are permitted only at the top level of a lookbehind assertion. |
This is an extension compared with Perl, which requires all branches to |
This is an extension compared with Perl, which requires all branches to |
match the same length of string. An assertion such as |
match the same length of string. An assertion such as |
|
|
(?<=ab(c|de)) |
(?<=ab(c|de)) |
|
|
is not permitted, because its single top-level branch can match two | is not permitted, because its single top-l is not permitted, because its single top-l |
different lengths, but it is acceptable to PCRE if rewritten to use two |
different lengths, but it is acceptable to PCRE if rewritten to use two |
top-level branches: |
top-level branches: |
|
|
(?<=abc|abde) |
(?<=abc|abde) |
|
|
In some cases, the escape sequence \K (see above) can be used instead | In some cases, the escape sequence \K (see above) can In some cases, the escape sequence \K (see above) can be used instead |
of a lookbehind assertion to get round the fixed-length restriction. |
of a lookbehind assertion to get round the fixed-length restriction. |
|
|
The implementation of lookbehind assertions is, for each alternative, | The implementation of lookbehind assertions is, for each alternative, |
to temporarily move the current position back by the fixed length and | to temporarily move the current position back by the fixed length and |
then try to match. If there are insufficient characters before the cur- |
then try to match. If there are insufficient characters before the cur- |
rent position, the assertion fails. |
rent position, the assertion fails. |
|
|
In a UTF mode, PCRE does not allow the \C escape (which matches a sin- | In a UTF mode, PCRE does not allow the \C escape (which matches a sin- |
gle data unit even in a UTF mode) to appear in lookbehind assertions, | gle data unit even in a UTF mode) to appear in lookbehind assertions, |
because it makes it impossible to calculate the length of the lookbe- | because it makes it impossible to calculate the length of the lookbe- |
hind. The \X and \R escapes, which can match different numbers of data | hind. The \X and \R escapes, which can match different numbers of data |
units, are also not permitted. |
units, are also not permitted. |
|
|
"Subroutine" calls (see below) such as (?2) or (?&X) are permitted in | "Subroutine" calls (see below) such as (?2) or (?&X) are permitted in |
lookbehinds, as long as the subpattern matches a fixed-length string. | lookbehinds, as long as the subpattern matches a fixed-length string. |
Recursion, however, is not supported. |
Recursion, however, is not supported. |
|
|
Possessive quantifiers can be used in conjunction with lookbehind | Possessive quantifiers can be used in conjunction with lookbehind |
assertions to specify efficient matching of fixed-length strings at the |
assertions to specify efficient matching of fixed-length strings at the |
end of subject strings. Consider a simple pattern such as |
end of subject strings. Consider a simple pattern such as |
|
|
abcd$ |
abcd$ |
|
|
when applied to a long string that does not match. Because matching | when applied to a long string that does not match. Because matching |
proceeds from left to right, PCRE will look for each "a" in the subject |
proceeds from left to right, PCRE will look for each "a" in the subject |
and then see if what follows matches the rest of the pattern. If the | and then see if what follows matches the rest of and then see if what follows matches the rest of the pattern. If the |
pattern is specified as |
pattern is specified as |
|
|
^.*abcd$ |
^.*abcd$ |
|
|
the initial .* matches the entire string at first, but when this fails | the initial .* matches the entire string at first, but when this fails |
(because there is no following "a"), it backtracks to match all but the |
(because there is no following "a"), it backtracks to match all but the |
last character, then all but the last two characters, and so on. Once | last character, then all but the last two characters, and so on. Once |
again the search for "a" covers the entire string, from right to left, | again the search for "a" covers the entire string, from right to left, |
so we are no better off. However, if the pattern is written as |
so we are no better off. However, if the pattern is written as |
|
|
^.*+(?<=abcd) |
^.*+(?<=abcd) |
|
|
there can be no backtracking for the .*+ item; it can match only the | there can be no backtracking for the .*+ item; it can match only the |
entire string. The subsequent lookbehind assertion does a single test | entire string. The subsequent lookbehind assertion does a single test |
on the last four characters. If it fails, the match fails immediately. | on the last four characters. If it fails, the match fails immediately. |
For long strings, this approach makes a significant difference to the | For long strings, this approach makes a significant difference to the |
processing time. |
processing time. |
|
|
Using multiple assertions |
Using multiple assertions |
Line 5676 ASSERTIONS
|
Line 6704 ASSERTIONS
|
|
|
(?<=\d{3})(?<!999)foo |
(?<=\d{3})(?<!999)foo |
|
|
matches "foo" preceded by three digits that are not "999". Notice that | matches "foo" preceded by three digits that are not "999". Notice that |
each of the assertions is applied independently at the same point in | each of the assertions is applied independently at the same point in |
the subject string. First there is a check that the previous three | the subject string. First there is a check that the previous three |
characters are all digits, and then there is a check that the same | characters are all digits, and then there is a check that the same |
three characters are not "999". This pattern does not match "foo" pre- |
three characters are not "999". This pattern does not match "foo" pre- |
ceded by six characters, the first of which are digits and the last | ceded by six characters, the first of which are digits and the last |
three of which are not "999". For example, it doesn't match "123abc- | three of which are not "999". For example, it doesn't match "123abc- |
foo". A pattern to do that is |
foo". A pattern to do that is |
|
|
(?<=\d{3}...)(?<!999)foo |
(?<=\d{3}...)(?<!999)foo |
|
|
This time the first assertion looks at the preceding six characters, | This time the first assertion looks at the preceding six characters, |
checking that the first three are digits, and then the second assertion |
checking that the first three are digits, and then the second assertion |
checks that the preceding three characters are not "999". |
checks that the preceding three characters are not "999". |
|
|
Line 5695 ASSERTIONS
|
Line 6723 ASSERTIONS
|
|
|
(?<=(?<!foo)bar)baz |
(?<=(?<!foo)bar)baz |
|
|
matches an occurrence of "baz" that is preceded by "bar" which in turn | matches an occurrence of "baz" that is preceded by "bar" which in turn |
is not preceded by "foo", while |
is not preceded by "foo", while |
|
|
(?<=\d{3}(?!999)...)foo |
(?<=\d{3}(?!999)...)foo |
|
|
is another pattern that matches "foo" preceded by three digits and any | is another pattern that matches "foo" preceded by three digits and any |
three characters that are not "999". |
three characters that are not "999". |
|
|
|
|
CONDITIONAL SUBPATTERNS |
CONDITIONAL SUBPATTERNS |
|
|
It is possible to cause the matching process to obey a subpattern con- | It is possible to cause the matching process to obey a subpattern con- |
ditionally or to choose between two alternative subpatterns, depending | ditionally or to choose between two alternative subpatterns, depending |
on the result of an assertion, or whether a specific capturing subpat- | on the result of an assertion, or whether a specific capturing subpat- |
tern has already been matched. The two possible forms of conditional | tern has already been matched. The two possible forms of conditional |
subpattern are: |
subpattern are: |
|
|
(?(condition)yes-pattern) |
(?(condition)yes-pattern) |
(?(condition)yes-pattern|no-pattern) |
(?(condition)yes-pattern|no-pattern) |
|
|
If the condition is satisfied, the yes-pattern is used; otherwise the | If the condition is satisfied, the yes-pattern is used; otherwise the |
no-pattern (if present) is used. If there are more than two alterna- | no-pattern (if present) is used. If there are more than two alterna- |
tives in the subpattern, a compile-time error occurs. Each of the two | tives in the subpattern, a compile-time error occurs. Each of the two |
alternatives may itself contain nested subpatterns of any form, includ- |
alternatives may itself contain nested subpatterns of any form, includ- |
ing conditional subpatterns; the restriction to two alternatives |
ing conditional subpatterns; the restriction to two alternatives |
applies only at the level of the condition. This pattern fragment is an |
applies only at the level of the condition. This pattern fragment is an |
Line 5726 CONDITIONAL SUBPATTERNS
|
Line 6754 CONDITIONAL SUBPATTERNS
|
(?(1) (A|B|C) | (D | (?(2)E|F) | E) ) |
(?(1) (A|B|C) | (D | (?(2)E|F) | E) ) |
|
|
|
|
There are four kinds of condition: references to subpatterns, refer- | There are four kinds of condition: references to subpatterns, refer- |
ences to recursion, a pseudo-condition called DEFINE, and assertions. |
ences to recursion, a pseudo-condition called DEFINE, and assertions. |
|
|
Checking for a used subpattern by number |
Checking for a used subpattern by number |
|
|
If the text between the parentheses consists of a sequence of digits, | If the text between the parentheses consists of a sequence of digits, |
the condition is true if a capturing subpattern of that number has pre- |
the condition is true if a capturing subpattern of that number has pre- |
viously matched. If there is more than one capturing subpattern with | viously matched. If there is more than one capturing subpattern with |
the same number (see the earlier section about duplicate subpattern | the same number (see the earlier section about duplicate subpattern |
numbers), the condition is true if any of them have matched. An alter- | numbers), the condition is true if any of them have matched. An alter- |
native notation is to precede the digits with a plus or minus sign. In | native notation is to precede the digits with a plus or minus sign. In |
this case, the subpattern number is relative rather than absolute. The | this case, the subpattern number is relative rather than absolute. The |
most recently opened parentheses can be referenced by (?(-1), the next | most recently opened parentheses can be referenced by (?(-1), the next |
most recent by (?(-2), and so on. Inside loops it can also make sense | most recent by (?(-2), and so on. Inside loops it can also make sense |
to refer to subsequent groups. The next parentheses to be opened can be |
to refer to subsequent groups. The next parentheses to be opened can be |
referenced as (?(+1), and so on. (The value zero in any of these forms | referenced as (?(+1), and so on. (The value zero in any of these forms |
is not used; it provokes a compile-time error.) |
is not used; it provokes a compile-time error.) |
|
|
Consider the following pattern, which contains non-significant white | Consider the following pattern, which contains non-significant white |
space to make it more readable (assume the PCRE_EXTENDED option) and to |
space to make it more readable (assume the PCRE_EXTENDED option) and to |
divide it into three parts for ease of discussion: |
divide it into three parts for ease of discussion: |
|
|
( \( )? [^()]+ (?(1) \) ) |
( \( )? [^()]+ (?(1) \) ) |
|
|
The first part matches an optional opening parenthesis, and if that | The first part matches an optional opening parenthes The first part matches an optional opening parenthes |
character is present, sets it as the first captured substring. The sec- |
character is present, sets it as the first captured substring. The sec- |
ond part matches one or more characters that are not parentheses. The | ond part matches one or more characters that are not parentheses. The |
third part is a conditional subpattern that tests whether or not the | third part is a conditional subpattern that tests whether or not the |
first set of parentheses matched. If they did, that is, if subject | first set of parentheses matched. If they did, that is, if subject |
started with an opening parenthesis, the condition is true, and so the | started with an opening parenthesis, the condition is true, and so the |
yes-pattern is executed and a closing parenthesis is required. Other- | yes-pattern is executed and a closing parenthesis is required. Other- |
wise, since no-pattern is not present, the subpattern matches nothing. | wise, since no-pattern is not present, the subpattern matches nothing. |
In other words, this pattern matches a sequence of non-parentheses, | In other words, this pattern matches a sequence of non-parentheses, |
optionally enclosed in parentheses. |
optionally enclosed in parentheses. |
|
|
If you were embedding this pattern in a larger one, you could use a | If you were embedding this pattern in a larger one, you could use a |
relative reference: |
relative reference: |
|
|
...other stuff... ( \( )? [^()]+ (?(-1) \) ) ... |
...other stuff... ( \( )? [^()]+ (?(-1) \) ) ... |
|
|
This makes the fragment independent of the parentheses in the larger | This makes the fragment independent of the parentheses in the larger |
pattern. |
pattern. |
|
|
Checking for a used subpattern by name |
Checking for a used subpattern by name |
|
|
Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a | Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a |
used subpattern by name. For compatibility with earlier versions of | used subpattern by name. For compatibility with earlier versions of |
PCRE, which had this facility before Perl, the syntax (?(name)...) is | PCRE, which had this facility before Perl, the syntax (?(name)...) is |
also recognized. However, there is a possible ambiguity with this syn- | also recognized. |
tax, because subpattern names may consist entirely of digits. PCRE | |
looks first for a named subpattern; if it cannot find one and the name | |
consists entirely of digits, PCRE looks for a subpattern of that num- | |
ber, which must be greater than zero. Using subpattern names that con- | |
sist entirely of digits is not recommended. | |
|
|
Rewriting the above example to use a named subpattern gives this: |
Rewriting the above example to use a named subpattern gives this: |
|
|
Line 6160 CALLOUTS
|
Line 7183 CALLOUTS
|
PCRE provides a similar feature, but of course it cannot obey arbitrary |
PCRE provides a similar feature, but of course it cannot obey arbitrary |
Perl code. The feature is called "callout". The caller of PCRE provides |
Perl code. The feature is called "callout". The caller of PCRE provides |
an external function by putting its entry point in the global variable |
an external function by putting its entry point in the global variable |
pcre_callout (8-bit library) or pcre16_callout (16-bit library). By | pcre_callout (8-bit library) or pcre[16|32]_callout (16-bit or 32-bit |
default, this variable contains NULL, which disables all calling out. | library). By default, this variable contains NULL, which disables all |
| calling out. |
|
|
Within a regular expression, (?C) indicates the points at which the | Within a regular expression, (?C) indicates the points at which the |
external function is to be called. If you want to identify different | external function is to be called. If you want to identify different |
callout points, you can put a number less than 256 after the letter C. | callout points, you can put a number less than 256 after the letter C. |
The default value is zero. For example, this pattern has two callout | The default value is zero. For example, this pattern has two callout |
points: |
points: |
|
|
(?C1)abc(?C2)def |
(?C1)abc(?C2)def |
|
|
If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, call- | If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, call- |
outs are automatically installed before each item in the pattern. They | outs are automatically installed before each item in the pattern. They |
are all numbered 255. | are all numbered 255. If there is a conditional group in the pattern |
| whose condition is an assertion, an additional callout is inserted just |
| before the condition. An explicit callout may also be set at this posi- |
| tion, as in this example: |
|
|
During matching, when PCRE reaches a callout point, the external func- | (?(?C9)(?=a)abc|def) |
tion is called. It is provided with the number of the callout, the | |
position in the pattern, and, optionally, one item of data originally | |
supplied by the caller of the matching function. The callout function | |
may cause matching to proceed, to backtrack, or to fail altogether. A | |
complete description of the interface to the callout function is given | |
in the pcrecallout documentation. | |
|
|
|
Note that this applies only to assertion conditions, not to other types |
|
of condition. |
|
|
BACKTRACKING CONTROL | During matching, when PCRE reaches a callout point, the external func- |
| tion is called. It is provided with the number of the callout, the |
| position in the pattern, and, optionally, one item of data originally |
| supplied by the caller of the matching function. The callout function |
| may cause matching to proceed, to backtrack, or to fail altogether. |
|
|
Perl 5.10 introduced a number of "Special Backtracking Control Verbs", | By default, PCRE implements a number of optimizations at compile time |
which are described in the Perl documentation as "experimental and sub- | and matching time, and one side-effect is that sometimes callouts are |
ject to change or removal in a future version of Perl". It goes on to | skipped. If you need all possible callouts to happen, you need to set |
say: "Their usage in production code should be noted to avoid problems | options that disable the relevant optimizations. More details, and a |
during upgrades." The same remarks apply to the PCRE features described | complete description of the interface to the callout function, are |
in this section. | given in the pcrecallout documentation. |
|
|
Since these verbs are specifically related to backtracking, most of |
|
them can be used only when the pattern is to be matched using one of |
|
the traditional matching functions, which use a backtracking algorithm. |
|
With the exception of (*FAIL), which behaves like a failing negative |
|
assertion, they cause an error if encountered by a DFA matching func- |
|
tion. |
|
|
|
If any of these verbs are used in an assertion or in a subpattern that | BACKTRACKING CONTROL |
is called as a subroutine (whether or not recursively), their effect is | |
confined to that subpattern; it does not extend to the surrounding pat- | |
tern, with one exception: the name from a *(MARK), (*PRUNE), or (*THEN) | |
that is encountered in a successful positive assertion is passed back | |
when a match succeeds (compare capturing parentheses in assertions). | |
Note that such subpatterns are processed as anchored at the point where | |
they are tested. Note also that Perl's treatment of subroutines and | |
assertions is different in some cases. | |
|
|
The new verbs make use of what was previously invalid syntax: an open- | Perl 5.10 introduced a number of "Special Backtracking Control Verbs", |
| which are still described in the Perl documentation as "experimental |
| and subject to change or removal in a future version of Perl". It goes |
| on to say: "Their usage in production code should be noted to avoid |
| problems during upgrades." The same remarks apply to the PCRE features |
| described in this section. |
| |
| The new verbs make use of what was previously invalid syntax: an open- |
ing parenthesis followed by an asterisk. They are generally of the form |
ing parenthesis followed by an asterisk. They are generally of the form |
(*VERB) or (*VERB:NAME). Some may take either form, with differing be- | (*VERB) or (*VERB:NAME). Some may take either form, possibly behaving |
haviour, depending on whether or not an argument is present. A name is | differently depending on whether or not a name is present. A name is |
any sequence of characters that does not include a closing parenthesis. |
any sequence of characters that does not include a closing parenthesis. |
The maximum length of name is 255 in the 8-bit library and 65535 in the |
The maximum length of name is 255 in the 8-bit library and 65535 in the |
16-bit library. If the name is empty, that is, if the closing parenthe- | 16-bit and 32-bit libraries. If the name is empty, that is, if the |
sis immediately follows the colon, the effect is as if the colon were | closing parenthesis immediately follows the colon, the effect is as if |
not there. Any number of these verbs may occur in a pattern. | the colon were not there. Any number of these verbs may occur in a |
| pattern. |
|
|
|
Since these verbs are specifically related to backtracking, most of |
|
them can be used only when the pattern is to be matched using one of |
|
the traditional matching functions, because these use a backtracking |
|
algorithm. With the exception of (*FAIL), which behaves like a failing |
|
negative assertion, the backtracking control verbs cause an error if |
|
encountered by a DFA matching function. |
|
|
|
The behaviour of these verbs in repeated groups, assertions, and in |
|
subpatterns called as subroutines (whether or not recursively) is docu- |
|
mented below. |
|
|
Optimizations that affect backtracking verbs |
Optimizations that affect backtracking verbs |
|
|
PCRE contains some optimizations that are used to speed up matching by | PCRE contains some optimizations that are used to speed up matching by |
running some checks at the start of each match attempt. For example, it |
running some checks at the start of each match attempt. For example, it |
may know the minimum length of matching subject, or that a particular | may know the minimum length of matching subject, or that a particular |
character must be present. When one of these optimizations suppresses | character must be present. When one of these optimizations bypasses the |
the running of a match, any included backtracking verbs will not, of | running of a match, any included backtracking verbs will not, of |
course, be processed. You can suppress the start-of-match optimizations |
course, be processed. You can suppress the start-of-match optimizations |
by setting the PCRE_NO_START_OPTIMIZE option when calling pcre_com- | by setting the PCRE_NO_START_OPTIMIZE option when calling pcre_com- |
pile() or pcre_exec(), or by starting the pattern with (*NO_START_OPT). |
pile() or pcre_exec(), or by starting the pattern with (*NO_START_OPT). |
There is more discussion of this option in the section entitled "Option |
There is more discussion of this option in the section entitled "Option |
bits for pcre_exec()" in the pcreapi documentation. |
bits for pcre_exec()" in the pcreapi documentation. |
|
|
Experiments with Perl suggest that it too has similar optimizations, | Experiments with Perl suggest that it too has similar optimizations, |
sometimes leading to anomalous results. |
sometimes leading to anomalous results. |
|
|
Verbs that act immediately |
Verbs that act immediately |
|
|
The following verbs act as soon as they are encountered. They may not | The following verbs act as soon as they are encountered. They may not |
be followed by a name. |
be followed by a name. |
|
|
(*ACCEPT) |
(*ACCEPT) |
|
|
This verb causes the match to end successfully, skipping the remainder | This verb causes the match to end successfully, skipping the remainder |
of the pattern. However, when it is inside a subpattern that is called | of the pattern. However, when it is inside a subpattern that is called |
as a subroutine, only that subpattern is ended successfully. Matching | as a subroutine, only that subpattern is ended successfully. Matching |
then continues at the outer level. If (*ACCEPT) is inside capturing | then continues at the outer level. If (*ACCEPT) in triggered in a posi- |
parentheses, the data so far is captured. For example: | tive assertion, the assertion succeeds; in a negative assertion, the |
| assertion fails. |
|
|
|
If (*ACCEPT) is inside capturing parentheses, the data so far is cap- |
|
tured. For example: |
|
|
A((?:A|B(*ACCEPT)|C)D) |
A((?:A|B(*ACCEPT)|C)D) |
|
|
This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap- | This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap- |
tured by the outer parentheses. |
tured by the outer parentheses. |
|
|
(*FAIL) or (*F) |
(*FAIL) or (*F) |
|
|
This verb causes a matching failure, forcing backtracking to occur. It | This verb causes a matching failure, forcing backtracking to occur. It |
is equivalent to (?!) but easier to read. The Perl documentation notes | is equivalent to (?!) but easier to read. The Perl documentation notes |
that it is probably useful only when combined with (?{}) or (??{}). | that it is probably useful only when combined with (?{}) or (??{}). |
Those are, of course, Perl features that are not present in PCRE. The | Those are, of course, Perl features that are not present in PCRE. The |
nearest equivalent is the callout feature, as for example in this pat- | nearest equivalent is the callout feature, as for example in this pat- |
tern: |
tern: |
|
|
a+(?C)(*FAIL) |
a+(?C)(*FAIL) |
|
|
A match with the string "aaaa" always fails, but the callout is taken | A match with the string "aaaa" always fails, but the callout is taken |
before each backtrack happens (in this example, 10 times). |
before each backtrack happens (in this example, 10 times). |
|
|
Recording which path was taken |
Recording which path was taken |
|
|
There is one verb whose main purpose is to track how a match was | There is one verb whose main purpose is to track how a match was |
arrived at, though it also has a secondary use in conjunction with | arrived at, though it also has a secondary use in conjunction with |
advancing the match starting point (see (*SKIP) below). |
advancing the match starting point (see (*SKIP) below). |
|
|
(*MARK:NAME) or (*:NAME) |
(*MARK:NAME) or (*:NAME) |
|
