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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 6.2.0. |
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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 367 OPTION NAMES
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Line 412 OPTION NAMES
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There are two new general option names, PCRE_UTF16 and |
There are two new general option names, PCRE_UTF16 and |
PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and |
PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and |
PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options |
PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options |
define the same bits in the options word. | define the same bits in the options word. There is a discussion about |
| the validity of UTF-16 strings in the pcreunicode page. |
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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 |
Line 413 ERROR NAMES
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Line 460 ERROR NAMES
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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 |
Line 436 TESTING
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Line 483 TESTING
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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 |
Line 460 AUTHOR
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Line 509 AUTHOR
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REVISION |
REVISION |
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Last updated: 08 January 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 char **errptr, int *erroffset, |
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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 |
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used for passing data to a callout function is pcre32_callout_block. |
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These structures contain the same fields, with the same names, as their |
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8-bit counterparts. The only difference is that pointers to character |
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strings are 32-bit instead of 8-bit types. |
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32-BIT FUNCTIONS |
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For every function in the 8-bit library there is a corresponding func- |
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tion in the 32-bit library with a name that starts with pcre32_ instead |
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of pcre_. The prototypes are listed above. In addition, there is one |
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extra function, pcre32_utf32_to_host_byte_order(). This is a utility |
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function that converts a UTF-32 character string to host byte order if |
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necessary. The other 32-bit functions expect the strings they are |
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passed to be in host byte order. |
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The input and output arguments of pcre32_utf32_to_host_byte_order() may |
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point to the same address, that is, conversion in place is supported. |
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The output buffer must be at least as long as the input. |
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The length argument specifies the number of 32-bit data units in the |
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input string; a negative value specifies a zero-terminated string. |
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If byte_order is NULL, it is assumed that the string starts off in host |
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byte order. This may be changed by byte-order marks (BOMs) anywhere in |
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the string (commonly as the first character). |
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If byte_order is not NULL, a non-zero value of the integer to which it |
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points means that the input starts off in host byte order, otherwise |
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the opposite order is assumed. Again, BOMs in the string can change |
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this. The final byte order is passed back at the end of processing. |
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If keep_boms is not zero, byte-order mark characters (0xfeff) are |
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copied into the output string. Otherwise they are discarded. |
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The result of the function is the number of 32-bit units placed into |
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the output buffer, including the zero terminator if the string was |
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zero-terminated. |
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SUBJECT STRING OFFSETS |
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The lengths and starting offsets of subject strings must be specified |
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in 32-bit data units, and the offsets within subject strings that are |
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returned by the matching functions are in also 32-bit units rather than |
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bytes. |
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NAMED SUBPATTERNS |
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The name-to-number translation table that is maintained for named sub- |
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patterns uses 32-bit characters. The pcre32_get_stringtable_entries() |
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function returns the length of each entry in the table as the number of |
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32-bit data units. |
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OPTION NAMES |
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There are two new general option names, PCRE_UTF32 and |
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PCRE_NO_UTF32_CHECK, which correspond to PCRE_UTF8 and |
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PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options |
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define the same bits in the options word. There is a discussion about |
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the validity of UTF-32 strings in the pcreunicode page. |
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For the pcre32_config() function there is an option PCRE_CONFIG_UTF32 |
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that returns 1 if UTF-32 support is configured, otherwise 0. If this |
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option is given to pcre_config() or pcre16_config(), or if the |
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PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF16 option is given to pcre32_con- |
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fig(), the result is the PCRE_ERROR_BADOPTION error. |
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|
|
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 546 C++ SUPPORT
|
Line 945 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 runtime | expects its input to be either ASCII or UTF-8 (depending on the run- |
option). It is not possible to support both EBCDIC and UTF-8 codes in | time option). It is not possible to support both EBCDIC and UTF-8 codes |
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 597 JUST-IN-TIME COMPILER SUPPORT
|
Line 997 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 610 JUST-IN-TIME COMPILER SUPPORT
|
Line 1010 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 629 CODE VALUE OF NEWLINE
|
Line 1029 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 672 POSIX MALLOC USAGE
|
Line 1072 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 runtime system. (This method of replacing the tables does not work if | C run-time system. (This method of replacing the tables does not work |
you are cross compiling, because dftables is run on the local host. If | if you are cross compiling, because dftables is run on the local host. |
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 842 PCRETEST OPTION FOR LIBREADLINE SUPPORT
|
Line 1259 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 856 AUTHOR
|
Line 1341 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 1010 THE ALTERNATIVE MATCHING ALGORITHM
|
Line 1497 THE ALTERNATIVE MATCHING ALGORITHM
|
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 |
Line 1068 REVISION
|
Line 1555 REVISION
|
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREAPI(3) PCREAPI(3) | PCREAPI(3) Library Functions Manual PCREAPI(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
Line 1139 PCRE NATIVE API STRING EXTRACTION FUNCTIONS
|
Line 1627 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 1174 PCRE NATIVE API INDIRECTED FUNCTIONS
|
Line 1667 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 1310 NEWLINES
|
Line 1809 NEWLINES
|
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 Unicode newline sequences |
ceding, or any Unicode newline sequence. The Unicode newline sequences |
are the three just mentioned, plus the single characters VT (vertical |
are the three just mentioned, plus the single characters VT (vertical |
tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line | tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line |
separator, U+2028), and PS (paragraph separator, U+2029). |
separator, U+2028), and PS (paragraph separator, U+2029). |
|
|
Each of the first three conventions is used by at least one operating |
Each of the first three conventions is used by at least one operating |
Line 1383 CHECKING BUILD-TIME OPTIONS
|
Line 1882 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 1407 CHECKING BUILD-TIME OPTIONS
|
Line 1915 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 1511 COMPILING A PATTERN
|
Line 2022 COMPILING A PATTERN
|
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_OPT options can be set at the time of matching as well as | PCRE_NO_START_OPTIMIZE options can be set at the time of matching 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 |
Line 1624 COMPILING A PATTERN
|
Line 2137 COMPILING A PATTERN
|
|
|
PCRE_EXTENDED |
PCRE_EXTENDED |
|
|
If this bit is set, whitespace data characters in the pattern are | If this bit is set, white space data 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. White |
space does not include the VT character (code 11). In addition, charac- |
space does not include the VT character (code 11). In addition, charac- |
ters between an unescaped # outside a character class and the next new- |
ters between an unescaped # outside a character class and the next new- |
line, inclusive, are also ignored. This is equivalent to Perl's /x |
line, inclusive, are also ignored. This is equivalent to Perl's /x |
Line 1641 COMPILING A PATTERN
|
Line 2154 COMPILING A PATTERN
|
|
|
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. |
Whitespace 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. |
|
|
Line 1697 COMPILING A PATTERN
|
Line 2210 COMPILING A PATTERN
|
|
|
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 |
newlines in the subject string, respectively, as well as at the very | newlines in the subject string, respectively, as well as at the very |
start and end. This is equivalent to Perl's /m option, and it can be | start and end. This is equivalent to Perl's /m option, and it can be |
changed within a pattern by a (?m) option setting. If there are no new- |
changed within a pattern by a (?m) option setting. If there are no new- |
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 |
Line 1725 COMPILING A PATTERN
|
Line 2250 COMPILING A PATTERN
|
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 (formfeed, | |
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. | |
|
|
The newline setting in the options word uses three bits that are | 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 |
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 |
more than one newline option, the combination may or may not be sensi- | more than one newline option, the combination may or may not be sensi- |
ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to |
ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to |
PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and | PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and |
cause an error. |
cause an error. |
|
|
The only time that a line break in a pattern is specially recognized | The only time that a line break in a pattern is specially recognized |
when compiling is when PCRE_EXTENDED is set. CR and LF are whitespace | when compiling is when PCRE_EXTENDED is set. CR and LF are white space |
characters, and so are ignored in this mode. Also, an unescaped # out- | characters, and so are ignored in this mode. Also, an unescaped # out- |
side a character class indicates a comment that lasts until after the | side a character class indicates a comment that lasts until after the |
next line break sequence. In other circumstances, line break sequences | next line break sequence. In other circumstances, line break sequences |
in patterns are treated as literal data. |
in patterns are treated as literal data. |
|
|
The newline option that is set at compile time becomes the default that |
The newline option that is set at compile time becomes the default that |
Line 1752 COMPILING A PATTERN
|
Line 2286 COMPILING A PATTERN
|
PCRE_NO_AUTO_CAPTURE |
PCRE_NO_AUTO_CAPTURE |
|
|
If this option is set, it disables the use of numbered capturing paren- |
If this option is set, it disables the use of numbered capturing paren- |
theses in the pattern. Any opening parenthesis that is not followed by | theses in the pattern. Any opening parenthesis that is not followed by |
? behaves as if it were followed by ?: but named parentheses can still | ? behaves as if it were followed by ?: but named parentheses can still |
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_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 |
|
|
Line 1802 COMPILING A PATTERN
|
Line 2337 COMPILING A PATTERN
|
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. Note that this option can also be |
passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity |
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 |
Line 1810 COMPILATION ERROR CODES
|
Line 2347 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 1876 COMPILATION ERROR CODES
|
Line 2413 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 1893 COMPILATION ERROR CODES
|
Line 2430 COMPILATION ERROR CODES
|
72 too many forward references |
72 too many forward references |
73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff) |
73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff) |
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) |
|
76 character value in \u.... sequence is too large |
|
77 invalid UTF-32 string (specifically UTF-32) |
|
|
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; different |
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. |
Line 1917 STUDYING A PATTERN
|
Line 2457 STUDYING A PATTERN
|
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 is only | The second argument of pcre_study() contains option bits. There are |
one option: PCRE_STUDY_JIT_COMPILE. If this is set, and the just-in- | three further options in addition to PCRE_STUDY_EXTRA_NEEDED: |
time compiler is available, the pattern is further compiled into | |
machine code that executes much faster than the pcre_exec() matching | |
function. If the just-in-time compiler is not available, this option is | |
ignored. All other bits in the options argument must be zero. | |
|
|
|
PCRE_STUDY_JIT_COMPILE |
|
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
|
PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE |
|
|
|
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 |
|
faster than the pcre_exec() interpretive matching function. If the |
|
just-in-time compiler is not available, these options are ignored. All |
|
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 |
Line 1947 STUDYING A PATTERN
|
Line 2497 STUDYING A PATTERN
|
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 PCRE_STUDY_JIT_COMPILE is not used, but it is | work in cases where JIT optimization is not used, but it is advisable |
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): |
Line 1970 STUDYING A PATTERN
|
Line 2520 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. | 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(), |
However, they are not used by pcre_exec() if pcre_study() is called | and the information is also used by the JIT compiler. The optimiza- |
with the PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling is | tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option. |
successful. The optimizations can be disabled by setting the | You might want to do this if your pattern contains callouts or (*MARK) |
