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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 25 INTRODUCTION
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Line 25 INTRODUCTION
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items, and there is an option for requesting some minor changes that |
items, and there is an option for requesting some minor changes that |
give better JavaScript compatibility. |
give better JavaScript compatibility. |
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Starting with release 8.30, it is possible to compile two separate PCRE |
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libraries: the original, which supports 8-bit character strings |
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(including UTF-8 strings), and a second library that supports 16-bit |
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character strings (including UTF-16 strings). The build process allows |
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either one or both to be built. The majority of the work to make this |
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possible was done by Zoltan Herczeg. |
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Starting with release 8.32 it is possible to compile a third separate |
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PCRE library that supports 32-bit character strings (including UTF-32 |
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strings). The build process allows any combination of the 8-, 16- and |
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32-bit libraries. The work to make this possible was done by Christian |
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Persch. |
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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 encoded strings and Unicode general | 5.12, including support for UTF-8/16/32 encoded strings and Unicode |
category properties. However, UTF-8 and Unicode support has to be | general category properties. However, UTF-8/16/32 and Unicode support |
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 39 INTRODUCTION
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Line 63 INTRODUCTION
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PCRE is written in C and released as a C library. A number of people |
PCRE is written in C and released as a C library. A number of people |
have written wrappers and interfaces of various kinds. In particular, |
have written wrappers and interfaces of various kinds. In particular, |
Google Inc. have provided a comprehensive C++ wrapper. This is now | Google Inc. have provided a comprehensive C++ wrapper for the 8-bit |
included as part of the PCRE distribution. The pcrecpp page has details | library. This is now included as part of the PCRE distribution. The |
of this interface. Other people's contributions can be found in the | pcrecpp page has details of this interface. Other people's contribu- |
Contrib directory at the primary FTP site, which is: | tions can be found in the Contrib directory at the primary FTP site, |
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ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre |
ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre |
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Details of exactly which Perl regular expression features are and are | Details of exactly which Perl regular expression features are and are |
not supported by PCRE are given in separate documents. See the pcrepat- |
not supported by PCRE are given in separate documents. See the pcrepat- |
tern and pcrecompat pages. There is a syntax summary in the pcresyntax | tern and pcrecompat pages. There is a syntax summary in the pcresyntax |
page. |
page. |
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Some features of PCRE can be included, excluded, or changed when the | Some features of PCRE can be included, excluded, or changed when the |
library is built. The pcre_config() function makes it possible for a | library is built. The pcre_config() function makes it possible for a |
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 library 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_", which hopefully will not provoke | Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which |
any name clashes. In some environments, it is possible to control which | hopefully will not provoke any name clashes. In some environments, it |
external symbols are exported when a shared library is built, and in | is possible to control which external symbols are exported when a |
these cases the undocumented symbols are not exported. | shared library is built, and in these cases the undocumented symbols |
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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- |
tions. In the "man" format, each of these is a separate "man page". In | tions. In the "man" format, each of these is a separate "man page". In |
the HTML format, each is a separate page, linked from the index page. | the HTML format, each is a separate page, linked from the index page. |
In the plain text format, all the sections, except the pcredemo sec- | In the plain text format, all the sections, except the pcredemo sec- |
tion, are concatenated, for ease of searching. The sections are as fol- |
tion, are concatenated, for ease of searching. The sections are as fol- |
lows: |
lows: |
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pcre this document |
pcre this document |
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 | pcrecpp details of the C++ wrapper for the 8-bit library |
pcredemo a demonstration C program that uses PCRE |
pcredemo a demonstration C program that uses PCRE |
pcregrep description of the pcregrep command | pcregrep description of the pcregrep command (8-bit only) |
pcrejit discussion of the just-in-time optimization support |
pcrejit discussion of the just-in-time optimization support |
pcrelimits details of size and other limits |
pcrelimits details of size and other limits |
pcrematching discussion of the two matching algorithms |
pcrematching discussion of the two matching algorithms |
Line 92 USER DOCUMENTATION
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Line 152 USER DOCUMENTATION
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pcrepattern syntax and semantics of supported |
pcrepattern syntax and semantics of supported |
regular expressions |
regular expressions |
pcreperform discussion of performance issues |
pcreperform discussion of performance issues |
pcreposix the POSIX-compatible C API | pcreposix the POSIX-compatible C API for the 8-bit library |
pcreprecompile details of saving and re-using precompiled patterns |
pcreprecompile details of saving and re-using precompiled patterns |
pcresample discussion of the pcredemo program |
pcresample discussion of the pcredemo program |
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 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 C library function, listing its arguments and results. |
each C library function, listing its arguments and results. |
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Line 110 AUTHOR
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Line 170 AUTHOR
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University Computing Service |
University Computing Service |
Cambridge CB2 3QH, England. |
Cambridge CB2 3QH, England. |
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Putting an actual email address here seems to have been a spam magnet, | Putting an actual email address here seems to have been a spam magnet, |
so I've taken it away. If you want to email me, use my two initials, | so I've taken it away. If you want to email me, use my two initials, |
followed by the two digits 10, at the domain cam.ac.uk. |
followed by the two digits 10, at the domain cam.ac.uk. |
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REVISION |
REVISION |
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Last updated: 24 August 2011 | Last updated: 13 May 2013 |
Copyright (c) 1997-2011 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 16-BIT API BASIC FUNCTIONS |
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pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options, |
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const char **errptr, int *erroffset, |
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const unsigned char *tableptr); |
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pcre16 *pcre16_compile2(PCRE_SPTR16 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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pcre16_extra *pcre16_study(const pcre16 *code, int options, |
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const char **errptr); |
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void pcre16_free_study(pcre16_extra *extra); |
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int pcre16_exec(const pcre16 *code, const pcre16_extra *extra, |
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PCRE_SPTR16 subject, int length, int startoffset, |
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int options, int *ovector, int ovecsize); |
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int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra, |
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PCRE_SPTR16 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 16-BIT API STRING EXTRACTION FUNCTIONS |
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int pcre16_copy_named_substring(const pcre16 *code, |
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PCRE_SPTR16 subject, int *ovector, |
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int stringcount, PCRE_SPTR16 stringname, |
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PCRE_UCHAR16 *buffer, int buffersize); |
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int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector, |
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int stringcount, int stringnumber, PCRE_UCHAR16 *buffer, |
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int buffersize); |
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int pcre16_get_named_substring(const pcre16 *code, |
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PCRE_SPTR16 subject, int *ovector, |
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int stringcount, PCRE_SPTR16 stringname, |
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PCRE_SPTR16 *stringptr); |
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int pcre16_get_stringnumber(const pcre16 *code, |
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PCRE_SPTR16 name); |
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int pcre16_get_stringtable_entries(const pcre16 *code, |
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PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last); |
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int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector, |
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int stringcount, int stringnumber, |
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PCRE_SPTR16 *stringptr); |
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int pcre16_get_substring_list(PCRE_SPTR16 subject, |
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int *ovector, int stringcount, PCRE_SPTR16 **listptr); |
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void pcre16_free_substring(PCRE_SPTR16 stringptr); |
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void pcre16_free_substring_list(PCRE_SPTR16 *stringptr); |
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PCRE 16-BIT API AUXILIARY FUNCTIONS |
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pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize); |
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void pcre16_jit_stack_free(pcre16_jit_stack *stack); |
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void pcre16_assign_jit_stack(pcre16_extra *extra, |
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pcre16_jit_callback callback, void *data); |
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const unsigned char *pcre16_maketables(void); |
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int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra, |
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int what, void *where); |
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int pcre16_refcount(pcre16 *code, int adjust); |
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int pcre16_config(int what, void *where); |
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const char *pcre16_version(void); |
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int pcre16_pattern_to_host_byte_order(pcre16 *code, |
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pcre16_extra *extra, const unsigned char *tables); |
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PCRE 16-BIT API INDIRECTED FUNCTIONS |