|
A name is always required with this verb. There may be as many | A name is always required with this verb. There may be as many |
instances of (*MARK) as you like in a pattern, and their names do not | instances of (*MARK) as you like in a pattern, and their names do not |
have to be unique. |
have to be unique. |
|
|
When a match succeeds, the name of the last-encountered (*MARK) on the | When a match succeeds, the name of the last-encountered (*MARK:NAME), |
matching path is passed back to the caller as described in the section | (*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to |
entitled "Extra data for pcre_exec()" in the pcreapi documentation. | the caller as described in the section entitled "Extra data for |
Here is an example of pcretest output, where the /K modifier requests | pcre_exec()" in the pcreapi documentation. Here is an example of |
the retrieval and outputting of (*MARK) data: | pcretest output, where the /K modifier requests the retrieval and out- |
| putting of (*MARK) data: |
|
|
re> /X(*MARK:A)Y|X(*MARK:B)Z/K |
re> /X(*MARK:A)Y|X(*MARK:B)Z/K |
data> XY |
data> XY |
Line 6299 BACKTRACKING CONTROL
|
Line 7336 BACKTRACKING CONTROL
|
efficient way of obtaining this information than putting each alterna- |
efficient way of obtaining this information than putting each alterna- |
tive in its own capturing parentheses. |
tive in its own capturing parentheses. |
|
|
If (*MARK) is encountered in a positive assertion, its name is recorded | If a verb with a name is encountered in a positive assertion that is |
and passed back if it is the last-encountered. This does not happen for | true, the name is recorded and passed back if it is the last-encoun- |
negative assertions. | tered. This does not happen for negative assertions or failing positive |
| assertions. |
|
|
After a partial match or a failed match, the name of the last encoun- | After a partial match or a failed match, the last encountered name in |
tered (*MARK) in the entire match process is returned. For example: | the entire match process is returned. For example: |
|
|
re> /X(*MARK:A)Y|X(*MARK:B)Z/K |
re> /X(*MARK:A)Y|X(*MARK:B)Z/K |
data> XP |
data> XP |
No match, mark = B |
No match, mark = B |
|
|
Note that in this unanchored example the mark is retained from the | Note that in this unanchored example the mark is retained from the |
match attempt that started at the letter "X" in the subject. Subsequent |
match attempt that started at the letter "X" in the subject. Subsequent |
match attempts starting at "P" and then with an empty string do not get |
match attempts starting at "P" and then with an empty string do not get |
as far as the (*MARK) item, but nevertheless do not reset it. |
as far as the (*MARK) item, but nevertheless do not reset it. |
|
|
If you are interested in (*MARK) values after failed matches, you | If you are interested in (*MARK) values after failed matches, you |
should probably set the PCRE_NO_START_OPTIMIZE option (see above) to | should probably set the PCRE_NO_START_OPTIMIZE option (see above) to |
ensure that the match is always attempted. |
ensure that the match is always attempted. |
|
|
Verbs that act after backtracking |
Verbs that act after backtracking |
|
|
The following verbs do nothing when they are encountered. Matching con- |
The following verbs do nothing when they are encountered. Matching con- |
tinues with what follows, but if there is no subsequent match, causing | tinues with what follows, but if there is no subsequent match, causing |
a backtrack to the verb, a failure is forced. That is, backtracking | a backtrack to the verb, a failure is forced. That is, backtracking |
cannot pass to the left of the verb. However, when one of these verbs | cannot pass to the left of the verb. However, when one of these verbs |
appears inside an atomic group, its effect is confined to that group, | appears inside an atomic group or an assertion that is true, its effect |
because once the group has been matched, there is never any backtrack- | is confined to that group, because once the group has been matched, |
ing into it. In this situation, backtracking can "jump back" to the | there is never any backtracking into it. In this situation, backtrack- |
left of the entire atomic group. (Remember also, as stated above, that | ing can "jump back" to the left of the entire atomic group or asser- |
this localization also applies in subroutine calls and assertions.) | tion. (Remember also, as stated above, that this localization also |
| applies in subroutine calls.) |
|
|
These verbs differ in exactly what kind of failure occurs when back- |
These verbs differ in exactly what kind of failure occurs when back- |
tracking reaches them. | tracking reaches them. The behaviour described below is what happens |
| when the verb is not in a subroutine or an assertion. Subsequent sec- |
| tions cover these special cases. |
|
|
(*COMMIT) |
(*COMMIT) |
|
|
This verb, which may not be followed by a name, causes the whole match |
This verb, which may not be followed by a name, causes the whole match |
to fail outright if the rest of the pattern does not match. Even if the | to fail outright if there is a later matching failure that causes back- |
pattern is unanchored, no further attempts to find a match by advancing | tracking to reach it. Even if the pattern is unanchored, no further |
the starting point take place. Once (*COMMIT) has been passed, | attempts to find a match by advancing the starting point take place. If |
pcre_exec() is committed to finding a match at the current starting | (*COMMIT) is the only backtracking verb that is encountered, once it |
point, or not at all. For example: | has been passed pcre_exec() is committed to finding a match at the cur- |
| rent starting point, or not at all. For example: |
|
|
a+(*COMMIT)b |
a+(*COMMIT)b |
|
|
This matches "xxaab" but not "aacaab". It can be thought of as a kind | This matches "xxaab" but not "aacaab". It can be thought of as a kind |
of dynamic anchor, or "I've started, so I must finish." The name of the |
of dynamic anchor, or "I've started, so I must finish." The name of the |
most recently passed (*MARK) in the path is passed back when (*COMMIT) | most recently passed (*MARK) in the path is passed back when (*COMMIT) |
forces a match failure. |
forces a match failure. |
|
|
|
If there is more than one backtracking verb in a pattern, a different |
|
one that follows (*COMMIT) may be triggered first, so merely passing |
|
(*COMMIT) during a match does not always guarantee that a match must be |
|
at this starting point. |
|
|
Note that (*COMMIT) at the start of a pattern is not the same as an |
Note that (*COMMIT) at the start of a pattern is not the same as an |
anchor, unless PCRE's start-of-match optimizations are turned off, as |
anchor, unless PCRE's start-of-match optimizations are turned off, as |
shown in this pcretest example: |
shown in this pcretest example: |
Line 6369 BACKTRACKING CONTROL
|
Line 7416 BACKTRACKING CONTROL
|
(*PRUNE) or (*PRUNE:NAME) |
(*PRUNE) or (*PRUNE:NAME) |
|
|
This verb causes the match to fail at the current starting position in |
This verb causes the match to fail at the current starting position in |
the subject if the rest of the pattern does not match. If the pattern | the subject if there is a later matching failure that causes backtrack- |
is unanchored, the normal "bumpalong" advance to the next starting | ing to reach it. If the pattern is unanchored, the normal "bumpalong" |
character then happens. Backtracking can occur as usual to the left of | advance to the next starting character then happens. Backtracking can |
(*PRUNE), before it is reached, or when matching to the right of | occur as usual to the left of (*PRUNE), before it is reached, or when |
(*PRUNE), but if there is no match to the right, backtracking cannot | matching to the right of (*PRUNE), but if there is no match to the |
cross (*PRUNE). In simple cases, the use of (*PRUNE) is just an alter- | right, backtracking cannot cross (*PRUNE). In simple cases, the use of |
native to an atomic group or possessive quantifier, but there are some | (*PRUNE) is just an alternative to an atomic group or possessive quan- |
uses of (*PRUNE) that cannot be expressed in any other way. The behav- | tifier, but there are some uses of (*PRUNE) that cannot be expressed in |
iour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE). In an | any other way. In an anchored pattern (*PRUNE) has the same effect as |
anchored pattern (*PRUNE) has the same effect as (*COMMIT). | (*COMMIT). |
|
|
|
The behaviour of (*PRUNE:NAME) is the not the same as |
|
(*MARK:NAME)(*PRUNE). It is like (*MARK:NAME) in that the name is |
|
remembered for passing back to the caller. However, (*SKIP:NAME) |
|
searches only for names set with (*MARK). |
|
|
(*SKIP) |
(*SKIP) |
|
|
This verb, when given without a name, is like (*PRUNE), except that if | This verb, when given without a name, is like (*PRUNE), except that if |
the pattern is unanchored, the "bumpalong" advance is not to the next | the pattern is unanchored, the "bumpalong" advance is not to the next |
character, but to the position in the subject where (*SKIP) was encoun- |
character, but to the position in the subject where (*SKIP) was encoun- |
tered. (*SKIP) signifies that whatever text was matched leading up to | tered. (*SKIP) signifies that whatever text was matched leading up to |
it cannot be part of a successful match. Consider: |
it cannot be part of a successful match. Consider: |
|
|
a+(*SKIP)b |
a+(*SKIP)b |
|
|
If the subject is "aaaac...", after the first match attempt fails | If the subject is "aaaac...", after the first match attempt fails |
(starting at the first character in the string), the starting point | (starting at the first character in the string), the starting point |
skips on to start the next attempt at "c". Note that a possessive quan- |
skips on to start the next attempt at "c". Note that a possessive quan- |
tifer does not have the same effect as this example; although it would | tifer does not have the same effect as this example; although it would |
suppress backtracking during the first match attempt, the second | suppress backtracking during the first match attempt, the second |
attempt would start at the second character instead of skipping on to | attempt would start at the second character instead of skipping on to |
"c". |
"c". |
|
|
(*SKIP:NAME) |
(*SKIP:NAME) |
|
|
When (*SKIP) has an associated name, its behaviour is modified. If the | When (*SKIP) has an associated name, its behaviour is modified. When it |
following pattern fails to match, the previous path through the pattern | is triggered, the previous path through the pattern is searched for the |
is searched for the most recent (*MARK) that has the same name. If one | most recent (*MARK) that has the same name. If one is found, the |
is found, the "bumpalong" advance is to the subject position that cor- | "bumpalong" advance is to the subject position that corresponds to that |
responds to that (*MARK) instead of to where (*SKIP) was encountered. | (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with |
If no (*MARK) with a matching name is found, the (*SKIP) is ignored. | a matching name is found, the (*SKIP) is ignored. |
|
|
|
Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It |
|
ignores names that are set by (*PRUNE:NAME) or (*THEN:NAME). |
|
|
(*THEN) or (*THEN:NAME) |
(*THEN) or (*THEN:NAME) |
|
|
This verb causes a skip to the next innermost alternative if the rest | This verb causes a skip to the next innermost alternative when back- |
of the pattern does not match. That is, it cancels pending backtrack- | tracking reaches it. That is, it cancels any further backtracking |
ing, but only within the current alternative. Its name comes from the | within the current alternative. Its name comes from the observation |
observation that it can be used for a pattern-based if-then-else block: | that it can be used for a pattern-based if-then-else block: |
|
|
( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ... |
( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ... |
|
|
If the COND1 pattern matches, FOO is tried (and possibly further items |
If the COND1 pattern matches, FOO is tried (and possibly further items |
after the end of the group if FOO succeeds); on failure, the matcher |
after the end of the group if FOO succeeds); on failure, the matcher |
skips to the second alternative and tries COND2, without backtracking |
skips to the second alternative and tries COND2, without backtracking |
into COND1. The behaviour of (*THEN:NAME) is exactly the same as | into COND1. If that succeeds and BAR fails, COND3 is tried. If subse- |
(*MARK:NAME)(*THEN). If (*THEN) is not inside an alternation, it acts | quently BAZ fails, there are no more alternatives, so there is a back- |
like (*PRUNE). | track to whatever came before the entire group. If (*THEN) is not |
| inside an alternation, it acts like (*PRUNE). |
|
|
Note that a subpattern that does not contain a | character is just a | The behaviour of (*THEN:NAME) is the not the same as |
part of the enclosing alternative; it is not a nested alternation with | (*MARK:NAME)(*THEN). It is like (*MARK:NAME) in that the name is |
only one alternative. The effect of (*THEN) extends beyond such a sub- | remembered for passing back to the caller. However, (*SKIP:NAME) |
pattern to the enclosing alternative. Consider this pattern, where A, | searches only for names set with (*MARK). |
B, etc. are complex pattern fragments that do not contain any | charac- | |
ters at this level: | |
|
|
|
A subpattern that does not contain a | character is just a part of the |
|
enclosing alternative; it is not a nested alternation with only one |
|
alternative. The effect of (*THEN) extends beyond such a subpattern to |
|
the enclosing alternative. Consider this pattern, where A, B, etc. are |
|
complex pattern fragments that do not contain any | characters at this |
|
level: |
|
|
A (B(*THEN)C) | D |
A (B(*THEN)C) | D |
|
|
If A and B are matched, but there is a failure in C, matching does not |
If A and B are matched, but there is a failure in C, matching does not |
Line 6444 BACKTRACKING CONTROL
|
Line 7505 BACKTRACKING CONTROL
|
tern to fail because there are no more alternatives to try. In this |
tern to fail because there are no more alternatives to try. In this |
case, matching does now backtrack into A. |
case, matching does now backtrack into A. |
|
|
Note also that a conditional subpattern is not considered as having two | Note that a conditional subpattern is not considered as having two |
alternatives, because only one is ever used. In other words, the | |
alternatives, because only one is ever used. In other words, the | |
character in a conditional subpattern has a different meaning. Ignoring |
character in a conditional subpattern has a different meaning. Ignoring |
white space, consider: |
white space, consider: |
Line 6468 BACKTRACKING CONTROL
|
Line 7529 BACKTRACKING CONTROL
|
the advance may be more than one character. (*COMMIT) is the strongest, |
the advance may be more than one character. (*COMMIT) is the strongest, |
causing the entire match to fail. |
causing the entire match to fail. |
|
|
If more than one such verb is present in a pattern, the "strongest" one | More than one backtracking verb |
wins. For example, consider this pattern, where A, B, etc. are complex | |
pattern fragments: | |
|
|
(A(*COMMIT)B(*THEN)C|D) | If more than one backtracking verb is present in a pattern, the one |
| that is backtracked onto first acts. For example, consider this pat- |
| tern, where A, B, etc. are complex pattern fragments: |
|
|
Once A has matched, PCRE is committed to this match, at the current | (A(*COMMIT)B(*THEN)C|ABD) |
starting position. If subsequently B matches, but C does not, the nor- | |
mal (*THEN) action of trying the next alternative (that is, D) does not | |
happen because (*COMMIT) overrides. | |
|
|
|
If A matches but B fails, the backtrack to (*COMMIT) causes the entire |
|
match to fail. However, if A and B match, but C fails, the backtrack to |
|
(*THEN) causes the next alternative (ABD) to be tried. This behaviour |
|
is consistent, but is not always the same as Perl's. It means that if |
|
two or more backtracking verbs appear in succession, all the the last |
|
of them has no effect. Consider this example: |
|
|
|
...(*COMMIT)(*PRUNE)... |
|
|
|
If there is a matching failure to the right, backtracking onto (*PRUNE) |
|
causes it to be triggered, and its action is taken. There can never be |
|
a backtrack onto (*COMMIT). |
|
|
|
Backtracking verbs in repeated groups |
|
|
|
PCRE differs from Perl in its handling of backtracking verbs in |
|
repeated groups. For example, consider: |
|
|
|
/(a(*COMMIT)b)+ac/ |
|
|
|
If the subject is "abac", Perl matches, but PCRE fails because the |
|
(*COMMIT) in the second repeat of the group acts. |
|
|
|
Backtracking verbs in assertions |
|
|
|
(*FAIL) in an assertion has its normal effect: it forces an immediate |
|
backtrack. |
|
|
|
(*ACCEPT) in a positive assertion causes the assertion to succeed with- |
|
out any further processing. In a negative assertion, (*ACCEPT) causes |
|
the assertion to fail without any further processing. |
|
|
|
The other backtracking verbs are not treated specially if they appear |
|
in a positive assertion. In particular, (*THEN) skips to the next |
|
alternative in the innermost enclosing group that has alternations, |
|
whether or not this is within the assertion. |
|
|
|
Negative assertions are, however, different, in order to ensure that |
|
changing a positive assertion into a negative assertion changes its |
|
result. Backtracking into (*COMMIT), (*SKIP), or (*PRUNE) causes a neg- |
|
ative assertion to be true, without considering any further alternative |
|
branches in the assertion. Backtracking into (*THEN) causes it to skip |
|
to the next enclosing alternative within the assertion (the normal be- |
|
haviour), but if the assertion does not have such an alternative, |
|
(*THEN) behaves like (*PRUNE). |
|
|
|
Backtracking verbs in subroutines |
|
|
|
These behaviours occur whether or not the subpattern is called recur- |
|
sively. Perl's treatment of subroutines is different in some cases. |
|
|
|
(*FAIL) in a subpattern called as a subroutine has its normal effect: |
|
it forces an immediate backtrack. |
|
|
|
(*ACCEPT) in a subpattern called as a subroutine causes the subroutine |
|
match to succeed without any further processing. Matching then contin- |
|
ues after the subroutine call. |
|
|
|
(*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine |
|
cause the subroutine match to fail. |
|
|
|
(*THEN) skips to the next alternative in the innermost enclosing group |
|
within the subpattern that has alternatives. If there is no such group |
|
within the subpattern, (*THEN) causes the subroutine match to fail. |
|
|
|
|
SEE ALSO |
SEE ALSO |
|
|
pcreapi(3), pcrecallout(3), pcrematching(3), pcresyntax(3), pcre(3), |
pcreapi(3), pcrecallout(3), pcrematching(3), pcresyntax(3), pcre(3), |
pcre16(3). | pcre16(3), pcre32(3). |
|
|
|
|
AUTHOR |
AUTHOR |
Line 6495 AUTHOR
|
Line 7618 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 17 June 2012 | Last updated: 03 December 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCRESYNTAX(3) PCRESYNTAX(3) | PCRESYNTAX(3) Library Functions Manual PCRESYNTAX(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
PCRE REGULAR EXPRESSION SYNTAX SUMMARY |
PCRE REGULAR EXPRESSION SYNTAX SUMMARY |
|
|
The full syntax and semantics of the regular expressions that are sup- |
The full syntax and semantics of the regular expressions that are sup- |
Line 6529 CHARACTERS
|
Line 7652 CHARACTERS
|
\n newline (hex 0A) |
\n newline (hex 0A) |
\r carriage return (hex 0D) |
\r carriage return (hex 0D) |
\t tab (hex 09) |
\t tab (hex 09) |
|
\0dd character with octal code 0dd |
\ddd character with octal code ddd, or backreference |
\ddd character with octal code ddd, or backreference |
|
\o{ddd..} character with octal code ddd.. |
\xhh character with hex code hh |
\xhh character with hex code hh |
\x{hhh..} character with hex code hhh.. |
\x{hhh..} character with hex code hhh.. |
|
|
|
Note that \0dd is always an octal code, and that \8 and \9 are the lit- |
|
eral characters "8" and "9". |
|
|
|
|
CHARACTER TYPES |
CHARACTER TYPES |
|
|
. any character except newline; |
. any character except newline; |
Line 6553 CHARACTER TYPES
|
Line 7681 CHARACTER TYPES
|
\V a character that is not a vertical white space character |
\V a character that is not a vertical white space character |
\w a "word" character |
\w a "word" character |
\W a "non-word" character |
\W a "non-word" character |
\X an extended Unicode sequence | \X a Unicode extended grapheme cluster |
|
|
In PCRE, by default, \d, \D, \s, \S, \w, and \W recognize only ASCII | By default, \d, \s, and \w match only ASCII characters, even in UTF-8 |
characters, even in a UTF mode. However, this can be changed by setting | mode or in the 16- bit and 32-bit libraries. However, if locale-spe- |
the PCRE_UCP option. | cific matching is happening, \s and \w may also match characters with |
| code points in the range 128-255. If the PCRE_UCP option is set, the |
| behaviour of these escape sequences is changed to use Unicode proper- |
| ties and they match many more characters. |
|
|
|
|
GENERAL CATEGORY PROPERTIES FOR \p and \P |
GENERAL CATEGORY PROPERTIES FOR \p and \P |
Line 6612 PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P
|
Line 7743 PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P
|
|
|
Xan Alphanumeric: union of properties L and N |
Xan Alphanumeric: union of properties L and N |
Xps POSIX space: property Z or tab, NL, VT, FF, CR |
Xps POSIX space: property Z or tab, NL, VT, FF, CR |
Xsp Perl space: property Z or tab, NL, FF, CR | Xsp Perl space: property Z or tab, NL, VT, FF, CR |
| Xuc Univerally-named character: one that can be |
| represented by a Universal Character Name |
Xwd Perl word: property Xan or underscore |
Xwd Perl word: property Xan or underscore |
|
|
|
Perl and POSIX space are now the same. Perl added VT to its space char- |
|
acter set at release 5.18 and PCRE changed at release 8.34. |
|
|
|
|
SCRIPT NAMES FOR \p AND \P |
SCRIPT NAMES FOR \p AND \P |
|
|
Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo, | Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo, |
Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma, | Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma, |
Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, | Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, |
Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, | Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, |
Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira- | Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira- |
gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- | gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- |
tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, | tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, |
Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, | Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, |
Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive, |
Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive, |
Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko, | Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko, |
Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic, | Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic, |
Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari- | Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari- |
tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese, | tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese, |
Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, | Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, |
Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, | Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, |
Yi. |
Yi. |
|
|
|
|
Line 6659 CHARACTER CLASSES
|
Line 7795 CHARACTER CLASSES
|
word same as \w |
word same as \w |
xdigit hexadecimal digit |
xdigit hexadecimal digit |
|
|
In PCRE, POSIX character set names recognize only ASCII characters by | In PCRE, POSIX character set names recognize only ASCII characters by |
default, but some of them use Unicode properties if PCRE_UCP is set. | default, but some of them use Unicode properties if PCRE_UCP is set. |
You can use \Q...\E inside a character class. |
You can use \Q...\E inside a character class. |
|
|
|
|
Line 6741 OPTION SETTING
|
Line 7877 OPTION SETTING
|
(?x) extended (ignore white space) |
(?x) extended (ignore white space) |
(?-...) unset option(s) |
(?-...) unset option(s) |
|
|
The following are recognized only at the start of a pattern or after | The following are recognized only at the start o The following are recognized only at the start of a pattern or after |
one of the newline-setting options with similar syntax: |
one of the newline-setting options with similar syntax: |
|
|
|
(*LIMIT_MATCH=d) set the match limit to d (decimal number) |
|
(*LIMIT_RECURSION=d) set the recursion limit to d (decimal number) |
(*NO_START_OPT) no start-match optimization (PCRE_NO_START_OPTIMIZE) |
(*NO_START_OPT) no start-match optimization (PCRE_NO_START_OPTIMIZE) |
(*UTF8) set UTF-8 mode: 8-bit library (PCRE_UTF8) |
(*UTF8) set UTF-8 mode: 8-bit library (PCRE_UTF8) |
(*UTF16) set UTF-16 mode: 16-bit library (PCRE_UTF16) |
(*UTF16) set UTF-16 mode: 16-bit library (PCRE_UTF16) |
|
(*UTF32) set UTF-32 mode: 32-bit library (PCRE_UTF32) |
|
(*UTF) set appropriate UTF mode for the library in use |
(*UCP) set PCRE_UCP (use Unicode properties for \d etc) |
(*UCP) set PCRE_UCP (use Unicode properties for \d etc) |
|
|
|
Note that LIMIT_MATCH and LIMIT_RECURSION can only reduce the value of |
|
the limits set by the caller of pcre_exec(), not increase them. |
|
|
|
|
LOOKAHEAD AND LOOKBEHIND ASSERTIONS |
LOOKAHEAD AND LOOKBEHIND ASSERTIONS |
|
|
(?=...) positive look ahead |
(?=...) positive look ahead |
Line 6835 BACKTRACKING CONTROL
|
Line 7978 BACKTRACKING CONTROL
|
NEWLINE CONVENTIONS |
NEWLINE CONVENTIONS |
|
|
These are recognized only at the very start of the pattern or after a |