PCRE_NO_START_OPTIMIZE option when calling pcre_exec() or | and you want to make use of these facilities in cases where matching |
pcre_dfa_exec(). You might want to do this if your pattern contains | fails. |
callouts or (*MARK) (which cannot be handled by the JIT compiler), and | |
you want to make use of these facilities 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 |
Line 2072 INFORMATION ABOUT A PATTERN
|
Line 2628 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- |
Line 2118 INFORMATION ABOUT A PATTERN
|
Line 2675 INFORMATION ABOUT A PATTERN
|
|
|
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 |
|
|
(a) the pattern was compiled with the PCRE_MULTILINE option, and every | (a) the pattern was compiled with the PCRE_MULTILINE option, and every |
branch starts with "^", or |
branch starts with "^", or |
|
|
(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not |
(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not |
set (if it were set, the pattern would be anchored), |
set (if it were set, the pattern would be anchored), |
|
|
-1 is returned, indicating that the pattern matches only at the start | -1 is returned, indicating that the pattern matches only at the start |
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 |
Line 2156 INFORMATION ABOUT A PATTERN
|
Line 2719 INFORMATION ABOUT A PATTERN
|
|
|
PCRE_INFO_JIT |
PCRE_INFO_JIT |
|
|
Return 1 if the pattern was studied with the PCRE_STUDY_JIT_COMPILE | Return 1 if the pattern was studied with one of the JIT options, and |
option, and just-in-time compiling was successful. The fourth argument | just-in-time compiling was successful. The fourth argument should point |
should point to an int variable. A return value of 0 means that JIT | to an int variable. A return value of 0 means that JIT support is not |
support is not available in this version of PCRE, or that the pattern | available in this version of PCRE, or that the pattern was not studied |
was not studied with the PCRE_STUDY_JIT_COMPILE option, or that the JIT | with a JIT option, or that the JIT compiler could not handle this par- |
compiler could not handle this particular pattern. See the pcrejit doc- | ticular pattern. See the pcrejit documentation for details of what can |
umentation 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 the PCRE_STUDY_JIT_COMPILE | If the pattern was successfully studied with a JIT option, return the |
option, return the size of the JIT compiled code, otherwise return | size of the JIT compiled code, otherwise return zero. The fourth argu- |
zero. The fourth argument should point to a size_t variable. | ment should point to a size_t variable. |
|
|
PCRE_INFO_LASTLITERAL |
PCRE_INFO_LASTLITERAL |
|
|
Line 2180 INFORMATION ABOUT A PATTERN
|
Line 2743 INFORMATION ABOUT A PATTERN
|
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 the character, this value |
|
is deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and |
|
PCRE_INFO_REQUIREDCHAR values should be used. |
|
|
|
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 |
|
|
|
Return the number of characters (NB not data units) in the longest |
|
lookbehind assertion in the pattern. This information is useful when |
|
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 |
least that long. |
least that long. |
|
|
PCRE_INFO_NAMECOUNT |
PCRE_INFO_NAMECOUNT |
PCRE_INFO_NAMEENTRYSIZE |
PCRE_INFO_NAMEENTRYSIZE |
PCRE_INFO_NAMETABLE |
PCRE_INFO_NAMETABLE |
|
|
PCRE supports the use of named as well as numbered capturing parenthe- | PCRE supports the use of named as well as numbered capturing parenthe- |
ses. The names are just an additional way of identifying the parenthe- | ses. The names are just an additional way of identifying the parenthe- |
ses, which still acquire numbers. Several convenience functions such as |
ses, which still acquire numbers. Several convenience functions such as |
pcre_get_named_substring() are provided for extracting captured sub- | pcre_get_named_substring() are provided for extracting captured sub- |
strings by name. It is also possible to extract the data directly, by | strings by name. It is also possible to extract the data directly, by |
first converting the name to a number in order to access the correct | first converting the name to a number in order to access the correct |
pointers in the output vector (described with pcre_exec() below). To do |
pointers in the output vector (described with pcre_exec() below). To do |
the conversion, you need to use the name-to-number map, which is | the conversion, you need to use the name-to-num the conversion, you need to use the name-to-number map, which is |
described by these three values. |
described by these three values. |
|
|
The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT |
The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT |
gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size |
gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size |
of each entry; both of these return an int value. The entry size | of each entry; both of these return an int value. The entry size |
depends on the length of the longest name. PCRE_INFO_NAMETABLE returns | depends on the length of the longest name. PCRE_INFO_NAMETABLE returns |
a pointer to the first entry of the table. This is a pointer to char in |
a pointer to the first entry of the table. This is a pointer to char in |
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. Duplicate names may appear if (?| |
is used to create multiple groups with the same number, as described in |
is used to create multiple groups with the same number, as described in |
the section on duplicate subpattern numbers in the pcrepattern page. | the section on duplicate subpattern numbers in the pcrepattern page. |
Duplicate names for subpatterns with different numbers are permitted | Duplicate names for subpatterns with different numbers are permitted |
only if PCRE_DUPNAMES is set. In all cases of duplicate names, they | only if PCRE_DUPNAMES is set. In all cases of duplicate names, they |
appear in the table in the order in which they were found in the pat- | appear in the table in the order in which they were found in the pat- |
tern. In the absence of (?| this is the order of increasing number; | tern. In the absence of (?| this is the order of increasing number; |
when (?| is used this is not necessarily the case because later subpat- |
when (?| is used this is not necessarily the case because later subpat- |
terns may have lower numbers. |
terns 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 2243 INFORMATION ABOUT A PATTERN
|
Line 2833 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 2279 INFORMATION ABOUT A PATTERN
|
Line 2869 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, if PCRE_INFO_FIRSTCHARACTER- |
|
FLAGS returned 1; otherwise returns 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. |
|
|
|
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), |
|
|
|
-1 is returned, indicating that the pattern matches only at the start |
|
of a subject string or after any newline within the string. Otherwise |
|
-2 is returned. For anchored patterns, -2 is returned. |
|
|
|
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 2383 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3046 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 a bitmap that specifies which of the other fields | In the 32-bit version of this structure, the mark field has type |
are set. The flag bits are: | "PCRE_UCHAR32 **". |
|
|
PCRE_EXTRA_STUDY_DATA | The flags field is used to specify which of the other fields are set. |
| The flag bits are: |
| |
| PCRE_EXTRA_CALLOUT_DATA |
PCRE_EXTRA_EXECUTABLE_JIT |
PCRE_EXTRA_EXECUTABLE_JIT |
|
PCRE_EXTRA_MARK |
PCRE_EXTRA_MATCH_LIMIT |
PCRE_EXTRA_MATCH_LIMIT |
PCRE_EXTRA_MATCH_LIMIT_RECURSION |
PCRE_EXTRA_MATCH_LIMIT_RECURSION |
PCRE_EXTRA_CALLOUT_DATA | PCRE_EXTRA_STUDY_DATA |
PCRE_EXTRA_TABLES |
PCRE_EXTRA_TABLES |
PCRE_EXTRA_MARK |
|
|
|
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 |
the 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 the PCRE_STUDY_JIT_COMPILE option, the way that the matching is | with a JIT option, the way that the matching is executed is entirely |
executed is entirely different. However, there is still the possibility | different. However, there is still the possibility of runaway matching |
of runaway matching that goes on for a very long time, and so the | that goes on for a very long time, and so the match_limit value is also |
match_limit value is also used in this case (but in a different way) to | used in this case (but in a different way) to limit how long the match- |
limit how long the matching 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 2436 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3111 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Limiting the recursion depth limits the amount of machine stack that |
Limiting the recursion depth limits the amount of machine stack that |
can be used, or, when PCRE has been compiled to use memory on the heap |
can be used, or, when PCRE has been compiled to use memory on the heap |
instead of the stack, the amount of heap memory that can be used. This |
instead of the stack, the amount of heap memory that can be used. This |
limit is not relevant, and is ignored, if the pattern was successfully | limit is not relevant, and is ignored, when matching is done using JIT |
studied with PCRE_STUDY_JIT_COMPILE. | compiled code. |
|
|
The default value for match_limit_recursion can be set when PCRE is |
The default value for match_limit_recursion can be set when PCRE is |
built; the default default is the same value as the default for |
built; the default default is the same value as the default for |
Line 2446 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3121 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 used to pass a character tables pointer to |
pcre_exec(); this overrides the value that is stored with the compiled | pcre_exec(); this overrides the value that is stored with the compiled |
pattern. A non-NULL value is stored with the compiled pattern only if | pattern. A non-NULL value is stored with the compiled pattern only if |
custom tables were supplied to pcre_compile() via its tableptr argu- | custom tables were supplied to pcre_compile() via its tableptr argu- |
ment. If NULL is passed to pcre_exec() using this mechanism, it forces |
ment. If NULL is passed to pcre_exec() using this mechanism, it forces |
PCRE's internal tables to be used. This facility is helpful when re- | PCRE's internal tables to be used. This facility is helpful when re- |
using patterns that have been saved after compiling with an external | using patterns that have been saved after compiling with an external |
set of tables, because the external tables might be at a different | set of tables, because the external tables might be at a different |
address when pcre_exec() is called. See the pcreprecompile documenta- | address when pcre_exec() is called. See the pcreprecompile documenta- |
tion for a discussion of saving compiled patterns for later use. |
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 | 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- | 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 | 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- | 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 | 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 | 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. | 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 | 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, | 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_SOFT, and | PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and |
PCRE_PARTIAL_HARD. | PCRE_PARTIAL_SOFT. |
|
|
If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE | If the pattern was successfully studied with one of the just-in-time |
option, 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, and | PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, |
PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not | PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an |
supported. If an unsupported option is used, JIT execution is disabled | unsupported option is used, JIT execution is disabled and the normal |
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 2508 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3192 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. | compile time, it cannot be unset at matching time. The use of |
| PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to |
| 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 2642 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3329 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
|
|
When PCRE_UTF8 is set at compile time, the validity of the subject as a |
When PCRE_UTF8 is set at compile time, the validity of the subject as a |
UTF-8 string is automatically checked when pcre_exec() is subsequently |
UTF-8 string is automatically checked when pcre_exec() is subsequently |
called. The value of startoffset is also checked to ensure that it | called. The entire string is checked before any other processing takes |
points to the start of a UTF-8 character. There is a discussion about | place. The value of startoffset is also checked to ensure that it |
the validity of UTF-8 strings in the pcreunicode page. If an invalid | points to the start of a UTF-8 character. There is a discussion about |
sequence of bytes is found, pcre_exec() returns the error | the validity of UTF-8 strings in the pcreunicode page. If an invalid |
| sequence of bytes is found, pcre_exec() returns the error |
PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a |
PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a |
truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In |
truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In |
both cases, information about the precise nature of the error may also | both cases, information about the precise nature of the error may also |
be returned (see the descriptions of these errors in the section enti- | be returned (see the descriptions of these errors in the section enti- |
tled Error return values from pcre_exec() below). If startoffset con- | tled Error return values from pcre_exec() below). If startoffset con- |
tains a value that does not point to the start of a UTF-8 character (or |
tains a value that does not point to the start of a UTF-8 character (or |
to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned. |
to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned. |
|
|
If you already know that your subject is valid, and you want to skip | If you already know that your subject is valid, and you want to skip |
these checks for performance reasons, you can set the | these checks for performance reasons, you can set the |
PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to | PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to |
do this for the second and subsequent calls to pcre_exec() if you are | do this for the second and subsequent calls to pcre_exec() if you are |
making repeated calls to find all the matches in a single subject | making repeated calls to find all the matches in a single subject |
string. However, you should be sure that the value of startoffset | string. However, you should be sure that the value of startoffset |
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. |
|
|
PCRE_PARTIAL_HARD |
PCRE_PARTIAL_HARD |
PCRE_PARTIAL_SOFT |
PCRE_PARTIAL_SOFT |
|
|
These options turn on the partial matching feature. For backwards com- | These options turn on the partial matching feature. For backwards com- |
patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial | patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial |
match occurs if the end of the subject string is reached successfully, | match occurs if the end of the subject string is reached successfully, |
but there are not enough subject characters to complete the match. If | but there are not enough subject characters to complete the match. If |
this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, |
this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, |
matching continues by testing any remaining alternatives. Only if no | matching continues by testing any remaining alternatives. Only if no |
complete match can be found is PCRE_ERROR_PARTIAL returned instead of | complete match can be found is PCRE_ERROR_PARTIAL returned instead of |
PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the | PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the |
caller is prepared to handle a partial match, but only if no complete | caller is prepared to handle a partial match, but only if no complete |
match can be found. |
match can be found. |
|
|
If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this | If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this |
case, if a partial match is found, pcre_exec() immediately returns | case, if a partial match is found, pcre_exec() immediately returns |
PCRE_ERROR_PARTIAL, without considering any other alternatives. In | PCRE_ERROR_PARTIAL, without considering any other alternatives. In |
other words, when PCRE_PARTIAL_HARD is set, a partial match is consid- | other words, when PCRE_PARTIAL_HARD is set, a partial match is consid- |
ered to be more important that an alternative complete match. |
ered to be more important that an alternative complete match. |
|