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void *(*pcre16_malloc)(size_t); |
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void (*pcre16_free)(void *); |
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void *(*pcre16_stack_malloc)(size_t); |
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void (*pcre16_stack_free)(void *); |
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int (*pcre16_callout)(pcre16_callout_block *); |
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PCRE 16-BIT API 16-BIT-ONLY FUNCTION |
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int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output, |
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PCRE_SPTR16 input, int length, int *byte_order, |
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int keep_boms); |
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THE PCRE 16-BIT LIBRARY |
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Starting with release 8.30, it is possible to compile a PCRE library |
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that supports 16-bit character strings, including UTF-16 strings, as |
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well as or instead of the original 8-bit library. The majority of the |
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work to make this possible was done by Zoltan Herczeg. The two |
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libraries contain identical sets of functions, used in exactly the same |
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way. Only the names of the functions and the data types of their argu- |
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ments and results are different. To avoid over-complication and reduce |
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the documentation maintenance load, most of the PCRE documentation |
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describes the 8-bit library, with only occasional references to the |
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16-bit library. This page describes what is different when you use the |
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16-bit library. |
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WARNING: A single application can be linked with both libraries, but |
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you must take care when processing any particular pattern to use func- |
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tions from just one library. For example, if you want to study a pat- |
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tern that was compiled with pcre16_compile(), you must do so with |
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pcre16_study(), not pcre_study(), and you must free the study data with |
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pcre16_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 16-bit library is called libpcre16, and can |
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normally be accesss by adding -lpcre16 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 16-bit library, |
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strings are passed as vectors of unsigned 16-bit quantities. The macro |
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PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is |
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defined as "const PCRE_UCHAR16 *". In very many environments, "short |
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int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16 |
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as "unsigned short int", but checks that it really is a 16-bit data |
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type. If it is not, the build fails with an error message telling the |
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maintainer 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 16-bit |
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patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively. |
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The type of the user-accessible structure that is returned by |
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pcre16_study() is pcre16_extra, and the type of the structure that is |
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used for passing data to a callout function is pcre16_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 16-bit instead of 8-bit types. |
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16-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 16-bit library with a name that starts with pcre16_ instead |
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of pcre_. The prototypes are listed above. In addition, there is one |
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extra function, pcre16_utf16_to_host_byte_order(). This is a utility |
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function that converts a UTF-16 character string to host byte order if |
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necessary. The other 16-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 pcre16_utf16_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 16-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 16-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 16-bit data units, and the offsets within subject strings that are |
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returned by the matching functions are in also 16-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 16-bit characters. The pcre16_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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16-bit data units. |
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OPTION NAMES |
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There are two new general option names, PCRE_UTF16 and |
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PCRE_NO_UTF16_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-16 strings in the pcreunicode page. |
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For the pcre16_config() function there is an option PCRE_CONFIG_UTF16 |
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that returns 1 if UTF-16 support is configured, otherwise 0. If this |
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option is given to pcre_config() or pcre32_config(), or if the |
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PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF32 option is given to pcre16_con- |
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fig(), the result is the PCRE_ERROR_BADOPTION error. |
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CHARACTER CODES |
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In 16-bit mode, when PCRE_UTF16 is not set, character values are |
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treated in the same way as in 8-bit, non UTF-8 mode, except, of course, |
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that they can range from 0 to 0xffff instead of 0 to 0xff. Character |
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types for characters less than 0xff can therefore be influenced by the |
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locale in the same way as before. Characters greater than 0xff have |
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only one case, and no "type" (such as letter or digit). |
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In UTF-16 mode, the character code is Unicode, in the range 0 to |
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0x10ffff, with the exception of values in the range 0xd800 to 0xdfff |
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because those are "surrogate" values that are used in pairs to encode |
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values greater than 0xffff. |
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A UTF-16 string can indicate its endianness by special code knows as a |
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byte-order mark (BOM). The PCRE functions do not handle this, expecting |
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strings to be in host byte order. A utility function called |
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pcre16_utf16_to_host_byte_order() is provided to help with this (see |
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above). |
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ERROR NAMES |
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The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre- |
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spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is |
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given when a compiled pattern is passed to a function that processes |
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patterns in the other mode, for example, if a pattern compiled with |
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pcre_compile() is passed to pcre16_exec(). |
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There are new error codes whose names begin with PCRE_UTF16_ERR for |
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invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for |
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UTF-8 strings that are described in the section entitled "Reason codes |
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for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors |
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are: |
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PCRE_UTF16_ERR1 Missing low surrogate at end of string |
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PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate |
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PCRE_UTF16_ERR3 Isolated low surrogate |
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PCRE_UTF16_ERR4 Non-character |
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ERROR TEXTS |
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If there is an error while compiling a pattern, the error text that is |
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passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit |
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character string, zero-terminated. |
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CALLOUTS |
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The subject and mark fields in the callout block that is passed to a |
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callout function point to 16-bit vectors. |
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|
TESTING |
|
|
|
The pcretest program continues to operate with 8-bit input and output |
|
files, but it can be used for testing the 16-bit library. If it is run |
|
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 |
|
library functions are used instead of the 8-bit ones. Returned 16-bit |
|
strings are converted to 8-bit for output. If both the 8-bit and the |
|
32-bit libraries were not compiled, pcretest defaults to 16-bit and the |
|
-16 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 16-BIT MODE |
|
|
|
Not all the features of the 8-bit library are available with the 16-bit |
|
library. The C++ and POSIX wrapper functions support only the 8-bit |
|
library, 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. |
|
------------------------------------------------------------------------------ |
|
|
|
|
|
PCRE(3) Library Functions Manual PCRE(3) |
|
|
|
|
|
|
|
NAME |
|
PCRE - Perl-compatible regular expressions |
|
|
|
#include <pcre.h> |
|
|
|
|
|
PCRE 32-BIT API BASIC FUNCTIONS |
|
|
|
pcre32 *pcre32_compile(PCRE_SPTR32 pattern, int options, |
|
const char **errptr, int *erroffset, |
|
const unsigned char *tableptr); |
|
|
|
pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options, |
|
int *errorcodeptr, |
|
const char **errptr, int *erroffset, |
|
const unsigned char *tableptr); |
|
|
|
pcre32_extra *pcre32_study(const pcre32 *code, int options, |
|
const char **errptr); |
|
|
|
void pcre32_free_study(pcre32_extra *extra); |
|
|
|
int pcre32_exec(const pcre32 *code, const pcre32_extra *extra, |
|
PCRE_SPTR32 subject, int length, int startoffset, |
|
int options, int *ovector, int ovecsize); |
|
|
|
int pcre32_dfa_exec(const pcre32 *code, const pcre32_extra *extra, |
|
PCRE_SPTR32 subject, int length, int startoffset, |
|
int options, int *ovector, int ovecsize, |
|
int *workspace, int wscount); |
|
|
|
|
|
PCRE 32-BIT API STRING EXTRACTION FUNCTIONS |
|
|
|
int pcre32_copy_named_substring(const pcre32 *code, |
|
PCRE_SPTR32 subject, int *ovector, |
|
int stringcount, PCRE_SPTR32 stringname, |
|
PCRE_UCHAR32 *buffer, int buffersize); |
|
|
|
int pcre32_copy_substring(PCRE_SPTR32 subject, int *ovector, |
|
int stringcount, int stringnumber, PCRE_UCHAR32 *buffer, |
|
int buffersize); |
|
|
|