These are recognized only at the very start of the pattern or after a |
(*BSR_...), (*UTF8), (*UTF16) or (*UCP) option. | (*BSR_...), (*UTF8), (*UTF16), (*UTF32) or (*UCP) option. |
|
|
(*CR) carriage return only |
(*CR) carriage return only |
(*LF) linefeed only |
(*LF) linefeed only |
Line 6873 AUTHOR
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Line 8016 AUTHOR
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REVISION |
REVISION |
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Last updated: 10 January 2012 | Last updated: 12 November 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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PCREUNICODE(3) PCREUNICODE(3) | PCREUNICODE(3) Library Functions Manual PCREUNICODE(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT |
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UTF-8, UTF-16, AND UNICODE PROPERTY SUPPORT | As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30) |
| and UTF-32 (from release 8.32), by means of two additional libraries. |
| They can be built as well as, or instead of, the 8-bit library. |
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From Release 8.30, in addition to its previous UTF-8 support, PCRE also |
|
supports UTF-16 by means of a separate 16-bit library. This can be |
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built as well as, or instead of, the 8-bit library. |
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UTF-8 SUPPORT |
UTF-8 SUPPORT |
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In order process UTF-8 strings, you must build PCRE's 8-bit library |
In order process UTF-8 strings, you must build PCRE's 8-bit library |
with UTF support, and, in addition, you must call pcre_compile() with |
with UTF support, and, in addition, you must call pcre_compile() with |
the PCRE_UTF8 option flag, or the pattern must start with the sequence |
the PCRE_UTF8 option flag, or the pattern must start with the sequence |
(*UTF8). When either of these is the case, both the pattern and any | (*UTF8) or (*UTF). When either of these is the case, both the pattern |
subject strings that are matched against it are treated as UTF-8 | and any subject strings that are matched against it are treated as |
strings instead of strings of 1-byte characters. | UTF-8 strings instead of strings of individual 1-byte characters. |
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UTF-16 SUPPORT | UTF-16 AND UTF-32 SUPPORT |
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In order process UTF-16 strings, you must build PCRE's 16-bit library | In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit |
with UTF support, and, in addition, you must call pcre16_compile() with | or 32-bit library with UTF support, and, in addition, you must call |
the PCRE_UTF16 option flag, or the pattern must start with the sequence | pcre16_compile() or pcre32_compile() with the PCRE_UTF16 or PCRE_UTF32 |
(*UTF16). When either of these is the case, both the pattern and any | option flag, as appropriate. Alternatively, the pattern must start with |
subject strings that are matched against it are treated as UTF-16 | the sequence (*UTF16), (*UTF32), as appropriate, or (*UTF), which can |
strings instead of strings of 16-bit characters. | be used with either library. When UTF mode is set, both the pattern and |
| any subject strings that are matched against it are treated as UTF-16 |
| or UTF-32 strings instead of strings of individual 16-bit or 32-bit |
| characters. |
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UTF SUPPORT OVERHEAD |
UTF SUPPORT OVERHEAD |
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If you compile PCRE with UTF support, but do not use it at run time, | If you compile PCRE with UTF support, but do not use it at run time, |
the library will be a bit bigger, but the additional run time overhead | the library will be a bit bigger, but the additional run time overhead |
is limited to testing the PCRE_UTF8/16 flag occasionally, so should not | is limited to testing the PCRE_UTF[8|16|32] flag occasionally, so |
be very big. | should not be very big. |
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UNICODE PROPERTY SUPPORT |
UNICODE PROPERTY SUPPORT |
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If PCRE is built with Unicode character property support (which implies |
If PCRE is built with Unicode character property support (which implies |
UTF support), the escape sequences \p{..}, \P{..}, and \X can be used. | UTF support), the escape sequences \p{..}, \P{..}, and \X can be used. |
The available properties that can be tested are limited to the general | The available properties that can be tested are limited to the general |
category properties such as Lu for an upper case letter or Nd for a | category properties such as Lu for an upper case letter or Nd for a |
decimal number, the Unicode script names such as Arabic or Han, and the |
decimal number, the Unicode script names such as Arabic or Han, and the |
derived properties Any and L&. A full list is given in the pcrepattern | derived properties Any and L&. Full lists is given in the pcrepattern |
documentation. Only the short names for properties are supported. For | and pcresyntax documentation. Only the short names for properties are |
example, \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not | supported. For example, \p{L} matches a letter. Its Perl synonym, |
supported. Furthermore, in Perl, many properties may optionally be | \p{Letter}, is not supported. Furthermore, in Perl, many properties |
prefixed by "Is", for compatibility with Perl 5.6. PCRE does not sup- | may optionally be prefixed by "Is", for compatibility with Perl 5.6. |
port this. | PCRE does not support this. |
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Validity of UTF-8 strings |
Validity of UTF-8 strings |
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|
When you set the PCRE_UTF8 flag, the byte strings passed as patterns | When you set the PCRE_UTF8 flag, the byte strings passed as patterns |
and subjects are (by default) checked for validity on entry to the rel- |
and subjects are (by default) checked for validity on entry to the rel- |
evant functions. The entire string is checked before any other process- |
evant functions. The entire string is checked before any other process- |
ing takes place. From release 7.3 of PCRE, the check is according the | ing takes place. From release 7.3 of PCRE, the check is according the |
rules of RFC 3629, which are themselves derived from the Unicode speci- |
rules of RFC 3629, which are themselves derived from the Unicode speci- |
fication. Earlier releases of PCRE followed the rules of RFC 2279, | fication. Earlier releases of PCRE followed the rules of RFC 2279, |
which allows the full range of 31-bit values (0 to 0x7FFFFFFF). The | which allows the full range of 31-bit values (0 to 0x7FFFFFFF). The |
current check allows only values in the range U+0 to U+10FFFF, exclud- | current check allows only values in the range U+0 to U+10FFFF, exclud- |
ing U+D800 to U+DFFF. | ing the surrogate area. (From release 8.33 the so-called "non-charac- |
| ter" code points are no longer excluded because Unicode corrigendum #9 |
| makes it clear that they should not be.) |
|
|
The excluded code points are the "Surrogate Area" of Unicode. They are | Characters in the "Surrogate Area" of Unicode are reserved for use by |
reserved for use by UTF-16, where they are used in pairs to encode | UTF-16, where they are used in pairs to encode codepoints with values |
codepoints with values greater than 0xFFFF. The code points that are | greater than 0xFFFF. The code points that are encoded by UTF-16 pairs |
encoded by UTF-16 pairs are available independently in the UTF-8 encod- | are available independently in the UTF-8 and UTF-32 encodings. (In |
ing. (In other words, the whole surrogate thing is a fudge for UTF-16 | other words, the whole surrogate thing is a fudge for UTF-16 which |
which unfortunately messes up UTF-8.) | unfortunately messes up UTF-8 and UTF-32.) |
|
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If an invalid UTF-8 string is passed to PCRE, an error return is given. |
If an invalid UTF-8 string is passed to PCRE, an error return is given. |
At compile time, the only additional information is the offset to the | At compile time, the only additional information is the offset to the |
first byte of the failing character. The run-time functions pcre_exec() |
first byte of the failing character. The run-time functions pcre_exec() |
and pcre_dfa_exec() also pass back this information, as well as a more | and pcre_dfa_exec() also pass back this information, as well as a more |
detailed reason code if the caller has provided memory in which to do | detailed reason code if the caller has provided memory in which to do |
this. |
this. |
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|
In some situations, you may already know that your strings are valid, | In some situations, you may already know that your strings are valid, |
and therefore want to skip these checks in order to improve perfor- | and therefore want to skip these checks in order to improve perfor- |
mance, for example in the case of a long subject string that is being | mance, for example in the case of a long subject string that is being |
scanned repeatedly with different patterns. If you set the | scanned repeatedly. If you set the PCRE_NO_UTF8_CHECK flag at compile |
PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE assumes | time or at run time, PCRE assumes that the pattern or subject it is |
that the pattern or subject it is given (respectively) contains only | given (respectively) contains only valid UTF-8 codes. In this case, it |
valid UTF-8 codes. In this case, it does not diagnose an invalid UTF-8 | |
string. | |
|
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If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, | Note that passing PCRE_NO_UTF8_CHECK to pcre_compile() just disables |
what happens depends on why the string is invalid. If the string con- | the check for the pattern; it does not also apply to subject strings. |
forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a | If you want to disable the check for a subject string you must pass |
string of characters in the range 0 to 0x7FFFFFFF by pcre_dfa_exec() | this option to pcre_exec() or pcre_dfa_exec(). |
and the interpreted version of pcre_exec(). In other words, apart from | |
the initial validity test, these functions (when in UTF-8 mode) handle | |
strings according to the more liberal rules of RFC 2279. However, the | |
just-in-time (JIT) optimization for pcre_exec() supports only RFC 3629. | |
If you are using JIT optimization, or if the string does not even con- | |
form to RFC 2279, the result is undefined. Your program may crash. | |
|
|
If you want to process strings of values in the full range 0 to | If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the |
0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you can | result is undefined and your program may crash. |
set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in | |
this situation, you will have to apply your own validity check, and | |
avoid the use of JIT optimization. | |
|
|
Validity of UTF-16 strings |
Validity of UTF-16 strings |
|
|
When you set the PCRE_UTF16 flag, the strings of 16-bit data units that |
When you set the PCRE_UTF16 flag, the strings of 16-bit data units that |
are passed as patterns and subjects are (by default) checked for valid- |
are passed as patterns and subjects are (by default) checked for valid- |
ity on entry to the relevant functions. Values other than those in the | ity on entry to the relevant functions. Values other than those in the |
surrogate range U+D800 to U+DFFF are independent code points. Values in |
surrogate range U+D800 to U+DFFF are independent code points. Values in |
the surrogate range must be used in pairs in the correct manner. |
the surrogate range must be used in pairs in the correct manner. |
|
|
If an invalid UTF-16 string is passed to PCRE, an error return is | If an invalid UTF-16 string is passed to PCRE, an error return is |
given. At compile time, the only additional information is the offset | given. At compile time, the only additional information is the offset |
to the first data unit of the failing character. The run-time functions |
to the first data unit of the failing character. The run-time functions |
pcre16_exec() and pcre16_dfa_exec() also pass back this information, as |
pcre16_exec() and pcre16_dfa_exec() also pass back this information, as |
|
well as a more detailed reason code if the caller has provided memory |
|
in which to do this. |
|
|
|
In some situations, you may already know that your strings are valid, |
|
and therefore want to skip these checks in order to improve perfor- |
|
mance. If you set the PCRE_NO_UTF16_CHECK flag at compile time or at |
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run time, PCRE assumes that the pattern or subject it is given (respec- |
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tively) contains only valid UTF-16 sequences. In this case, it does not |
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diagnose an invalid UTF-16 string. However, if an invalid string is |
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passed, the result is undefined. |
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|
Validity of UTF-32 strings |
|
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|
When you set the PCRE_UTF32 flag, the strings of 32-bit data units that |
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are passed as patterns and subjects are (by default) checked for valid- |
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ity on entry to the relevant functions. This check allows only values |
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in the range U+0 to U+10FFFF, excluding the surrogate area U+D800 to |
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U+DFFF. |
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|
If an invalid UTF-32 string is passed to PCRE, an error return is |
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given. At compile time, the only additional information is the offset |
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to the first data unit of the failing character. The run-time functions |
|
pcre32_exec() and pcre32_dfa_exec() also pass back this information, as |
well as a more detailed reason code if the caller has provided memory |
well as a more detailed reason code if the caller has provided memory |
in which to do this. |
in which to do this. |
|
|
In some situations, you may already know that your strings are valid, |
In some situations, you may already know that your strings are valid, |
and therefore want to skip these checks in order to improve perfor- |
and therefore want to skip these checks in order to improve perfor- |
mance. If you set the PCRE_NO_UTF16_CHECK flag at compile time or at | mance. If you set the PCRE_NO_UTF32_CHECK flag at compile time or at |
run time, PCRE assumes that the pattern or subject it is given (respec- |
run time, PCRE assumes that the pattern or subject it is given (respec- |
tively) contains only valid UTF-16 sequences. In this case, it does not | tively) contains only valid UTF-32 sequences. In this case, it does not |
diagnose an invalid UTF-16 string. | diagnose an invalid UTF-32 string. However, if an invalid string is |
| passed, the result is undefined. |
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General comments about UTF modes |
General comments about UTF modes |
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1. Codepoints less than 256 can be specified by either braced or | 1. Codepoints less than 256 can be specified in patterns by either |
unbraced hexadecimal escape sequences (for example, \x{b3} or \xb3). | braced or unbraced hexadecimal escape sequences (for example, \x{b3} or |
Larger values have to use braced sequences. | \xb3). Larger values have to use braced sequences. |
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2. Octal numbers up to \777 are recognized, and in UTF-8 mode, they | 2. Octal numbers up to \777 are recognized, and in UT 2. Octal numbers up to \777 are recognized, and in UT |
match two-byte characters for values greater than \177. |
match two-byte characters for values greater than \177. |
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3. Repeat quantifiers apply to complete UTF characters, not to individ- |
3. Repeat quantifiers apply to complete UTF characters, not to individ- |
ual data units, for example: \x{100}{3}. |
ual data units, for example: \x{100}{3}. |
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4. The dot metacharacter matches one UTF character instead of a single | 4. The dot metacharacter matches one UTF character instead of a single |
data unit. |
data unit. |
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5. The escape sequence \C can be used to match a single byte in UTF-8 | 5. The escape sequence \C can be used to match a single byte in UTF-8 |
mode, or a single 16-bit data unit in UTF-16 mode, but its use can lead | mode, or a single 16-bit data unit in UTF-16 mode, or a single 32-bit |
to some strange effects because it breaks up multi-unit characters (see | data unit in UTF-32 mode, but its use can lead to some strange effects |
the description of \C in the pcrepattern documentation). The use of \C | because it breaks up multi-unit characters (see the description of \C |
is not supported in the alternative matching function | in the pcrepattern documentation). The use of \C is not supported in |
pcre[16]_dfa_exec(), nor is it supported in UTF mode by the JIT opti- | the alternative matching function pcre[16|32]_dfa_exec(), nor is it |
mization of pcre[16]_exec(). If JIT optimization is requested for a UTF | supported in UTF mode by the JIT optimization of pcre[16|32]_exec(). If |
pattern that contains \C, it will not succeed, and so the matching will | JIT optimization is requested for a UTF pattern that contains \C, it |
be carried out by the normal interpretive function. | will not succeed, and so the matching will be carried out by the normal |
| interpretive function. |
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6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly |
6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly |
test characters of any code value, but, by default, the characters that |
test characters of any code value, but, by default, the characters that |
Line 7056 UNICODE PROPERTY SUPPORT
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Line 8219 UNICODE PROPERTY SUPPORT
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9. Case-insensitive matching applies only to characters whose values |
9. Case-insensitive matching applies only to characters whose values |
are less than 128, unless PCRE is built with Unicode property support. |
are less than 128, unless PCRE is built with Unicode property support. |
Even when Unicode property support is available, PCRE still uses its | A few Unicode characters such as Greek sigma have more than two code- |
own character tables when checking the case of low-valued characters, | points that are case-equivalent. Up to and including PCRE release 8.31, |
so as not to degrade performance. The Unicode property information is | only one-to-one case mappings were supported, but later releases (with |
used only for characters with higher values. Furthermore, PCRE supports | Unicode property support) do treat as case-equivalent all versions of |
case-insensitive matching only when there is a one-to-one mapping | characters such as Greek sigma. |
between a letter's cases. There are a small number of many-to-one map- | |
pings in Unicode; these are not supported by PCRE. | |
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AUTHOR |
AUTHOR |
Line 7074 AUTHOR
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Line 8235 AUTHOR
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REVISION |
REVISION |
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Last updated: 14 April 2012 | Last updated: 27 February 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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PCREJIT(3) PCREJIT(3) | PCREJIT(3) Library Functions Manual PCREJIT(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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PCRE JUST-IN-TIME COMPILER SUPPORT |
PCRE JUST-IN-TIME COMPILER SUPPORT |
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Just-in-time compiling is a heavyweight optimization that can greatly |
Just-in-time compiling is a heavyweight optimization that can greatly |
Line 7103 PCRE JUST-IN-TIME COMPILER SUPPORT
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Line 8264 PCRE JUST-IN-TIME COMPILER SUPPORT
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used. The code for this support was written by Zoltan Herczeg. |
used. The code for this support was written by Zoltan Herczeg. |
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8-BIT and 16-BIT SUPPORT | 8-BIT, 16-BIT AND 32-BIT SUPPORT |
|
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JIT support is available for both the 8-bit and 16-bit PCRE libraries. | JIT support is available for all of the 8-bit, 16-bit and 32-bit PCRE |
To keep this documentation simple, only the 8-bit interface is | libraries. To keep this documentation simple, only the 8-bit interface |
described in what follows. If you are using the 16-bit library, substi- | is described in what follows. If you are using the 16-bit library, sub- |
tute the 16-bit functions and 16-bit structures (for example, | stitute the 16-bit functions and 16-bit structures (for example, |
pcre16_jit_stack instead of pcre_jit_stack). | pcre16_jit_stack instead of pcre_jit_stack). If you are using the |
| 32-bit library, substitute the 32-bit functions and 32-bit structures |
| (for example, pcre32_jit_stack instead of pcre_jit_stack). |
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AVAILABILITY OF JIT SUPPORT |
AVAILABILITY OF JIT SUPPORT |
Line 7123 AVAILABILITY OF JIT SUPPORT
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Line 8286 AVAILABILITY OF JIT SUPPORT
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Intel x86 32-bit and 64-bit |
Intel x86 32-bit and 64-bit |
MIPS 32-bit |
MIPS 32-bit |
Power PC 32-bit and 64-bit |
Power PC 32-bit and 64-bit |
|
SPARC 32-bit (experimental) |
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If --enable-jit is set on an unsupported platform, compilation fails. |
If --enable-jit is set on an unsupported platform, compilation fails. |
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Line 7130 AVAILABILITY OF JIT SUPPORT
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Line 8294 AVAILABILITY OF JIT SUPPORT
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port is available by calling pcre_config() with the PCRE_CONFIG_JIT |
port is available by calling pcre_config() with the PCRE_CONFIG_JIT |
option. The result is 1 when JIT is available, and 0 otherwise. How- |
option. The result is 1 when JIT is available, and 0 otherwise. How- |
ever, a simple program does not need to check this in order to use JIT. |
ever, a simple program does not need to check this in order to use JIT. |
The API is implemented in a way that falls back to the interpretive | The normal API is implemented in a way that falls back to the interpre- |
code if JIT is not available. | tive code if JIT is not available. For programs that need the best pos- |
| sible performance, there is also a "fast path" API that is JIT-spe- |
| cific. |
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If your program may sometimes be linked with versions of PCRE that are |
If your program may sometimes be linked with versions of PCRE that are |
older than 8.20, but you want to use JIT when it is available, you can |
older than 8.20, but you want to use JIT when it is available, you can |
Line 7149 SIMPLE USE OF JIT
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Line 8315 SIMPLE USE OF JIT
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pcre_exec(). |
pcre_exec(). |
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(2) Use pcre_free_study() to free the pcre_extra block when it is |
(2) Use pcre_free_study() to free the pcre_extra block when it is |
no longer needed, instead of just freeing it yourself. This | no longer needed, instead of just freeing it yourself. This |
ensures that any JIT data is also freed. | ensures that |
| any JIT data is also freed. |
|
|
For a program that may be linked with pre-8.20 versions of PCRE, you | For a program that may be linked with pre-8.20 versions of PCRE, you |
can insert |
can insert |
|
|
#ifndef PCRE_STUDY_JIT_COMPILE |
#ifndef PCRE_STUDY_JIT_COMPILE |
#define PCRE_STUDY_JIT_COMPILE 0 |
#define PCRE_STUDY_JIT_COMPILE 0 |
#endif |
#endif |
|
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so that no option is passed to pcre_study(), and then use something | so that no opt so that no option is passed to pcre_study(), and then use something |
like this to free the study data: |
like this to free the study data: |
|
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#ifdef PCRE_CONFIG_JIT |
#ifdef PCRE_CONFIG_JIT |
Line 7168 SIMPLE USE OF JIT
|
Line 8335 SIMPLE USE OF JIT
|
pcre_free(study_ptr); |
pcre_free(study_ptr); |
#endif |
#endif |
|
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PCRE_STUDY_JIT_COMPILE requests the JIT compiler to generate code for | PCRE_STUDY_JIT_COMPILE requests the JIT compiler to generate code for |
complete matches. If you want to run partial matches using the | complete matches. If you want to run partial matches using the |
PCRE_PARTIAL_HARD or PCRE_PARTIAL_SOFT options of pcre_exec(), you | PCRE_PARTIAL_HARD or PCRE_PARTIAL_SOFT options of pcre_exec(), you |
should set one or both of the following options in addition to, or | should set one or both of the following options in addition to, or |
instead of, PCRE_STUDY_JIT_COMPILE when you call pcre_study(): |
instead of, PCRE_STUDY_JIT_COMPILE when you call pcre_study(): |