|
In both cases, the portion of the string that was inspected when the | In both cases, the portion of the string that was inspect In both cases, the portion of the string that was inspect |
partial match was found is set as the first matching string. There is a |
partial match was found is set as the first matching string. There is a |
more detailed discussion of partial and multi-segment matching, with | more detailed discussion of partial and multi-segment matching, with |
examples, in the pcrepartial documentation. |
examples, in the pcrepartial documentation. |
|
|
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 |
pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is | items for the 16-bit library, and 32-bit data items for the 32-bit |
zero, the search for a match starts at the beginning of the subject, | library. |
and this is by far the most common case. In UTF-8 mode, the byte offset | |
must point to the start of a UTF-8 character (or the end of the sub- | |
ject). Unlike the pattern string, the subject may contain binary zero | |
bytes. | |
|
|
|
If startoffset is negative or greater than the length of the subject, |
|
pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is |
|
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 or UTF-16 mode, the |
|
offset must point to the start of a character, or the end of the sub- |
|
ject (in UTF-32 mode, one data unit equals one character, so all off- |
|
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 |
Line 2762 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3455 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
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 |
Line 2782 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3477 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
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 |
not 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 |
Line 2973 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3668 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
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 the PCRE_STUDY_JIT_COMPILE option is being matched, but the mem- | using a JIT compile option is being matched, but the memory available |
ory available for the just-in-time processing stack is not large | for the just-in-time processing stack is not large enough. See the |
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 and -22 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 |
offset of the start of the invalid UTF-8 character is placed in the | offset of the start of the invalid UTF-8 character is placed in the |
first output vector element (ovector[0]) and a reason code is placed in |
first output vector element (ovector[0]) and a reason code is placed in |
the second element (ovector[1]). The reason codes are given names in | the second element (ovector[1]). The reason codes are given names in |
the pcre.h header file: |
the pcre.h header file: |
|
|
PCRE_UTF8_ERR1 |
PCRE_UTF8_ERR1 |
Line 3009 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3719 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_UTF8_ERR4 |
PCRE_UTF8_ERR4 |
PCRE_UTF8_ERR5 |
PCRE_UTF8_ERR5 |
|
|
The string ends with a truncated UTF-8 character; the code specifies | The string ends with a truncated UTF-8 character; the code specifies |
how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 | how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 |
characters to be no longer than 4 bytes, the encoding scheme (origi- | characters to be no longer than 4 bytes, the encoding scheme (origi- |
nally defined by RFC 2279) allows for up to 6 bytes, and this is | nally defined by RFC 2279) allows for up to 6 bytes, and this is |
checked first; hence the possibility of 4 or 5 missing bytes. |
checked first; hence the possibility of 4 or 5 missing bytes. |
|
|
PCRE_UTF8_ERR6 |
PCRE_UTF8_ERR6 |
Line 3022 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3732 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_UTF8_ERR10 |
PCRE_UTF8_ERR10 |
|
|
The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of |
The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of |
the character do not have the binary value 0b10 (that is, either the | the character do not have the binary value 0b10 (that is, either the |
most significant bit is 0, or the next bit is 1). |
most significant bit is 0, or the next bit is 1). |
|
|
PCRE_UTF8_ERR11 |
PCRE_UTF8_ERR11 |
PCRE_UTF8_ERR12 |
PCRE_UTF8_ERR12 |
|
|
A character that is valid by the RFC 2279 rules is either 5 or 6 bytes | A character that is valid by the RFC 2279 rules is either 5 or 6 bytes |
long; these code points are excluded by RFC 3629. |
long; these code points are excluded by RFC 3629. |
|
|
PCRE_UTF8_ERR13 |
PCRE_UTF8_ERR13 |
|
|
A 4-byte character has a value greater than 0x10fff; these code points | A 4-byte character has a value greater than 0x10fff; these code points |
are excluded by RFC 3629. |
are excluded by RFC 3629. |
|
|
PCRE_UTF8_ERR14 |
PCRE_UTF8_ERR14 |
|
|
A 3-byte character has a value in the range 0xd800 to 0xdfff; this | A 3-byte character has a value i A 3-byte character has a value i |
range of code points are reserved by RFC 3629 for use with UTF-16, and | range of code points are reserved by RFC 3629 for use with UTF-16, and |
so are excluded from UTF-8. |
so are excluded from UTF-8. |
|
|
PCRE_UTF8_ERR15 |
PCRE_UTF8_ERR15 |
Line 3048 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3758 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_UTF8_ERR18 |
PCRE_UTF8_ERR18 |
PCRE_UTF8_ERR19 |
PCRE_UTF8_ERR19 |
|
|
A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes | A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes |
for a value that can be represented by fewer bytes, which is invalid. | for a value that can be represented by fewer bytes, which is invalid. |
For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor- | For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor- |
rect coding uses just one byte. |
rect coding uses just one byte. |
|
|
PCRE_UTF8_ERR20 |
PCRE_UTF8_ERR20 |
|
|
The two most significant bits of the first byte of a character have the |
The two most significant bits of the first byte of a character have the |
binary value 0b10 (that is, the most significant bit is 1 and the sec- | binary value 0b10 (that is, the most significant bit is 1 and the sec- |
ond is 0). Such a byte can only validly occur as the second or subse- | ond is 0). Such a byte can only validly occur as the second or subse- |
quent byte of a multi-byte character. |
quent byte of a multi-byte character. |
|
|
PCRE_UTF8_ERR21 |
PCRE_UTF8_ERR21 |
|
|
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 3452 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
Line 4169 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
This error is given if the output vector is not large enough. This |
This error is given if the output vector is not large enough. This |
should be extremely rare, as a vector of size 1000 is used. |
should be extremely rare, as a vector of size 1000 is used. |
|
|
|
PCRE_ERROR_DFA_BADRESTART (-30) |
|
|
|
When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some |
|
plausibility checks are made on the contents of the workspace, which |
|
should contain data about the previous partial match. If any of these |
|
checks fail, this error is given. |
|
|
|
|
SEE ALSO |
SEE ALSO |
|
|
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). |
|
|
|
|
AUTHOR |
AUTHOR |
Line 3469 AUTHOR
|
Line 4193 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 21 January 2012 | Last updated: 12 May 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCRECALLOUT(3) PCRECALLOUT(3) | PCRECALLOUT(3) Library Functions Manual PCRECALLOUT(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
SYNOPSIS |
|
|
PCRE CALLOUTS | #include <pcre.h> |
|
|
int (*pcre_callout)(pcre_callout_block *); |
int (*pcre_callout)(pcre_callout_block *); |
|
|
int (*pcre16_callout)(pcre16_callout_block *); |
int (*pcre16_callout)(pcre16_callout_block *); |
|
|
|
int (*pcre32_callout)(pcre32_callout_block *); |
|
|
|
|
|
DESCRIPTION |
|
|
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. |
|
|
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 3514 PCRE CALLOUTS
|
Line 4245 PCRE CALLOUTS
|
(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) |
(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) |
|
|
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. | |
|
|
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. | |
|
|
|
This applies only to assertion conditions (because they are themselves |
|
independent groups). |
|
|
|
Automatic callouts can be used for tracking the progress of pattern |
|
matching. The pcretest command has an option that sets automatic call- |
|
outs; when it is used, the output indicates how the pattern is matched. |
|
This is useful information when you are trying to optimize the perfor- |
|
mance of a particular pattern. |
|
|
|
|
MISSING CALLOUTS |
MISSING CALLOUTS |
|
|
You should be aware that, because of optimizations in the way PCRE |
You should be aware that, because of optimizations in the way PCRE |
Line 3552 MISSING CALLOUTS
|
Line 4289 MISSING CALLOUTS
|
THE CALLOUT INTERFACE |
THE CALLOUT INTERFACE |
|
|
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: |
|
|
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 3572 THE CALLOUT INTERFACE
|
Line 4311 THE CALLOUT INTERFACE
|
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) |
|
const PCRE_UCHAR32 *mark; (32-bit version) |
|
|
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 |
version number will change again in future if additional fields are | version number will change again in future if additional fields are |
added, but the intention is never to remove any of the existing fields. |
added, but the intention is never to remove any of the existing fields. |
|
|
The callout_number field contains the number of the callout, as com- | The callout_number field contains the number of the callout, as com- |
piled into the pattern (that is, the number after ?C for manual call- | piled into the pattern (that is, the number after ?C for manual call- |
outs, and 255 for automatically generated callouts). |
outs, and 255 for automatically generated callouts). |
|
|
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. |
|
|
The subject and subject_length fields contain copies of the values that |
The subject and subject_length fields contain copies of the values that |
were passed to the matching function. |
were passed to the matching function. |
|
|
The start_match field normally contains the offset within the subject | The start_match field normally contains the offset within the subject |
at which the current match attempt started. However, if the escape | at which the current match attempt started. However, if the escape |
sequence \K has been encountered, this value is changed to reflect the | sequence \K has been encountered, this value is changed to reflect the |
modified starting point. If the pattern is not anchored, the callout | modified starting point. If the pattern is not anchored, the callout |
function may be called several times from the same point in the pattern |
function may be called several times from the same point in the pattern |
for different starting points in the subject. |
for different starting points in the subject. |
|
|
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. |
|
|
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. |
|
|
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. |
|
|
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. |
|
|
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 |
Line 3635 THE CALLOUT INTERFACE
|
Line 4378 THE CALLOUT INTERFACE
|
the same callout number. However, they are set for all callouts. |
the same callout number. However, they are set for all callouts. |
|
|
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. |
|
|
|
|
RETURN VALUES |
RETURN VALUES |
Line 3668 AUTHOR
|
Line 4411 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 08 Janurary 2012 | Last updated: 03 March 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCRECOMPAT(3) PCRECOMPAT(3) | PCRECOMPAT(3) Library Functions Manual PCRECOMPAT(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
DIFFERENCES BETWEEN PCRE AND PERL |
DIFFERENCES BETWEEN PCRE AND PERL |
|
|
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 3698 DIFFERENCES BETWEEN PCRE AND PERL
|
Line 4441 DIFFERENCES BETWEEN PCRE AND PERL
|
|
|
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. | |
|
|
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 3727 DIFFERENCES BETWEEN PCRE AND PERL
|
Line 4468 DIFFERENCES BETWEEN PCRE AND PERL
|
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." |
|
|
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: |
|
|
Pattern PCRE matches Perl matches |
Pattern PCRE matches Perl matches |
Line 3745 DIFFERENCES BETWEEN PCRE AND PERL
|
Line 4481 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 |
|
|
The \Q...\E sequence is recognized both inside and outside character | The \Q...\E sequence is recognized both inside and outside character |
classes. |
classes. |
|
|
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. |
|
|
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. |
|
|
11. If (*THEN) is present in a group that is called as a subroutine, | 10. If any of the backtracking control verbs are used in a subpattern |
its action is limited to that group, even if the group does not contain | that is called as a subroutine (whether or not recursively), their |
any | characters. | effect is confined to that subpattern; it does not extend to the sur- |
| rounding pattern. This is not always the case in Perl. In particular, |
| if (*THEN) is present in a group that is called as a subroutine, its |
| action is limited to that group, even if the group does not contain any |
| | characters. Note that such subpatterns are processed as anchored at |
| the point where they are tested. |
|
|
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". |
|
|
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. |
|
|
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 whitespace between ( and ? but PCRE never | modifier is set, Perl allows white space between ( and ? but PCRE never |
does, even if the PCRE_EXTENDED option is set. |
does, even if the PCRE_EXTENDED option is set. |
|
|
15. PCRE provides some extensions to the Perl regular expression facil- | 16. 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. |
| |
| 17. 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 3825 DIFFERENCES BETWEEN PCRE AND PERL
|
Line 4582 DIFFERENCES BETWEEN PCRE AND PERL
|
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 3843 AUTHOR
|
Line 4600 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 08 Januray 2012 | Last updated: 19 March 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREPATTERN(3) PCREPATTERN(3) | PCREPATTERN(3) Library Functions Manual PCREPATTERN(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
PCRE REGULAR EXPRESSION DETAILS |
PCRE REGULAR EXPRESSION DETAILS |
|
|
The syntax and semantics of the regular expressions that are supported |
The syntax and semantics of the regular expressions that are supported |
Line 3872 PCRE REGULAR EXPRESSION DETAILS
|
Line 4629 PCRE REGULAR EXPRESSION DETAILS
|
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. |
|
|
|
This document discusses the patterns that are supported by PCRE when |
|
one its main matching functions, pcre_exec() (8-bit) or |
|
pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has alternative |
|
matching functions, pcre_dfa_exec() and pcre[16|32_dfa_exec(), which |
|
match using a different algorithm that is not Perl-compatible. Some of |
|
the 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 |
|
pcrematching page. |
|
|
|
|
|
SPECIAL START-OF-PATTERN ITEMS |
|
|
|
A number of options that can be passed to pcre_compile() can also be |
|
set by special items at the start of a pattern. These are not Perl-com- |
|
patible, but are provided to make these options accessible to pattern |
|
writers who are not able to change the program that processes the pat- |
|
tern. Any number of these items may appear, but they must all be |
|
together right at the start of the pattern string, and the letters must |
|
be in upper case. |
|
|
|
UTF support |
|
|
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: |
|
|
(*UTF8) |
(*UTF8) |
(*UTF16) |
(*UTF16) |
|
(*UTF32) |
|
(*UTF) |
|
|
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. |
|
|
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. |
|
|
|
Unicode property support |
|
|
|
Another special sequence that may appear at the start of a pattern is |
|
|
(*UCP) |
(*UCP) |
|
|
This has the same effect as setting the PCRE_UCP option: it causes |
This has the same effect as setting the PCRE_UCP option: it causes |
Line 3898 PCRE REGULAR EXPRESSION DETAILS
|
Line 4688 PCRE REGULAR EXPRESSION DETAILS
|
character types, instead of recognizing only characters with codes less |
character types, instead of recognizing only characters with codes less |
than 128 via a lookup table. |
than 128 via a lookup table. |
|
|
|
Disabling start-up optimizations |
|
|
If a pattern starts with (*NO_START_OPT), it has the same effect as |
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 |
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- | time. |
cerned with the handling of newlines; they are described below. | |