int pcre32_get_named_substring(const pcre32 *code, |
|
PCRE_SPTR32 subject, int *ovector, |
|
int stringcount, PCRE_SPTR32 stringname, |
|
PCRE_SPTR32 *stringptr); |
|
|
|
int pcre32_get_stringnumber(const pcre32 *code, |
|
PCRE_SPTR32 name); |
|
|
|
int pcre32_get_stringtable_entries(const pcre32 *code, |
|
PCRE_SPTR32 name, PCRE_UCHAR32 **first, PCRE_UCHAR32 **last); |
|
|
|
int pcre32_get_substring(PCRE_SPTR32 subject, int *ovector, |
|
int stringcount, int stringnumber, |
|
PCRE_SPTR32 *stringptr); |
|
|
|
int pcre32_get_substring_list(PCRE_SPTR32 subject, |
|
int *ovector, int stringcount, PCRE_SPTR32 **listptr); |
|
|
|
void pcre32_free_substring(PCRE_SPTR32 stringptr); |
|
|
|
void pcre32_free_substring_list(PCRE_SPTR32 *stringptr); |
|
|
|
|
|
PCRE 32-BIT API AUXILIARY FUNCTIONS |
|
|
|
pcre32_jit_stack *pcre32_jit_stack_alloc(int startsize, int maxsize); |
|
|
|
void pcre32_jit_stack_free(pcre32_jit_stack *stack); |
|
|
|
void pcre32_assign_jit_stack(pcre32_extra *extra, |
|
pcre32_jit_callback callback, void *data); |
|
|
|
const unsigned char *pcre32_maketables(void); |
|
|
|
int pcre32_fullinfo(const pcre32 *code, const pcre32_extra *extra, |
|
int what, void *where); |
|
|
|
int pcre32_refcount(pcre32 *code, int adjust); |
|
|
|
int pcre32_config(int what, void *where); |
|
|
|
const char *pcre32_version(void); |
|
|
|
int pcre32_pattern_to_host_byte_order(pcre32 *code, |
|
pcre32_extra *extra, const unsigned char *tables); |
|
|
|
|
|
PCRE 32-BIT API INDIRECTED FUNCTIONS |
|
|
|
void *(*pcre32_malloc)(size_t); |
|
|
|
void (*pcre32_free)(void *); |
|
|
|
void *(*pcre32_stack_malloc)(size_t); |
|
|
|
void (*pcre32_stack_free)(void *); |
|
|
|
int (*pcre32_callout)(pcre32_callout_block *); |
|
|
|
|
|
PCRE 32-BIT API 32-BIT-ONLY FUNCTION |
|
|
|
int pcre32_utf32_to_host_byte_order(PCRE_UCHAR32 *output, |
|
PCRE_SPTR32 input, int length, int *byte_order, |
|
int keep_boms); |
|
|
|
|
|
THE PCRE 32-BIT LIBRARY |
|
|
|
Starting with release 8.32, it is possible to compile a PCRE library |
|
that supports 32-bit character strings, including UTF-32 strings, as |
|
well as or instead of the original 8-bit library. This work was done by |
|
Christian Persch, based on the work done by Zoltan Herczeg for the |
|
16-bit library. All three libraries contain identical sets of func- |
|
tions, used in exactly the same way. Only the names of the functions |
|
and the data types of their arguments and results are different. To |
|
avoid over-complication and reduce the documentation maintenance load, |
|
most of the PCRE documentation describes the 8-bit library, with only |
|
occasional references to the 16-bit and 32-bit libraries. This page |
|
describes what is different when you use the 32-bit library. |
|
|
|
WARNING: A single application can be linked with all or any of the |
|
three libraries, but you must take care when processing any particular |
|
pattern to use functions from just one library. For example, if you |
|
want to study a pattern that was compiled with pcre32_compile(), you |
|
must do so with pcre32_study(), not pcre_study(), and you must free the |
|
study data with pcre32_free_study(). |
|
|
|
|
|
THE HEADER FILE |
|
|
|
There is only one header file, pcre.h. It contains prototypes for all |
|
the functions in all libraries, as well as definitions of flags, struc- |
|
tures, error codes, etc. |
|
|
|
|
|
THE LIBRARY NAME |
|
|
|
In Unix-like systems, the 32-bit library is called libpcre32, and can |
|
normally be accesss by adding -lpcre32 to the command for linking an |
|
application that uses PCRE. |
|
|
|
|
|
STRING TYPES |
|
|
|
In the 8-bit library, strings are passed to PCRE library functions as |
|
vectors of bytes with the C type "char *". In the 32-bit library, |
|
strings are passed as vectors of unsigned 32-bit quantities. The macro |
|
PCRE_UCHAR32 specifies an appropriate data type, and PCRE_SPTR32 is |
|
defined as "const PCRE_UCHAR32 *". In very many environments, "unsigned |
|
int" is a 32-bit data type. When PCRE is built, it defines PCRE_UCHAR32 |
|
as "unsigned int", but checks that it really is a 32-bit data type. If |
|
it is not, the build fails with an error message telling the maintainer |
|
to modify the definition appropriately. |
|
|
|
|
|
STRUCTURE TYPES |
|
|
|
The types of the opaque structures that are used for compiled 32-bit |
|
patterns and JIT stacks are pcre32 and pcre32_jit_stack respectively. |
|
The type of the user-accessible structure that is returned by |
|
pcre32_study() is pcre32_extra, and the type of the structure that is |
|
used for passing data to a callout function is pcre32_callout_block. |
|
These structures contain the same fields, with the same names, as their |
|
8-bit counterparts. The only difference is that pointers to character |
|
strings are 32-bit instead of 8-bit types. |
|
|
|
|
|
32-BIT FUNCTIONS |
|
|
|
For every function in the 8-bit library there is a corresponding func- |
|
tion in the 32-bit library with a name that starts with pcre32_ instead |
|
of pcre_. The prototypes are listed above. In addition, there is one |
|
extra function, pcre32_utf32_to_host_byte_order(). This is a utility |
|
function that converts a UTF-32 character string to host byte order if |
|
necessary. The other 32-bit functions expect the strings they are |
|
passed to be in host byte order. |
|
|
|
The input and output arguments of pcre32_utf32_to_host_byte_order() may |
|
point to the same address, that is, conversion in place is supported. |
|
The output buffer must be at least as long as the input. |
|
|
|
The length argument specifies the number of 32-bit data units in the |
|
input string; a negative value specifies a zero-terminated string. |
|
|
|
If byte_order is NULL, it is assumed that the string starts off in host |
|
byte order. This may be changed by byte-order marks (BOMs) anywhere in |
|
the string (commonly as the first character). |
|
|
|
If byte_order is not NULL, a non-zero value of the integer to which it |
|
points means that the input starts off in host byte order, otherwise |
|
the opposite order is assumed. Again, BOMs in the string can change |
|
this. The final byte order is passed back at the end of processing. |
|
|
|
If keep_boms is not zero, byte-order mark characters (0xfeff) are |
|
copied into the output string. Otherwise they are discarded. |
|
|
|
The result of the function is the number of 32-bit units placed into |
|
the output buffer, including the zero terminator if the string was |
|
zero-terminated. |
|
|
|
|
|
SUBJECT STRING OFFSETS |
|
|
|
The lengths and starting offsets of subject strings must be specified |
|
in 32-bit data units, and the offsets within subject strings that are |
|
returned by the matching functions are in also 32-bit units rather than |
|
bytes. |
|
|
|
|
|
NAMED SUBPATTERNS |
|
|
|
The name-to-number translation table that is maintained for named sub- |
|
patterns uses 32-bit characters. The pcre32_get_stringtable_entries() |
|
function returns the length of each entry in the table as the number of |
|
32-bit data units. |
|
|
|
|
|
OPTION NAMES |
|
|
|
There are two new general option names, PCRE_UTF32 and |
|
PCRE_NO_UTF32_CHECK, which correspond to PCRE_UTF8 and |
|
PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options |
|
define the same bits in the options word. There is a discussion about |
|
the validity of UTF-32 strings in the pcreunicode page. |
|
|
|
For the pcre32_config() function there is an option PCRE_CONFIG_UTF32 |
|
that returns 1 if UTF-32 support is configured, otherwise 0. If this |
|
option is given to pcre_config() or pcre16_config(), or if the |
|
PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF16 option is given to pcre32_con- |
|
fig(), the result is the PCRE_ERROR_BADOPTION error. |
|
|
|
|
|
CHARACTER CODES |
|
|
|
In 32-bit mode, when PCRE_UTF32 is not set, character values are |
|
treated in the same way as in 8-bit, non UTF-8 mode, except, of course, |
|
that they can range from 0 to 0x7fffffff instead of 0 to 0xff. Charac- |
|
ter types for characters less than 0xff can therefore be influenced by |
|
the locale in the same way as before. Characters greater than 0xff |
|
have only one case, and no "type" (such as letter or digit). |
|
|
|
In UTF-32 mode, the character code is Unicode, in the range 0 to |
|
0x10ffff, with the exception of values in the range 0xd800 to 0xdfff |
|
because those are "surrogate" values that are ill-formed in UTF-32. |
|
|
|
A UTF-32 string can indicate its endianness by special code knows as a |
|
byte-order mark (BOM). The PCRE functions do not handle this, expecting |
|
strings to be in host byte order. A utility function called |
|
pcre32_utf32_to_host_byte_order() is provided to help with this (see |
|
above). |
|
|
|
|
|
ERROR NAMES |
|
|
|
The error PCRE_ERROR_BADUTF32 corresponds to its 8-bit counterpart. |
|
The error PCRE_ERROR_BADMODE is given when a compiled pattern is passed |
|
to a function that processes patterns in the other mode, for example, |
|
if a pattern compiled with pcre_compile() is passed to pcre32_exec(). |
|
|
|
There are new error codes whose names begin with PCRE_UTF32_ERR for |
|
invalid UTF-32 strings, corresponding to the PCRE_UTF8_ERR codes for |
|
UTF-8 strings that are described in the section entitled "Reason codes |
|
for invalid UTF-8 strings" in the main pcreapi page. The UTF-32 errors |
|
are: |
|
|
|
PCRE_UTF32_ERR1 Surrogate character (range from 0xd800 to 0xdfff) |
|
PCRE_UTF32_ERR2 Non-character |
|
PCRE_UTF32_ERR3 Character > 0x10ffff |
|
|
|
|
|
ERROR TEXTS |
|
|
|
If there is an error while compiling a pattern, the error text that is |
|
passed back by pcre32_compile() or pcre32_compile2() is still an 8-bit |
|
character string, zero-terminated. |
|
|
|
|
|
CALLOUTS |
|
|
|
The subject and mark fields in the callout block that is passed to a |
|
callout function point to 32-bit vectors. |
|
|
|
|
|
TESTING |
|
|
|
The pcretest program continues to operate with 8-bit input and output |
|
files, but it can be used for testing the 32-bit library. If it is run |
|
with the command line option -32, patterns and subject strings are con- |
|
verted from 8-bit to 32-bit before being passed to PCRE, and the 32-bit |
|
library functions are used instead of the 8-bit ones. Returned 32-bit |
|
strings are converted to 8-bit for output. If both the 8-bit and the |
|
16-bit libraries were not compiled, pcretest defaults to 32-bit and the |
|
-32 option is ignored. |
|
|
|
When PCRE is being built, the RunTest script that is called by "make |
|
check" uses the pcretest -C option to discover which of the 8-bit, |
|
16-bit and 32-bit libraries has been built, and runs the tests appro- |
|
priately. |
|
|
|
|
|
NOT SUPPORTED IN 32-BIT MODE |
|
|
|
Not all the features of the 8-bit library are available with the 32-bit |
|
library. The C++ and POSIX wrapper functions support only the 8-bit |
|
library, and the pcregrep program is at present 8-bit only. |
|
|
|
|
|
AUTHOR |
|
|
|
Philip Hazel |
|
University Computing Service |
|
Cambridge CB2 3QH, England. |
|
|
|
|
|
REVISION |
|
|
|
Last updated: 12 May 2013 |
|
Copyright (c) 1997-2013 University of Cambridge. |
|
------------------------------------------------------------------------------ |
|
|
|
|
|
PCREBUILD(3) Library Functions Manual PCREBUILD(3) |
|
|
|
|
|
|
|
NAME |
|
PCRE - Perl-compatible regular expressions |
|
|
|
BUILDING PCRE |
|
|
|
PCRE is distributed with a configure script that can be used to build |
|
the library in Unix-like environments using the applications known as |
|
Autotools. Also in the distribution are files to support building |
|
using CMake instead of configure. The text file README contains general |
|
information about building with Autotools (some of which is repeated |
|
below), and also has some comments about building on various operating |
|
systems. There is a lot more information about building PCRE without |
|
using Autotools (including information about using CMake and building |
|
"by hand") in the text file called NON-AUTOTOOLS-BUILD. You should |
|
consult this file as well as the README file if you are building in a |
|
non-Unix-like environment. |
|
|
|
|
PCRE BUILD-TIME OPTIONS |
PCRE BUILD-TIME OPTIONS |
|
|
This document describes the optional features of PCRE that can be | The rest of this document describes the optional features of PCRE that |
selected when the library is compiled. It assumes use of the configure | can be selected when the library is compiled. It assumes use of the |
script, where the optional features are selected or deselected by pro- | configure script, where the optional features are selected or dese- |
viding options to configure before running the make command. However, | lected by providing options to configure before running the make com- |
the same options can be selected in both Unix-like and non-Unix-like | mand. However, the same options can be selected in both Unix-like and |
environments using the GUI facility of cmake-gui if you are using CMake | non-Unix-like environments using the GUI facility of cmake-gui if you |
instead of configure to build PCRE. | are using CMake instead of configure to build PCRE. |