|
|
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE |
PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE |
|
|
The JIT compiler generates different optimized code for each of the | The JIT compiler generates different optimized code for each of the |
three modes (normal, soft partial, hard partial). When pcre_exec() is | three modes (normal, soft partial, hard partial). When pcre_exec() is |
called, the appropriate code is run if it is available. Otherwise, the | called, the appropriate code is run if it is available. Otherwise, the |
pattern is matched using interpretive code. |
pattern is matched using interpretive code. |
|
|
In some circumstances you may need to call additional functions. These | In some circumstances you may need to call additional functions. These |
are described in the section entitled "Controlling the JIT stack" | are described in the section entitled "Controlling the JIT stack" |
below. |
below. |
|
|
If JIT support is not available, PCRE_STUDY_JIT_COMPILE etc. are | If JIT support is not available, PCRE_STUDY_JIT_COMPILE etc. are |
ignored, and no JIT data is created. Otherwise, the compiled pattern is |
ignored, and no JIT data is created. Otherwise, the compiled pattern is |
passed to the JIT compiler, which turns it into machine code that exe- | passed to the JIT compiler, which turns it into machine code that exe- |
cutes much faster than the normal interpretive code. When pcre_exec() | cutes much faster than the normal interpretive code. When pcre_exec() |
is passed a pcre_extra block containing a pointer to JIT code of the | is passed a pcre_extra block containing a pointer to JIT code of the |
appropriate mode (normal or hard/soft partial), it obeys that code | appropriate mode (normal or hard/soft partial), it obeys that code |
instead of running the interpreter. The result is identical, but the | instead of running the interpreter. The result is identical, but the |
compiled JIT code runs much faster. |
compiled JIT code runs much faster. |
|
|
There are some pcre_exec() options that are not supported for JIT exe- | There are some pcre_exec() options that are not supported for JIT exe- |
cution. There are also some pattern items that JIT cannot handle. | cution. There are also some pattern items that JIT cannot handle. |
Details are given below. In both cases, execution automatically falls | Details are given below. In both cases, execution automatically falls |
back to the interpretive code. If you want to know whether JIT was | back to the interpretive code. If you want to know whether JIT was |
actually used for a particular match, you should arrange for a JIT | actually used for a particular match, you should arrange for a JIT |
callback function to be set up as described in the section entitled | callback function to be set up as described in the section entitled |
"Controlling the JIT stack" below, even if you do not need to supply a | "Controlling the JIT stack" below, even if you do not need to supply a |
non-default JIT stack. Such a callback function is called whenever JIT | non-default JIT stack. Such a callback function is called whenever JIT |
code is about to be obeyed. If the execution options are not right for | code is about to be obeyed. If the execution options are not right for |
JIT execution, the callback function is not obeyed. |
JIT execution, the callback function is not obeyed. |
|
|
If the JIT compiler finds an unsupported item, no JIT data is gener- | If the JIT compiler finds an unsupported item, no JIT data is gener- |
ated. You can find out if JIT execution is available after studying a | ated. You can find out if JIT execution is available after studying a |
pattern by calling pcre_fullinfo() with the PCRE_INFO_JIT option. A | pattern by calling pcre_fullinfo() with the PCRE_INFO_JIT option. A |
result of 1 means that JIT compilation was successful. A result of 0 | result of 1 means that JIT compilation was successful. A result of 0 |
means that JIT support is not available, or the pattern was not studied |
means that JIT support is not available, or the pattern was not studied |
with PCRE_STUDY_JIT_COMPILE etc., or the JIT compiler was not able to | with PCRE_STUDY_JIT_COMPILE etc., or the JIT compiler was not able to |
handle the pattern. |
handle the pattern. |
|
|
Once a pattern has been studied, with or without JIT, it can be used as |
Once a pattern has been studied, with or without JIT, it can be used as |
Line 7220 SIMPLE USE OF JIT
|
Line 8387 SIMPLE USE OF JIT
|
|
|
UNSUPPORTED OPTIONS AND PATTERN ITEMS |
UNSUPPORTED OPTIONS AND PATTERN ITEMS |
|
|
The only pcre_exec() options that are supported for JIT execution are | The only pcre_exec() options that are supported for JIT execution are |
PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, | PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK, PCRE_NO_UTF32_CHECK, PCRE_NOT- |
PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PAR- | BOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PAR- |
TIAL_SOFT. | TIAL_HARD, and PCRE_PARTIAL_SOFT. |
|
|
The unsupported pattern items are: | The only unsupported pattern items are \C (match a single data unit) |
| when running in a UTF mode, and a callout immediately before an asser- |
| tion condition in a conditional group. |
|
|
\C match a single byte; not supported in UTF-8 mode |
|
(?Cn) callouts |
|
(*PRUNE) ) |
|
(*SKIP) ) backtracking control verbs |
|
(*THEN) ) |
|
|
|
Support for some of these may be added in future. |
|
|
|
|
|
RETURN VALUES FROM JIT EXECUTION |
RETURN VALUES FROM JIT EXECUTION |
|
|
When a pattern is matched using JIT execution, the return values are | When a pattern is matched using JIT execution, the return values are |
the same as those given by the interpretive pcre_exec() code, with the | the same as those given by the interpretive pcre_exec() code, with the |
addition of one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means | addition of one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means |
that the memory used for the JIT stack was insufficient. See "Control- | that the memory used for the JIT stack was insufficient. See "Control- |
ling the JIT stack" below for a discussion of JIT stack usage. For com- |
ling the JIT stack" below for a discussion of JIT stack usage. For com- |
patibility with the interpretive pcre_exec() code, no more than two- | patibility with the interpretive pcre_exec() code, no more than two- |
thirds of the ovector argument is used for passing back captured sub- | thirds of the ovector argument is used for passing back captured sub- |
strings. |
strings. |
|
|
The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if | The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if |
searching a very large pattern tree goes on for too long, as it is in | searching a very large pattern tree goes on for too long, as it is in |
the same circumstance when JIT is not used, but the details of exactly | the same circumstance when JIT is not used, but the details of exactly |
what is counted are not the same. The PCRE_ERROR_RECURSIONLIMIT error | what is counted are not the same. The PCRE_ERROR_RECURSIONLIMIT error |
code is never returned by JIT execution. |
code is never returned by JIT execution. |
|
|
|
|
SAVING AND RESTORING COMPILED PATTERNS |
SAVING AND RESTORING COMPILED PATTERNS |
|
|
The code that is generated by the JIT compiler is architecture-spe- | The code that is generated by the JIT compiler is architecture-spe- |
cific, and is also position dependent. For those reasons it cannot be | cific, and is also position dependent. For those reasons it cannot be |
saved (in a file or database) and restored later like the bytecode and | saved (in a file or database) and restored later like the bytecode and |
other data of a compiled pattern. Saving and restoring compiled pat- | other data of a compiled pattern. Saving and restoring compiled pat- |
terns is not something many people do. More detail about this facility | terns is not something many people do. More detail about this facility |
is given in the pcreprecompile documentation. It should be possible to | is given in the pcreprecompile documentation. It should be possible to |
run pcre_study() on a saved and restored pattern, and thereby recreate | run pcre_study() on a saved and restored pattern, and thereby recreate |
the JIT data, but because JIT compilation uses significant resources, | the JIT data, but because JIT compilation uses significant resources, |
it is probably not worth doing this; you might as well recompile the | it is probably not worth doing this; you might as well recompile the |
original pattern. |
original pattern. |
|
|
|
|
CONTROLLING THE JIT STACK |
CONTROLLING THE JIT STACK |
|
|
When the compiled JIT code runs, it needs a block of memory to use as a |
When the compiled JIT code runs, it needs a block of memory to use as a |
stack. By default, it uses 32K on the machine stack. However, some | stack. By default, it uses 32K on the machine stack. However, some |
large or complicated patterns need more than this. The error | large or complicated patterns need more than this. The error |
PCRE_ERROR_JIT_STACKLIMIT is given when there is not enough stack. | PCRE_ERROR_JIT_STACKLIMIT is given when there is not enough stack. |
Three functions are provided for managing blocks of memory for use as | Three functions are provided for managing blocks of memory for use as |
JIT stacks. There is further discussion about the use of JIT stacks in | JIT stacks. There is further discussion about the use of JIT stacks in |
the section entitled "JIT stack FAQ" below. |
the section entitled "JIT stack FAQ" below. |
|
|
The pcre_jit_stack_alloc() function creates a JIT stack. Its arguments | The pcre_jit_stack_alloc() function creates a JIT stack. Its arguments |
are a starting size and a maximum size, and it returns a pointer to an | are a starting size and a maximum size, and it returns a pointer to an |
opaque structure of type pcre_jit_stack, or NULL if there is an error. | opaque structure of type pcre_jit_stack, or NULL if there is an error. |
The pcre_jit_stack_free() function can be used to free a stack that is | The pcre_jit_stack_free() function can be used to free a stack that is |
no longer needed. (For the technically minded: the address space is | no longer needed. (For the technically minded: the address space is |
allocated by mmap or VirtualAlloc.) |
allocated by mmap or VirtualAlloc.) |
|
|
JIT uses far less memory for recursion than the interpretive code, and | JIT uses far less memory for recursion than the interpretive code, and |
a maximum stack size of 512K to 1M should be more than enough for any | a maximum stack size of 512K to 1M should be more than enough for any |
pattern. |
pattern. |
|
|
The pcre_assign_jit_stack() function specifies which stack JIT code | The pcre_assign_jit_stack() function specifies which stack JIT code |
should use. Its arguments are as follows: |
should use. Its arguments are as follows: |
|
|
pcre_extra *extra |
pcre_extra *extra |
pcre_jit_callback callback |
pcre_jit_callback callback |
void *data |
void *data |
|
|
The extra argument must be the result of studying a pattern with | The extra argument must be the result of studying a patter The extra argument must be the result of studying a patter |
PCRE_STUDY_JIT_COMPILE etc. There are three cases for the values of the |
PCRE_STUDY_JIT_COMPILE etc. There are three cases for the values of the |
other two options: |
other two options: |
|
|
Line 7313 CONTROLLING THE JIT STACK
|
Line 8474 CONTROLLING THE JIT STACK
|
return value must be a valid JIT stack, the result of calling |
return value must be a valid JIT stack, the result of calling |
pcre_jit_stack_alloc(). |
pcre_jit_stack_alloc(). |
|
|
A callback function is obeyed whenever JIT code is about to be run; it | A callback function is obeyed whenever JIT code is about to be run; it |
is not obeyed when pcre_exec() is called with options that are incom- | is not obeyed when pcre_exec() is called with options that are incom- |
patible for JIT execution. A callback function can therefore be used to |
patible for JIT execution. A callback function can therefore be used to |
determine whether a match operation was executed by JIT or by the | determine whether a match operation was executed by JIT or by the |
interpreter. |
interpreter. |
|
|
You may safely use the same JIT stack for more than one pattern (either |
You may safely use the same JIT stack for more than one pattern (either |
by assigning directly or by callback), as long as the patterns are all | by assigning directly or by callback), as long as the patterns are all |
matched sequentially in the same thread. In a multithread application, | matched sequentially in the same thread. In a multithread application, |
if you do not specify a JIT stack, or if you assign or pass back NULL | if you do not specify a JIT stack, or if you assign or pass back NULL |
from a callback, that is thread-safe, because each thread has its own | from a callback, that is thread-safe, because each thread has its own |
machine stack. However, if you assign or pass back a non-NULL JIT | machine stack. However, if you assign or pass back a non-NULL JIT |
stack, this must be a different stack for each thread so that the | stack, this must be a different stack for each thread so that the |
application is thread-safe. |
application is thread-safe. |
|
|
Strictly speaking, even more is allowed. You can assign the same non- | Strictly speaking, even more is allowed. You can assign the same non- |
NULL stack to any number of patterns as long as they are not used for | NULL stack to any number of patterns as long as they are not used for |
matching by multiple threads at the same time. For example, you can | matching by multiple threads at the same time. For example, you can |
assign the same stack to all compiled patterns, and use a global mutex | assign the same stack to all compiled patterns, and use a global mutex |
in the callback to wait until the stack is available for use. However, | in the callback to wait until the stack is available for use. However, |
this is an inefficient solution, and not recommended. |
this is an inefficient solution, and not recommended. |
|
|
This is a suggestion for how a multithreaded program that needs to set | This is a suggestion for how a multithreaded program that needs to set |
up non-default JIT stacks might operate: |
up non-default JIT stacks might operate: |
|
|
During thread initalization |
During thread initalization |
Line 7347 CONTROLLING THE JIT STACK
|
Line 8508 CONTROLLING THE JIT STACK
|
Use a one-line callback function |
Use a one-line callback function |
return thread_local_var |
return thread_local_var |
|
|
All the functions described in this section do nothing if JIT is not | All the functions described in this section do nothing if JIT is not |
available, and pcre_assign_jit_stack() does nothing unless the extra | available, and pcre_assign_jit_stack() does nothing unless the extra |
argument is non-NULL and points to a pcre_extra block that is the | argument is non-NULL and points to a pcre_extra block that is the |
result of a successful study with PCRE_STUDY_JIT_COMPILE etc. |
result of a successful study with PCRE_STUDY_JIT_COMPILE etc. |
|
|
|
|
Line 7357 JIT STACK FAQ
|
Line 8518 JIT STACK FAQ
|
|
|
(1) Why do we need JIT stacks? |
(1) Why do we need JIT stacks? |
|
|
PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack | PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack |
where the local data of the current node is pushed before checking its | where the local data of the current node is pushed before checking its |
child nodes. Allocating real machine stack on some platforms is diffi- |
child nodes. Allocating real machine stack on some platforms is diffi- |
cult. For example, the stack chain needs to be updated every time if we |
cult. For example, the stack chain needs to be updated every time if we |
extend the stack on PowerPC. Although it is possible, its updating | extend the stack on PowerPC. Although it is possible, its updating |
time overhead decreases performance. So we do the recursion in memory. |
time overhead decreases performance. So we do the recursion in memory. |
|
|
(2) Why don't we simply allocate blocks of memory with malloc()? |
(2) Why don't we simply allocate blocks of memory with malloc()? |
|
|
Modern operating systems have a nice feature: they can reserve an | Modern operating systems have a nice feature: they can reserve an |
address space instead of allocating memory. We can safely allocate mem- |
address space instead of allocating memory. We can safely allocate mem- |
ory pages inside this address space, so the stack could grow without | ory pages inside this address space, so the stack could grow without |
moving memory data (this is important because of pointers). Thus we can |
moving memory data (this is important because of pointers). Thus we can |
allocate 1M address space, and use only a single memory page (usually | allocate 1M address space, and use only a single memory page (usually |
4K) if that is enough. However, we can still grow up to 1M anytime if | 4K) if that is enough. However, we can still grow up to 1M anytime if |
needed. |
needed. |
|
|
(3) Who "owns" a JIT stack? |
(3) Who "owns" a JIT stack? |
|
|
The owner of the stack is the user program, not the JIT studied pattern |
The owner of the stack is the user program, not the JIT studied pattern |
or anything else. The user program must ensure that if a stack is used | or anything else. The user program must ensure that if a stack is used |
by pcre_exec(), (that is, it is assigned to the pattern currently run- | by pcre_exec(), (that is, it is assigned to the pattern currently run- |
ning), that stack must not be used by any other threads (to avoid over- |
ning), that stack must not be used by any other threads (to avoid over- |
writing the same memory area). The best practice for multithreaded pro- |
writing the same memory area). The best practice for multithreaded pro- |
grams is to allocate a stack for each thread, and return this stack | grams is to allocate a stack for each thread, and return this stack |
through the JIT callback function. |
through the JIT callback function. |
|
|
(4) When should a JIT stack be freed? |
(4) When should a JIT stack be freed? |
|
|
You can free a JIT stack at any time, as long as it will not be used by |
You can free a JIT stack at any time, as long as it will not be used by |
pcre_exec() again. When you assign the stack to a pattern, only a | pcre_exec() again. When you assign the stack to a pattern, only a |
pointer is set. There is no reference counting or any other magic. You | pointer is set. There is no reference counting or any other magic. You |
can free the patterns and stacks in any order, anytime. Just do not | can free the patterns and stacks in any order, anytime. Just do not |
call pcre_exec() with a pattern pointing to an already freed stack, as | call pcre_exec() with a pattern pointing to an already freed stack, as |
that will cause SEGFAULT. (Also, do not free a stack currently used by | that will cause SEGFAULT. (Also, do not free a stack currently used by |
pcre_exec() in another thread). You can also replace the stack for a | pcre_exec() in another thread). You can also replace the stack for a |
pattern at any time. You can even free the previous stack before | pattern at any time. You can even free the previous stack before |
assigning a replacement. |
assigning a replacement. |
|
|
(5) Should I allocate/free a stack every time before/after calling | (5) Should I allocate/free a stack every time before/after calling |
pcre_exec()? |
pcre_exec()? |
|
|
No, because this is too costly in terms of resources. However, you | No, because this is too costly in terms of resources. However, you |
could implement some clever idea which release the stack if it is not | could implement some clever idea which release the stack if it is not |
used in let's say two minutes. The JIT callback can help to achive this | used in let's say two minutes. The JIT callback can help to achieve |
without keeping a list of the currently JIT studied patterns. | this without keeping a list of the currently JIT studied patterns. |
|
|
(6) OK, the stack is for long term memory allocation. But what happens | (6) OK, the stack is for long term memory allocation. But what happens |
if a pattern causes stack overflow with a stack of 1M? Is that 1M kept | if a pattern causes stack overflow with a stack of 1M? Is that 1M kept |
until the stack is freed? |
until the stack is freed? |
|
|
Especially on embedded sytems, it might be a good idea to release mem- | Especially on embedded sytems, it might be a good idea to release mem- |
ory sometimes without freeing the stack. There is no API for this at | ory sometimes without freeing the stack. There is no API for this at |
the moment. Probably a function call which returns with the currently | the moment. Probably a function call which returns with the currently |
allocated memory for any stack and another which allows releasing mem- | allocated memory for any stack and another which allows releasing mem- |
ory (shrinking the stack) would be a good idea if someone needs this. |
ory (shrinking the stack) would be a good idea if someone needs this. |
|
|
(7) This is too much of a headache. Isn't there any better solution for |
(7) This is too much of a headache. Isn't there any better solution for |
JIT stack handling? |
JIT stack handling? |
|
|
No, thanks to Windows. If POSIX threads were used everywhere, we could | No, thanks to Windows. If POSIX threads were used everywhere, we could |
throw out this complicated API. |
throw out this complicated API. |
|
|
|
|
EXAMPLE CODE |
EXAMPLE CODE |
|
|
This is a single-threaded example that specifies a JIT stack without | This is a single-threaded example that specifies a JIT stack without |
using a callback. |
using a callback. |
|
|
int rc; |
int rc; |
Line 7445 EXAMPLE CODE
|
Line 8606 EXAMPLE CODE
|
pcre_jit_stack_free(jit_stack); |
pcre_jit_stack_free(jit_stack); |
|
|
|
|
|
JIT FAST PATH API |
|
|
|
Because the API described above falls back to interpreted execution |
|
when JIT is not available, it is convenient for programs that are writ- |
|
ten for general use in many environments. However, calling JIT via |
|
pcre_exec() does have a performance impact. Programs that are written |
|
for use where JIT is known to be available, and which need the best |
|
possible performance, can instead use a "fast path" API to call JIT |
|
execution directly instead of calling pcre_exec() (obviously only for |
|
patterns that have been successfully studied by JIT). |
|
|
|
The fast path function is called pcre_jit_exec(), and it takes exactly |
|
the same arguments as pcre_exec(), plus one additional argument that |
|
must point to a JIT stack. The JIT stack arrangements described above |
|
do not apply. The return values are the same as for pcre_exec(). |
|
|
|
When you call pcre_exec(), as well as testing for invalid options, a |
|
number of other sanity checks are performed on the arguments. For exam- |
|
ple, if the subject pointer is NULL, or its length is negative, an |
|
immediate error is given. Also, unless PCRE_NO_UTF[8|16|32] is set, a |
|
UTF subject string is tested for validity. In the interests of speed, |
|
these checks do not happen on the JIT fast path, and if invalid data is |
|
passed, the result is undefined. |
|
|
|
Bypassing the sanity checks and the pcre_exec() wrapping can give |
|
speedups of more than 10%. |
|
|
|
|
SEE ALSO |
SEE ALSO |
|
|
pcreapi(3) |
pcreapi(3) |
Line 7459 AUTHOR
|
Line 8648 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 04 May 2012 | Last updated: 17 March 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREPARTIAL(3) PCREPARTIAL(3) | PCREPARTIAL(3) Library Functions Manual PCREPARTIAL(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
PARTIAL MATCHING IN PCRE |
PARTIAL MATCHING IN PCRE |
|
|
In normal use of PCRE, if the subject string that is passed to a match- |
In normal use of PCRE, if the subject string that is passed to a match- |
Line 7504 PARTIAL MATCHING IN PCRE
|
Line 8693 PARTIAL MATCHING IN PCRE
|
precedence. |
precedence. |
|
|
If you want to use partial matching with just-in-time optimized code, |
If you want to use partial matching with just-in-time optimized code, |
you must call pcre_study() or pcre16_study() with one or both of these | you must call pcre_study(), pcre16_study() or pcre32_study() with one |
options: | or both of these options: |
|
|
PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE |
PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE |
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
Line 7524 PARTIAL MATCHING IN PCRE
|
Line 8713 PARTIAL MATCHING IN PCRE
|
abled for partial matching. |
abled for partial matching. |
|
|
|
|
PARTIAL MATCHING USING pcre_exec() OR pcre16_exec() | PARTIAL MATCHING USING pcre_exec() OR pcre[16|32]_exec() |
|
|
A partial match occurs during a call to pcre_exec() or pcre16_exec() | A partial match occurs during a call to pcre_exec() or |
when the end of the subject string is reached successfully, but match- | pcre[16|32]_exec() when the end of the subject string is reached suc- |
ing cannot continue because more characters are needed. However, at | cessfully, but matching cannot continue because more characters are |
least one character in the subject must have been inspected. This char- | needed. However, at least one character in the subject must have been |
acter need not form part of the final matched string; lookbehind asser- | inspected. This character need not form part of the final matched |
tions and the \K escape sequence provide ways of inspecting characters | string; lookbehind assertions and the \K escape sequence provide ways |
before the start of a matched substring. The requirement for inspecting | of inspecting characters before the start of a matched substring. The |
at least one character exists because an empty string can always be | requirement for inspecting at least one character exists because an |