|
|
The remainder of this document discusses the patterns that are sup- | Newline conventions |
ported by PCRE when one its main matching functions, pcre_exec() | |
(8-bit) or pcre16_exec() (16-bit), is used. PCRE also has alternative | |
matching functions, pcre_dfa_exec() and pcre16_dfa_exec(), which match | |
using a different algorithm that is not Perl-compatible. Some of the | |
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. | |
|
|
| 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. |
|
|
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: |
|
|
(*CR) carriage return |
(*CR) carriage return |
Line 3933 NEWLINE CONVENTIONS
|
Line 4713 NEWLINE CONVENTIONS
|
(*ANY) all Unicode newline sequences |
(*ANY) all Unicode newline sequences |
|
|
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 |
|
|
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. |
|
|
|
Setting match and recursion limits |
|
|
|
The caller of pcre_exec() can set a limit on the number of times the |
|
internal match() function is called and on the maximum depth of recur- |
|
sive calls. These facilities are provided to catch runaway matches that |
|
are provoked by patterns with huge matching trees (a typical example is |
|
a pattern with nested unlimited repeats) and to avoid running out of |
|
system stack by too much recursion. When one of these limits is |
|
reached, pcre_exec() gives an error return. The limits can also be set |
|
by items at the start of the pattern of the form |
|
|
|
(*LIMIT_MATCH=d) |
|
(*LIMIT_RECURSION=d) |
|
|
|
where d is any number of decimal digits. However, the value of the set- |
|
ting must be less than the value set by the caller of pcre_exec() for |
|
it to have any effect. In other words, the pattern writer can lower the |
|
limit set by the programmer, but not raise it. If there is more than |
|
one setting of one of these limits, the lower value is used. |
|
|
|
|
|
EBCDIC CHARACTER CODES |
|
|
|
PCRE can be compiled to run in an environment that uses EBCDIC as its |
|
character code rather than ASCII or Unicode (typically a mainframe sys- |
|
tem). In the sections below, character code values are ASCII or Uni- |
|
code; in an EBCDIC environment these characters may have different code |
|
values, and there are no code points greater than 255. |
|
|
|
|
CHARACTERS AND METACHARACTERS |
CHARACTERS AND METACHARACTERS |
|
|
A regular expression is a pattern that is matched against a subject | A regular expression is a pattern that is matched against a subject |
string from left to right. Most characters stand for themselves in a | string from left to right. Most characters stand for themselves in a |
pattern, and match the corresponding characters in the subject. As a | pattern, and match the corresponding characters in the subject. As a |
trivial example, the pattern |
trivial example, the pattern |
|
|
The quick brown fox |
The quick brown fox |
|
|
matches a portion of a subject string that is identical to itself. When |
matches a portion of a subject string that is identical to itself. When |
caseless matching is specified (the PCRE_CASELESS option), letters are | caseless matching is specified (the PCRE_CASELESS option), letters are |
matched independently of case. In a UTF mode, PCRE always understands | matched independently of case. In a UTF mode, PCRE always understands |
the concept of case for characters whose values are less than 128, so | the concept of case for characters whose values are less than 128, so |
caseless matching is always possible. For characters with higher val- | caseless matching is always possible. For characters with higher val- |
ues, the concept of case is supported if PCRE is compiled with Unicode | ues, the concept of case is supported if PCRE is compiled with Unicode |
property support, but not otherwise. If you want to use caseless | property support, but not otherwise. If you want to use caseless |
matching for characters 128 and above, you must ensure that PCRE is | matching for characters 128 and above, you must ensure that PCRE is |
compiled with Unicode property support as well as with UTF support. |
compiled with Unicode property support as well as with UTF support. |
|
|
The power of regular expressions comes from the ability to include | The power of regular expressions comes from the ability to include |
alternatives and repetitions in the pattern. These are encoded in the | alternatives and repetitions in the pattern. These are encoded in the |
pattern by the use of metacharacters, which do not stand for themselves |
pattern by the use of metacharacters, which do not stand for themselves |
but instead are interpreted in some special way. |
but instead are interpreted in some special way. |
|
|
There are two different sets of metacharacters: those that are recog- | There are two different sets of metacharacters: those that are recog- |
nized anywhere in the pattern except within square brackets, and those | nized anywhere in the pattern except within square brackets, and those |
that are recognized within square brackets. Outside square brackets, | that are recognized within square brackets. Outside square brackets, |
the metacharacters are as follows: |
the metacharacters are as follows: |
|
|
\ general escape character with several uses |
\ general escape character with several uses |
Line 3998 CHARACTERS AND METACHARACTERS
|
Line 4806 CHARACTERS AND METACHARACTERS
|
also "possessive quantifier" |
also "possessive quantifier" |
{ start min/max quantifier |
{ start min/max quantifier |
|
|
Part of a pattern that is in square brackets is called a "character | Part of a pattern that is in square brackets is called a "character |
class". In a character class the only metacharacters are: |
class". In a character class the only metacharacters are: |
|
|
\ general escape character |
\ general escape character |
Line 4015 BACKSLASH
|
Line 4823 BACKSLASH
|
|
|
The backslash character has several uses. Firstly, if it is followed by |
The backslash character has several uses. Firstly, if it is followed by |
a character that is not a number or a letter, it takes away any special |
a character that is not a number or a letter, it takes away any special |
meaning that character may have. This use of backslash as an escape | meaning that character may have. This use of backslash as an escape |
character applies both inside and outside character classes. |
character applies both inside and outside character classes. |
|
|
For example, if you want to match a * character, you write \* in the | For example, if you want to match a * character, you write \* in the |
pattern. This escaping action applies whether or not the following | pattern. This escaping action applies whether or not the following |
character would otherwise be interpreted as a metacharacter, so it is | character would otherwise be interpreted as a metacharacter, so it is |
always safe to precede a non-alphanumeric with backslash to specify | always safe to precede a non-alphanumeric with backslash to specify |
that it stands for itself. In particular, if you want to match a back- | that it stands for itself. In particular, if you want to match a back- |
slash, you write \\. |
slash, you write \\. |
|
|
In a UTF mode, only ASCII numbers and letters have any special meaning | In a UTF mode, only ASCII numbers and letters have any special meaning |
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. |
|
|
If a pattern is compiled with the PCRE_EXTENDED option, whitespace in | If a pattern is compiled with the PCRE_EXTENDED option, white spac If a pattern is compiled with the PCRE_EXTENDED option, white spac |
the pattern (other than in a character class) and characters between a | the pattern (other than in a character class) and characters between a |
# outside a character class and the next newline are ignored. An escap- |
# outside a character class and the next newline are ignored. An escap- |
ing backslash can be used to include a whitespace or # character as | ing backslash can be used to include a white space or # character as |
part of the pattern. |
part of the pattern. |
|
|
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- |
ent from Perl in that $ and @ are handled as literals in \Q...\E | ent from Perl in that $ and @ are handled as literals in \Q...\E |
sequences in PCRE, whereas in Perl, $ and @ cause variable interpola- | sequences in PCRE, whereas in Perl, $ and @ cause variable interpola- |
tion. Note the following examples: |
tion. Note the following examples: |
|
|
Pattern PCRE matches Perl matches |
Pattern PCRE matches Perl matches |
Line 4048 BACKSLASH
|
Line 4856 BACKSLASH
|
\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 |
|
|
The \Q...\E sequence is recognized both inside and outside character | The \Q...\E sequence is recognized both inside and outside character |
classes. An isolated \E that is not preceded by \Q is ignored. If \Q | classes. An isolated \E that is not preceded by \Q is ignored. If \Q |
is not followed by \E later in the pattern, the literal interpretation | is not followed by \E later in the pattern, the literal interpretation |
continues to the end of the pattern (that is, \E is assumed at the | continues to the end of the pattern (that is, \E is assumed at the |
end). If the isolated \Q is inside a character class, this causes an | end). If the isolated \Q is inside a character class, this causes an |
error, because the character class is not terminated. |
error, because the character class is not terminated. |
|
|
Non-printing characters |
Non-printing characters |
|
|
A second use of backslash provides a way of encoding non-printing char- |
A second use of backslash provides a way of encoding non-printing char- |
acters in patterns in a visible manner. There is no restriction on the | acters in patterns in a visible manner. There is no restriction on the |
appearance of non-printing characters, apart from the binary zero that | appearance of non-printing characters, apart from the binary zero that |
terminates a pattern, but when a pattern is being prepared by text | terminates a pattern, but when a pattern is being prepared by text |
editing, it is often easier to use one of the following escape | editing, it is often easier to use one of the following escape |
sequences than the binary character it represents: |
sequences than the binary character it represents: |
|
|
\a alarm, that is, the BEL character (hex 07) |
\a alarm, that is, the BEL character (hex 07) |
\cx "control-x", where x is any ASCII character |
\cx "control-x", where x is any ASCII character |
\e escape (hex 1B) |
\e escape (hex 1B) |
\f formfeed (hex 0C) | \f form feed (hex 0C) |
\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) |
Line 4076 BACKSLASH
|
Line 4884 BACKSLASH
|
\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) |
|
|
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 |
| hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c |
has a value greater than 127, a compile-time error occurs. This locks |
has a value greater than 127, a compile-time error occurs. This locks |
out non-ASCII characters in all modes. (When PCRE is compiled in EBCDIC | out non-ASCII characters in all modes. |
mode, all byte values are valid. A lower case letter is converted to | |
upper case, and then the 0xc0 bits are flipped.) | |
|
|
|
The \c facility was designed for use with ASCII characters, but with |
|
the extension to Unicode it is even less useful than it once was. It |
|
is, however, recognized when PCRE is compiled in EBCDIC mode, where |
|
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. |
|
|
By default, after \x, from zero to two hexadecimal digits are read |
By default, after \x, from zero to two hexadecimal digits are read |
(letters can be in upper or lower case). Any number of hexadecimal dig- |
(letters can be in upper or lower case). Any number of hexadecimal dig- |
its may appear between \x{ and }, but the character code is constrained |
its may appear between \x{ and }, but the character code is constrained |
Line 4094 BACKSLASH
|
Line 4911 BACKSLASH
|
8-bit UTF-8 mode less than 0x10ffff and a valid codepoint |
8-bit UTF-8 mode less than 0x10ffff and a valid codepoint |
16-bit non-UTF mode less than 0x10000 |
16-bit non-UTF mode less than 0x10000 |
16-bit UTF-16 mode less than 0x10ffff and a valid codepoint |
16-bit UTF-16 mode less than 0x10ffff and a valid codepoint |
|
32-bit non-UTF mode less than 0x80000000 |
|
32-bit UTF-32 mode less than 0x10ffff and a valid codepoint |
|
|
Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- |
Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- |
called "surrogate" codepoints). | called "surrogate" codepoints), and 0xffef. |
|
|
If characters other than hexadecimal digits appear between \x{ and }, |
If characters other than hexadecimal digits appear between \x{ and }, |
or if there is no terminating }, this form of escape is not recognized. |
or if there is no terminating }, this form of escape is not recognized. |
Line 4109 BACKSLASH
|
Line 4928 BACKSLASH
|
its. Otherwise, it matches a literal "x" character. In JavaScript |
its. Otherwise, it matches a literal "x" character. In JavaScript |
mode, support for code points greater than 256 is provided by \u, which |
mode, support for code points greater than 256 is provided by \u, which |
must be followed by four hexadecimal digits; otherwise it matches a |
must be followed by four hexadecimal digits; otherwise it matches a |
literal "u" character. | 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 |
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- |
two syntaxes for \x (or by \u in JavaScript mode). There is no differ- |
Line 4137 BACKSLASH
|
Line 4958 BACKSLASH
|
value of the character is constrained in the same way as characters |
value of the character is constrained in the same way as characters |
specified in hexadecimal. For example: |
specified in hexadecimal. 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 4196 BACKSLASH
|
Line 5017 BACKSLASH
|
|
|
\d any decimal digit |
\d any decimal digit |
\D any character that is not a decimal digit |
\D any character that is not a decimal digit |
\h any horizontal whitespace character | \h any horizontal white space character |
\H any character that is not a horizontal whitespace character | \H any character that is not a horizontal white space character |
\s any whitespace character | \s any white space character |
\S any character that is not a whitespace character | \S any character that is not a white space character |
\v any vertical whitespace character | \v any vertical white space character |
\V any character that is not a vertical whitespace character | \V any character that is not a vertical white space character |
\w any "word" character |
\w any "word" character |
\W any "non-word" character |
\W any "non-word" character |
|
|
Line 4257 BACKSLASH
|
Line 5078 BACKSLASH
|
codepoints, whether or not PCRE_UCP is set. The horizontal space char- |
codepoints, 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 4279 BACKSLASH
|
Line 5100 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 Formfeed | 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 4301 BACKSLASH
|
Line 5122 BACKSLASH
|
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 (formfeed, U+000C), CR (carriage | U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car- |
return, U+000D), or NEL (next line, U+0085). The two-character sequence | riage return, U+000D), or NEL (next line, U+0085). The two-character |
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- |
Line 4332 BACKSLASH
|
Line 5153 BACKSLASH
|
|
|
(*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 |
|
|
Line 4347 BACKSLASH
|
Line 5168 BACKSLASH
|
|
|
\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 |
Line 4366 BACKSLASH
|
Line 5187 BACKSLASH
|
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, Bengali, Bopomofo, Braille, | Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo, |
Buginese, Buhid, Canadian_Aboriginal, Carian, Cham, Cherokee, Common, | Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma, |
Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Egyp- | Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, |
tian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, Gothic, Greek, | Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, |
Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Impe- | Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira- |
rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian, | gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- |
Javanese, Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao, | tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, |
Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam, | Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, |
Meetei_Mayek, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic, | Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive, |
Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki, Oriya, Osmanya, | Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko, |
Phags_Pa, Phoenician, Rejang, Runic, Samaritan, Saurashtra, Shavian, | Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic, |
Sinhala, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, | Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari- |
Tai_Tham, Tai_Viet, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, | tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese, |