|
|
There is a lot more information about building PCRE in non-Unix-like | If you are not using Autotools or CMake, option selection can be done |
environments in the file called NON_UNIX_USE, which is part of the PCRE | by editing the config.h file, or by passing parameter settings to the |
distribution. You should consult this file as well as the README file | compiler, as described in NON-AUTOTOOLS-BUILD. |
if you are building in a non-Unix-like environment. | |
|
|
The complete list of options for configure (which includes the standard |
The complete list of options for configure (which includes the standard |
ones such as the selection of the installation directory) can be | ones such as the selection of the installation directory) can be |
obtained by running |
obtained by running |
|
|
./configure --help |
./configure --help |
|
|
The following sections include descriptions of options whose names | The following sections include descriptions of options whos The following sections include descriptions of options whos |
begin with --enable or --disable. These settings specify changes to the |
begin with --enable or --disable. These settings specify changes to the |
defaults for the configure command. Because of the way that configure | defaults for the configure command. Because of the way that configure |
works, --enable and --disable always come in pairs, so the complemen- | works, --enable and --disable always come in pairs, so the complemen- |
tary option always exists as well, but as it specifies the default, it | tary option always exists as well, but as it specifies the default, it |
is not described. |
is not described. |
|
|
|
|
|
BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES |
|
|
|
By default, a library called libpcre is built, containing functions |
|
that take string arguments contained in vectors of bytes, either as |
|
single-byte characters, or interpreted as UTF-8 strings. You can also |
|
build a separate library, called libpcre16, in which strings are con- |
|
tained in vectors of 16-bit data units and interpreted either as sin- |
|
gle-unit characters or UTF-16 strings, by adding |
|
|
|
--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 |
|
|
|
--disable-pcre8 |
|
|
|
as well. At least one of the three libraries must be built. Note that |
|
the C++ and POSIX wrappers are for the 8-bit library only, and that |
|
pcregrep is an 8-bit program. None of these are built if you select |
|
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 172 BUILDING SHARED AND STATIC LIBRARIES
|
Line 935 BUILDING SHARED AND STATIC LIBRARIES
|
|
|
C++ SUPPORT |
C++ SUPPORT |
|
|
By default, the configure script will search for a C++ compiler and C++ | By default, if the 8-bit library is being built, the configure script |
header files. If it finds them, it automatically builds the C++ wrapper | will search for a C++ compiler and C++ header files. If it finds them, |
library for PCRE. You can disable this by adding | it automatically builds the C++ wrapper library (which supports only |
| 8-bit strings). You can disable this by adding |
|
|
--disable-cpp |
--disable-cpp |
|
|
to the configure command. |
to the configure command. |
|
|
|
|
UTF-8 SUPPORT | UTF-8, UTF-16 AND UTF-32 SUPPORT |
|
|
To build PCRE with support for UTF-8 Unicode character strings, add | To build PCRE with support for UTF Unicode character strings, add |
|
|
--enable-utf8 | --enable-utf |
|
|
to the configure command. Of itself, this does not make PCRE treat | to the configure command. This setting applies to all three libraries, |
strings as UTF-8. As well as compiling PCRE with this option, you also | adding support for UTF-8 to the 8-bit library, support for UTF-16 to |
have have to set the PCRE_UTF8 option when you call the pcre_compile() | the 16-bit library, and support for UTF-32 to the to the 32-bit |
or pcre_compile2() functions. | library. There are no separate options for enabling UTF-8, UTF-16 and |
| UTF-32 independently because that would allow ridiculous settings such |
| as requesting UTF-16 support while building only the 8-bit library. It |
| is not possible to build one library with UTF support and another with- |
| out in the same configuration. (For backwards compatibility, --enable- |
| utf8 is a synonym of --enable-utf.) |
|
|
If you set --enable-utf8 when compiling in an EBCDIC environment, PCRE | Of itself, this setting does not make PCRE treat strings as UTF-8, |
expects its input to be either ASCII or UTF-8 (depending on the runtime | UTF-16 or UTF-32. As well as compiling PCRE with this option, you also |
option). It is not possible to support both EBCDIC and UTF-8 codes in | have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as |
the same version of the library. Consequently, --enable-utf8 and | appropriate) when you call one of the pattern compiling functions. |
| |
| If you set --enable-utf when compiling in an EBCDIC environment, PCRE |
| expects its input to be either ASCII or UTF-8 (depending on the run- |
| time option). It is not possible to support both EBCDIC and UTF-8 codes |
| in the same version of the library. Consequently, --enable-utf and |
--enable-ebcdic are mutually exclusive. |
--enable-ebcdic are mutually exclusive. |
|
|
|
|
UNICODE CHARACTER PROPERTY SUPPORT |
UNICODE CHARACTER PROPERTY SUPPORT |
|
|
UTF-8 support allows PCRE to process character values greater than 255 | UTF support allows the libraries to process character codepoints up to |
in the strings that it handles. On its own, however, it does not pro- | 0x10ffff in the strings that they handle. On its own, however, it does |
vide any facilities for accessing the properties of such characters. If | not provide any facilities for accessing the properties of such charac- |
you want to be able to use the pattern escapes \P, \p, and \X, which | ters. If you want to be able to use the pattern escapes \P, \p, and \X, |
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-8 support, even if you have | to the configure command. This implies UTF support, even if yo to the configure command. This implies UTF support, even if yo |
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 223 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 236 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 255 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 PCRE is called through the POSIX interface (see the pcreposix doc- | When the 8-bit library is called through the POSIX interface (see the |
umentation), additional working storage is required for holding the | pcreposix documentation), additional working storage is required for |
pointers to capturing substrings, because PCRE requires three integers | holding the pointers to capturing substrings, because PCRE requires |
per substring, whereas the POSIX interface provides only two. If the | three integers per substring, whereas the POSIX interface provides only |
number of expected substrings is small, the wrapper function uses space | two. If the number of expected substrings is small, the wrapper func- |
on the stack, because this is faster than using malloc() for each call. | tion uses space on the stack, because this is faster than using mal- |
The default threshold above which the stack is no longer used is 10; it | loc() for each call. The default threshold above which the stack is no |
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 298 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 truyl 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. Using | to the configure command. The value given must be 2, 3, or 4. For the |
longer offsets slows down the operation of PCRE because it has to load | 16-bit library, a value of 3 is rounded up to 4. In these libraries, |
additional bytes when handling them. | using longer offsets slows down the operation of PCRE because it has to |
| 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 |
Line 385 CREATING CHARACTER TABLES AT BUILD TIME
|
Line 1162 CREATING CHARACTER TABLES AT BUILD TIME
|
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".) |
|
|
|
|
Line 403 USING EBCDIC CODE
|
Line 1180 USING EBCDIC CODE
|
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-utf8. | --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 416 PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
|
Line 1208 PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
|
--enable-pcregrep-libbz2 |
--enable-pcregrep-libbz2 |
|
|
to the configure command. These options naturally require that the rel- |
to the configure command. These options naturally require that the rel- |
evant libraries are installed on your system. Configuration will fail | evant libraries are installed on your system. Configuration will fail |
if they are not. |
if they are not. |
|
|
|
|
PCREGREP BUFFER SIZE |
PCREGREP BUFFER SIZE |
|
|
pcregrep uses an internal buffer to hold a "window" on the file it is | pcregrep uses an internal buffer to hold a "window" on the file it is |
scanning, in order to be able to output "before" and "after" lines when |
scanning, in order to be able to output "before" and "after" lines when |
it finds a match. The size of the buffer is controlled by a parameter | it finds a match. The size of the buffer is controlled by a parameter |
whose default value is 20K. The buffer itself is three times this size, |
whose default value is 20K. The buffer itself is three times this size, |
but because of the way it is used for holding "before" lines, the long- |
but because of the way it is used for holding "before" lines, the long- |
est line that is guaranteed to be processable is the parameter size. | est line that is guaranteed to be processable is the paramete est line that is guaranteed to be processable is the paramete |
You can change the default parameter value by adding, for example, |
You can change the default parameter value by adding, for example, |
|
|
--with-pcregrep-bufsize=50K |
--with-pcregrep-bufsize=50K |
Line 442 PCRETEST OPTION FOR LIBREADLINE SUPPORT
|
Line 1234 PCRETEST OPTION FOR LIBREADLINE SUPPORT
|
|
|
--enable-pcretest-libreadline |
--enable-pcretest-libreadline |
|
|
to the configure command, pcretest is linked with the libreadline | to the configure command, pcretest is linked with the libreadline |
library, and when its input is from a terminal, it reads it using the | library, and when its input is from a terminal, it reads it using the |
readline() function. This provides line-editing and history facilities. |
readline() function. This provides line-editing and history facilities. |
Note that libreadline is GPL-licensed, so if you distribute a binary of |
Note that libreadline is GPL-licensed, so if you distribute a binary of |
pcretest linked in this way, there may be licensing issues. |
pcretest linked in this way, there may be licensing issues. |
|
|
Setting this option causes the -lreadline option to be added to the | Setting this option causes the -lreadline option to be added to the |
pcretest build. In many operating environments with a sytem-installed | pcretest build. In many operating environments with a sytem-installed |
libreadline this is sufficient. However, in some environments (e.g. if |
libreadline this is sufficient. However, in some environments (e.g. if |
an unmodified distribution version of readline is in use), some extra | an unmodified distribution version of readline is in use), some extra |
configuration may be necessary. The INSTALL file for libreadline says | configuration may be necessary. The INSTALL file for libreadline says |
this: |
this: |
|
|
"Readline uses the termcap functions, but does not link with the |
"Readline uses the termcap functions, but does not link with the |
termcap or curses library itself, allowing applications which link |
termcap or curses library itself, allowing applications which link |
with readline the to choose an appropriate library." |
with readline the to choose an appropriate library." |
|
|
If your environment has not been set up so that an appropriate library | If your environment has not been set up so that an appropriate library |
is automatically included, you may need to add something like |
is automatically included, you may need to add something like |
|
|
LIBS="-ncurses" |
LIBS="-ncurses" |
Line 467 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), pcre_config(3). | pcreapi(3), pcre16, pcre32, pcre_config(3). |
|
|
|
|
AUTHOR |
AUTHOR |
Line 481 AUTHOR
|
Line 1341 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 06 September 2011 | Last updated: 12 May 2013 |
Copyright (c) 1997-2011 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() function. This works in the same was as Perl's matching | pcre_exec(), pcre16_exec() and pcre32_exec() functions. These work in |
function, and provides a Perl-compatible matching operation. | the same as as Perl's matching function, and provide a Perl-compatible |
| matching operation. The just-in-time (JIT) optimization that is |
| described in the pcrejit documentation is compatible with these func- |
| tions. |
|
|