matched; without such a restriction there would always be a partial | empty string can always be matched; without such a restriction there |
match of an empty string at the end of the subject. | would always be a partial match of an empty string at the end of the |
| subject. |
|
|
If there are at least two slots in the offsets vector when a partial | If there are at least two slots in the offsets vector when a partial |
match is returned, the first slot is set to the offset of the earliest | match is returned, the first slot is set to the offset of the earliest |
character that was inspected. For convenience, the second offset points |
character that was inspected. For convenience, the second offset points |
to the end of the subject so that a substring can easily be identified. |
to the end of the subject so that a substring can easily be identified. |
|
If there are at least three slots in the offsets vector, the third slot |
|
is set to the offset of the character where matching started. |
|
|
For the majority of patterns, the first offset identifies the start of | For the majority of patterns, the contents of the first and third slots |
the partially matched string. However, for patterns that contain look- | will be the same. However, for patterns that contain lookbehind asser- |
behind assertions, or \K, or begin with \b or \B, earlier characters | tions, or begin with \b or \B, characters before the one where matching |
have been inspected while carrying out the match. For example: | started may have been inspected while carrying out the match. For exam- |
| ple, consider this pattern: |
|
|
/(?<=abc)123/ |
/(?<=abc)123/ |
|
|
This pattern matches "123", but only if it is preceded by "abc". If the |
This pattern matches "123", but only if it is preceded by "abc". If the |
subject string is "xyzabc12", the offsets after a partial match are for | subject string is "xyzabc12", the first two offsets after a partial |
the substring "abc12", because all these characters are needed if | match are for the substring "abc12", because all these characters were |
another match is tried with extra characters added to the subject. | inspected. However, the third offset is set to 6, because that is the |
| offset where matching began. |
|
|
What happens when a partial match is identified depends on which of the |
What happens when a partial match is identified depends on which of the |
two partial matching options are set. |
two partial matching options are set. |
|
|
PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre16_exec() | PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre[16|32]_exec() |
|
|
If PCRE_PARTIAL_SOFT is set when pcre_exec() or pcre16_exec() identi- | If PCRE_PARTIAL_SOFT is set when pcre_exec() or pcre[16|32]_exec() |
fies a partial match, the partial match is remembered, but matching | identifies a partial match, the partial match is remembered, but match- |
continues as normal, and other alternatives in the pattern are tried. | ing continues as normal, and other alternatives in the pattern are |
If no complete match can be found, PCRE_ERROR_PARTIAL is returned | tried. If no complete match can be found, PCRE_ERROR_PARTIAL is |
instead of PCRE_ERROR_NOMATCH. | returned instead of PCRE_ERROR_NOMATCH. |
|
|
This option is "soft" because it prefers a complete match over a par- | This option is "soft" because it prefers a complete match over a par- |
tial match. All the various matching items in a pattern behave as if | tial match. All the various matching items in a pattern behave as if |
the subject string is potentially complete. For example, \z, \Z, and $ | the subject string is potentially complete. For example, \z, \Z, and $ |
match at the end of the subject, as normal, and for \b and \B the end | match at the end of the subject, as normal, and for \b and \B the end |
of the subject is treated as a non-alphanumeric. |
of the subject is treated as a non-alphanumeric. |
|
|
If there is more than one partial match, the first one that was found | If there is more than one partial match, the first one that was found |
provides the data that is returned. Consider this pattern: |
provides the data that is returned. Consider this pattern: |
|
|
/123\w+X|dogY/ |
/123\w+X|dogY/ |
|
|
If this is matched against the subject string "abc123dog", both alter- | If this is matched against the subject string "abc123dog", both alter- |
natives fail to match, but the end of the subject is reached during | natives fail to match, but the end of the subject is reached during |
matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3 | matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3 |
and 9, identifying "123dog" as the first partial match that was found. | and 9, identifying "123dog" as the first partial match that was found. |
(In this example, there are two partial matches, because "dog" on its | (In this example, there are two partial matches, because "dog" on its |
own partially matches the second alternative.) |
own partially matches the second alternative.) |
|
|
PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre16_exec() | PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre[16|32]_exec() |
|
|
If PCRE_PARTIAL_HARD is set for pcre_exec() or pcre16_exec(), | If PCRE_PARTIAL_HARD is set for pcre_exec() or pcre[16|32]_exec(), |
PCRE_ERROR_PARTIAL is returned as soon as a partial match is found, | PCRE_ERROR_PARTIAL is returned as soon as a partial match is found, |
without continuing to search for possible complete matches. This option |
without continuing to search for possible complete matches. This option |
is "hard" because it prefers an earlier partial match over a later com- |
is "hard" because it prefers an earlier partial match over a later com- |
plete match. For this reason, the assumption is made that the end of | plete match. For this reason, the assumption is made that the end of |
the supplied subject string may not be the true end of the available | the supplied subject string may not be the true end of the available |
data, and so, if \z, \Z, \b, \B, or $ are encountered at the end of the |
data, and so, if \z, \Z, \b, \B, or $ are encountered at the end of the |
subject, the result is PCRE_ERROR_PARTIAL, provided that at least one | subject, the result is PCRE_ERROR_PARTIAL, provided that at least one |
character in the subject has been inspected. |
character in the subject has been inspected. |
|
|
Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16 subject |
Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16 subject |
strings are checked for validity. Normally, an invalid sequence causes | strings are checked for validity. Normally, an invalid sequence causes |
the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the | the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the |
special case of a truncated character at the end of the subject, | special case of a truncated character at the end of the subject, |
PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when | PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when |
PCRE_PARTIAL_HARD is set. |
PCRE_PARTIAL_HARD is set. |
|
|
Comparing hard and soft partial matching |
Comparing hard and soft partial matching |
|
|
The difference between the two partial matching options can be illus- | The difference between the two partial matching options can be illus- |
trated by a pattern such as: |
trated by a pattern such as: |
|
|
/dog(sbody)?/ |
/dog(sbody)?/ |
|
|
This matches either "dog" or "dogsbody", greedily (that is, it prefers | This matches either "dog" or "dogsbody", greedily (that is, it prefers |
the longer string if possible). If it is matched against the string | the longer string if possible). If it is matched against the string |
"dog" with PCRE_PARTIAL_SOFT, it yields a complete match for "dog". | "dog" with PCRE_PARTIAL_SOFT, it yields a complete match for "dog". |
However, if PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL. |
However, if PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL. |
On the other hand, if the pattern is made ungreedy the result is dif- | On the other hand, if the pattern is made ungreedy the result is dif- |
ferent: |
ferent: |
|
|
/dog(sbody)??/ |
/dog(sbody)??/ |
|
|
In this case the result is always a complete match because that is | In this case the result is always a complete match because that is |
found first, and matching never continues after finding a complete | found first, and matching never continues after finding a complete |
match. It might be easier to follow this explanation by thinking of the |
match. It might be easier to follow this explanation by thinking of the |
two patterns like this: |
two patterns like this: |
|
|
/dog(sbody)?/ is the same as /dogsbody|dog/ |
/dog(sbody)?/ is the same as /dogsbody|dog/ |
/dog(sbody)??/ is the same as /dog|dogsbody/ |
/dog(sbody)??/ is the same as /dog|dogsbody/ |
|
|
The second pattern will never match "dogsbody", because it will always | The second pattern will never match "dogsbody", because it will always |
find the shorter match first. |
find the shorter match first. |
|
|
|
|
PARTIAL MATCHING USING pcre_dfa_exec() OR pcre16_dfa_exec() | PARTIAL MATCHING USING pcre_dfa_exec() OR pcre[16|32]_dfa_exec() |
|
|
The DFA functions move along the subject string character by character, |
The DFA functions move along the subject string character by character, |
without backtracking, searching for all possible matches simultane- | without backtracking, searching for all possible matches simultane- |
ously. If the end of the subject is reached before the end of the pat- | ously. If the end of the subject is reached before the end of the pat- |
tern, there is the possibility of a partial match, again provided that | tern, there is the possibility of a partial match, again provided that |
at least one character has been inspected. |
at least one character has been inspected. |
|
|
When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if | When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if |
there have been no complete matches. Otherwise, the complete matches | there have been no complete matches. Otherwise, the complete matches |
are returned. However, if PCRE_PARTIAL_HARD is set, a partial match | are returned. However, if PCRE_PARTIAL_HARD is set, a partial match |
takes precedence over any complete matches. The portion of the string | takes precedence over any complete matches. The portion of the string |
that was inspected when the longest partial match was found is set as | that was inspected when the longest partial match was found is set as |
the first matching string, provided there are at least two slots in the |
the first matching string, provided there are at least two slots in the |
offsets vector. |
offsets vector. |
|
|
Because the DFA functions always search for all possible matches, and | Because the DFA functions always search for all possible matches, and |
there is no difference between greedy and ungreedy repetition, their | there is no difference between greedy and ungreedy repetition, their |
behaviour is different from the standard functions when PCRE_PAR- | behaviour is different from the standard functions when PCRE_PAR- |
TIAL_HARD is set. Consider the string "dog" matched against the | TIAL_HARD is set. Consider the string "dog" matched against the |
ungreedy pattern shown above: |
ungreedy pattern shown above: |
|
|
/dog(sbody)??/ |
/dog(sbody)??/ |
|
|
Whereas the standard functions stop as soon as they find the complete | Whereas the standard functions stop as soon as they find the complete |
match for "dog", the DFA functions also find the partial match for | match for "dog", the DFA functions also find the partial match for |
"dogsbody", and so return that when PCRE_PARTIAL_HARD is set. |
"dogsbody", and so return that when PCRE_PARTIAL_HARD is set. |
|
|
|
|
PARTIAL MATCHING AND WORD BOUNDARIES |
PARTIAL MATCHING AND WORD BOUNDARIES |
|
|
If a pattern ends with one of sequences \b or \B, which test for word | If a pattern ends with one of sequences \b or \B, which test for word |
boundaries, partial matching with PCRE_PARTIAL_SOFT can give counter- | boundaries, partial matching with PCRE_PARTIAL_SOFT can give counter- |
intuitive results. Consider this pattern: |
intuitive results. Consider this pattern: |
|
|
/\bcat\b/ |
/\bcat\b/ |
|
|
This matches "cat", provided there is a word boundary at either end. If |
This matches "cat", provided there is a word boundary at either end. If |
the subject string is "the cat", the comparison of the final "t" with a |
the subject string is "the cat", the comparison of the final "t" with a |
following character cannot take place, so a partial match is found. | following character cannot take place, so a partial match is found. |
However, normal matching carries on, and \b matches at the end of the | However, normal matching carries on, and \b matches at the end of the |
subject when the last character is a letter, so a complete match is | subject when the last character is a letter, so a complete match is |
found. The result, therefore, is not PCRE_ERROR_PARTIAL. Using | found. The result, therefore, is not PCRE_ERROR_PARTIAL. Using |
PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because | PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because |
then the partial match takes precedence. |
then the partial match takes precedence. |
|
|
|
|
FORMERLY RESTRICTED PATTERNS |
FORMERLY RESTRICTED PATTERNS |
|
|
For releases of PCRE prior to 8.00, because of the way certain internal |
For releases of PCRE prior to 8.00, because of the way certain internal |
optimizations were implemented in the pcre_exec() function, the | optimizations were implemented in the pcre_exec() function, the |
PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be | PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be |
used with all patterns. From release 8.00 onwards, the restrictions no | used with all patterns. From release 8.00 onwards, the restrictions no |
longer apply, and partial matching with can be requested for any pat- | longer apply, and partial matching with can be requested for any pat- |
tern. |
tern. |
|
|
Items that were formerly restricted were repeated single characters and |
Items that were formerly restricted were repeated single characters and |
repeated metasequences. If PCRE_PARTIAL was set for a pattern that did | repeated metasequences. If PCRE_PARTIAL was set for a pattern that did |
not conform to the restrictions, pcre_exec() returned the error code | not conform to the restrictions, pcre_exec() returned the error code |
PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The | PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The |
PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if a compiled | PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if a compiled |
pattern can be used for partial matching now always returns 1. |
pattern can be used for partial matching now always returns 1. |
|
|
|
|
EXAMPLE OF PARTIAL MATCHING USING PCRETEST |
EXAMPLE OF PARTIAL MATCHING USING PCRETEST |
|
|
If the escape sequence \P is present in a pcretest data line, the | If the escape sequence \P is present in a pcretest data line, the |
PCRE_PARTIAL_SOFT option is used for the match. Here is a run of | PCRE_PARTIAL_SOFT option is used for the match. Here is a run of |
pcretest that uses the date example quoted above: |
pcretest that uses the date example quoted above: |
|
|
re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ |
re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ |
Line 7713 EXAMPLE OF PARTIAL MATCHING USING PCRETEST
|
Line 8907 EXAMPLE OF PARTIAL MATCHING USING PCRETEST
|
data> j\P |
data> j\P |
No match |
No match |
|
|
The first data string is matched completely, so pcretest shows the | The first data string is matched completely, so pcretest shows the |
matched substrings. The remaining four strings do not match the com- | matched substrings. The remaining four strings do not match the com- |
plete pattern, but the first two are partial matches. Similar output is |
plete pattern, but the first two are partial matches. Similar output is |
obtained if DFA matching is used. |
obtained if DFA matching is used. |
|
|
If the escape sequence \P is present more than once in a pcretest data | If the escape sequence \P is present more than once in a pcretest data |
line, the PCRE_PARTIAL_HARD option is set for the match. |
line, the PCRE_PARTIAL_HARD option is set for the match. |
|
|
|
|
MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_dfa_exec() | MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre[16|32]_dfa_exec() |
|
|
When a partial match has been found using a DFA matching function, it | When a partial match has been found using a DFA matching function, it |
is possible to continue the match by providing additional subject data | is possible to continue the match by providing additional subject data |
and calling the function again with the same compiled regular expres- | and calling the function again with the same compiled regular expres- |
sion, this time setting the PCRE_DFA_RESTART option. You must pass the | sion, this time setting the PCRE_DFA_RESTART option. You must pass the |
same working space as before, because this is where details of the pre- |
same working space as before, because this is where details of the pre- |
vious partial match are stored. Here is an example using pcretest, | vious partial match are stored. Here is an example using pcretest, |
using the \R escape sequence to set the PCRE_DFA_RESTART option (\D | using the \R escape sequence to set the PCRE_DFA_RESTART option (\D |
specifies the use of the DFA matching function): |
specifies the use of the DFA matching function): |
|
|
re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ |
re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ |
Line 7739 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_
|
Line 8933 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_
|
data> n05\R\D |
data> n05\R\D |
0: n05 |
0: n05 |
|
|
The first call has "23ja" as the subject, and requests partial match- | The first call has "23ja" as the subject, and requests partial match- |
ing; the second call has "n05" as the subject for the continued | ing; the second call has "n05" as the subject for the continued |
(restarted) match. Notice that when the match is complete, only the | (restarted) match. Notice that when the match is complete, only the |
last part is shown; PCRE does not retain the previously partially- | last part is shown; PCRE does not retain the previously partially- |
matched string. It is up to the calling program to do that if it needs | matched string. It is up to the calling program to do that if it needs |
to. |
to. |
|
|
You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with | That means that, for an unanchored pattern, if a continued match fails, |
PCRE_DFA_RESTART to continue partial matching over multiple segments. | it is not possible to try again at a new starting point. All this |
This facility can be used to pass very long subject strings to the DFA | facility is capable of doing is continuing with the previous match |
| attempt. In the previous example, if the second set of data is "ug23" |
| the result is no match, even though there would be a match for "aug23" |
| if the entire string were given at once. Depending on the application, |
| this may or may not be what you want. The only way to allow for start- |
| ing again at the next character is to retain the matched part of the |
| subject and try a new complete match. |
| |
| You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with |
| PCRE_DFA_RESTART to continue partial matching over multiple segments. |
| This facility can be used to pass very long subject strings to the DFA |
matching functions. |
matching functions. |
|
|
|
|
MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre16_exec() | MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre[16|32]_exec() |
|
|
From release 8.00, the standard matching functions can also be used to | From release 8.00, the standard matching functions can also be used to |
do multi-segment matching. Unlike the DFA functions, it is not possible |
do multi-segment matching. Unlike the DFA functions, it is not possible |
to restart the previous match with a new segment of data. Instead, new | to restart the previous match with a new segment of data. Instead, new |
data must be added to the previous subject string, and the entire match |
data must be added to the previous subject string, and the entire match |
re-run, starting from the point where the partial match occurred. Ear- | re-run, starting from the point where the partial match occurred. Ear- |
lier data can be discarded. |
lier data can be discarded. |
|
|
It is best to use PCRE_PARTIAL_HARD in this situation, because it does | It is best to use PCRE_PARTIAL_HARD in this situation, because it does |
not treat the end of a segment as the end of the subject when matching | not treat the end of a segment as the end of the subject when matching |
\z, \Z, \b, \B, and $. Consider an unanchored pattern that matches | \z, \Z, \b, \B, and $. Consider an unanchored pattern that matches |
dates: |
dates: |
|
|
re> /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/ |
re> /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/ |
data> The date is 23ja\P\P |
data> The date is 23ja\P\P |
Partial match: 23ja |
Partial match: 23ja |
|
|
At this stage, an application could discard the text preceding "23ja", | At this stage, an application could discard the text preceding "23ja", |
add on text from the next segment, and call the matching function | add on text from the next segment, and call the matching function |
again. Unlike the DFA matching functions, the entire matching string | again. Unlike the DFA matching functions, the entire matching string |
must always be available, and the complete matching process occurs for | must always be available, and the complete matching process occurs for |
each call, so more memory and more processing time is needed. |
each call, so more memory and more processing time is needed. |
|
|
Note: If the pattern contains lookbehind assertions, or \K, or starts | Note: If the pattern contains lookbehind assertions, or \K, or starts |
with \b or \B, the string that is returned for a partial match includes |
with \b or \B, the string that is returned for a partial match includes |
characters that precede the partially matched string itself, because | characters that precede the start of what would be returned for a com- |
these must be retained when adding on more characters for a subsequent | plete match, because it contains all the characters that were inspected |
matching attempt. However, in some cases you may need to retain even | during the partial match. |
earlier characters, as discussed in the next section. | |
|
|
|
|
ISSUES WITH MULTI-SEGMENT MATCHING |
ISSUES WITH MULTI-SEGMENT MATCHING |
Line 7800 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 9003 ISSUES WITH MULTI-SEGMENT MATCHING
|
hind assertion later in the pattern could require even earlier charac- |
hind assertion later in the pattern could require even earlier charac- |
ters to be inspected. You can handle this case by using the |
ters to be inspected. You can handle this case by using the |
PCRE_INFO_MAXLOOKBEHIND option of the pcre_fullinfo() or |
PCRE_INFO_MAXLOOKBEHIND option of the pcre_fullinfo() or |
pcre16_fullinfo() functions to obtain the length of the largest lookbe- | pcre[16|32]_fullinfo() functions to obtain the length of the longest |
hind in the pattern. This length is given in characters, not bytes. If | lookbehind in the pattern. This length is given in characters, not |
you always retain at least that many characters before the partially | bytes. If you always retain at least that many characters before the |
matched string, all should be well. (Of course, near the start of the | partially matched string, all should be well. (Of course, near the |
subject, fewer characters may be present; in that case all characters | start of the subject, fewer characters may be present; in that case all |
should be retained.) | characters should be retained.) |
|
|
3. Because a partial match must always contain at least one character, | From release 8.33, there is a more accurate way of deciding which char- |
what might be considered a partial match of an empty string actually | acters to retain. Instead of subtracting the length of the longest |
| lookbehind from the earliest inspected character (offsets[0]), the |
| match start position (offsets[2]) should be used, and the next match |
| attempt started at the offsets[2] character by setting the startoffset |
| argument of pcre_exec() or pcre_dfa_exec(). |
| |
| For example, if the pattern "(?<=123)abc" is partially matched against |
| the string "xx123a", the three offset values returned are 2, 6, and 5. |
| This indicates that the matching process that gave a partial match |
| started at offset 5, but the characters "123a" were all inspected. The |
| maximum lookbehind for that pattern is 3, so taking that away from 5 |
| shows that we need only keep "123a", and the next match attempt can be |
| started at offset 3 (that is, at "a") when further characters have been |
| added. When the match start is not the earliest inspected character, |
| pcretest shows it explicitly: |
| |
| re> "(?<=123)abc" |
| data> xx123a\P\P |
| Partial match at offset 5: 123a |
| |
| 3. Because a partial match must always contain at least one character, |
| what might be considered a partial match of an empty string actually |
gives a "no match" result. For example: |
gives a "no match" result. For example: |
|
|
re> /c(?<=abc)x/ |
re> /c(?<=abc)x/ |
Line 7816 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 9040 ISSUES WITH MULTI-SEGMENT MATCHING
|
No match |
No match |
|
|
If the next segment begins "cx", a match should be found, but this will |
If the next segment begins "cx", a match should be found, but this will |
only happen if characters from the previous segment are retained. For | only happen if characters from the previous segment are retained. For |
this reason, a "no match" result should be interpreted as "partial | this reason, a "no match" result should be interpreted as "partial |