Ugaritic, Vai, Yi. | Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, |
| Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, |
| 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- |
Line 4448 BACKSLASH
|
Line 5271 BACKSLASH
|
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 |
Line 4461 BACKSLASH
|
Line 5284 BACKSLASH
|
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} alw For example, \p{Lu} alw |
| different from the behaviour of current versions of Perl. |
|
|
|
Matching characters by Unicode property is not fast, because PCRE has |
|
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 |
The \X escape matches any number of Unicode characters that form an |
extended Unicode sequence. \X is equivalent to | "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 and POSIX character classes to use Unicode |
to use Unicode properties. PCRE uses these non-standard, non-Perl prop- | properties. PCRE uses these non-standard, non-Perl properties inter- |
erties internally when PCRE_UCP is set. They are: | nally when PCRE_UCP is set. However, 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, |
formfeed, 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, except that vertical tab |
is excluded. Xwd matches the same characters as Xan, plus underscore. |
is excluded. 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 4543 BACKSLASH
|
Line 5405 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 4673 MATCHING A SINGLE DATA UNIT
|
Line 5540 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 option is used). | (and by default it checks this at the start of processing unless the |
| 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- |
Line 4732 SQUARE BRACKETS AND CHARACTER CLASSES
|
Line 5601 SQUARE BRACKETS AND CHARACTER CLASSES
|
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. |
|
|
Line 4940 INTERNAL OPTION SETTING
|
Line 5809 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 4955 SUBPATTERNS
|
Line 5827 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 4974 SUBPATTERNS
|
Line 5846 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 4987 SUBPATTERNS
|
Line 5859 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 5025 DUPLICATE SUBPATTERN NUMBERS
|
Line 5897 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. |
Named capturing parentheses are still allocated numbers as well as | Named capturing parentheses are still allocated numbers as well as |
names, exactly as if the names were not present. The PCRE API provides | names, exactly as if the names were not present. The PCRE API provides |
function calls for extracting the name-to-number translation table from |
function calls for extracting the name-to-number translation table from |
a compiled pattern. There is also a convenience function for extracting |
a compiled pattern. There is also a convenience function for extracting |
a captured substring by name. |
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 5086 NAMED SUBPATTERNS
|
Line 5958 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 one that corresponds to the first occur- |
rence of the name is used. In the absence of duplicate numbers (see the |
rence 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 | 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 | named reference in a condition test (see the section about conditions |
below), either to check whether a subpattern has matched, or to check | below), either to check whether a subpattern has matched, or to check |
for recursion, all subpatterns with the same name are tested. If the | 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. | 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 |
This is the same behaviour as testing by number. For further details of |
the interfaces for handling named subpatterns, see the pcreapi documen- |
the interfaces for handling named subpatterns, see the pcreapi documen- |
tation. |
tation. |
|
|
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 give the same name to subpatterns with the same number, even when |
PCRE_DUPNAMES is not set. |
PCRE_DUPNAMES is not set. |
|
|
|
|
REPETITION |
REPETITION |
|
|
Repetition is specified by quantifiers, which can follow any of the | Repetition is specified by quantifiers, which can follow any of the |
following items: |
following items: |
|
|
a literal data character |
a literal data character |
Line 5131 REPETITION
|
Line 6003 REPETITION
|
a parenthesized subpattern (including assertions) |
a parenthesized subpattern (including assertions) |
a subroutine call to a subpattern (recursive or otherwise) |
a subroutine call to a subpattern (recursive or otherwise) |
|
|
The general repetition quantifier specifies a minimum and maximum num- | The general repetition quantifier specifies a minimum and maximum num- |
ber of permitted matches, by giving the two numbers in curly brackets | ber of permitted matches, by giving the two numbers in curly brackets |
(braces), separated by a comma. The numbers must be less than 65536, | (braces), separated by a comma. The numbers must be less than 65536, |
and the first must be less than or equal to the second. For example: |
and the first must be less than or equal to the second. For example: |
|
|
z{2,4} |
z{2,4} |
|
|
matches "zz", "zzz", or "zzzz". A closing brace on its own is not a | matches "zz", "zzz", or "zzzz". A closing brace on its own is not a |
special character. If the second number is omitted, but the comma is | special character. If the second number is omitted, but the comma is |
present, there is no upper limit; if the second number and the comma | present, there is no upper limit; if the second number and the comma |
are both omitted, the quantifier specifies an exact number of required | are both omitted, the quantifier specifies an exact number of required |
matches. Thus |
matches. Thus |
|
|
[aeiou]{3,} |
[aeiou]{3,} |
Line 5150 REPETITION
|
Line 6022 REPETITION
|
|
|
\d{8} |
\d{8} |
|
|
matches exactly 8 digits. An opening curly bracket that appears in a | matches exactly 8 digits. An opening curly bracket that appears in a |
position where a quantifier is not allowed, or one that does not match | position where a quantifier is not allowed, or one that does not match |
the syntax of a quantifier, is taken as a literal character. For exam- | the syntax of a quantifier, is taken as a literal character. For exam- |
ple, {,6} is not a quantifier, but a literal string of four characters. |
ple, {,6} is not a quantifier, but a literal string of four characters. |
|
|
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- |
Line 5243 REPETITION
|
Line 6116 REPETITION
|
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: |
Line 5253 REPETITION
|
Line 6126 REPETITION
|
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 |
|
|
(tweedle[dume]{3}\s*)+ |
(tweedle[dume]{3}\s*)+ |
|
|
has matched "tweedledum tweedledee" the value of the captured substring |
has matched "tweedledum tweedledee" the value of the captured substring |
is "tweedledee". However, if there are nested capturing subpatterns, | is "tweedledee". However, if there are nested capturing subpatterns, |
the corresponding captured values may have been set in previous itera- | the corresponding captured values may have been set in previous itera- |
tions. For example, after |
tions. For example, after |
|
|
/(a|(b))+/ |
/(a|(b))+/ |
Line 5270 REPETITION
|
Line 6152 REPETITION
|
|
|
ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS |
ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS |
|
|
With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy") | With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy") |
repetition, failure of what follows normally causes the repeated item | repetition, failure of what follows normally causes the repeated item |
to be re-evaluated to see if a different number of repeats allows the | to be re-evaluated to see if a different number of repeats allows the |
rest of the pattern to match. Sometimes it is useful to prevent this, | rest of the pattern to match. Sometimes it is useful to prevent this, |
either to change the nature of the match, or to cause it fail earlier | either to change the nature of the match, or to cause it fail earlier |
than it otherwise might, when the author of the pattern knows there is | than it otherwise might, when the author of the pattern knows there is |
no point in carrying on. |
no point in carrying on. |
|
|
Consider, for example, the pattern \d+foo when applied to the subject | Consider, for example, the pattern \d+foo when applied to the subject |
line |
line |
|
|
123456bar |
123456bar |
|
|
After matching all 6 digits and then failing to match "foo", the normal |
After matching all 6 digits and then failing to match "foo", the normal |
action of the matcher is to try again with only 5 digits matching the | action of the matcher is to try again with only 5 digits matching the |
\d+ item, and then with 4, and so on, before ultimately failing. | \d+ item, and then with 4, and so on, before ultimately failing. |
"Atomic grouping" (a term taken from Jeffrey Friedl's book) provides | "Atomic grouping" (a term taken from Jeffrey Friedl's book) provides |
the means for specifying that once a subpattern has matched, it is not | the means for specifying that once a subpattern has matched, it is not |
to be re-evaluated in this way. |
to be re-evaluated in this way. |
|
|
If we use atomic grouping for the previous example, the matcher gives | If we use atomic grouping for the previous example, the matcher gives |
up immediately on failing to match "foo" the first time. The notation | up immediately on failing to match "foo" the first time. The notation |
is a kind of special parenthesis, starting with (?> as in this example: |
is a kind of special parenthesis, starting with (?> as in this example: |
|
|
(?>\d+)foo |
(?>\d+)foo |
|
|
This kind of parenthesis "locks up" the part of the pattern it con- | This kind of parenthesis "locks up" the part of the pattern it con- |
tains once it has matched, and a failure further into the pattern is | tains once it has matched, and a failure further into the pattern is |
prevented from backtracking into it. Backtracking past it to previous | prevented from backtracking into it. Backtracking past it to previous |
items, however, works as normal. |
items, however, works as normal. |
|
|
An alternative description is that a subpattern of this type matches | An alternative description is that a subpattern of this type matches |
the string of characters that an identical standalone pattern would | the string of characters that an identical standalone pattern would |
match, if anchored at the current point in the subject string. |
match, if anchored at the current point in the subject string. |
|
|
Atomic grouping subpatterns are not capturing subpatterns. Simple cases |
Atomic grouping subpatterns are not capturing subpatterns. Simple cases |
such as the above example can be thought of as a maximizing repeat that |
such as the above example can be thought of as a maximizing repeat that |
must swallow everything it can. So, while both \d+ and \d+? are pre- | must swallow everything it can. So, while both \d+ and \d+? are pre- |
pared to adjust the number of digits they match in order to make the | pared to adjust the number of digits they match in order to make the |
rest of the pattern match, (?>\d+) can only match an entire sequence of |
rest of the pattern match, (?>\d+) can only match an entire sequence of |
digits. |
digits. |
|
|
Atomic groups in general can of course contain arbitrarily complicated | Atomic groups in general can of course contain arbitrarily complicated |
subpatterns, and can be nested. However, when the subpattern for an | subpatterns, and can be nested. However, when the subpattern for an |
atomic group is just a single repeated item, as in the example above, a |
atomic group is just a single repeated item, as in the example above, a |
simpler notation, called a "possessive quantifier" can be used. This | simpler notation, called a "possessive quantifier" can be used. This |
consists of an additional + character following a quantifier. Using | consists of an additional + character following a quantifier. Using |
this notation, the previous example can be rewritten as |
this notation, the previous example can be rewritten as |
|
|
\d++foo |
\d++foo |
Line 5326 ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
|
Line 6208 ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
|
|
|
(abc|xyz){2,3}+ |
(abc|xyz){2,3}+ |
|
|
Possessive quantifiers are always greedy; the setting of the | Possessive quantifiers are always greedy; the setting of the |
PCRE_UNGREEDY option is ignored. They are a convenient notation for the |
PCRE_UNGREEDY option is ignored. They are a convenient notation for the |
simpler forms of atomic group. However, there is no difference in the | simpler forms of atomic group. However, there is no difference in the |
meaning of a possessive quantifier and the equivalent atomic group, | meaning of a possessive quantifier and the equivalent atomic group, |
though there may be a performance difference; possessive quantifiers | though there may be a performance difference; possessive quantifiers |
should be slightly faster. |
should be slightly faster. |
|
|
The possessive quantifier syntax is an extension to the Perl 5.8 syn- | The possessive quantifier syntax is an extension to the Perl 5.8 syn- |
tax. Jeffrey Friedl originated the idea (and the name) in the first | tax. Jeffrey Friedl originated the idea (and the name) in the first |
edition of his book. Mike McCloskey liked it, so implemented it when he |
edition of his book. Mike McCloskey liked it, so implemented it when he |
built Sun's Java package, and PCRE copied it from there. It ultimately | built Sun's Java package, and PCRE copied it from there. It ultimately |
found its way into Perl at release 5.10. |
found its way into Perl at release 5.10. |
|
|
PCRE has an optimization that automatically "possessifies" certain sim- |
PCRE has an optimization that automatically "possessifies" certain sim- |
ple pattern constructs. For example, the sequence A+B is treated as | ple pattern constructs. For example, the sequence A+B is treated as |
A++B because there is no point in backtracking into a sequence of A's | A++B because there is no point in backtracking into a sequence of A's |
when B must follow. |
when B must follow. |
|
|
When a pattern contains an unlimited repeat inside a subpattern that | When a pattern contains an unlimited repeat inside a subpattern that |
can itself be repeated an unlimited number of times, the use of an | can itself be repeated an unlimited number of times, the use of an |
atomic group is the only way to avoid some failing matches taking a | atomic group is the only way to avoid some failing matches taking a |
very long time indeed. The pattern |
very long time indeed. The pattern |
|
|
(\D+|<\d+>)*[!?] |
(\D+|<\d+>)*[!?] |
|
|
matches an unlimited number of substrings that either consist of non- | matches an unlimited number of substrings that either consist of non- |
digits, or digits enclosed in <>, followed by either ! or ?. When it | digits, or digits enclosed in <>, followed by either ! or ?. When it |
matches, it runs quickly. However, if it is applied to |
matches, it runs quickly. However, if it is applied to |
|
|
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |
|
|
it takes a long time before reporting failure. This is because the | it takes a long time before reporting failure. This is because the |
string can be divided between the internal \D+ repeat and the external | string can be divided between the internal \D+ repeat and the external |
* repeat in a large number of ways, and all have to be tried. (The | * repeat in a large number of ways, and all have to be tried. (The |
example uses [!?] rather than a single character at the end, because | example uses [!?] rather than a single character at the end, because |
both PCRE and Perl have an optimization that allows for fast failure | both PCRE and Perl have an optimization that allows for fast failure |
when a single character is used. They remember the last single charac- | when a single character is used. They remember the last single charac- |
ter that is required for a match, and fail early if it is not present | ter that is required for a match, and fail early if it is not present |
in the string.) If the pattern is changed so that it uses an atomic | in the string.) If the pattern is changed so that it uses an atomic |
group, like this: |
group, like this: |
|
|
((?>\D+)|<\d+>)*[!?] |
((?>\D+)|<\d+>)*[!?] |
Line 5376 BACK REFERENCES
|
Line 6258 BACK REFERENCES
|
|
|
Outside a character class, a backslash followed by a digit greater than |
Outside a character class, a backslash followed by a digit greater than |
0 (and possibly further digits) is a back reference to a capturing sub- |
0 (and possibly further digits) is a back reference to a capturing sub- |
pattern earlier (that is, to its left) in the pattern, provided there | pattern earlier (that is, to its left) in the pattern, provided there |
have been that many previous capturing left parentheses. |
have been that many previous capturing left parentheses. |
|
|
However, if the decimal number following the backslash is less than 10, |
However, if the decimal number following the backslash is less than 10, |