An alternative algorithm is provided by the pcre_dfa_exec() function; | An alternative algorithm is provided by the pcre_dfa_exec(), |
this operates in a different way, and is not Perl-compatible. It has | pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a |
advantages and disadvantages compared with the standard algorithm, and | different way, and are not Perl-compatible. This alternative has advan- |
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 632 THE ALTERNATIVE MATCHING ALGORITHM
|
Line 1496 THE ALTERNATIVE MATCHING ALGORITHM
|
6. Callouts are supported, but the value of the capture_top field is |
6. Callouts are supported, but the value of the capture_top field is |
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) matches a | 7. The \C escape sequence, which (in the standard algorithm) always |
single byte, even in UTF-8 mode, is not supported in UTF-8 mode, | matches a single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is |
because the alternative algorithm moves through the subject string one | not supported in these modes, because the alternative algorithm moves |
character at a time, for all active paths through the tree. | through the subject string one character (not data unit) at a time, for |
| all active paths through the tree. |
|
|
8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) | 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) |
are not supported. (*FAIL) is supported, and behaves like a failing | are not supported. (*FAIL) is supported, and behaves like a failing |
negative assertion. |
negative assertion. |
|
|
|
|
ADVANTAGES OF THE ALTERNATIVE ALGORITHM |
ADVANTAGES OF THE ALTERNATIVE ALGORITHM |
|
|
Using the alternative matching algorithm provides the following advan- | Using the alternative matching algorithm provides the following advan- |
tages: |
tages: |
|
|
1. All possible matches (at a single point in the subject) are automat- |
1. All possible matches (at a single point in the subject) are automat- |
ically found, and in particular, the longest match is found. To find | ically found, and in particular, the longest match is found. To find |
more than one match using the standard algorithm, you have to do kludgy |
more than one match using the standard algorithm, you have to do kludgy |
things with callouts. |
things with callouts. |
|
|
2. Because the alternative algorithm scans the subject string just | 2. Because the alternative algorithm scans the subject string just |
once, and never needs to backtrack, it is possible to pass very long | once, and never needs to backtrack (except for lookbehinds), it is pos- |
subject strings to the matching function in several pieces, checking | sible to pass very long subject strings to the matching function in |
for partial matching each time. Although it is possible to do multi- | several pieces, checking for partial matching each time. Although it is |
segment matching using the standard algorithm (pcre_exec()), by retain- | possible to do multi-segment matching using the standard algorithm by |
ing partially matched substrings, it is more complicated. The pcrepar- | retaining partially matched substrings, it is more complicated. The |
tial documentation gives details of partial matching and discusses | pcrepartial documentation gives details of partial matching and dis- |
multi-segment matching. | cusses multi-segment matching. |
|
|
|
|
DISADVANTAGES OF THE ALTERNATIVE ALGORITHM |
DISADVANTAGES OF THE ALTERNATIVE ALGORITHM |
|
|
The alternative algorithm suffers from a number of disadvantages: |
The alternative algorithm suffers from a number of disadvantages: |
|
|
1. It is substantially slower than the standard algorithm. This is | 1. It is substantially slower than the standard algorithm. This is |
partly because it has to search for all possible matches, but is also | partly because it has to search for all possible matches, but is also |
because it is less susceptible to optimization. |
because it is less susceptible to optimization. |
|
|
2. Capturing parentheses and back references are not supported. |
2. Capturing parentheses and back references are not supported. |
Line 685 AUTHOR
|
Line 1550 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 19 November 2011 | Last updated: 08 January 2012 |
Copyright (c) 1997-2010 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
PCREAPI(3) PCREAPI(3) | PCREAPI(3) Library Functions Manual PCREAPI(3) |
|
|
|
|
|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
#include <pcre.h> |
|
|
|
|
PCRE NATIVE API BASIC FUNCTIONS |
PCRE NATIVE API BASIC FUNCTIONS |
|
|
#include <pcre.h> |
|
|
|
pcre *pcre_compile(const char *pattern, int options, |
pcre *pcre_compile(const char *pattern, int options, |
const char **errptr, int *erroffset, |
const char **errptr, int *erroffset, |
const unsigned char *tableptr); |
const unsigned char *tableptr); |
Line 719 PCRE NATIVE API BASIC FUNCTIONS
|
Line 1585 PCRE NATIVE API BASIC FUNCTIONS
|
const char *subject, int length, int startoffset, |
const char *subject, int length, int startoffset, |
int options, int *ovector, int ovecsize); |
int options, int *ovector, int ovecsize); |
|
|
|
|
PCRE NATIVE API AUXILIARY FUNCTIONS |
|
|
|
pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize); |
|
|
|
void pcre_jit_stack_free(pcre_jit_stack *stack); |
|
|
|
void pcre_assign_jit_stack(pcre_extra *extra, |
|
pcre_jit_callback callback, void *data); |
|
|
|
int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, |
int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, |
const char *subject, int length, int startoffset, |
const char *subject, int length, int startoffset, |
int options, int *ovector, int ovecsize, |
int options, int *ovector, int ovecsize, |
int *workspace, int wscount); |
int *workspace, int wscount); |
|
|
|
|
|
PCRE NATIVE API STRING EXTRACTION FUNCTIONS |
|
|
int pcre_copy_named_substring(const pcre *code, |
int pcre_copy_named_substring(const pcre *code, |
const char *subject, int *ovector, |
const char *subject, int *ovector, |
int stringcount, const char *stringname, |
int stringcount, const char *stringname, |
Line 765 PCRE NATIVE API AUXILIARY FUNCTIONS
|
Line 1624 PCRE NATIVE API AUXILIARY FUNCTIONS
|
|
|
void pcre_free_substring_list(const char **stringptr); |
void pcre_free_substring_list(const char **stringptr); |
|
|
|
|
|
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); |
|
|
|
void pcre_jit_stack_free(pcre_jit_stack *stack); |
|
|
|
void pcre_assign_jit_stack(pcre_extra *extra, |
|
pcre_jit_callback callback, void *data); |
|
|
const unsigned char *pcre_maketables(void); |
const unsigned char *pcre_maketables(void); |
|
|
int pcre_fullinfo(const pcre *code, const pcre_extra *extra, |
int pcre_fullinfo(const pcre *code, const pcre_extra *extra, |
int what, void *where); |
int what, void *where); |
|
|
int pcre_info(const pcre *code, int *optptr, int *firstcharptr); |
|
|
|
int pcre_refcount(pcre *code, int adjust); |
int pcre_refcount(pcre *code, int adjust); |
|
|
int pcre_config(int what, void *where); |
int pcre_config(int what, void *where); |
|
|
char *pcre_version(void); | const char *pcre_version(void); |
|
|
|
int pcre_pattern_to_host_byte_order(pcre *code, |
|
pcre_extra *extra, const unsigned char *tables); |
|
|
|
|
PCRE NATIVE API INDIRECTED FUNCTIONS |
PCRE NATIVE API INDIRECTED FUNCTIONS |
|
|
void *(*pcre_malloc)(size_t); |
void *(*pcre_malloc)(size_t); |
Line 792 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, 16-BIT, AND 32-BIT LIBRARIES |
|
|
|
As well as support for 8-bit character strings, PCRE also supports |
|
16-bit strings (from release 8.30) and 32-bit strings (from release |
|
8.32), by means of two additional libraries. They can be built as well |
|
as, or instead of, the 8-bit library. To avoid too much complication, |
|
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 and 32-bit functions operate in the same way as their 8-bit |
|
counterparts; they just use different data types for their arguments |
|
and results, and their names start with pcre16_ or pcre32_ instead of |
|
pcre_. For every option that has UTF8 in its name (for example, |
|
PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8 |
|
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. |
|
|
|
References to bytes and UTF-8 in this document should be read as refer- |
|
ences to 16-bit data units and UTF-16 when using the 16-bit library, or |
|
32-bit data units and UTF-32 when using the 32-bit library, unless |
|
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 that correspond to the POSIX regular | are also some wrapper functions (for the 8-bit library only) that cor- |
expression API, but they do not give access to all the functionality. | respond to the POSIX regular expression API, but they do not give |
They are described in the pcreposix documentation. Both of these APIs | access to all the functionality. They are described in the pcreposix |
define a set of C function calls. A C++ wrapper is also distributed | documentation. Both of these APIs define a set of C function calls. A |
with PCRE. It is documented in the pcrecpp page. | C++ wrapper (again for the 8-bit library only) is also distributed with |
| 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 systems the library itself is called libpcre. It | pcre.h, and on Unix-like systems the (8-bit) library itself is called |
can normally be accessed by adding -lpcre to the command for linking an | libpcre. It can normally be accessed by adding -lpcre to the command |
application that uses PCRE. The header file defines the macros | for linking an application that uses PCRE. The header file defines the |
PCRE_MAJOR and PCRE_MINOR to contain the major and minor release num- | macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release |
bers 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 865 PCRE API OVERVIEW
|
Line 1769 PCRE API OVERVIEW
|
built are used. |
built are used. |
|
|
The function pcre_fullinfo() is used to find out information about a |
The function pcre_fullinfo() is used to find out information about a |
compiled pattern; pcre_info() is an obsolete version that returns only | compiled pattern. The function pcre_version() returns a pointer to a |
some of the available information, but is retained for backwards com- | string containing the version of PCRE and its date of release. |
patibility. The function pcre_version() returns a pointer to a string | |
containing the version of PCRE and its date of release. | |
|
|
The function pcre_refcount() maintains a reference count in a data |
The function pcre_refcount() maintains a reference count in a data |
block containing a compiled pattern. This is provided for the benefit |
block containing a compiled pattern. This is provided for the benefit |
Line 907 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 955 SAVING PRECOMPILED PATTERNS FOR LATER USE
|
Line 1857 SAVING PRECOMPILED PATTERNS FOR LATER USE
|
The compiled form of a regular expression can be saved and re-used at a |
The compiled form of a regular expression can be saved and re-used at a |
later time, possibly by a different program, and even on a host other |
later time, possibly by a different program, and even on a host other |
than the one on which it was compiled. Details are given in the |
than the one on which it was compiled. Details are given in the |
pcreprecompile documentation. However, compiling a regular expression | pcreprecompile documentation, which includes a description of the |
with one version of PCRE for use with a different version is not guar- | pcre_pattern_to_host_byte_order() function. However, compiling a regu- |
anteed to work and may cause crashes. | lar expression with one version of PCRE for use with a different ver- |
| sion is not guaranteed to work and may cause crashes. |
|
|
|
|
CHECKING BUILD-TIME OPTIONS |
CHECKING BUILD-TIME OPTIONS |
|
|
int pcre_config(int what, void *where); |
int pcre_config(int what, void *where); |
|
|
The function pcre_config() makes it possible for a PCRE client to dis- | The function pcre_config() makes it possible for a PCRE client to dis- |
cover which optional features have been compiled into the PCRE library. |
cover which optional features have been compiled into the PCRE library. |
The pcrebuild documentation has more details about these optional fea- | The pcrebuild documentation has more details about these optional fea- |
tures. |
tures. |
|
|
The first argument for pcre_config() is an integer, specifying which | The first argument for pcre_config() is an integer, specifyin The first argument for pcre_config() is an integer, specifyin |
information is required; the second argument is a pointer to a variable |
information is required; the second argument is a pointer to a variable |
into which the information is placed. The following information is | into which the information is placed. The returned value is zero on |
| success, or the negative error code PCRE_ERROR_BADOPTION if the value |
| in the first argument is not recognized. The following information is |
available: |
available: |
|
|