match of an empty string" when the pattern contains lookbehinds. |
match of an empty string" when the pattern contains lookbehinds. |
|
|
4. Matching a subject string that is split into multiple segments may | 4. Matching a subject string that is split into multiple segments may |
not always produce exactly the same result as matching over one single | not always produce exactly the same result as matching over one single |
long string, especially when PCRE_PARTIAL_SOFT is used. The section | long string, especially when PCRE_PARTIAL_SOFT is used. The section |
"Partial Matching and Word Boundaries" above describes an issue that | "Partial Matching and Word Boundaries" above describes an issue that |
arises if the pattern ends with \b or \B. Another kind of difference | arises if the pattern ends with \b or \B. Another kind of difference |
may occur when there are multiple matching possibilities, because (for | may occur when there are multiple matching possibilities, because (for |
PCRE_PARTIAL_SOFT) a partial match result is given only when there are | PCRE_PARTIAL_SOFT) a partial match result is given only when there are |
no completed matches. This means that as soon as the shortest match has |
no completed matches. This means that as soon as the shortest match has |
been found, continuation to a new subject segment is no longer possi- | been found, continuation to a new subject segment is no longer possi- |
ble. Consider again this pcretest example: |
ble. Consider again this pcretest example: |
|
|
re> /dog(sbody)?/ |
re> /dog(sbody)?/ |
Line 7842 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 9066 ISSUES WITH MULTI-SEGMENT MATCHING
|
0: dogsbody |
0: dogsbody |
1: dog |
1: dog |
|
|
The first data line passes the string "dogsb" to a standard matching | The first data line passes the string "dogsb" to a standard matching |
function, setting the PCRE_PARTIAL_SOFT option. Although the string is | function, setting the PCRE_PARTIAL_SOFT option. Although the string is |
a partial match for "dogsbody", the result is not PCRE_ERROR_PARTIAL, | a partial match for "dogsbody", the result is not PCRE_ERROR_PARTIAL, |
because the shorter string "dog" is a complete match. Similarly, when | because the shorter string "dog" is a complete match. Similarly, when |
the subject is presented to a DFA matching function in several parts | the subject is presented to a DFA matching function in several parts |
("do" and "gsb" being the first two) the match stops when "dog" has | ("do" and "gsb" being the first two) the match stops when "dog" has |
been found, and it is not possible to continue. On the other hand, if | been found, and it is not possible to continue. On the other hand, if |
"dogsbody" is presented as a single string, a DFA matching function | "dogsbody" is presented as a single string, a DFA matching function |
finds both matches. |
finds both matches. |
|
|
Because of these problems, it is best to use PCRE_PARTIAL_HARD when | Because of these problems, it is best to use PCRE_PARTIAL_HARD when |
matching multi-segment data. The example above then behaves differ- | matching multi-segment data. The example above then behaves differ- |
ently: |
ently: |
|
|
re> /dog(sbody)?/ |
re> /dog(sbody)?/ |
Line 7865 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 9089 ISSUES WITH MULTI-SEGMENT MATCHING
|
Partial match: gsb |
Partial match: gsb |
|
|
5. Patterns that contain alternatives at the top level which do not all |
5. Patterns that contain alternatives at the top level which do not all |
start with the same pattern item may not work as expected when | start with the same pattern item may not work as expected when |
PCRE_DFA_RESTART is used. For example, consider this pattern: |
PCRE_DFA_RESTART is used. For example, consider this pattern: |
|
|
1234|3789 |
1234|3789 |
|
|
If the first part of the subject is "ABC123", a partial match of the | If the first part of the subject is "ABC123", a partial match of the |
first alternative is found at offset 3. There is no partial match for | first alternative is found at offset 3. There is no partial match for |
the second alternative, because such a match does not start at the same |
the second alternative, because such a match does not start at the same |
point in the subject string. Attempting to continue with the string | point in the subject string. Attempting to continue with the string |
"7890" does not yield a match because only those alternatives that | "7890" does not yield a match because only those alternatives that |
match at one point in the subject are remembered. The problem arises | match at one point in the subject are remembered. The problem arises |
because the start of the second alternative matches within the first | because the start of the second alternative matches within the first |
alternative. There is no problem with anchored patterns or patterns | alternative. There is no problem with anchored patterns or patterns |
such as: |
such as: |
|
|
1234|ABCD |
1234|ABCD |
|
|
where no string can be a partial match for both alternatives. This is | where no string can be a partial match for both alternatives. This is |
not a problem if a standard matching function is used, because the | not a problem if a standard matching function is used, because the |
entire match has to be rerun each time: |
entire match has to be rerun each time: |
|
|
re> /1234|3789/ |
re> /1234|3789/ |
Line 7893 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 9117 ISSUES WITH MULTI-SEGMENT MATCHING
|
0: 3789 |
0: 3789 |
|
|
Of course, instead of using PCRE_DFA_RESTART, the same technique of re- |
Of course, instead of using PCRE_DFA_RESTART, the same technique of re- |
running the entire match can also be used with the DFA matching func- | running the entire match can also be used with the DFA matching func- |
tions. Another possibility is to work with two buffers. If a partial | tions. Another possibility is to work with two buffers. If a partial |
match at offset n in the first buffer is followed by "no match" when | match at offset n in the first buffer is followed by "no match" when |
PCRE_DFA_RESTART is used on the second buffer, you can then try a new | PCRE_DFA_RESTART is used on the second buffer, you can then try a new |
match starting at offset n+1 in the first buffer. |
match starting at offset n+1 in the first buffer. |
|
|
|
|
Line 7909 AUTHOR
|
Line 9133 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 24 February 2012 | Last updated: 02 July 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREPRECOMPILE(3) PCREPRECOMPILE(3) | PCREPRECOMPILE(3) Library Functions Manual PCREPRECOMPILE(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
SAVING AND RE-USING PRECOMPILED PCRE PATTERNS |
SAVING AND RE-USING PRECOMPILED PCRE PATTERNS |
|
|
If you are running an application that uses a large number of regular |
If you are running an application that uses a large number of regular |
Line 7934 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
|
Line 9158 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
|
|
|
If you save compiled patterns to a file, you can copy them to a differ- |
If you save compiled patterns to a file, you can copy them to a differ- |
ent host and run them there. If the two hosts have different endianness |
ent host and run them there. If the two hosts have different endianness |
(byte order), you should run the pcre[16]_pattern_to_host_byte_order() | (byte order), you should run the pcre[16|32]_pat- |
function on the new host before trying to match the pattern. The match- | tern_to_host_byte_order() function on the new host before trying to |
ing functions return PCRE_ERROR_BADENDIANNESS if they detect a pattern | match the pattern. The matching functions return PCRE_ERROR_BADENDIAN- |
with the wrong endianness. | NESS if they detect a pattern with the wrong endianness. |
|
|
Compiling regular expressions with one version of PCRE for use with a |
Compiling regular expressions with one version of PCRE for use with a |
different version is not guaranteed to work and may cause crashes, and |
different version is not guaranteed to work and may cause crashes, and |
Line 7947 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
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Line 9171 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
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|
|
SAVING A COMPILED PATTERN |
SAVING A COMPILED PATTERN |
|
|
The value returned by pcre[16]_compile() points to a single block of | The value returned by pcre[16|32]_compile() points to a single block of |
memory that holds the compiled pattern and associated data. You can |
memory that holds the compiled pattern and associated data. You can |
find the length of this block in bytes by calling pcre[16]_fullinfo() | find the length of this block in bytes by calling |
with an argument of PCRE_INFO_SIZE. You can then save the data in any | pcre[16|32]_fullinfo() with an argument of PCRE_INFO_SIZE. You can then |
appropriate manner. Here is sample code for the 8-bit library that com- | save the data in any appropriate manner. Here is sample code for the |
piles a pattern and writes it to a file. It assumes that the variable | 8-bit library that compiles a pattern and writes it to a file. It |
fd refers to a file that is open for output: | assumes that the variable fd refers to a file that is open for output: |
|
|
int erroroffset, rc, size; |
int erroroffset, rc, size; |
char *error; |
char *error; |
Line 7988 SAVING A COMPILED PATTERN
|
Line 9212 SAVING A COMPILED PATTERN
|
the PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is cre- |
the PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is cre- |
ated cannot be saved because it is too dependent on the current envi- |
ated cannot be saved because it is too dependent on the current envi- |
ronment. When studying generates additional information, |
ronment. When studying generates additional information, |
pcre[16]_study() returns a pointer to a pcre[16]_extra data block. Its | pcre[16|32]_study() returns a pointer to a pcre[16|32]_extra data |
format is defined in the section on matching a pattern in the pcreapi | block. Its format is defined in the section on matching a pattern in |
documentation. The study_data field points to the binary study data, | the pcreapi documentation. The study_data field points to the binary |
and this is what you must save (not the pcre[16]_extra block itself). | study data, and this is what you must save (not the pcre[16|32]_extra |
The length of the study data can be obtained by calling | block itself). The length of the study data can be obtained by calling |
pcre[16]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remember | pcre[16|32]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remem- |
to check that pcre[16]_study() did return a non-NULL value before try- | ber to check that pcre[16|32]_study() did return a non-NULL value |
ing to save the study data. | before trying to save the study data. |
|
|
|
|
RE-USING A PRECOMPILED PATTERN |
RE-USING A PRECOMPILED PATTERN |
|
|
Re-using a precompiled pattern is straightforward. Having reloaded it |
Re-using a precompiled pattern is straightforward. Having reloaded it |
into main memory, called pcre[16]_pattern_to_host_byte_order() if nec- | into main memory, called pcre[16|32]_pattern_to_host_byte_order() if |
essary, you pass its pointer to pcre[16]_exec() or pcre[16]_dfa_exec() | necessary, you pass its pointer to pcre[16|32]_exec() or |
in the usual way. | pcre[16|32]_dfa_exec() in the usual way. |
|
|
However, if you passed a pointer to custom character tables when the |
However, if you passed a pointer to custom character tables when the |
pattern was compiled (the tableptr argument of pcre[16]_compile()), you | pattern was compiled (the tableptr argument of pcre[16|32]_compile()), |
must now pass a similar pointer to pcre[16]_exec() or | you must now pass a similar pointer to pcre[16|32]_exec() or |
pcre[16]_dfa_exec(), because the value saved with the compiled pattern | pcre[16|32]_dfa_exec(), because the value saved with the compiled pat- |
will obviously be nonsense. A field in a pcre[16]_extra() block is used | tern will obviously be nonsense. A field in a pcre[16|32]_extra() block |
to pass this data, as described in the section on matching a pattern in | is used to pass this data, as described in the section on matching a |
the pcreapi documentation. | pattern in the pcreapi documentation. |
|
|
|
Warning: The tables that pcre_exec() and pcre_dfa_exec() use must be |
|
the same as those that were used when the pattern was compiled. If this |
|
is not the case, the behaviour is undefined. |
|
|
If you did not provide custom character tables when the pattern was |
If you did not provide custom character tables when the pattern was |
compiled, the pointer in the compiled pattern is NULL, which causes the |
compiled, the pointer in the compiled pattern is NULL, which causes the |
matching functions to use PCRE's internal tables. Thus, you do not need |
matching functions to use PCRE's internal tables. Thus, you do not need |
to take any special action at run time in this case. |
to take any special action at run time in this case. |
|
|
If you saved study data with the compiled pattern, you need to create |
If you saved study data with the compiled pattern, you need to create |
your own pcre[16]_extra data block and set the study_data field to | your own pcre[16|32]_extra data block and set the study_data field to |
point to the reloaded study data. You must also set the |
point to the reloaded study data. You must also set the |
PCRE_EXTRA_STUDY_DATA bit in the flags field to indicate that study |
PCRE_EXTRA_STUDY_DATA bit in the flags field to indicate that study |
data is present. Then pass the pcre[16]_extra block to the matching | data is present. Then pass the pcre[16|32]_extra block to the matching |
function in the usual way. If the pattern was studied for just-in-time |
function in the usual way. If the pattern was studied for just-in-time |
optimization, that data cannot be saved, and so is lost by a |
optimization, that data cannot be saved, and so is lost by a |
save/restore cycle. |
save/restore cycle. |
Line 8044 AUTHOR
|
Line 9272 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 10 January 2012 | Last updated: 12 November 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREPERFORM(3) PCREPERFORM(3) | PCREPERFORM(3) Library Functions Manual PCREPERFORM(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
PCRE PERFORMANCE |
PCRE PERFORMANCE |
|
|
Two aspects of performance are discussed below: memory usage and pro- |
Two aspects of performance are discussed below: memory usage and pro- |
Line 8115 COMPILED PATTERN MEMORY USAGE
|
Line 9343 COMPILED PATTERN MEMORY USAGE
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|
|
STACK USAGE AT RUN TIME |
STACK USAGE AT RUN TIME |
|
|
When pcre_exec() or pcre16_exec() is used for matching, certain kinds | When pcre_exec() or pcre[16|32]_exec() is used for matching, certain |
of pattern can cause it to use large amounts of the process stack. In | kinds of pattern can cause it to use large amounts of the process |
some environments the default process stack is quite small, and if it | stack. In some environments the default process stack is quite small, |
runs out the result is often SIGSEGV. This issue is probably the most | and if it runs out the result is often SIGSEGV. This issue is probably |
frequently raised problem with PCRE. Rewriting your pattern can often | the most frequently raised problem with PCRE. Rewriting your pattern |
help. The pcrestack documentation discusses this issue in detail. | can often help. The pcrestack documentation discusses this issue in |
| detail. |
|
|
|
|
PROCESSING TIME |
PROCESSING TIME |
|
|
Certain items in regular expression patterns are processed more effi- | Certain items in regular expression patterns are processed more effi- |
ciently than others. It is more efficient to use a character class like |
ciently than others. It is more efficient to use a character class like |
[aeiou] than a set of single-character alternatives such as | [aeiou] than a set of single-character alternatives such as |
(a|e|i|o|u). In general, the simplest construction that provides the | (a|e|i|o|u). In general, the simplest construction that provides the |
required behaviour is usually the most efficient. Jeffrey Friedl's book |
required behaviour is usually the most efficient. Jeffrey Friedl's book |
contains a lot of useful general discussion about optimizing regular | contains a lot of useful general discussion about optimizing regular |
expressions for efficient performance. This document contains a few | expressions for efficient performance. This document contains a few |
observations about PCRE. |
observations about PCRE. |
|
|
Using Unicode character properties (the \p, \P, and \X escapes) is | Using Unicode character properties (the \p, \P, and \X escapes) is |
slow, because PCRE has to scan a structure that contains data for over | slow, because PCRE has to use a multi-stage table lookup whenever it |
fifteen thousand characters whenever it needs a character's property. | needs a character's property. If you can find an alternative pattern |
If you can find an alternative pattern that does not use character | that does not use character properties, it will probably be faster. |
properties, it will probably be faster. | |
|
|
By default, the escape sequences \b, \d, \s, and \w, and the POSIX |
By default, the escape sequences \b, \d, \s, and \w, and the POSIX |
character classes such as [:alpha:] do not use Unicode properties, |
character classes such as [:alpha:] do not use Unicode properties, |
Line 8214 AUTHOR
|
Line 9442 AUTHOR
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|
|
REVISION |
REVISION |
|
|
Last updated: 09 January 2012 | Last updated: 25 August 2012 |
Copyright (c) 1997-2012 University of Cambridge. |
Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREPOSIX(3) PCREPOSIX(3) | PCREPOSIX(3) Library Functions Manual PCREPOSIX(3) |
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|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions. |
PCRE - Perl-compatible regular expressions. |
|
|
|
SYNOPSIS |
|
|
SYNOPSIS OF POSIX API |
|
|
|
#include <pcreposix.h> |
#include <pcreposix.h> |
|
|
int regcomp(regex_t *preg, const char *pattern, |
int regcomp(regex_t *preg, const char *pattern, |
Line 8235 SYNOPSIS OF POSIX API
|
Line 9463 SYNOPSIS OF POSIX API
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|
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int regexec(regex_t *preg, const char *string, |
int regexec(regex_t *preg, const char *string, |
size_t nmatch, regmatch_t pmatch[], int eflags); |
size_t nmatch, regmatch_t pmatch[], int eflags); |
| size_t regerror(int errcode, const regex_t *preg, |
size_t regerror(int errcode, const regex_t *preg, | |
char *errbuf, size_t errbuf_size); |
char *errbuf, size_t errbuf_size); |
|
|
void regfree(regex_t *preg); |
void regfree(regex_t *preg); |
Line 8247 DESCRIPTION
|
Line 9474 DESCRIPTION
|
This set of functions provides a POSIX-style API for the PCRE regular |
This set of functions provides a POSIX-style API for the PCRE regular |
expression 8-bit library. See the pcreapi documentation for a descrip- |
expression 8-bit library. See the pcreapi documentation for a descrip- |
tion of PCRE's native API, which contains much additional functional- |
tion of PCRE's native API, which contains much additional functional- |
ity. There is no POSIX-style wrapper for PCRE's 16-bit library. | ity. There is no POSIX-style wrapper for PCRE's 16-bit and 32-bit |
| library. |
|
|
The functions described here are just wrapper functions that ultimately |
The functions described here are just wrapper functions that ultimately |
call the PCRE native API. Their prototypes are defined in the |
call the PCRE native API. Their prototypes are defined in the |
pcreposix.h header file, and on Unix systems the library itself is | pcreposix.h header file, and on Unix systems the library itself is |
called pcreposix.a, so can be accessed by adding -lpcreposix to the | called pcreposix.a, so can be accessed by adding -lpcreposix to the |
command for linking an application that uses them. Because the POSIX | command for linking an application that uses them. Because the POSIX |
functions call the native ones, it is also necessary to add -lpcre. |
functions call the native ones, it is also necessary to add -lpcre. |
|
|
I have implemented only those POSIX option bits that can be reasonably | I have implemented only those POSIX option bits that can be reasonably |
mapped to PCRE native options. In addition, the option REG_EXTENDED is | mapped to PCRE native options. In addition, the option REG_EXTENDED is |
defined with the value zero. This has no effect, but since programs | defined with the value zero. This has no effect, but since programs |
that are written to the POSIX interface often use it, this makes it | that are written to the POSIX interface often use it, this makes it |
easier to slot in PCRE as a replacement library. Other POSIX options | easier to slot in PCRE as a replacement library. Other POSIX options |
are not even defined. |
are not even defined. |
|
|
There are also some other options that are not defined by POSIX. These | There are also some other options that are not defined by POSIX. These |
have been added at the request of users who want to make use of certain |
have been added at the request of users who want to make use of certain |
PCRE-specific features via the POSIX calling interface. |
PCRE-specific features via the POSIX calling interface. |
|
|
When PCRE is called via these functions, it is only the API that is | When PCRE is called via these functions, it is only the API that is |
POSIX-like in style. The syntax and semantics of the regular expres- | POSIX-like in style. The syntax and semantics of the regular expres- |
sions themselves are still those of Perl, subject to the setting of | sions themselves are still those of Perl, subject to the setting of |
various PCRE options, as described below. "POSIX-like in style" means | various PCRE options, as described below. "POSIX-like in style" means |
that the API approximates to the POSIX definition; it is not fully | that the API approximates to the POSIX definition; it is not fully |
POSIX-compatible, and in multi-byte encoding domains it is probably | POSIX-compatible, and in multi-byte encoding domains it is probably |
even less compatible. |
even less compatible. |
|
|
The header for these functions is supplied as pcreposix.h to avoid any | The header for these functions is supplied as pcreposix.h to avoid any |
potential clash with other POSIX libraries. It can, of course, be | potential clash with other POSIX libraries. It can, of course, be |
renamed or aliased as regex.h, which is the "correct" name. It provides |
renamed or aliased as regex.h, which is the "correct" name. It provides |
two structure types, regex_t for compiled internal forms, and reg- | two structure types, regex_t for compiled internal forms, and reg- |
match_t for returning captured substrings. It also defines some con- | match_t for returning captured substrings. It also defines some con- |
stants whose names start with "REG_"; these are used for setting | stants whose names start with "REG_"; these are used for setting |
options and identifying error codes. |
options and identifying error codes. |
|
|
|
|
COMPILING A PATTERN |
COMPILING A PATTERN |
|
|
The function regcomp() is called to compile a pattern into an internal | The function regcomp() is called to compile a pattern into an internal |
form. The pattern is a C string terminated by a binary zero, and is | form. The pattern is a C string terminated by a binary zero, and is |
passed in the argument pattern. The preg argument is a pointer to a | passed in the argument pattern. The preg argument is a pointer to a |
regex_t structure that is used as a base for storing information about | regex_t structure that is used as a base for storing information about |
the compiled regular expression. |
the compiled regular expression. |
|
|
The argument cflags is either zero, or contains one or more of the bits |
The argument cflags is either zero, or contains one or more of the bits |
Line 8303 COMPILING A PATTERN
|
Line 9531 COMPILING A PATTERN
|
|
|
REG_ICASE |
REG_ICASE |
|
|
The PCRE_CASELESS option is set when the regular expression is passed | The PCRE_CASELESS option is set when the regular expression is passed |
for compilation to the native function. |
for compilation to the native function. |
|
|
REG_NEWLINE |
REG_NEWLINE |
|
|
The PCRE_MULTILINE option is set when the regular expression is passed | The PCRE_MULTILINE option is set when the regular expression is passed |
for compilation to the native function. Note that this does not mimic | for compilation to the native function. Note that this does not mimic |
the defined POSIX behaviour for REG_NEWLINE (see the following sec- | the defined POSIX behaviour for REG_NEWLINE (see the following sec- |
tion). |
tion). |
|
|
REG_NOSUB |
REG_NOSUB |
|
|
The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is | The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is |
passed for compilation to the native function. In addition, when a pat- |
passed for compilation to the native function. In addition, when a pat- |
tern that is compiled with this flag is passed to regexec() for match- | tern that is compiled with this flag is passed to regexec() for match- |
ing, the nmatch and pmatch arguments are ignored, and no captured | ing, the nmatch and pmatch arguments are ignored, and no captured |
strings are returned. |
strings are returned. |
|
|
REG_UCP |
REG_UCP |
|
|
The PCRE_UCP option is set when the regular expression is passed for | The PCRE_UCP option is set when the regular expression is passed for |
compilation to the native function. This causes PCRE to use Unicode | compilation to the native function. This causes PCRE to use Unicode |
properties when matchine \d, \w, etc., instead of just recognizing | properties when matchine \d, \w, etc., instead of just recognizing |