it is always taken as a back reference, and causes an error only if | it is always taken as a back reference, and causes an error only if |
there are not that many capturing left parentheses in the entire pat- | there are not that many capturing left parentheses in the entire pat- |
tern. In other words, the parentheses that are referenced need not be | tern. In other words, the parentheses that are referenced need not be |
to the left of the reference for numbers less than 10. A "forward back | to the left of the reference for numbers less than 10. A "forward back |
reference" of this type can make sense when a repetition is involved | reference" of this type can make sense when a repetition is involved |
and the subpattern to the right has participated in an earlier itera- | and the subpattern to the right has participated in an earlier itera- |
tion. |
tion. |
|
|
It is not possible to have a numerical "forward back reference" to a | It is not possible to have a numerical "forward back reference" to a |
subpattern whose number is 10 or more using this syntax because a | subpattern whose number is 10 or more using this syntax because a |
sequence such as \50 is interpreted as a character defined in octal. | sequence such as \50 is interpreted as a character defined in octal. |
See the subsection entitled "Non-printing characters" above for further |
See the subsection entitled "Non-printing characters" above for further |
details of the handling of digits following a backslash. There is no | details of the handling of digits following a backslash. There is no |
such problem when named parentheses are used. A back reference to any | such problem when named parentheses are used. A back reference to any |
subpattern is possible using named parentheses (see below). |
subpattern is possible using named parentheses (see below). |
|
|
Another way of avoiding the ambiguity inherent in the use of digits | Another way of avoiding the ambiguity inherent in the use of digits |
following a backslash is to use the \g escape sequence. This escape | following a backslash is to use the \g escape sequence. This escape |
must be followed by an unsigned number or a negative number, optionally |
must be followed by an unsigned number or a negative number, optionally |
enclosed in braces. These examples are all identical: |
enclosed in braces. These examples are all identical: |
|
|
Line 5405 BACK REFERENCES
|
Line 6287 BACK REFERENCES
|
(ring), \g1 |
(ring), \g1 |
(ring), \g{1} |
(ring), \g{1} |
|
|
An unsigned number specifies an absolute reference without the ambigu- | An unsigned number specifies an absolute reference without the ambigu- |
ity that is present in the older syntax. It is also useful when literal |
ity that is present in the older syntax. It is also useful when literal |
digits follow the reference. A negative number is a relative reference. |
digits follow the reference. A negative number is a relative reference. |
Consider this example: |
Consider this example: |
Line 5414 BACK REFERENCES
|
Line 6296 BACK REFERENCES
|
|
|
The sequence \g{-1} is a reference to the most recently started captur- |
The sequence \g{-1} is a reference to the most recently started captur- |
ing subpattern before \g, that is, is it equivalent to \2 in this exam- |
ing subpattern before \g, that is, is it equivalent to \2 in this exam- |
ple. Similarly, \g{-2} would be equivalent to \1. The use of relative | ple. Similarly, \g{-2} would be equivalent to \1. The use of relative |
references can be helpful in long patterns, and also in patterns that | references can be helpful in long patterns, and also in patterns that |
are created by joining together fragments that contain references | are created by joining together fragments that contain references |
within themselves. |
within themselves. |
|
|
A back reference matches whatever actually matched the capturing sub- | A back reference matches whatever actually matched the capturing sub- |
pattern in the current subject string, rather than anything matching | pattern in the current subject string, rather than anything matching |
the subpattern itself (see "Subpatterns as subroutines" below for a way |
the subpattern itself (see "Subpatterns as subroutines" below for a way |
of doing that). So the pattern |
of doing that). So the pattern |
|
|
(sens|respons)e and \1ibility |
(sens|respons)e and \1ibility |
|
|
matches "sense and sensibility" and "response and responsibility", but | matches "sense and sensibility" and "response and responsibility", but |
not "sense and responsibility". If caseful matching is in force at the | not "sense and responsibility". If caseful matching is in force at the |
time of the back reference, the case of letters is relevant. For exam- | time of the back reference, the case of letters is relevant. For exam- |
ple, |
ple, |
|
|
((?i)rah)\s+\1 |
((?i)rah)\s+\1 |
|
|
matches "rah rah" and "RAH RAH", but not "RAH rah", even though the | matches "rah rah" and "RAH RAH", but not "RAH rah", even though the |
original capturing subpattern is matched caselessly. |
original capturing subpattern is matched caselessly. |
|
|
There are several different ways of writing back references to named | There are several different ways of writing back references to named |
subpatterns. The .NET syntax \k{name} and the Perl syntax \k<name> or | subpatterns. The .NET syntax \k{name} and the Perl syntax \k<name> or |
\k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's | \k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's |
unified back reference syntax, in which \g can be used for both numeric |
unified back reference syntax, in which \g can be used for both numeric |
and named references, is also supported. We could rewrite the above | and named references, is also supported and named references, is also supported. We could rewrite the above |
example in any of the following ways: |
example in any of the following ways: |
|
|
(?<p1>(?i)rah)\s+\k<p1> |
(?<p1>(?i)rah)\s+\k<p1> |
Line 5448 BACK REFERENCES
|
Line 6330 BACK REFERENCES
|
(?P<p1>(?i)rah)\s+(?P=p1) |
(?P<p1>(?i)rah)\s+(?P=p1) |
(?<p1>(?i)rah)\s+\g{p1} |
(?<p1>(?i)rah)\s+\g{p1} |
|
|
A subpattern that is referenced by name may appear in the pattern | A subpattern that is referenced by name may appear in the pattern |
before or after the reference. |
before or after the reference. |
|
|
There may be more than one back reference to the same subpattern. If a | There may be more than one back reference to the same subpattern. If a |
subpattern has not actually been used in a particular match, any back | subpattern has not actually been used in a particular match, any back |
references to it always fail by default. For example, the pattern |
references to it always fail by default. For example, the pattern |
|
|
(a|(bc))\2 |
(a|(bc))\2 |
|
|
always fails if it starts to match "a" rather than "bc". However, if | always fails if it starts to match "a" rather than "bc". However, if |
the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer- |
the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer- |
ence to an unset value matches an empty string. |
ence to an unset value matches an empty string. |
|
|
Because there may be many capturing parentheses in a pattern, all dig- | Because there may be many capturing parentheses in a pattern, all dig- |
its following a backslash are taken as part of a potential back refer- | its following a backslash are taken as part of a potential back refer- |
ence number. If the pattern continues with a digit character, some | ence number. If the pattern continues with a digit character, some |
delimiter must be used to terminate the back reference. If the | delimiter must be used to terminate the back reference. If the |
PCRE_EXTENDED option is set, this can be whitespace. Otherwise, the \g{ | PCRE_EXTENDED option is set, this can be white space. Otherwise, the |
syntax or an empty comment (see "Comments" below) can be used. | \g{ syntax or an empty comment (see "Comments" below) can be used. |
|
|
Recursive back references |
Recursive back references |
|
|
A back reference that occurs inside the parentheses to which it refers | A back reference that occurs inside the parentheses to which it refers |
fails when the subpattern is first used, so, for example, (a\1) never | fails when the subpattern is first used, so, for example, (a\1) never |
matches. However, such references can be useful inside repeated sub- | matches. However, such references can be useful inside repeated sub- |
patterns. For example, the pattern |
patterns. For example, the pattern |
|
|
(a|b\1)+ |
(a|b\1)+ |
|
|
matches any number of "a"s and also "aba", "ababbaa" etc. At each iter- |
matches any number of "a"s and also "aba", "ababbaa" etc. At each iter- |
ation of the subpattern, the back reference matches the character | ation of the subpattern, the back reference matches the character |
string corresponding to the previous iteration. In order for this to | string corresponding to the previous iteration. In order for this to |
work, the pattern must be such that the first iteration does not need | work, the pattern must be such that the first iteration does not need |
to match the back reference. This can be done using alternation, as in | to match the back reference. This can be done using alternation, as in |
the example above, or by a quantifier with a minimum of zero. |
the example above, or by a quantifier with a minimum of zero. |
|
|
Back references of this type cause the group that they reference to be | Back references of this type cause the group that they reference to be |
treated as an atomic group. Once the whole group has been matched, a | treated as an atomic group. Once the whole group has been matched, a |
subsequent matching failure cannot cause backtracking into the middle | subsequent matching failure cannot cause backtracking into the middle |
of the group. |
of the group. |
|
|
|
|
ASSERTIONS |
ASSERTIONS |
|
|
An assertion is a test on the characters following or preceding the | An assertion is a test on the characters following or preceding the |
current matching point that does not actually consume any characters. | current matching point that does not actually consume any characters. |
The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are | The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are |
described above. |
described above. |
|
|
More complicated assertions are coded as subpatterns. There are two | More complicated assertions are coded as subpatterns. There are two |
kinds: those that look ahead of the current position in the subject | kinds: those that look ahead of the current position in the subject |
string, and those that look behind it. An assertion subpattern is | string, and those that look behind it. An assertion subpattern is |
matched in the normal way, except that it does not cause the current | matched in the normal way, except that it does not cause the current |
matching position to be changed. |
matching position to be changed. |
|
|
Assertion subpatterns are not capturing subpatterns. If such an asser- | Assertion subpatterns are not capturing subpatterns. If such an asser- |
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 |
Line 5778 CONDITIONAL SUBPATTERNS
|
Line 6661 CONDITIONAL SUBPATTERNS
|
DEFINE is that it can be used to define subroutines that can be refer- |
DEFINE is that it can be used to define subroutines that can be refer- |
enced from elsewhere. (The use of subroutines is described below.) For |
enced from elsewhere. (The use of subroutines is described below.) For |
example, a pattern to match an IPv4 address such as "192.168.23.245" |
example, a pattern to match an IPv4 address such as "192.168.23.245" |
could be written like this (ignore whitespace and line breaks): | could be written like this (ignore white space and line breaks): |
|
|
(?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) ) |
(?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) ) |
\b (?&byte) (\.(?&byte)){3} \b |
\b (?&byte) (\.(?&byte)){3} \b |
Line 6122 CALLOUTS
|
Line 7005 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 | Note that this applies only to assertion conditions, not to other types |
supplied by the caller of the matching function. The callout function | of condition. |
may cause matching to proceed, to backtrack, or to fail altogether. A | |
complete description of the interface to the callout function is given | 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. A |
| complete description of the interface to the callout function is given |
in the pcrecallout documentation. |
in the pcrecallout documentation. |
|
|
|
|
BACKTRACKING CONTROL |
BACKTRACKING CONTROL |
|
|
Perl 5.10 introduced a number of "Special Backtracking Control Verbs", | Perl 5.10 introduced a number of "Special Backtracking Control Verbs", |
which are described in the Perl documentation as "experimental and sub- | which are still described in the Perl documentation as "experimental |
ject to change or removal in a future version of Perl". It goes on to | and subject to change or removal in a future version of Perl". It goes |
say: "Their usage in production code should be noted to avoid problems | on to say: "Their usage in production code should be noted to avoid |
during upgrades." The same remarks apply to the PCRE features described | problems during upgrades." The same remarks apply to the PCRE features |
in this section. | 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 |
|
(*VERB) or (*VERB:NAME). Some may take either form, possibly behaving |
|
differently depending on whether or not a name is present. A name is |
|
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 |
|
16-bit and 32-bit libraries. If the name is empty, that is, if the |
|
closing parenthesis immediately follows the colon, the effect is as if |
|
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 |
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 |
them can be used only when the pattern is to be matched using one of |
the traditional matching functions, which use a backtracking algorithm. | the traditional matching functions, because these use a backtracking |
With the exception of (*FAIL), which behaves like a failing negative | algorithm. With the exception of (*FAIL), which behaves like a failing |
assertion, they cause an error if encountered by a DFA matching func- | negative assertion, the backtracking control verbs cause an error if |
tion. | encountered by a DFA matching function. |
|
|
If any of these verbs are used in an assertion or in a subpattern that | The behaviour of these verbs in repeated groups, assertions, and in |
is called as a subroutine (whether or not recursively), their effect is | subpatterns called as subroutines (whether or not recursively) is docu- |
confined to that subpattern; it does not extend to the surrounding pat- | mented below. |
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 is dif- | |
ferent in some cases. | |
|
|
The new verbs make use of what was previously invalid syntax: an open- | Optimizations that affect backtracking verbs |
ing parenthesis followed by an asterisk. They are generally of the form | |
(*VERB) or (*VERB:NAME). Some may take either form, with differing be- | |
haviour, depending on whether or not an argument is present. A name is | |
any sequence of characters that does not include a closing parenthesis. | |
If the name is empty, that is, if the closing parenthesis immediately | |
follows the colon, the effect is as if the colon were not there. Any | |
number of these verbs may occur in a pattern. | |
|
|
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 |
|
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 6256 BACKTRACKING CONTROL
|
Line 7153 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". Subsequent match attempts | match attempt that started at the letter "X" in the subject. Subsequent |
starting at "P" and then with an empty string do not get as far as the | match attempts starting at "P" and then with an empty string do not get |
(*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 |
|
should probably set the PCRE_NO_START_OPTIMIZE option (see above) to |
|
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 6322 BACKTRACKING CONTROL
|
Line 7233 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 6397 BACKTRACKING CONTROL
|
Line 7322 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 6421 BACKTRACKING CONTROL
|
Line 7346 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) |
|
cases 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 6448 AUTHOR
|
Line 7435 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 09 January 2012 | Last updated: 26 April 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 6478 CHARACTERS
|
Line 7465 CHARACTERS
|
\a alarm, that is, the BEL character (hex 07) |
\a alarm, that is, the BEL character (hex 07) |
\cx "control-x", where x is any ASCII character |
\cx "control-x", where x is any ASCII character |
\e escape (hex 1B) |
\e escape (hex 1B) |
\f formfeed (hex 0C) | \f form feed (hex 0C) |
\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) |
Line 6494 CHARACTER TYPES
|
Line 7481 CHARACTER TYPES
|
\C one data unit, even in UTF mode (best avoided) |
\C one data unit, even in UTF mode (best avoided) |
\d a decimal digit |
\d a decimal digit |
\D a character that is not a decimal digit |
\D a character that is not a decimal digit |
\h a horizontal whitespace character | \h a horizontal white space character |