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. | able; otherwise it is set to zero. This value should normally be given |
| 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_CONFIG_UTF16 |
|
|
|
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 |
|
to the 16-bit version of this function, pcre16_config(). If it is given |
|
to the 8-bit or 32-bit version of this function, the result is |
|
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 |
Line 989 CHECKING BUILD-TIME OPTIONS
|
Line 1913 CHECKING BUILD-TIME OPTIONS
|
The output is an integer that is set to one if support for just-in-time |
The output is an integer that is set to one if support for just-in-time |
compiling is available; otherwise it is set to zero. |
compiling is available; otherwise it is set to zero. |
|
|
|
PCRE_CONFIG_JITTARGET |
|
|
|
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- |
|
ture for which the JIT compiler is configured, for example "x86 32bit |
|
(little endian + unaligned)". If JIT support is not available, the |
|
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 |
Line 1009 CHECKING BUILD-TIME OPTIONS
|
Line 1943 CHECKING BUILD-TIME OPTIONS
|
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 bytes used for |
internal linkage in compiled regular expressions. The value is 2, 3, or | internal linkage in compiled regular expressions. For the 8-bit |
4. Larger values allow larger regular expressions to be compiled, at | library, the value can be 2, 3, or 4. For the 16-bit library, the value |
the expense of slower matching. The default value of 2 is sufficient | is either 2 or 4 and is still a number of bytes. For the 32-bit |
for all but the most massive patterns, since it allows the compiled | library, the value is either 2 or 4 and is still a number of bytes. The |
pattern to be up to 64K in size. | default value of 2 is sufficient for all but the most massive patterns, |
| since it allows the compiled pattern to be up to 64K in size. Larger |
| values allow larger regular expressions to be compiled, at the expense |
| of slower matching. |
|
|
PCRE_CONFIG_POSIX_MALLOC_THRESHOLD |
PCRE_CONFIG_POSIX_MALLOC_THRESHOLD |
|
|
The output is an integer that contains the threshold above which the | The output is an integer that contains the threshold above which the |
POSIX interface uses malloc() for output vectors. Further details are | POSIX interface uses malloc() for output vectors. Further details are |
given in the pcreposix documentation. |
given in the pcreposix documentation. |
|
|
PCRE_CONFIG_MATCH_LIMIT |
PCRE_CONFIG_MATCH_LIMIT |
|
|
The output is a long integer that gives the default limit for the num- | The output is a long integer that gives the default limit for the num- |
ber of internal matching function calls in a pcre_exec() execution. | ber of internal matching function calls in a pcre_exec() execution. |
Further details are given with pcre_exec() below. |
Further details are given with pcre_exec() below. |
|
|
PCRE_CONFIG_MATCH_LIMIT_RECURSION |
PCRE_CONFIG_MATCH_LIMIT_RECURSION |
|
|
The output is a long integer that gives the default limit for the depth |
The output is a long integer that gives the default limit for the depth |
of recursion when calling the internal matching function in a | of recursion when calling the internal matching function in a |
pcre_exec() execution. Further details are given with pcre_exec() | pcre_exec() execution. Further details are given with pcre_exec() |
below. |
below. |
|
|
PCRE_CONFIG_STACKRECURSE |
PCRE_CONFIG_STACKRECURSE |
|
|
The output is an integer that is set to one if internal recursion when | The output is an integer that is set to one if internal recursion when |
running pcre_exec() is implemented by recursive function calls that use |
running pcre_exec() is implemented by recursive function calls that use |
the stack to remember their state. This is the usual way that PCRE is | the stack to remember their state. This is the usual way that PCRE is |
compiled. The output is zero if PCRE was compiled to use blocks of data |
compiled. The output is zero if PCRE was compiled to use blocks of data |
on the heap instead of recursive function calls. In this case, | on the heap instead of recursive function calls. In this case, |
pcre_stack_malloc and pcre_stack_free are called to manage memory | pcre_stack_malloc and pcre_stack_free are called to manage memory |
blocks on the heap, thus avoiding the use of the stack. |
blocks on the heap, thus avoiding the use of the stack. |
|
|
|
|
Line 1058 COMPILING A PATTERN
|
Line 1995 COMPILING A PATTERN
|
|
|
Either of the functions pcre_compile() or pcre_compile2() can be called |
Either of the functions pcre_compile() or pcre_compile2() can be called |
to compile a pattern into an internal form. The only difference between |
to compile a pattern into an internal form. The only difference between |
the two interfaces is that pcre_compile2() has an additional argument, | the two interfaces is that pcre_compile2() has an additional argument, |
errorcodeptr, via which a numerical error code can be returned. To | errorcodeptr, via which a numerical error code can be returned. To |
avoid too much repetition, we refer just to pcre_compile() below, but | avoid too much repetition, we refer just to pcre_compile() below, but |
the information applies equally to pcre_compile2(). |
the information applies equally to pcre_compile2(). |
|
|
The pattern is a C string terminated by a binary zero, and is passed in |
The pattern is a C string terminated by a binary zero, and is passed in |
the pattern argument. A pointer to a single block of memory that is | the pattern argument. A pointer to a single block of memory that is |
obtained via pcre_malloc is returned. This contains the compiled code | obtained via pcre_malloc is returned. This contains the compiled code |
and related data. The pcre type is defined for the returned block; this |
and related data. The pcre type is defined for the returned block; this |
is a typedef for a structure whose contents are not externally defined. |
is a typedef for a structure whose contents are not externally defined. |
It is up to the caller to free the memory (via pcre_free) when it is no |
It is up to the caller to free the memory (via pcre_free) when it is no |
longer required. |
longer required. |
|
|
Although the compiled code of a PCRE regex is relocatable, that is, it | Although the compiled code of a PCRE regex is relocatable, that is, it |
does not depend on memory location, the complete pcre data block is not |
does not depend on memory location, the complete pcre data block is not |
fully relocatable, because it may contain a copy of the tableptr argu- | fully relocatable, because it may contain a copy of the tableptr argu- |
ment, which is an address (see below). |
ment, which is an address (see below). |
|
|
The options argument contains various bit settings that affect the com- |
The options argument contains various bit settings that affect the com- |
pilation. It should be zero if no options are required. The available | pilation. It should be zero if no options are required. The available |
options are described below. Some of them (in particular, those that | options are described below. Some of them (in particular, those that |
are compatible with Perl, but some others as well) can also be set and | are compatible with Perl, but some others as well) can also be set and |
unset from within the pattern (see the detailed description in the | unset from within the pattern (see the detailed description in the |
pcrepattern documentation). For those options that can be different in | pcrepattern documentation). For those options that can be different in |
different parts of the pattern, the contents of the options argument | different parts of the pattern, the contents of the options argument |
specifies their settings at the start of compilation and execution. The |
specifies their settings at the start of compilation and execution. The |
PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and | PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and |
PCRE_NO_START_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() retur if compilation of a pattern fails, pcre_compile() retur |
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 |
Also, some errors are not detected until checks are carried out when | failing character. |
the whole pattern has been scanned; 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. | Some errors are not detected until the whole pattern has been scanned; |
It may sometimes point into the middle of a UTF-8 character. | in these cases, the offset passed back is the length of the pattern. |
| Note that the offset is in data units, not characters, even in a UTF |
| 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 1199 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 1216 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 1272 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 1300 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). 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 1327 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 1361 COMPILING A PATTERN
|
Line 2321 COMPILING A PATTERN
|
PCRE_UTF8 |
PCRE_UTF8 |
|
|
This option causes PCRE to regard both the pattern and the subject as |
This option causes PCRE to regard both the pattern and the subject as |
strings of UTF-8 characters instead of single-byte character strings. | strings of UTF-8 characters instead of single-byte strings. However, it |
However, it is available only when PCRE is built to include UTF-8 sup- | is available only when PCRE is built to include UTF support. If not, |
port. If not, the use of this option provokes an error. Details of how | the use of this option provokes an error. Details of how this option |
this option changes the behaviour of PCRE are given in the pcreunicode | changes the behaviour of PCRE are given in the pcreunicode page. |
page. | |
|
|
PCRE_NO_UTF8_CHECK |
PCRE_NO_UTF8_CHECK |
|
|
When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is |
When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is |
automatically checked. There is a discussion about the validity of | automatically checked. There is a discussion about the validity of |
UTF-8 strings in the main pcre page. If an invalid UTF-8 sequence of | UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is |
bytes is found, pcre_compile() returns an error. If you already know | found, pcre_compile() returns an error. If you already know that your |
that your pattern is valid, and you want to skip this check for perfor- | pattern is valid, and you want to skip this check for performance rea- |
mance reasons, you can set the PCRE_NO_UTF8_CHECK option. When it is | sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the |
set, the effect of passing an invalid UTF-8 string as a pattern is | effect of passing an invalid UTF-8 string as a pattern is undefined. It |
undefined. It may cause your program to crash. Note that this option | may cause your program to crash. Note that this option can also be |
can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the | passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity |
UTF-8 validity checking of subject strings. | checking of subject strings only. If the same string is being matched |
| many times, the option can be safely set for the second and subsequent |
| matchings to improve performance. |
|
|
|
|
COMPILATION ERROR CODES |
COMPILATION ERROR CODES |
|
|
The following table lists the error codes than may be returned by | The following table lists the error codes than may be returned by |
pcre_compile2(), along with the error messages that may be returned by | pcre_compile2(), along with the error messages that may be returned by |
both compiling functions. As PCRE has developed, some error codes have | both compiling functions. Note that error messages are always 8-bit |
fallen out of use. To avoid confusion, they have not been re-used. | ASCII strings, even in 16-bit or 32-bit mode. As PCRE has developed, |
| some error codes have fallen out of use. To avoid confusion, they have |
| not been re-used. |
|
|
0 no error |
0 no error |
1 \ at end of pattern |
1 \ at end of pattern |
Line 1420 COMPILATION ERROR CODES
|
Line 2383 COMPILATION ERROR CODES
|
29 (?R or (?[+-]digits must be followed by ) |
29 (?R or (?[+-]digits must be followed by ) |
30 unknown POSIX class name |
30 unknown POSIX class name |
31 POSIX collating elements are not supported |
31 POSIX collating elements are not supported |
32 this version of PCRE is not compiled with PCRE_UTF8 support | 32 this version of PCRE is compiled without UTF support |
33 [this code is not in use] |
33 [this code is not in use] |
34 character value in \x{...} sequence is too large |
34 character value in \x{...} sequence is too large |
35 invalid condition (?(0) |
35 invalid condition (?(0) |
Line 1432 COMPILATION ERROR CODES
|
Line 2395 COMPILATION ERROR CODES
|
41 unrecognized character after (?P |
41 unrecognized character after (?P |
42 syntax error in subpattern name (missing terminator) |