ASCII values. Note that REG_UTF8 is not part of the POSIX standard. |
ASCII values. Note that REG_UTF8 is not part of the POSIX standard. |
|
|
REG_UNGREEDY |
REG_UNGREEDY |
|
|
The PCRE_UNGREEDY option is set when the regular expression is passed | The PCRE_UNGREEDY option is set when the regular expression is passed |
for compilation to the native function. Note that REG_UNGREEDY is not | for compilation to the native function. Note that REG_UNGREEDY is not |
part of the POSIX standard. |
part of the POSIX standard. |
|
|
REG_UTF8 |
REG_UTF8 |
|
|
The PCRE_UTF8 option is set when the regular expression is passed for | The PCRE_UTF8 option is set when the regular expression is passed for |
compilation to the native function. This causes the pattern itself and | compilation to the native function. This causes the pattern itself and |
all data strings used for matching it to be treated as UTF-8 strings. | all data strings used for matching it to be treated as UTF-8 strings. |
Note that REG_UTF8 is not part of the POSIX standard. |
Note that REG_UTF8 is not part of the POSIX standard. |
|
|
In the absence of these flags, no options are passed to the native | In the absence of these flags, no options are passed to the native |
function. This means the the regex is compiled with PCRE default | function. This means the the regex is compiled with PCRE default |
semantics. In particular, the way it handles newline characters in the | semantics. In particular, the way it handles newline characters in the |
subject string is the Perl way, not the POSIX way. Note that setting | subject string is the Perl way, not the POSIX way. Note that setting |
PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE. | PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE. |
It does not affect the way newlines are matched by . (they are not) or | It does not affect the way newlines are matched by . (they are not) or |
by a negative class such as [^a] (they are). |
by a negative class such as [^a] (they are). |
|
|
The yield of regcomp() is zero on success, and non-zero otherwise. The | The yield of regcomp() is zero on success, and non-zero otherwise. The |
preg structure is filled in on success, and one member of the structure |
preg structure is filled in on success, and one member of the structure |
is public: re_nsub contains the number of capturing subpatterns in the | is public: re_nsub contains the number of capturing subpatterns in the |
regular expression. Various error codes are defined in the header file. |
regular expression. Various error codes are defined in the header file. |
|
|
NOTE: If the yield of regcomp() is non-zero, you must not attempt to | NOTE: If the yield of regcomp() is non-zero, you must not attempt to |
use the contents of the preg structure. If, for example, you pass it to |
use the contents of the preg structure. If, for example, you pass it to |
regexec(), the result is undefined and your program is likely to crash. |
regexec(), the result is undefined and your program is likely to crash. |
|
|
Line 8362 COMPILING A PATTERN
|
Line 9590 COMPILING A PATTERN
|
MATCHING NEWLINE CHARACTERS |
MATCHING NEWLINE CHARACTERS |
|
|
This area is not simple, because POSIX and Perl take different views of |
This area is not simple, because POSIX and Perl take different views of |
things. It is not possible to get PCRE to obey POSIX semantics, but | things. It is not possible to get PCRE to obey POSIX semantics, but |
then PCRE was never intended to be a POSIX engine. The following table | then PCRE was never intended to be a POSIX engine. The following table |
lists the different possibilities for matching newline characters in | lists the different possibilities for matching newline characters in |
PCRE: |
PCRE: |
|
|
Default Change with |
Default Change with |
Line 8386 MATCHING NEWLINE CHARACTERS
|
Line 9614 MATCHING NEWLINE CHARACTERS
|
^ matches \n in middle no REG_NEWLINE |
^ matches \n in middle no REG_NEWLINE |
|
|
PCRE's behaviour is the same as Perl's, except that there is no equiva- |
PCRE's behaviour is the same as Perl's, except that there is no equiva- |
lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is | lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is |
no way to stop newline from matching [^a]. |
no way to stop newline from matching [^a]. |
|
|
The default POSIX newline handling can be obtained by setting | The default POSIX newline handling can be obtained by setting |
PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE | PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE |
behave exactly as for the REG_NEWLINE action. |
behave exactly as for the REG_NEWLINE action. |
|
|
|
|
MATCHING A PATTERN |
MATCHING A PATTERN |
|
|
The function regexec() is called to match a compiled pattern preg | The function regexec() is called to match a compiled pattern preg |
against a given string, which is by default terminated by a zero byte | against a given string, which is by default terminated by a zero byte |
(but see REG_STARTEND below), subject to the options in eflags. These | (but see REG_STARTEND below), subject to the options in eflags. These |
can be: |
can be: |
|
|
REG_NOTBOL |
REG_NOTBOL |
Line 8420 MATCHING A PATTERN
|
Line 9648 MATCHING A PATTERN
|
|
|
REG_STARTEND |
REG_STARTEND |
|
|
The string is considered to start at string + pmatch[0].rm_so and to | The string is considered to start at string + pmatch[0].rm_so and to |
have a terminating NUL located at string + pmatch[0].rm_eo (there need | have a terminating NUL located at string + pmatch[0].rm_eo (there need |
not actually be a NUL at that location), regardless of the value of | not actually be a NUL at that location), regardless of the value of |
nmatch. This is a BSD extension, compatible with but not specified by | nmatch. This is a BSD extension, compatible with but not specified by |
IEEE Standard 1003.2 (POSIX.2), and should be used with caution in | IEEE Standard 1003.2 (POSIX.2), and should be used with caution in |
software intended to be portable to other systems. Note that a non-zero |
software intended to be portable to other systems. Note that a non-zero |
rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location |
rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location |
of the string, not how it is matched. |
of the string, not how it is matched. |
|
|
If the pattern was compiled with the REG_NOSUB flag, no data about any | If the pattern was compiled with the REG_NOSUB flag, no data about any |
matched strings is returned. The nmatch and pmatch arguments of | matched strings is returned. The nmatch and pmatch arguments of |
regexec() are ignored. |
regexec() are ignored. |
|
|
If the value of nmatch is zero, or if the value pmatch is NULL, no data |
If the value of nmatch is zero, or if the value pmatch is NULL, no data |
Line 8438 MATCHING A PATTERN
|
Line 9666 MATCHING A PATTERN
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|
|
Otherwise,the portion of the string that was matched, and also any cap- |
Otherwise,the portion of the string that was matched, and also any cap- |
tured substrings, are returned via the pmatch argument, which points to |
tured substrings, are returned via the pmatch argument, which points to |
an array of nmatch structures of type regmatch_t, containing the mem- | an array of nmatch structures of type regmatch_t, containing the mem- |
bers rm_so and rm_eo. These contain the offset to the first character | bers rm_so and rm_eo. These contain the offset to the first character |
of each substring and the offset to the first character after the end | of each substring and the offset to the first character after the end |
of each substring, respectively. The 0th element of the vector relates | of each substring, respectively. The 0th element of the vector relates |
to the entire portion of string that was matched; subsequent elements | to the entire portion of string that was matched; subsequent elements |
relate to the capturing subpatterns of the regular expression. Unused | relate to the capturing subpatterns of the regular expression. Unused |
entries in the array have both structure members set to -1. |
entries in the array have both structure members set to -1. |
|
|
A successful match yields a zero return; various error codes are | A successful match yields a zero return; various error codes are |
defined in the header file, of which REG_NOMATCH is the "expected" | defined in the header file, of which REG_NOMATCH is the "expected" |
failure code. |
failure code. |
|
|
|
|
ERROR MESSAGES |
ERROR MESSAGES |
|
|
The regerror() function maps a non-zero errorcode from either regcomp() |
The regerror() function maps a non-zero errorcode from either regcomp() |
or regexec() to a printable message. If preg is not NULL, the error | or regexec() to a printable message. If preg is not NULL, the error |
should have arisen from the use of that structure. A message terminated |
should have arisen from the use of that structure. A message terminated |
by a binary zero is placed in errbuf. The length of the message, | by a binary zero is placed in errbuf. The length of the message, |
including the zero, is limited to errbuf_size. The yield of the func- | including the zero, is limited to errbuf_size. The yield of the func- |
tion is the size of buffer needed to hold the whole message. |
tion is the size of buffer needed to hold the whole message. |
|
|
|
|
MEMORY USAGE |
MEMORY USAGE |
|
|
Compiling a regular expression causes memory to be allocated and asso- | Compiling a regular expression causes memory to be allocated and asso- |
ciated with the preg structure. The function regfree() frees all such | ciated with the preg structure. The function regfree() frees all such |
memory, after which preg may no longer be used as a compiled expres- | memory, after which preg may no longer be used as a compiled expres- |
sion. |
sion. |
|
|
|
|
Line 8483 REVISION
|
Line 9711 REVISION
|
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCRECPP(3) PCRECPP(3) | PCRECPP(3) Library Functions Manual PCRECPP(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions. |
PCRE - Perl-compatible regular expressions. |
|
|
|
|
SYNOPSIS OF C++ WRAPPER |
SYNOPSIS OF C++ WRAPPER |
|
|
#include <pcrecpp.h> |
#include <pcrecpp.h> |
Line 8501 DESCRIPTION
|
Line 9729 DESCRIPTION
|
functionality was added by Giuseppe Maxia. This brief man page was con- |
functionality was added by Giuseppe Maxia. This brief man page was con- |
structed from the notes in the pcrecpp.h file, which should be con- |
structed from the notes in the pcrecpp.h file, which should be con- |
sulted for further details. Note that the C++ wrapper supports only the |
sulted for further details. Note that the C++ wrapper supports only the |
original 8-bit PCRE library. There is no 16-bit support at present. | original 8-bit PCRE library. There is no 16-bit or 32-bit support at |
| present. |
|
|
|
|
MATCHING INTERFACE |
MATCHING INTERFACE |
|
|
The "FullMatch" operation checks that supplied text matches a supplied | The "FullMatch" operation checks that supplied text matches a supplied |
pattern exactly. If pointer arguments are supplied, it copies matched | pattern exactly. If pointer arguments are supplied, it copies matched |
sub-strings that match sub-patterns into them. |
sub-strings that match sub-patterns into them. |
|
|
Example: successful match |
Example: successful match |
Line 8521 MATCHING INTERFACE
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Line 9750 MATCHING INTERFACE
|
Example: creating a temporary RE object: |
Example: creating a temporary RE object: |
pcrecpp::RE("h.*o").FullMatch("hello"); |
pcrecpp::RE("h.*o").FullMatch("hello"); |
|
|
You can pass in a "const char*" or a "string" for "text". The examples | You can pass in a "const char*" or a "string" for "text". The examples |
below tend to use a const char*. You can, as in the different examples | below tend to use a const char*. You can, as in the different examples |
above, store the RE object explicitly in a variable or use a temporary | above, store the RE object explicitly in a variable or use a temporary |
RE object. The examples below use one mode or the other arbitrarily. | RE object. The examples below use one mode or the other arbitrarily. |
Either could correctly be used for any of these examples. |
Either could correctly be used for any of these examples. |
|
|
You must supply extra pointer arguments to extract matched subpieces. |
You must supply extra pointer arguments to extract matched subpieces. |
Line 8550 MATCHING INTERFACE
|
Line 9779 MATCHING INTERFACE
|
Example: fails because string cannot be stored in integer |
Example: fails because string cannot be stored in integer |
!pcrecpp::RE("(.*)").FullMatch("ruby", &i); |
!pcrecpp::RE("(.*)").FullMatch("ruby", &i); |
|
|
The provided pointer arguments can be pointers to any scalar numeric | The provided pointer arguments can be pointers to any scalar numeric |
type, or one of: |
type, or one of: |
|
|
string (matched piece is copied to string) |
string (matched piece is copied to string) |
Line 8558 MATCHING INTERFACE
|
Line 9787 MATCHING INTERFACE
|
T (where "bool T::ParseFrom(const char*, int)" exists) |
T (where "bool T::ParseFrom(const char*, int)" exists) |
NULL (the corresponding matched sub-pattern is not copied) |
NULL (the corresponding matched sub-pattern is not copied) |
|
|
The function returns true iff all of the following conditions are sat- | The function returns true iff all of the following conditions are sat- |
isfied: |
isfied: |
|
|
a. "text" matches "pattern" exactly; |
a. "text" matches "pattern" exactly; |
Line 8573 MATCHING INTERFACE
|
Line 9802 MATCHING INTERFACE
|
number of sub-patterns, "i"th captured sub-pattern is |
number of sub-patterns, "i"th captured sub-pattern is |
ignored. |
ignored. |
|
|
CAVEAT: An optional sub-pattern that does not exist in the matched | CAVEAT: An optional sub-pattern that does not exist in the matched |
string is assigned the empty string. Therefore, the following will | string is assigned the empty string. Therefore, the following will |
return false (because the empty string is not a valid number): |
return false (because the empty string is not a valid number): |
|
|
int number; |
int number; |
pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number); |
pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number); |
|
|
The matching interface supports at most 16 arguments per call. If you | The matching interface supports at most 16 arguments per call. If you |
need more, consider using the more general interface | need more, consider using the more general interface |
pcrecpp::RE::DoMatch. See pcrecpp.h for the signature for DoMatch. |
pcrecpp::RE::DoMatch. See pcrecpp.h for the signature for DoMatch. |
|
|
NOTE: Do not use no_arg, which is used internally to mark the end of a | NOTE: Do not use no_arg, which is used internally to mark the end of a |
list of optional arguments, as a placeholder for missing arguments, as | list of optional arguments, as a placeholder for missing arguments, as |
this can lead to segfaults. |
this can lead to segfaults. |
|
|
|
|
QUOTING METACHARACTERS |
QUOTING METACHARACTERS |
|
|
You can use the "QuoteMeta" operation to insert backslashes before all | You can use the "QuoteMeta" operation to insert backslashes before all |
potentially meaningful characters in a string. The returned string, | potentially meaningful characters in a string. The returned string, |
used as a regular expression, will exactly match the original string. |
used as a regular expression, will exactly match the original string. |
|
|
Example: |
Example: |
string quoted = RE::QuoteMeta(unquoted); |
string quoted = RE::QuoteMeta(unquoted); |
|
|
Note that it's legal to escape a character even if it has no special | Note that it's legal to escape a character even if it has no special |
meaning in a regular expression -- so this function does that. (This | meaning in a regular expression -- so this function does that. (This |
also makes it identical to the perl function of the same name; see | also makes it identical to the perl function of the same name; see |
"perldoc -f quotemeta".) For example, "1.5-2.0?" becomes | "perldoc -f quotemeta".) For example, "1.5-2.0?" becomes |
"1\.5\-2\.0\?". |
"1\.5\-2\.0\?". |
|
|
|
|
PARTIAL MATCHES |
PARTIAL MATCHES |
|
|
You can use the "PartialMatch" operation when you want the pattern to | You can use the "PartialMatch" operation when you want the pattern to |
match any substring of the text. |
match any substring of the text. |
|
|
Example: simple search for a string: |
Example: simple search for a string: |
Line 8622 PARTIAL MATCHES
|
Line 9851 PARTIAL MATCHES
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|
|
UTF-8 AND THE MATCHING INTERFACE |
UTF-8 AND THE MATCHING INTERFACE |
|
|
By default, pattern and text are plain text, one byte per character. | By default, pattern and text are plain text, one byte per character. |
The UTF8 flag, passed to the constructor, causes both pattern and | The UTF8 flag, passed to the constructor, causes both pattern and |
string to be treated as UTF-8 text, still a byte stream but potentially |
string to be treated as UTF-8 text, still a byte stream but potentially |
multiple bytes per character. In practice, the text is likelier to be | multiple bytes per character. In practice, the text is likelier to be |
UTF-8 than the pattern, but the match returned may depend on the UTF8 | UTF-8 than the pattern, but the match returned may depend on the UTF8 |
flag, so always use it when matching UTF8 text. For example, "." will | flag, so always use it when matching UTF8 text. For example, "." will |
match one byte normally but with UTF8 set may match up to three bytes | match one byte normally but with UTF8 set may match up to three bytes |
of a multi-byte character. |
of a multi-byte character. |
|
|
Example: |
Example: |
Line 8647 UTF-8 AND THE MATCHING INTERFACE
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Line 9876 UTF-8 AND THE MATCHING INTERFACE
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|
|
PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE |
PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE |
|
|
PCRE defines some modifiers to change the behavior of the regular | PCRE defines some modifiers to change the behavior of the regular |
expression engine. The C++ wrapper defines an auxiliary class, | expression engine. The C++ wrapper defines an auxiliary class, |
RE_Options, as a vehicle to pass such modifiers to a RE class. Cur- | RE_Options, as a vehicle to pass such modifiers to a RE class. Cur- |
rently, the following modifiers are supported: |
rently, the following modifiers are supported: |
|
|
modifier description Perl corresponding |
modifier description Perl corresponding |
Line 8664 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 9893 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
PCRE_UNGREEDY reverses * and *? N/A |
PCRE_UNGREEDY reverses * and *? N/A |
PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*) |
PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*) |
|
|
(*) Both Perl and PCRE allow non capturing parentheses by means of the | (*) Both Perl and PCRE allow non capturing parentheses by means of the |
"?:" modifier within the pattern itself. e.g. (?:ab|cd) does not cap- | "?:" modifier within the pattern itself. e.g. (?:ab|cd) does not cap- |
ture, while (ab|cd) does. |
ture, while (ab|cd) does. |
|
|
For a full account on how each modifier works, please check the PCRE | For a full account on how each modifier works, please check the PCRE |
API reference page. |
API reference page. |
|
|
For each modifier, there are two member functions whose name is made | For each modifier, there are two member functions whose name is made |
out of the modifier in lowercase, without the "PCRE_" prefix. For | out of the modifier in lowercase, without the "PCRE_" prefix. For |
instance, PCRE_CASELESS is handled by |
instance, PCRE_CASELESS is handled by |
|
|
bool caseless() |
bool caseless() |
Line 8682 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 9911 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
RE_Options & set_caseless(bool) |
RE_Options & set_caseless(bool) |
|
|
which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can |
which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can |
be accessed through the set_match_limit() and match_limit() member | be accessed through the set_match_limit() and match_limit() member |
functions. Setting match_limit to a non-zero value will limit the exe- | functions. Setting match_limit to a non-zero value will limit the exe- |
cution of pcre to keep it from doing bad things like blowing the stack | cution of pcre to keep it from doing bad things like blowing the stack |
or taking an eternity to return a result. A value of 5000 is good | or taking an eternity to return a result. A value of 5000 is good |
enough to stop stack blowup in a 2MB thread stack. Setting match_limit | enough to stop stack blowup in a 2MB thread stack. Setting match_limit |
to zero disables match limiting. Alternatively, you can call | to zero disables match limiting. Alternatively, you can call |
match_limit_recursion() which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to | match_limit_recursion() which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to |
limit how much PCRE recurses. match_limit() limits the number of | limit how much PCRE recurses. match_limit() limits the number of |
matches PCRE does; match_limit_recursion() limits the depth of internal |
matches PCRE does; match_limit_recursion() limits the depth of internal |
recursion, and therefore the amount of stack that is used. |
recursion, and therefore the amount of stack that is used. |
|
|
Normally, to pass one or more modifiers to a RE class, you declare a | Normally, to pass one or more modifiers to a RE class, you declare a |
RE_Options object, set the appropriate options, and pass this object to |
RE_Options object, set the appropriate options, and pass this object to |
a RE constructor. Example: |
a RE constructor. Example: |
|
|
Line 8702 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 9931 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
if (RE("HELLO", opt).PartialMatch("hello world")) ... |
if (RE("HELLO", opt).PartialMatch("hello world")) ... |
|
|
RE_options has two constructors. The default constructor takes no argu- |
RE_options has two constructors. The default constructor takes no argu- |
ments and creates a set of flags that are off by default. The optional | ments and creates a set of flags that are off by default. The optional |
parameter option_flags is to facilitate transfer of legacy code from C | parameter option_flags is to facilitate transfer of legacy code from C |
programs. This lets you do |
programs. This lets you do |
|
|
RE(pattern, |
RE(pattern, |
Line 8717 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 9946 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
|
|
If you are going to pass one of the most used modifiers, there are some |
If you are going to pass one of the most used modifiers, there are some |
convenience functions that return a RE_Options class with the appropri- |
convenience functions that return a RE_Options class with the appropri- |
ate modifier already set: CASELESS(), UTF8(), MULTILINE(), DOTALL(), | ate modifier already set: CASELESS(), UTF8(), MULTILINE() ate modifier already set: CASELESS(), UTF8(), MULTILINE() |
and EXTENDED(). |
and EXTENDED(). |
|
|
If you need to set several options at once, and you don't want to go | If you need to set several options at once, and you don't want to go |
through the pains of declaring a RE_Options object and setting several | through the pains of declaring a RE_Options object and setting several |
options, there is a parallel method that give you such ability on the | options, there is a parallel method that give you such ability on the |
fly. You can concatenate several set_xxxxx() member functions, since | fly. You can concatenate several set_xxxxx() member functions, since |
each of them returns a reference to its class object. For example, to | each of them returns a reference to its class object. For example, to |
pass PCRE_CASELESS, PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one | pass PCRE_CASELESS, PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one |
statement, you may write: |
statement, you may write: |
|
|
RE(" ^ xyz \\s+ .* blah$", |
RE(" ^ xyz \\s+ .* blah$", |
Line 8737 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 9966 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
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|
|
SCANNING TEXT INCREMENTALLY |
SCANNING TEXT INCREMENTALLY |
|
|
The "Consume" operation may be useful if you want to repeatedly match | The "Consume" operation may be useful if you want to repeatedly match |
regular expressions at the front of a string and skip over them as they |
regular expressions at the front of a string and skip over them as they |
match. This requires use of the "StringPiece" type, which represents a | match. This requires use of the "StringPiece" type, which represents a |
sub-range of a real string. Like RE, StringPiece is defined in the | sub-range of a real string. Like RE, StringPiece is defined in the |
pcrecpp namespace. |
pcrecpp namespace. |
|
|
Example: read lines of the form "var = value" from a string. |
Example: read lines of the form "var = value" from a string. |
Line 8754 SCANNING TEXT INCREMENTALLY
|
Line 9983 SCANNING TEXT INCREMENTALLY
|
...; |
...; |
} |
} |
|
|
Each successful call to "Consume" will set "var/value", and also | Each successful call to "Consume" will set "var/value", and also |
advance "input" so it points past the matched text. |
advance "input" so it points past the matched text. |
|
|
The "FindAndConsume" operation is similar to "Consume" but does not | The "FindAndConsume" operation is similar to "Consume" but does not |
anchor your match at the beginning of the string. For example, you | anchor your match at the beginning of the string. For example, you |
could extract all words from a string by repeatedly calling |