\H a character that is not a horizontal whitespace character | \H a character that is not a horizontal white space character |
\N a character that is not a newline |
\N a character that is not a newline |
\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 |
\R a newline sequence |
\R a newline sequence |
\s a whitespace character | \s a white space character |
\S a character that is not a whitespace character | \S a character that is not a white space character |
\v a vertical whitespace character | \v a vertical white space character |
\V a character that is not a vertical whitespace 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 |
In PCRE, by default, \d, \D, \s, \S, \w, and \W recognize only ASCII |
characters, even in a UTF mode. However, this can be changed by setting |
characters, even in a UTF mode. However, this can be changed by setting |
Line 6566 PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P
|
Line 7553 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, 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 |
|
|
|
|
SCRIPT NAMES FOR \p AND \P |
SCRIPT NAMES FOR \p AND \P |
|
|
Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille, | Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo, |
Buginese, Buhid, Canadian_Aboriginal, Carian, Cham, Cherokee, Common, | Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma, |
Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Egyp- | Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, |
tian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, Gothic, Greek, | Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, |
Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Impe- | Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira- |
rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian, | gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- |
Javanese, Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao, | tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, |
Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam, | Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, |
Meetei_Mayek, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic, | Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive, |
Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki, Oriya, Osmanya, | Meroitic_Hieroglyphs, Miao, Mongolian, Myanmar, New_Tai_Lue, Nko, |
Phags_Pa, Phoenician, Rejang, Runic, Samaritan, Saurashtra, Shavian, | Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic, |
Sinhala, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, | Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samari- |
Tai_Tham, Tai_Viet, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, | tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese, |
Ugaritic, Vai, Yi. | Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, |
| Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, |
| Yi. |
|
|
|
|
CHARACTER CLASSES |
CHARACTER CLASSES |
Line 6605 CHARACTER CLASSES
|
Line 7596 CHARACTER CLASSES
|
lower lower case letter |
lower lower case letter |
print printing, including space |
print printing, including space |
punct printing, excluding alphanumeric |
punct printing, excluding alphanumeric |
space whitespace | space white space |
upper upper case letter |
upper upper case letter |
word same as \w |
word same as \w |
xdigit hexadecimal digit |
xdigit hexadecimal digit |
Line 6695 OPTION SETTING
|
Line 7686 OPTION SETTING
|
The following are recognized only at the start of a pattern or after |
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) |
|
|
|
|
Line 6786 BACKTRACKING CONTROL
|
Line 7781 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 6824 AUTHOR
|
Line 7819 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 10 January 2012 | Last updated: 26 April 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREUNICODE(3) PCREUNICODE(3) | PCREUNICODE(3) Library Functions Manual PCREUNICODE(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT |
|
|
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. |
|
|
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 |
|
built as well as, or instead of, the 8-bit library. |
|
|
|
|
|
UTF-8 SUPPORT |
UTF-8 SUPPORT |
|
|
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. |
|
|
|
|
UTF-16 SUPPORT | UTF-16 AND UTF-32 SUPPORT |
|
|
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. |
|
|
|
|
UTF SUPPORT OVERHEAD |
UTF SUPPORT OVERHEAD |
|
|
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. |
|
|
|
|
UNICODE PROPERTY SUPPORT |
UNICODE PROPERTY SUPPORT |
|
|
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. |
|
|
Validity of UTF-8 strings |
Validity of UTF-8 strings |
|
|
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. From release 7.3 of PCRE, the check is according the | 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 |
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.) |
|
|
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 runtime 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. |
|
|
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_UTF8_CHECK flag at compile time or at run | mance, for example in the case of a long subject string that is being |
time, PCRE assumes that the pattern or subject it is given (respec- | scanned repeatedly. If you set the PCRE_NO_UTF8_CHECK flag at compile |
tively) contains only valid UTF-8 codes. In this case, it does not | time or at run time, PCRE assumes that the pattern or subject it is |
diagnose an invalid UTF-8 string. | given (respectively) contains only valid UTF-8 codes. In this case, it |
| does not diagnose an invalid UTF-8 string. |
|
|
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() | |
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 |
|
|
Line 6944 UNICODE PROPERTY SUPPORT
|
Line 7937 UNICODE PROPERTY SUPPORT
|
|
|
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 runtime 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 |
well as a more detailed reason code if the caller has provided memory |
in which to do this. |
in which to do this. |
Line 6954 UNICODE PROPERTY SUPPORT
|
Line 7947 UNICODE PROPERTY SUPPORT
|
mance. If you set the PCRE_NO_UTF16_CHECK flag at compile time or at |
mance. If you set the PCRE_NO_UTF16_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-16 sequences. In this case, it does not |
diagnose an invalid UTF-16 string. | diagnose an invalid UTF-16 string. However, if an invalid string is |
| passed, the result is undefined. |
|
|
|
Validity of UTF-32 strings |
|
|
|
When you set the PCRE_UTF32 flag, the strings of 32-bit data units that |
|
are passed as patterns and subjects are (by default) checked for valid- |
|
ity on entry to the relevant functions. This check allows only values |
|
in the range U+0 to U+10FFFF, excluding the surrogate area U+D800 to |
|
U+DFFF. |
|
|
|
If an invalid UTF-32 string is passed to PCRE, an error return is |
|
given. At compile time, the only additional information is the offset |
|
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 |
|
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_UTF32_CHECK flag at compile time or at |
|
run time, PCRE assumes that the pattern or subject it is given (respec- |
|
tively) contains only valid UTF-32 sequences. In this case, it does not |
|
diagnose an invalid UTF-32 string. However, if an invalid string is |
|
passed, the result is undefined. |
|
|
General comments about UTF modes |
General comments about UTF modes |
|
|
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. |
|
|
2. Octal numbers up to \777 are recognized, and in UTF-8 mode, they | 2. Octal numbers up to \777 are recognized, and in UTF-8 mode they |
match two-byte characters for values greater than \177. |
match two-byte characters for values greater than \177. |
|
|
3. Repeat quantifiers apply to complete UTF characters, not to individ- |
3. Repeat quantifiers apply to complete UTF characters, not to individ- |
Line 6972 UNICODE PROPERTY SUPPORT
|
Line 7989 UNICODE PROPERTY SUPPORT
|
data unit. |
data unit. |
|
|
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. |
|
|
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 |
PCRE recognizes as digits, spaces, or word characters remain the same | PCRE recognizes as digits, spaces, or word characters remain the same |
set as in non-UTF mode, all with values less than 256. This remains | set as in non-UTF mode, all with values less than 256. This remains |
true even when PCRE is built to include Unicode property support, | true even when PCRE is built to include Unicode property support, |
because to do otherwise would slow down PCRE in many common cases. Note |
because to do otherwise would slow down PCRE in many common cases. Note |
in particular that this applies to \b and \B, because they are defined | in particular that this applies to \b and \B, because they are defined |
in terms of \w and \W. If you really want to test for a wider sense of, |
in terms of \w and \W. If you really want to test for a wider sense of, |
say, "digit", you can use explicit Unicode property tests such as | say, "digit", you can use explicit Unicode property tests such as |
\p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that the |
\p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that the |
character escapes work is changed so that Unicode properties are used | character escapes work is changed so that Unicode properties are used |
to determine which characters match. There are more details in the sec- |
to determine which characters match. There are more details in the sec- |
tion on generic character types in the pcrepattern documentation. |
tion on generic character types in the pcrepattern documentation. |
|
|
7. Similarly, characters that match the POSIX named character classes | 7. Similarly, characters that match the POSIX named characte 7. Similarly, characters that match the POSIX named characte |
are all low-valued characters, unless the PCRE_UCP option is set. |
are all low-valued characters, unless the PCRE_UCP option is set. |
|
|
8. However, the horizontal and vertical whitespace matching escapes | 8. However, the horizontal and vertical white space matching escapes |
(\h, \H, \v, and \V) do match all the appropriate Unicode characters, | (\h, \H, \v, and \V) do match all the appropriate Unicode characters, |
whether or not PCRE_UCP is set. |
whether or not PCRE_UCP is set. |
|
|
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. | |
|
|
|
|
AUTHOR |
AUTHOR |
Line 7022 AUTHOR
|
Line 8038 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 13 January 2012 | Last updated: 27 February 2013 |
Copyright (c) 1997-2012 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREJIT(3) PCREJIT(3) | PCREJIT(3) Library Functions Manual PCREJIT(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
PCRE JUST-IN-TIME COMPILER SUPPORT |
PCRE JUST-IN-TIME COMPILER SUPPORT |
|
|
Just-in-time compiling is a heavyweight optimization that can greatly |
Just-in-time compiling is a heavyweight optimization that can greatly |
Line 7051 PCRE JUST-IN-TIME COMPILER SUPPORT
|
Line 8067 PCRE JUST-IN-TIME COMPILER SUPPORT
|
used. The code for this support was written by Zoltan Herczeg. |
used. The code for this support was written by Zoltan Herczeg. |
|
|
|
|
8-BIT and 16-BIT SUPPORT | 8-BIT, 16-BIT AND 32-BIT SUPPORT |
|
|
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). |
|
|
|
|
AVAILABILITY OF JIT SUPPORT |
AVAILABILITY OF JIT SUPPORT |
Line 7071 AVAILABILITY OF JIT SUPPORT
|
Line 8089 AVAILABILITY OF JIT SUPPORT
|
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) |
|
|
The Power PC support is designated as experimental because it has not | If --enable-jit is set on an unsupported platform, compilation fails. |
been fully tested. If --enable-jit is set on an unsupported platform, | |
compilation fails. | |
|
|
A program that is linked with PCRE 8.20 or later can tell if JIT sup- |
A program that is linked with PCRE 8.20 or later can tell if JIT sup- |
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 ordinary PCRE | 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. |
|
|
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 7099 SIMPLE USE OF JIT
|
Line 8118 SIMPLE USE OF JIT
|
pcre_exec(). |
pcre_exec(). |
|
|
(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 |
|
|
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: |
|
|
#ifdef PCRE_CONFIG_JIT |
#ifdef PCRE_CONFIG_JIT |
Line 7118 SIMPLE USE OF JIT
|
Line 8138 SIMPLE USE OF JIT
|
pcre_free(study_ptr); |
pcre_free(study_ptr); |
#endif |
#endif |
|
|
|
PCRE_STUDY_JIT_COMPILE requests the JIT compiler to generate code for |
|
complete matches. If you want to run partial matches using the |
|
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 |
|
instead of, PCRE_STUDY_JIT_COMPILE when you call pcre_study(): |
|
|
|
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
|
PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE |
|
|
|
The JIT compiler generates different optimized code for each of the |
|
three modes (normal, soft partial, hard partial). When pcre_exec() is |
|
called, the appropriate code is run if it is available. Otherwise, the |
|
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 is ignored, and | If JIT support is not available, PCRE_STUDY_JIT_COMPILE etc. are |
no JIT data is set up. Otherwise, the compiled pattern is passed to the | ignored, and no JIT data is created. Otherwise, the compiled pattern is |
JIT compiler, which turns it into machine code that executes much | passed to the JIT compiler, which turns it into machine code that exe- |
faster than the normal interpretive code. When pcre_exec() is passed a | cutes much faster than the normal interpretive code. When pcre_exec() |
pcre_extra block containing a pointer to JIT code, it obeys that | is passed a pcre_extra block containing a pointer to JIT code of the |
instead of the normal code. The result is identical, but the code runs | appropriate mode (normal or hard/soft partial), it obeys that code |
much faster. | instead of running the interpreter. The result is identical, but the |
| 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. | 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 |
| 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 |
| 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 |
| 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, or the JIT compiler was not able to handle | with PCRE_STUDY_JIT_COMPILE etc., or the JIT compiler was not able to |
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 |
many times as you like for matching different subject strings. |
many times as you like for matching different subject strings. |
Line 7149 SIMPLE USE OF JIT
|
Line 8190 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_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and | PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK, PCRE_NO_UTF32_CHECK, PCRE_NOT- |
PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not | BOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PAR- |
supported. | 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 |
|
(*COMMIT) ) |
|
(*MARK) ) |
|
(*PRUNE) ) the backtracking control verbs |
|
(*SKIP) ) |
|
(*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 The extra argument must be the result |
PCRE_STUDY_JIT_COMPILE. 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: |
|
|
(1) If callback is NULL and data is NULL, an internal 32K block |
(1) If callback is NULL and data is NULL, an internal 32K block |
Line 7237 CONTROLLING THE JIT STACK
|
Line 8270 CONTROLLING THE JIT STACK
|
(2) If callback is NULL and data is not NULL, data must be |
(2) If callback is NULL and data is not NULL, data must be |
a valid JIT stack, the result of calling pcre_jit_stack_alloc(). |
a valid JIT stack, the result of calling pcre_jit_stack_alloc(). |
|
|
(3) If callback not NULL, it must point to a function that is called | (3) If callback is not NULL, it must point to a function that is |
with data as an argument at the start of matching, in order to | called with data as an argument at the start of matching, in |
set up a JIT stack. If the result is NULL, the internal 32K stack | order to set up a JIT stack. If the return from the callback |
is used; otherwise the return value must be a valid JIT stack, | function is NULL, the internal 32K stack is used; otherwise the |
the result of calling pcre_jit_stack_alloc(). | return value must be a valid JIT stack, the result of calling |
| pcre_jit_stack_alloc(). |
|
|
You may safely assign the same JIT stack to more than one pattern, as | A callback function is obeyed whenever JIT code is about to be run; it |
long as they are all matched sequentially in the same thread. In a mul- | is not obeyed when pcre_exec() is called with options that are incom- |
tithread application, each thread must use its own JIT stack. | patible for JIT execution. A callback function can therefore be used to |
| determine whether a match operation was executed by JIT or by the |
| interpreter. |
|
|
Strictly speaking, even more is allowed. You can assign the same stack | You may safely use the same JIT stack for more than one pattern (either |
to any number of patterns as long as they are not used for matching by | by assigning directly or by callback), as long as the patterns are all |
multiple threads at the same time. For example, you can assign the same | matched sequentially in the same thread. In a multithread application, |