42 syntax error in subpattern name (missing terminator) |
43 two named subpatterns have the same name |
43 two named subpatterns have the same name |
44 invalid UTF-8 string | 44 invalid UTF-8 string (specifically UTF-8) |
45 support for \P, \p, and \X has not been compiled |
45 support for \P, \p, and \X has not been compiled |
46 malformed \P or \p sequence |
46 malformed \P or \p sequence |
47 unknown property name after \P or \p |
47 unknown property name after \P or \p |
48 subpattern name is too long (maximum 32 characters) |
48 subpattern name is too long (maximum 32 characters) |
49 too many named subpatterns (maximum 10000) |
49 too many named subpatterns (maximum 10000) |
50 [this code is not in use] |
50 [this code is not in use] |
51 octal value is greater than \377 (not in UTF-8 mode) | 51 octal value is greater than \377 in 8-bit non-UTF-8 mode |
52 internal error: overran compiling workspace |
52 internal error: overran compiling workspace |
53 internal error: previously-checked referenced subpattern |
53 internal error: previously-checked referenced subpattern |
not found |
not found |
Line 1450 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 1458 COMPILATION ERROR CODES
|
Line 2421 COMPILATION ERROR CODES
|
65 different names for subpatterns of the same number are |
65 different names for subpatterns of the same number are |
not allowed |
not allowed |
66 (*MARK) must have an argument |
66 (*MARK) must have an argument |
67 this version of PCRE is not compiled with PCRE_UCP support | 67 this version of PCRE is not compiled with Unicode property |
| support |
68 \c must be followed by an ASCII character |
68 \c must be followed by an ASCII character |
69 \k is not followed by a braced, angle-bracketed, or quoted name |
69 \k is not followed by a braced, angle-bracketed, or quoted name |
|
70 internal error: unknown opcode in find_fixedlength() |
|
71 \N is not supported in a class |
|
72 too many forward references |
|
73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff) |
|
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 1471 STUDYING A PATTERN
|
Line 2443 STUDYING A PATTERN
|
pcre_extra *pcre_study(const pcre *code, int options |
pcre_extra *pcre_study(const pcre *code, int options |
const char **errptr); |
const char **errptr); |
|
|
If a compiled pattern is going to be used several times, it is worth | If a compiled pattern is going to be used several times, it is worth |
spending more time analyzing it in order to speed up the time taken for |
spending more time analyzing it in order to speed up the time taken for |
matching. The function pcre_study() takes a pointer to a compiled pat- | matching. The function pcre_study() takes a pointer to a compiled pat- |
tern as its first argument. If studying the pattern produces additional |
tern as its first argument. If studying the pattern produces additional |
information that will help speed up matching, pcre_study() returns a | information that will help speed up matching, pcre_study() returns a |
pointer to a pcre_extra block, in which the study_data field points to | pointer to a pcre_extra block, in which the study_data field points to |
the results of the study. |
the results of the study. |
|
|
The returned value from pcre_study() can be passed directly to |
The returned value from pcre_study() can be passed directly to |
pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con- | pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con- |
tains other fields that can be set by the caller before the block is | tains other fields that can be set by the caller before the block is |
passed; these are described below in the section on matching a pattern. |
passed; these are described below in the section on matching a pattern. |
|
|
If studying the pattern does not produce any useful information, | If studying the pattern does not produce any useful information, |
pcre_study() returns NULL. In that circumstance, if the calling program | pcre_study() returns NULL by default. In that circumstance, if the |
wants to pass any of the other fields to pcre_exec() or | calling program wants to pass any of the other fields to pcre_exec() or |
pcre_dfa_exec(), it must set up its own pcre_extra block. | pcre_dfa_exec(), it must set up its own pcre_extra block. However, if |
| pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it |
| returns a pcre_extra block even if studying did not find any additional |
| information. It may still return NULL, however, if an error occurs in |
| pcre_study(). |
|
|
The second argument of pcre_study() contains option bits. There is only | The second argument 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. | |
|
|
JIT compilation is a heavyweight optimization. It can take some time | PCRE_STUDY_JIT_COMPILE |
for patterns to be analyzed, and for one-off matches and simple pat- | PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
terns the benefit of faster execution might be offset by a much slower | 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 |
| 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 |
study time. Not all patterns can be optimized by the JIT compiler. For |
study time. Not all patterns can be optimized by the JIT compiler. For |
those that cannot be handled, matching automatically falls back to the | those that cannot be handled, matching automatically falls back to the |
pcre_exec() interpreter. For more details, see the pcrejit documenta- | pcre_exec() interpreter. For more details, see the pcrejit documenta- |
tion. |
tion. |
|
|
The third argument for pcre_study() is a pointer for an error message. | The third argument for pcre_study() is a pointer for an error message. |
If studying succeeds (even if no data is returned), the variable it | If studying succeeds (even if no data is returned), the variable it |
points to is set to NULL. Otherwise it is set to point to a textual | points to is set to NULL. Otherwise it is set to point to a textual |
error message. This is a static string that is part of the library. You |
error message. This is a static string that is part of the library. You |
must not try to free it. You should test the error pointer for NULL | must not try to free it. You should test the error pointer for NULL |
after calling pcre_study(), to be sure that it has run successfully. |
after calling pcre_study(), to be sure that it has run successfully. |
|
|
When you are finished with a pattern, you can free the memory used for | When you are finished with a pattern, you can free the memory used for |
the study data by calling pcre_free_study(). This function was added to |
the study data by calling pcre_free_study(). This function was added to |
the API for release 8.20. For earlier versions, the memory could be | the API for release 8.20. For earlier versions, the memory could be |
freed with pcre_free(), just like the pattern itself. This will still | freed with pcre_free(), just like the pattern itself. This will still |
work in cases where 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): |
|
|
int rc; |
int rc; |
Line 1538 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. | 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.) |
|
|
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 1623 INFORMATION ABOUT A PATTERN
|
Line 2612 INFORMATION ABOUT A PATTERN
|
int what, void *where); |
int what, void *where); |
|
|
The pcre_fullinfo() function returns information about a compiled pat- |
The pcre_fullinfo() function returns information about a compiled pat- |
tern. It replaces the obsolete pcre_info() function, which is neverthe- | tern. It replaces the pcre_info() function, which was removed from the |
less retained for backwards compability (and is documented below). | library at version 8.30, after more than 10 years of obsolescence. |
|
|
The first argument for pcre_fullinfo() is a pointer to the compiled |
The first argument for pcre_fullinfo() is a pointer to the compiled |
pattern. The second argument is the result of pcre_study(), or NULL if |
pattern. The second argument is the result of pcre_study(), or NULL if |
Line 1633 INFORMATION ABOUT A PATTERN
|
Line 2622 INFORMATION ABOUT A PATTERN
|
variable to receive the data. The yield of the function is zero for |
variable to receive the data. The yield of the function is zero for |
success, or one of the following negative numbers: |
success, or one of the following negative numbers: |
|
|
PCRE_ERROR_NULL the argument code was NULL | PCRE_ERROR_NULL the argument code was NULL |
the argument where was NULL | the argument where was NULL |
PCRE_ERROR_BADMAGIC the "magic number" was not found | PCRE_ERROR_BADMAGIC the "magic number" was not found |
PCRE_ERROR_BADOPTION the value of what was invalid | PCRE_ERROR_BADENDIANNESS the pattern was compiled with different |
| endianness |
| 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. Here is a | an simple check against passing an arbitrary memory pointer. The endi- |
typical call of pcre_fullinfo(), to obtain the length of the compiled | anness error can occur if a compiled pattern is saved and reloaded on a |
pattern: | different host. Here is a typical call of pcre_fullinfo(), to obtain |
| the length of the compiled pattern: |
|
|
int rc; |
int rc; |
size_t length; |
size_t length; |
Line 1651 INFORMATION ABOUT A PATTERN
|
Line 2644 INFORMATION ABOUT A PATTERN
|
PCRE_INFO_SIZE, /* what is required */ |
PCRE_INFO_SIZE, /* what is required */ |
&length); /* where to put the data */ |
&length); /* where to put the data */ |
|
|
The possible values for the third argument are defined in pcre.h, and | The possible values for the third argument are defined The possible values for the third argument are defined in pcre.h, and |
are as follows: |
are as follows: |
|
|
PCRE_INFO_BACKREFMAX |
PCRE_INFO_BACKREFMAX |
|
|
Return the number of the highest back reference in the pattern. The | Return the number of the highest back reference in the pattern. The |
fourth argument should point to an int variable. Zero is returned if | fourth argument should point to an int variable. Zero is returned if |
there are no back references. |
there are no back references. |
|
|
PCRE_INFO_CAPTURECOUNT |
PCRE_INFO_CAPTURECOUNT |
|
|
Return the number of capturing subpatterns in the pattern. The fourth | Return the number of capturing subpatterns in the pattern. The fourth |
argument should point to an int variable. |
argument should point to an int variable. |
|
|
PCRE_INFO_DEFAULT_TABLES |
PCRE_INFO_DEFAULT_TABLES |
|
|
Return a pointer to the internal default character tables within PCRE. | Return a pointer to the internal default character tables within PCRE. |
The fourth argument should point to an unsigned char * variable. This | The fourth argument should point to an unsigned char * variable. This |
information call is provided for internal use by the pcre_study() func- |
information call is provided for internal use by the pcre_study() func- |
tion. External callers can cause PCRE to use its internal tables by | tion. External callers can cause PCRE to use its internal tables by |
passing a NULL table pointer. |
passing a NULL table pointer. |
|
|
PCRE_INFO_FIRSTBYTE |
PCRE_INFO_FIRSTBYTE |
|
|
Return information about the first byte of any matched string, for a | Return information about the first data unit of any matched string, for |
non-anchored pattern. The fourth argument should point to an int vari- | a non-anchored pattern. (The name of this option refers to the 8-bit |
able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name | library, where data units are bytes.) The fourth argument should point |
is still recognized for backwards compatibility.) | to an int variable. |
|
|
If there is a fixed first byte, for example, from a pattern such as | If there is a fixed first value, for example, the letter "c" from a |
(cat|cow|coyote), its value is returned. Otherwise, if either | 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 |
| 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 |
|
|
(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 |
|
|
Line 1693 INFORMATION ABOUT A PATTERN
|
Line 2691 INFORMATION ABOUT A PATTERN
|
of a subject string or after any newline within the string. Otherwise |
of a subject string or after any newline within the string. Otherwise |
-2 is returned. For anchored patterns, -2 is returned. |
-2 is returned. For anchored patterns, -2 is returned. |
|
|
|
Since for the 32-bit library using the non-UTF-32 mode, this function |
|
is unable to return the full 32-bit range of the character, this value |
|
is deprecated; instead the PCRE_INFO_FIRSTCHARACTERFLAGS and |
|
PCRE_INFO_FIRSTCHARACTER values should be used. |
|
|
PCRE_INFO_FIRSTTABLE |
PCRE_INFO_FIRSTTABLE |
|
|
If the pattern was studied, and this resulted in the construction of a | If the pattern was studied, and this resulted in the construction of a |
256-bit table indicating a fixed set of bytes for the first byte in any | 256-bit table indicating a fixed set of values for the first data unit |