could extract all words from a string by repeatedly calling |
|
|
pcrecpp::RE("(\\w+)").FindAndConsume(&input, &word) |
pcrecpp::RE("(\\w+)").FindAndConsume(&input, &word) |
Line 8767 SCANNING TEXT INCREMENTALLY
|
Line 9996 SCANNING TEXT INCREMENTALLY
|
PARSING HEX/OCTAL/C-RADIX NUMBERS |
PARSING HEX/OCTAL/C-RADIX NUMBERS |
|
|
By default, if you pass a pointer to a numeric value, the corresponding |
By default, if you pass a pointer to a numeric value, the corresponding |
text is interpreted as a base-10 number. You can instead wrap the | text is interpreted as a base-10 number. You can instead wrap the |
pointer with a call to one of the operators Hex(), Octal(), or CRadix() |
pointer with a call to one of the operators Hex(), Octal(), or CRadix() |
to interpret the text in another base. The CRadix operator interprets | to interpret the text in another base. The CRadix operator interprets |
C-style "0" (base-8) and "0x" (base-16) prefixes, but defaults to | C-style "0" (base-8) and "0x" (base-16) prefixes, but defaults to |
base-10. |
base-10. |
|
|
Example: |
Example: |
Line 8785 PARSING HEX/OCTAL/C-RADIX NUMBERS
|
Line 10014 PARSING HEX/OCTAL/C-RADIX NUMBERS
|
|
|
REPLACING PARTS OF STRINGS |
REPLACING PARTS OF STRINGS |
|
|
You can replace the first match of "pattern" in "str" with "rewrite". | You can replace the first match of "pattern" in "str" with "rewrite". |
Within "rewrite", backslash-escaped digits (\1 to \9) can be used to | Within "rewrite", backslash-escaped digits (\1 to \9) can be used to |
insert text matching corresponding parenthesized group from the pat- | insert text matching corresponding parenthesized group from the pat- |
tern. \0 in "rewrite" refers to the entire matching text. For example: |
tern. \0 in "rewrite" refers to the entire matching text. For example: |
|
|
string s = "yabba dabba doo"; |
string s = "yabba dabba doo"; |
pcrecpp::RE("b+").Replace("d", &s); |
pcrecpp::RE("b+").Replace("d", &s); |
|
|
will leave "s" containing "yada dabba doo". The result is true if the | will leave "s" containing "yada dabba doo". The result is true if the |
pattern matches and a replacement occurs, false otherwise. |
pattern matches and a replacement occurs, false otherwise. |
|
|
GlobalReplace is like Replace except that it replaces all occurrences | GlobalReplace is like Replace except that it replaces all occurrences |
of the pattern in the string with the rewrite. Replacements are not | of the pattern in the string with the rewrite. Replacements are not |
subject to re-matching. For example: |
subject to re-matching. For example: |
|
|
string s = "yabba dabba doo"; |
string s = "yabba dabba doo"; |
pcrecpp::RE("b+").GlobalReplace("d", &s); |
pcrecpp::RE("b+").GlobalReplace("d", &s); |
|
|
will leave "s" containing "yada dada doo". It returns the number of | will leave "s" containing "yada dada doo". It returns the number of |
replacements made. |
replacements made. |
|
|
Extract is like Replace, except that if the pattern matches, "rewrite" | Extract is like Replace, except that if the pattern matches, "rewrite" |
is copied into "out" (an additional argument) with substitutions. The | is copied into "out" (an additional argument) with substitutions. The |
non-matching portions of "text" are ignored. Returns true iff a match | non-matching portions of "text" are ignored. Returns true iff a match |
occurred and the extraction happened successfully; if no match occurs, |
occurred and the extraction happened successfully; if no match occurs, |
the string is left unaffected. |
the string is left unaffected. |
|
|
Line 8825 REVISION
|
Line 10054 REVISION
|
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCRESAMPLE(3) PCRESAMPLE(3) | PCRESAMPLE(3) Library Functions Manual PCRESAMPLE(3) |
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|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
PCRE SAMPLE PROGRAM |
PCRE SAMPLE PROGRAM |
|
|
A simple, complete demonstration program, to get you started with using |
A simple, complete demonstration program, to get you started with using |
Line 8911 REVISION
|
Line 10140 REVISION
|
Last updated: 10 January 2012 |
Last updated: 10 January 2012 |
Copyright (c) 1997-2012 University of Cambridge. |
Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
PCRELIMITS(3) PCRELIMITS(3) | PCRELIMITS(3) Library Functions Manual PCRELIMITS(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
SIZE AND OTHER LIMITATIONS |
SIZE AND OTHER LIMITATIONS |
|
|
There are some size limitations in PCRE but it is hoped that they will |
There are some size limitations in PCRE but it is hoped that they will |
Line 8925 SIZE AND OTHER LIMITATIONS
|
Line 10154 SIZE AND OTHER LIMITATIONS
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|
|
The maximum length of a compiled pattern is approximately 64K data |
The maximum length of a compiled pattern is approximately 64K data |
units (bytes for the 8-bit library, 16-bit units for the 16-bit |
units (bytes for the 8-bit library, 16-bit units for the 16-bit |
library) if PCRE is compiled with the default internal linkage size of | library, and 32-bit units for the 32-bit library) if PCRE is compiled |
2 bytes. If you want to process regular expressions that are truly | with the default internal linkage size, which is 2 bytes for the 8-bit |
enormous, you can compile PCRE with an internal linkage size of 3 or 4 | and 16-bit libraries, and 4 bytes for the 32-bit library. If you want |
(when building the 16-bit library, 3 is rounded up to 4). See the | to process regular expressions that are truly enormous, you can compile |
README file in the source distribution and the pcrebuild documentation | PCRE with an internal linkage size of 3 or 4 (when building the 16-bit |
for details. In these cases the limit is substantially larger. How- | or 32-bit library, 3 is rounded up to 4). See the README file in the |
ever, the speed of execution is slower. | source distribution and the pcrebuild documentation for details. In |
| these cases the limit is substantially larger. However, the speed of |
| execution is slower. |
|
|
All values in repeating quantifiers must be less than 65536. |
All values in repeating quantifiers must be less than 65536. |
|
|
There is no limit to the number of parenthesized subpatterns, but there |
There is no limit to the number of parenthesized subpatterns, but there |
can be no more than 65535 capturing subpatterns. | can be no more than 65535 capturing subpatterns. There is, however, a |
| limit to the depth of nesting of parenthesized subpatterns of all |
| kinds. This is imposed in order to limit the amount of system stack |
| used at compile time. The limit can be specified when PCRE is built; |
| the default is 250. |
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There is a limit to the number of forward references to subsequent sub- |
There is a limit to the number of forward references to subsequent sub- |
patterns of around 200,000. Repeated forward references with fixed |
patterns of around 200,000. Repeated forward references with fixed |
Line 8948 SIZE AND OTHER LIMITATIONS
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Line 10183 SIZE AND OTHER LIMITATIONS
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the maximum number of named subpatterns is 10000. |
the maximum number of named subpatterns is 10000. |
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The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or |
The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or |
(*THEN) verb is 255 for the 8-bit library and 65535 for the 16-bit | (*THEN) verb is 255 for the 8-bit library and 65535 for the 16-bit and |
library. | 32-bit libraries. |
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The maximum length of a subject string is the largest positive number |
The maximum length of a subject string is the largest positive number |
that an integer variable can hold. However, when using the traditional |
that an integer variable can hold. However, when using the traditional |
Line 8968 AUTHOR
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Line 10203 AUTHOR
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REVISION |
REVISION |
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Last updated: 04 May 2012 | Last updated: 05 November 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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PCRESTACK(3) PCRESTACK(3) | PCRESTACK(3) Library Functions Manual PCRESTACK(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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PCRE DISCUSSION OF STACK USAGE |
PCRE DISCUSSION OF STACK USAGE |
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When you call pcre[16]_exec(), it makes use of an internal function | When you call pcre[16|32]_exec(), it makes use of an internal function |
called match(). This calls itself recursively at branch points in the |
called match(). This calls itself recursively at branch points in the |
pattern, in order to remember the state of the match so that it can |
pattern, in order to remember the state of the match so that it can |
back up and try a different alternative if the first one fails. As |
back up and try a different alternative if the first one fails. As |
Line 8998 PCRE DISCUSSION OF STACK USAGE
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Line 10233 PCRE DISCUSSION OF STACK USAGE
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result of the current call (a "tail recursion"), the function is just |
result of the current call (a "tail recursion"), the function is just |
restarted instead. |
restarted instead. |
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The above comments apply when pcre[16]_exec() is run in its normal | The above comments apply when pcre[16|32]_exec() is run in its normal |
interpretive manner. If the pattern was studied with the |
interpretive manner. If the pattern was studied with the |
PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was success- |
PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was success- |
ful, and the options passed to pcre[16]_exec() were not incompatible, | ful, and the options passed to pcre[16|32]_exec() were not incompati- |
the matching process uses the JIT-compiled code instead of the match() | ble, the matching process uses the JIT-compiled code instead of the |
function. In this case, the memory requirements are handled entirely | match() function. In this case, the memory requirements are handled |
differently. See the pcrejit documentation for details. | entirely differently. See the pcrejit documentation for details. |
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The pcre[16]_dfa_exec() function operates in an entirely different way, | The pcre[16|32]_dfa_exec() function operates in an entirely different |
and uses recursion only when there is a regular expression recursion or | way, and uses recursion only when there is a regular expression recur- |
subroutine call in the pattern. This includes the processing of asser- | sion or subroutine call in the pattern. This includes the processing of |
tion and "once-only" subpatterns, which are handled like subroutine | assertion and "once-only" subpatterns, which are handled like subrou- |
calls. Normally, these are never very deep, and the limit on the com- | tine calls. Normally, these are never very deep, and the limit on the |
plexity of pcre[16]_dfa_exec() is controlled by the amount of workspace | complexity of pcre[16|32]_dfa_exec() is controlled by the amount of |
it is given. However, it is possible to write patterns with runaway | workspace it is given. However, it is possible to write patterns with |
infinite recursions; such patterns will cause pcre[16]_dfa_exec() to | runaway infinite recursions; such patterns will cause |
run out of stack. At present, there is no protection against this. | pcre[16|32]_dfa_exec() to run out of stack. At present, there is no |
| protection against this. |
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The comments that follow do NOT apply to pcre[16]_dfa_exec(); they are | The comments that follow do NOT apply to pcre[16|32]_dfa_exec(); they |
relevant only for pcre[16]_exec() without the JIT optimization. | are relevant only for pcre[16|32]_exec() without the JIT optimization. |
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Reducing pcre[16]_exec()'s stack usage | Reducing pcre[16|32]_exec()'s stack usage |
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Each time that match() is actually called recursively, it uses memory | Each time that match() is actually called recursively, it uses memory |
from the process stack. For certain kinds of pattern and data, very | from the process stack. For certain kinds of pattern and data, very |
large amounts of stack may be needed, despite the recognition of "tail | large amounts of stack may be needed, despite the recognition of "tail |
recursion". You can often reduce the amount of recursion, and there- | recursion". You can often reduce the amount of recursion, and there- |
fore the amount of stack used, by modifying the pattern that is being | fore the amount of stack used, by modifying the pattern that is being |
matched. Consider, for example, this pattern: |
matched. Consider, for example, this pattern: |
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([^<]|<(?!inet))+ |
([^<]|<(?!inet))+ |
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It matches from wherever it starts until it encounters "<inet" or the | It matches from wherever it starts until it encounters "<inet" or the |
end of the data, and is the kind of pattern that might be used when | end of the data, and is the kind of pattern that might be used when |
processing an XML file. Each iteration of the outer parentheses matches |
processing an XML file. Each iteration of the outer parentheses matches |
either one character that is not "<" or a "<" that is not followed by | either one character that is not "<" or a "<" that is not followed by |
"inet". However, each time a parenthesis is processed, a recursion | "inet". However, each time a parenthesis is processed, a recursion |
occurs, so this formulation uses a stack frame for each matched charac- |
occurs, so this formulation uses a stack frame for each matched charac- |
ter. For a long string, a lot of stack is required. Consider now this | ter. For a long string, a lot of stack is required. Consider now this |
rewritten pattern, which matches exactly the same strings: |
rewritten pattern, which matches exactly the same strings: |
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([^<]++|<(?!inet))+ |
([^<]++|<(?!inet))+ |
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This uses very much less stack, because runs of characters that do not | This uses very much less stack, because runs of characters that do not |
contain "<" are "swallowed" in one item inside the parentheses. Recur- | contain "<" are "swallowed" in one item inside the parentheses. Recur- |
sion happens only when a "<" character that is not followed by "inet" | sion happens only when a "<" character that is not followed by "inet" |
is encountered (and we assume this is relatively rare). A possessive | is encountered (and we assume this is relatively rare). A possessive |
quantifier is used to stop any backtracking into the runs of non-"<" | quantifier is used to stop any backtracking into the runs of non-"<" |
characters, but that is not related to stack usage. |
characters, but that is not related to stack usage. |
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This example shows that one way of avoiding stack problems when match- | This example shows that one way of avoiding stack problems when match- |
ing long subject strings is to write repeated parenthesized subpatterns |
ing long subject strings is to write repeated parenthesized subpatterns |
to match more than one character whenever possible. |
to match more than one character whenever possible. |
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Compiling PCRE to use heap instead of stack for pcre[16]_exec() | Compiling PCRE to use heap instead of stack for pcre[16|32]_exec() |
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In environments where stack memory is constrained, you might want to | In environments where stack memory is constrained, you might want to |
compile PCRE to use heap memory instead of stack for remembering back- | compile PCRE to use heap memory instead of stack for remembering back- |
up points when pcre[16]_exec() is running. This makes it run a lot more | up points when pcre[16|32]_exec() is running. This makes it run a lot |
slowly, however. Details of how to do this are given in the pcrebuild | more slowly, however. Details of how to do this are given in the pcre- |
documentation. When built in this way, instead of using the stack, PCRE | build documentation. When built in this way, instead of using the |
obtains and frees memory by calling the functions that are pointed to | stack, PCRE obtains and frees memory by calling the functions that are |
by the pcre[16]_stack_malloc and pcre[16]_stack_free variables. By | pointed to by the pcre[16|32]_stack_malloc and pcre[16|32]_stack_free |
default, these point to malloc() and free(), but you can replace the | variables. By default, these point to malloc() and free(), but you can |
pointers to cause PCRE to use your own functions. Since the block sizes | replace the pointers to cause PCRE to use your own functions. Since the |
are always the same, and are always freed in reverse order, it may be | block sizes are always the same, and are always freed in reverse order, |
possible to implement customized memory handlers that are more effi- | it may be possible to implement customized memory handlers that are |
cient than the standard functions. | more efficient than the standard functions. |
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Limiting pcre[16]_exec()'s stack usage | Limiting pcre[16|32]_exec()'s stack usage |
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You can set limits on the number of times that match() is called, both | You can set limits on the number of times that match() is called, both |
in total and recursively. If a limit is exceeded, pcre[16]_exec() | in total and recursively. If a limit is exceeded, pcre[16|32]_exec() |
returns an error code. Setting suitable limits should prevent it from | returns an error code. Setting suitable limits should prevent it from |
running out of stack. The default values of the limits are very large, | running out of stack. The default values of the limits are very large, |
and unlikely ever to operate. They can be changed when PCRE is built, | and unlikely ever to operate. They can be changed when PCRE is built, |
and they can also be set when pcre[16]_exec() is called. For details of | and they can also be set when pcre[16|32]_exec() is called. For details |
these interfaces, see the pcrebuild documentation and the section on | of these interfaces, see the pcrebuild documentation and the section on |
extra data for pcre[16]_exec() in the pcreapi documentation. | extra data for pcre[16|32]_exec() in the pcreapi documentation. |
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As a very rough rule of thumb, you should reckon on about 500 bytes per |
As a very rough rule of thumb, you should reckon on about 500 bytes per |
recursion. Thus, if you want to limit your stack usage to 8Mb, you | recursion. Thus, if you want to limit your stack usage to 8Mb, you |
should set the limit at 16000 recursions. A 64Mb stack, on the other | should set the limit at 16000 recursions. A 64Mb stack, on the other |
hand, can support around 128000 recursions. |
hand, can support around 128000 recursions. |
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In Unix-like environments, the pcretest test program has a command line |
In Unix-like environments, the pcretest test program has a command line |
option (-S) that can be used to increase the size of its stack. As long |
option (-S) that can be used to increase the size of its stack. As long |
as the stack is large enough, another option (-M) can be used to find | as the stack is large enough, another option (-M) can be used to find |
the smallest limits that allow a particular pattern to match a given | the smallest limits that allow a particular pattern to match a given |
subject string. This is done by calling pcre[16]_exec() repeatedly with | subject string. This is done by calling pcre[16|32]_exec() repeatedly |
different limits. | with different limits. |
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Obtaining an estimate of stack usage |
Obtaining an estimate of stack usage |
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The actual amount of stack used per recursion can vary quite a lot, | The actual amount of stack used per recursion can vary quite a lot, |
depending on the compiler that was used to build PCRE and the optimiza- |
depending on the compiler that was used to build PCRE and the optimiza- |
tion or debugging options that were set for it. The rule of thumb value |
tion or debugging options that were set for it. The rule of thumb value |
of 500 bytes mentioned above may be larger or smaller than what is | of 500 bytes mentioned above may be larger or smal of 500 bytes mentioned above may be larger or smal |
actually needed. A better approximation can be obtained by running this |
actually needed. A better approximation can be obtained by running this |
command: |
command: |
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pcretest -m -C |
pcretest -m -C |
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The -C option causes pcretest to output information about the options | The -C option causes pcretest to output information about the options |
with which PCRE was compiled. When -m is also given (before -C), infor- |
with which PCRE was compiled. When -m is also given (before -C), infor- |
mation about stack use is given in a line like this: |
mation about stack use is given in a line like this: |
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Line 9110 PCRE DISCUSSION OF STACK USAGE
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Line 10346 PCRE DISCUSSION OF STACK USAGE
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The value is approximate because some recursions need a bit more (up to |
The value is approximate because some recursions need a bit more (up to |
perhaps 16 more bytes). |
perhaps 16 more bytes). |
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If the above command is given when PCRE is compiled to use the heap | If the above command is given when PCRE is compiled to use the heap |
instead of the stack for recursion, the value that is output is the | instead of the stack for recursion, the value that is output is the |
size of each block that is obtained from the heap. |
size of each block that is obtained from the heap. |
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Changing stack size in Unix-like systems |
Changing stack size in Unix-like systems |
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In Unix-like environments, there is not often a problem with the stack | In Unix-like environments, there is not often a problem with the stack |
unless very long strings are involved, though the default limit on | unless very long strings are involved, though the default limit on |
stack size varies from system to system. Values from 8Mb to 64Mb are | stack size varies from system to system. Values from 8Mb to 64Mb are |
common. You can find your default limit by running the command: |
common. You can find your default limit by running the command: |
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ulimit -s |
ulimit -s |
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Unfortunately, the effect of running out of stack is often SIGSEGV, | Unfortunately, the effect of running out of stack is often SIGSEGV, |
though sometimes a more explicit error message is given. You can nor- | though sometimes a more explicit error message is given. You can nor- |
mally increase the limit on stack size by code such as this: |
mally increase the limit on stack size by code such as this: |
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struct rlimit rlim; |
struct rlimit rlim; |
Line 9132 PCRE DISCUSSION OF STACK USAGE
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Line 10368 PCRE DISCUSSION OF STACK USAGE
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rlim.rlim_cur = 100*1024*1024; |
rlim.rlim_cur = 100*1024*1024; |
setrlimit(RLIMIT_STACK, &rlim); |
setrlimit(RLIMIT_STACK, &rlim); |
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This reads the current limits (soft and hard) using getrlimit(), then | This reads the current limits (soft and hard) using getrlimit(), then |
attempts to increase the soft limit to 100Mb using setrlimit(). You | attempts to increase the soft limit to 100Mb using setrlimit(). You |
must do this before calling pcre[16]_exec(). | must do this before calling pcre[16|32]_exec(). |
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Changing stack size in Mac OS X |
Changing stack size in Mac OS X |
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Using setrlimit(), as described above, should also work on Mac OS X. It |
Using setrlimit(), as described above, should also work on Mac OS X. It |
is also possible to set a stack size when linking a program. There is a |
is also possible to set a stack size when linking a program. There is a |
discussion about stack sizes in Mac OS X at this web site: | discussion about stack sizes in Mac OS X at this web site: |
http://developer.apple.com/qa/qa2005/qa1419.html. |
http://developer.apple.com/qa/qa2005/qa1419.html. |
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Line 9153 AUTHOR
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Line 10389 AUTHOR
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REVISION |
REVISION |
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Last updated: 21 January 2012 | Last updated: 24 June 2012 |
Copyright (c) 1997-2012 University of Cambridge. |
Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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