stack to all compiled patterns, and use a global mutex in the callback | if you do not specify a JIT stack, or if you assign or pass back NULL |
to wait until the stack is available for use. However, this is an inef- | from a callback, that is thread-safe, because each thread has its own |
ficient solution, and not recommended. | 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 |
| application is thread-safe. |
|
|
This is a suggestion for how a typical multithreaded program might | Strictly speaking, even more is allowed. You can assign the same non- |
operate: | 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 |
| 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, |
| this is an inefficient solution, and not recommended. |
|
|
|
This is a suggestion for how a multithreaded program that needs to set |
|
up non-default JIT stacks might operate: |
|
|
During thread initalization |
During thread initalization |
thread_local_var = pcre_jit_stack_alloc(...) |
thread_local_var = pcre_jit_stack_alloc(...) |
|
|
Line 7269 CONTROLLING THE JIT STACK
|
Line 8314 CONTROLLING THE JIT STACK
|
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. | result of a successful study with PCRE_STUDY_JIT_COMPILE etc. |
|
|
|
|
JIT STACK FAQ |
JIT STACK FAQ |
Line 7320 JIT STACK FAQ
|
Line 8365 JIT STACK FAQ
|
|
|
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 |
Line 7329 JIT STACK FAQ
|
Line 8374 JIT STACK FAQ
|
|
|
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. |
|
|
Line 7364 EXAMPLE CODE
|
Line 8409 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 7378 AUTHOR
|
Line 8451 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 08 January 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 7422 PARTIAL MATCHING IN PCRE
|
Line 8495 PARTIAL MATCHING IN PCRE
|
matching function. If both options are set, PCRE_PARTIAL_HARD takes |
matching function. If both options are set, PCRE_PARTIAL_HARD takes |
precedence. |
precedence. |
|
|
Setting a partial matching option disables the use of any just-in-time | If you want to use partial matching with just-in-time optimized code, |
code that was set up by studying the compiled pattern with the | you must call pcre_study(), pcre16_study() or pcre32_study() with one |
PCRE_STUDY_JIT_COMPILE option. It also disables two of PCRE's standard | or both of these options: |
optimizations. PCRE remembers the last literal data unit in a pattern, | |
and abandons matching immediately if it is not present in the subject | PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE |
| PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
| |
| PCRE_STUDY_JIT_COMPILE should also be set if you are going to run non- |
| partial matches on the same pattern. If the appropriate JIT study mode |
| has not been set for a match, the interpretive matching code is used. |
| |
| Setting a partial matching option disables two of PCRE's standard opti- |
| mizations. PCRE remembers the last literal data unit in a pattern, and |
| abandons matching immediately if it is not present in the subject |
string. This optimization cannot be used for a subject string that |
string. This optimization cannot be used for a subject string that |
might match only partially. If the pattern was studied, PCRE knows the |
might match only partially. If the pattern was studied, PCRE knows the |
minimum length of a matching string, and does not bother to run the |
minimum length of a matching string, and does not bother to run the |
Line 7434 PARTIAL MATCHING IN PCRE
|
Line 8516 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 7623 EXAMPLE OF PARTIAL MATCHING USING PCRETEST
|
Line 8710 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 7649 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_
|
Line 8736 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 | You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with |
PCRE_DFA_RESTART to continue partial matching over multiple segments. | PCRE_DFA_RESTART to continue partial matching over multiple segments. |
This facility can be used to pass very long subject strings to the DFA | 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. | during the partial match. |
|
|
|
|
ISSUES WITH MULTI-SEGMENT MATCHING |
ISSUES WITH MULTI-SEGMENT MATCHING |
Line 7699 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 8786 ISSUES WITH MULTI-SEGMENT MATCHING
|
whichever matching function is used. |
whichever matching function is used. |
|
|
1. If the pattern contains a test for the beginning of a line, you need |
1. If the pattern contains a test for the beginning of a line, you need |
to pass the PCRE_NOTBOL option when the subject string for any call | to pass the PCRE_NOTBOL option when the subject string for any call |
does start at the beginning of a line. There is also a PCRE_NOTEOL | does start at the beginning of a line. There is also a PCRE_NOTEOL |
option, but in practice when doing multi-segment matching you should be |
option, but in practice when doing multi-segment matching you should be |
using PCRE_PARTIAL_HARD, which includes the effect of PCRE_NOTEOL. |
using PCRE_PARTIAL_HARD, which includes the effect of PCRE_NOTEOL. |
|
|
2. Lookbehind assertions at the start of a pattern are catered for in | 2. Lookbehind assertions that have already been obeyed are catered for |
the offsets that are returned for a partial match. However, in theory, | in the offsets that are returned for a partial match. However a lookbe- |
a lookbehind assertion later in the pattern could require even earlier | hind assertion later in the pattern could require even earlier charac- |
characters to be inspected, and it might not have been reached when a | ters to be inspected. You can handle this case by using the |
partial match occurs. This is probably an extremely unlikely case; you | PCRE_INFO_MAXLOOKBEHIND option of the pcre_fullinfo() or |
could guard against it to a certain extent by always including extra | pcre[16|32]_fullinfo() functions to obtain the length of the longest |
characters at the start. | lookbehind in the pattern. This length is given in characters, not |
| bytes. If you always retain at least that many characters before the |
| partially matched string, all should be well. (Of course, near the |
| start of the subject, fewer characters may be present; in that case all |
| characters should be retained.) |
|
|
3. Matching a subject string that is split into multiple segments may | From release 8.33, there is a more accurate way of deciding which char- |
not always produce exactly the same result as matching over one single | acters to retain. Instead of subtracting the length of the longest |
long string, especially when PCRE_PARTIAL_SOFT is used. The section | lookbehind from the earliest inspected character (offsets[0]), the |
"Partial Matching and Word Boundaries" above describes an issue that | match start position (offsets[2]) should be used, and the next match |
arises if the pattern ends with \b or \B. Another kind of difference | attempt started at the offsets[2] character by setting the startoffset |
may occur when there are multiple matching possibilities, because (for | argument of pcre_exec() or pcre_dfa_exec(). |
PCRE_PARTIAL_SOFT) a partial match result is given only when there are | |
| 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: |
| |
| re> /c(?<=abc)x/ |
| data> ab\P |
| No match |
| |
| 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 |
| this reason, a "no match" result should be interpreted as "partial |
| match of an empty string" when the pattern contains lookbehinds. |
| |
| 4. Matching a subject string that is split into multiple segments may |
| not always produce exactly the same result as matching over one single |
| long string, especially when PCRE_PARTIAL_SOFT is used. The section |
| "Partial Matching and Word Boundaries" above describes an issue that |
| arises if the pattern ends with \b or \B. Another kind of difference |
| may occur when there are multiple matching possibilities, because (for |
| 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 7734 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 8859 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 7756 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 8881 ISSUES WITH MULTI-SEGMENT MATCHING
|
data> gsb\R\P\P\D |
data> gsb\R\P\P\D |
Partial match: gsb |
Partial match: gsb |
|
|
4. 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 7785 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 8910 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 7801 AUTHOR
|
Line 8926 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 21 January 2012 | Last updated: 20 February 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 7826 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
|
Line 8951 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 7839 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
|
Line 8964 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
|
|
|
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 7880 SAVING A COMPILED PATTERN
|
Line 9005 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. |
|
|
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 |
Line 7911 RE-USING A PRECOMPILED PATTERN
|
Line 9036 RE-USING A PRECOMPILED PATTERN
|
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 7936 AUTHOR
|
Line 9061 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 10 January 2012 | Last updated: 24 June 2012 |
Copyright (c) 1997-2012 University of Cambridge. |
Copyright (c) 1997-2012 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 8007 COMPILED PATTERN MEMORY USAGE
|
Line 9132 COMPILED PATTERN MEMORY USAGE
|
|
|
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 8106 AUTHOR
|
Line 9231 AUTHOR
|
|
|
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) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions. |
PCRE - Perl-compatible regular expressions. |
|
|
|
|
SYNOPSIS OF POSIX API |
SYNOPSIS OF POSIX API |
|
|
#include <pcreposix.h> |
#include <pcreposix.h> |
Line 8139 DESCRIPTION
|
Line 9264 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 8195 COMPILING A PATTERN
|
Line 9321 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 8254 COMPILING A PATTERN
|
Line 9380 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 8278 MATCHING NEWLINE CHARACTERS
|
Line 9404 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 8312 MATCHING A PATTERN
|
Line 9438 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 8330 MATCHING A PATTERN
|
Line 9456 MATCHING A PATTERN
|
|
|
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 8375 REVISION
|
Line 9501 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 8393 DESCRIPTION
|
Line 9519 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 8413 MATCHING INTERFACE
|
Line 9540 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 8442 MATCHING INTERFACE
|
Line 9569 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 8450 MATCHING INTERFACE
|
Line 9577 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 8465 MATCHING INTERFACE
|
Line 9592 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 8514 PARTIAL MATCHES
|
Line 9641 PARTIAL MATCHES
|
|
|
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 8539 UTF-8 AND THE MATCHING INTERFACE
|
Line 9666 UTF-8 AND THE MATCHING INTERFACE
|
|
|
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 8551 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 9678 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
PCRE_DOTALL dot matches newlines /s |
PCRE_DOTALL dot matches newlines /s |
PCRE_DOLLAR_ENDONLY $ matches only at end N/A |
PCRE_DOLLAR_ENDONLY $ matches only at end N/A |
PCRE_EXTRA strict escape parsing N/A |
PCRE_EXTRA strict escape parsing N/A |
PCRE_EXTENDED ignore whitespaces /x | PCRE_EXTENDED ignore white spaces /x |
PCRE_UTF8 handles UTF8 chars built-in |
PCRE_UTF8 handles UTF8 chars built-in |
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 8574 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 9701 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 8594 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 9721 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 8609 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 9736 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 8629 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 9756 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
|
|
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 8646 SCANNING TEXT INCREMENTALLY
|
Line 9773 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 8659 SCANNING TEXT INCREMENTALLY
|
Line 9786 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 8677 PARSING HEX/OCTAL/C-RADIX NUMBERS
|
Line 9804 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 8717 REVISION
|
Line 9844 REVISION
|
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCRESAMPLE(3) PCRESAMPLE(3) | PCRESAMPLE(3) Library Functions Manual PCRESAMPLE(3) |
|
|
|
|
|
|
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 8803 REVISION
|
Line 9930 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 |
never in practice be relevant. |
never in practice be relevant. |
|
|
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, 32-bit units for the 32-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 of 2 bytes. If you want to |
enormous, you can compile PCRE with an internal linkage size of 3 or 4 | process regular expressions that are truly enormous, you can compile |
(when building the 16-bit library, 3 is rounded up to 4). See the | PCRE with an internal linkage size of 3 or 4 (when building the 16-bit |
README file in the source distribution and the pcrebuild documentation | or 32-bit library, 3 is rounded up to 4). See the README file in the |
for details. In these cases the limit is substantially larger. How- | source distribution and the pcrebuild documentation for details. In |
ever, the speed of execution is slower. | 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. |
|
|
Line 8831 SIZE AND OTHER LIMITATIONS
|
Line 9959 SIZE AND OTHER LIMITATIONS
|
can be no more than 65535 capturing subpatterns. |
can be no more than 65535 capturing subpatterns. |
|
|
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 |
upper limits, for example, (?2){0,100} when subpattern number 2 is to | upper limits, for example, (?2){0,100} when subpattern number 2 is to |
the right, are included in the count. There is no limit to the number | the right, are included in the count. There is no limit to the number |
of backward references. |
of backward references. |
|
|
The maximum length of name for a named subpattern is 32 characters, and |
The maximum length of name for a named subpattern is 32 characters, and |
the maximum number of named subpatterns is 10000. |
the maximum number of named subpatterns is 10000. |
|
|
The maximum length of a subject string is the largest positive number | The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or |
that an integer variable can hold. However, when using the traditional | (*THEN) verb is 255 for the 8-bit library and 65535 for the 16-bit and |
| 32-bit library. |
| |
| The maximum length of a subject string is the largest positive number |
| that an integer variable can hold. However, when using the traditional |
matching function, PCRE uses recursion to handle subpatterns and indef- |
matching function, PCRE uses recursion to handle subpatterns and indef- |
inite repetition. This means that the available stack space may limit | inite repetition. This means that the available stack space may limit |
the size of a subject string that can be processed by certain patterns. |
the size of a subject string that can be processed by certain patterns. |
For a discussion of stack issues, see the pcrestack documentation. |
For a discussion of stack issues, see the pcrestack documentation. |
|
|
Line 8856 AUTHOR
|
Line 9988 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 08 January 2012 | Last updated: 04 May 2012 |
Copyright (c) 1997-2012 University of Cambridge. |
Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCRESTACK(3) PCRESTACK(3) | PCRESTACK(3) Library Functions Manual PCRESTACK(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
PCRE DISCUSSION OF STACK USAGE |
PCRE DISCUSSION OF STACK USAGE |
|
|
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 8886 PCRE DISCUSSION OF STACK USAGE
|
Line 10018 PCRE DISCUSSION OF STACK USAGE
|
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. |
|
|
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. |
|
|
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. |
|
|
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. |
|
|
Reducing pcre[16]_exec()'s stack usage | Reducing pcre[16|32]_exec()'s stack usage |
|
|
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: |
|
|
([^<]|<(?!inet))+ |
([^<]|<(?!inet))+ |
|
|
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: |
|
|
([^<]++|<(?!inet))+ |
([^<]++|<(?!inet))+ |
|
|
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 8998 PCRE DISCUSSION OF STACK USAGE
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Line 10131 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 9020 PCRE DISCUSSION OF STACK USAGE
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Line 10153 PCRE DISCUSSION OF STACK USAGE
|
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 9041 AUTHOR
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Line 10174 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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