matching string, a pointer to the table is returned. Otherwise NULL is | in any matching string, a pointer to the table is returned. Otherwise |
returned. The fourth argument should point to an unsigned char * vari- | NULL is returned. The fourth argument should point to an unsigned char |
able. | * variable. |
|
|
PCRE_INFO_HASCRORLF |
PCRE_INFO_HASCRORLF |
|
|
Return 1 if the pattern contains any explicit matches for CR or LF | Return 1 if the pattern contains any explicit matches for CR or LF |
characters, otherwise 0. The fourth argument should point to an int | characters, otherwise 0. The fourth argument should point to an int |
variable. An explicit match is either a literal CR or LF character, or | variable. An explicit match is either a literal CR or LF character, or |
\r or \n. |
\r or \n. |
|
|
PCRE_INFO_JCHANGED |
PCRE_INFO_JCHANGED |
|
|
Return 1 if the (?J) or (?-J) option setting is used in the pattern, | Return 1 if the (?J) or (?-J) option setting is used in the pattern, |
otherwise 0. The fourth argument should point to an int variable. (?J) | otherwise 0. The fourth argument should point to an int variable. (?J) |
and (?-J) set and unset the local PCRE_DUPNAMES option, respectively. |
and (?-J) set and unset the local PCRE_DUPNAMES option, respectively. |
|
|
PCRE_INFO_JIT |
PCRE_INFO_JIT |
|
|
Return 1 if the pattern was studied with 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 |
|
|
Return the value of the rightmost literal byte that must exist in any | Return the value of the rightmost literal data unit that must exist in |
matched string, other than at its start, if such a byte has been | any matched string, other than at its start, if such a value has been |
recorded. The fourth argument should point to an int variable. If there |
recorded. The fourth argument should point to an int variable. If there |
is no such byte, -1 is returned. For anchored patterns, a last literal | is no such value, -1 is returned. For anchored patterns, a last literal |
byte is recorded only if it follows something of variable length. For | value is recorded only if it follows something of variable length. For |
example, for the pattern /^a\d+z\d+/ the returned value is "z", but for |
example, for the pattern /^a\d+z\d+/ the returned value is "z", but for |
/^a\dz\d/ the returned value is -1. |
/^a\dz\d/ the returned value is -1. |
|
|
|
Since for the 32-bit library using the non-UTF-32 mode, this function |
|
is unable to return the full 32-bit range of 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, not bytes (this may | value is -1. The value is a number of characters, which in UTF mode may |
be relevant in UTF-8 mode). The fourth argument should point to an int | be different from the number of data units. The fourth argument should |
variable. A non-negative value is a lower bound to the length of any | point to an int variable. A non-negative value is a lower bound to the |
matching string. There may not be any strings of that length that do | length of any matching string. There may not be any strings of that |
actually match, but every string that does match is at least that long. | length that do actually match, but every string that does match is at |
| 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 (a pointer to char). The | a pointer to the first entry of the table. This is a pointer to char in |
first two bytes of each entry are the number of the capturing parenthe- | the 8-bit library, where the first two bytes of each entry are the num- |
sis, most significant byte first. The rest of the entry is the corre- | ber of the capturing parenthesis, most significant byte first. In the |
sponding name, zero terminated. | 16-bit library, the pointer points to 16-bit data units, the first of |
| which contains the parenthesis number. In the 32-bit library, the |
| 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 table, consider the following |
pattern (assume PCRE_EXTENDED is set, so white space - including new- | pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is |
lines - 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 1800 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 1836 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. The fourth argument should | Return the size of the compiled pattern in bytes (for all three |
point to a size_t variable. This value does not include the size of the | libraries). The fourth argument should point to a size_t variable. This |
pcre structure that is returned by pcre_compile(). The value that is | value does not include the size of the pcre structure that is returned |
passed as the argument to pcre_malloc() when pcre_compile() is getting | by pcre_compile(). The value that is passed as the argument to |
memory in which to place the compiled data is the value returned by | pcre_malloc() when pcre_compile() is getting memory in which to place |
this option plus the size of the pcre structure. Studying a compiled | the compiled data is the value returned by this option plus the size of |
pattern, with or without JIT, does not alter the value returned by this | the pcre structure. Studying a compiled pattern, with or without JIT, |
option. | does not alter the value returned by this option. |
|
|
PCRE_INFO_STUDYSIZE |
PCRE_INFO_STUDYSIZE |
|
|
Return the size of the data block pointed to by the study_data field in | Return the size in bytes (for all three libraries) of the data block |
a pcre_extra block. If pcre_extra is NULL, or there is no study data, | pointed to by the study_data field in a pcre_extra block. If pcre_extra |
zero is returned. The fourth argument should point to a size_t vari- | is NULL, or there is no study data, zero is returned. The fourth argu- |
able. The study_data field is set by pcre_study() to record informa- | ment should point to a size_t variable. The study_data field is set by |
tion that will speed up matching (see the section entitled "Studying a | pcre_study() to record information that will speed up matching (see the |
pattern" above). The format of the study_data block is private, but its | section entitled "Studying a pattern" above). The format of the |
length is made available via this option so that it can be saved and | study_data block is private, but its length is made available via this |
restored (see the pcreprecompile documentation for details). | option so that it can be saved and restored (see the pcreprecompile |
| documentation for details). |
|
|
|
PCRE_INFO_FIRSTCHARACTERFLAGS |
|
|
OBSOLETE INFO FUNCTION | 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. |
|
|
int pcre_info(const pcre *code, int *optptr, int *firstcharptr); | 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. |
|
|
The pcre_info() function is now obsolete because its interface is too | If there is no fixed first value, and if either |
restrictive to return all the available data about a compiled pattern. | |
New programs should use pcre_fullinfo() instead. The yield of | |
pcre_info() is the number of capturing subpatterns, or one of the fol- | |
lowing negative numbers: | |
|
|
PCRE_ERROR_NULL the argument code was NULL | (a) the pattern was compiled with the PCRE_MULTILINE option, and every |
PCRE_ERROR_BADMAGIC the "magic number" was not found | branch starts with "^", or |
|
|
If the optptr argument is not NULL, a copy of the options with which | (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not |
the pattern was compiled is placed in the integer it points to (see | set (if it were set, the pattern would be anchored), |
PCRE_INFO_OPTIONS above). | |
|
|
If the pattern is not anchored and the firstcharptr argument is not | 2 is returned, indicating that the pattern matches only at the start of |
NULL, it is used to pass back information about the first character of | a subject string or after any newline within the string. Otherwise 0 is |
any matched string (see PCRE_INFO_FIRSTBYTE above). | 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); |
|
|
The pcre_refcount() function is used to maintain a reference count in | The pcre_refcount() function is used to maintain a reference count in |
the data block that contains a compiled pattern. It is provided for the |
the data block that contains a compiled pattern. It is provided for the |
benefit of applications that operate in an object-oriented manner, | benefit of applications that operate in an object-oriented manner, |
where different parts of the application may be using the same compiled |
where different parts of the application may be using the same compiled |
pattern, but you want to free the block when they are all done. |
pattern, but you want to free the block when they are all done. |
|
|
When a pattern is compiled, the reference count field is initialized to |
When a pattern is compiled, the reference count field is initialized to |
zero. It is changed only by calling this function, whose action is to | zero. It is changed only by calling this function, whose action is to |
add the adjust value (which may be positive or negative) to it. The | add the adjust value (which may be positive or negative) to it. The |
yield of the function is the new value. However, the value of the count |
yield of the function is the new value. However, the value of the count |
is constrained to lie between 0 and 65535, inclusive. If the new value | is constrained to lie between 0 and 65535, inclusive. If the new value |
is outside these limits, it is forced to the appropriate limit value. |
is outside these limits, it is forced to the appropriate limit value. |
|
|
Except when it is zero, the reference count is not correctly preserved | Except when it is zero, the reference count is not correctly preserved |
if a pattern is compiled on one host and then transferred to a host | if a pattern is compiled on one host and then transferred to a host |
whose byte-order is different. (This seems a highly unlikely scenario.) |
whose byte-order is different. (This seems a highly unlikely scenario.) |
|
|
|
|
Line 1909 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 2994 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
const char *subject, int length, int startoffset, |
const char *subject, int length, int startoffset, |
int options, int *ovector, int ovecsize); |
int options, int *ovector, int ovecsize); |
|
|
The function pcre_exec() is called to match a subject string against a | The function pcre_exec() is called to match a subject string against a |
compiled pattern, which is passed in the code argument. If the pattern | compiled pattern, which is passed in the code argument. If the pattern |
was studied, the result of the study should be passed in the extra | was studied, the result of the study should be passed in the extra |
argument. You can call pcre_exec() with the same code and extra argu- | argument. You can call pcre_exec() with the same code and extra argu- |
ments as many times as you like, in order to match different subject | ments as many times as you like, in order to match different subject |
strings with the same pattern. |
strings with the same pattern. |
|
|
This function is the main matching facility of the library, and it | This function is the main matching facility of the library, and it |
operates in a Perl-like manner. For specialist use there is also an | operates in a Perl-like manner. For specialist use there is also an |
alternative matching function, which is described below in the section | alternative matching function, which is described below in the section |
about the pcre_dfa_exec() function. |
about the pcre_dfa_exec() function. |
|
|
In most applications, the pattern will have been compiled (and option- | In most applications, the pattern will have been compiled (and option- |
ally studied) in the same process that calls pcre_exec(). However, it | ally studied) in the same process that calls pcre_exec(). However, it |
is possible to save compiled patterns and study data, and then use them |
is possible to save compiled patterns and study data, and then use them |
later in different processes, possibly even on different hosts. For a | later in different processes, possibly even on different hosts. For a |
discussion about this, see the pcreprecompile documentation. |
discussion about this, see the pcreprecompile documentation. |
|
|
Here is an example of a simple call to pcre_exec(): |
Here is an example of a simple call to pcre_exec(): |
Line 1943 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3028 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
|
|
Extra data for pcre_exec() |
Extra data for pcre_exec() |
|
|
If the extra argument is not NULL, it must point to a pcre_extra data | If the extra argument is not NULL, it must point to a pcre_extra data |
block. The pcre_study() function returns such a block (when it doesn't | block. The pcre_study() function returns such a block (when it doesn't |
return NULL), but you can also create one for yourself, and pass addi- | return NULL), but you can also create one for yourself, and pass addi- |
tional information in it. The pcre_extra block contains the following | tional information in it. The pcre_extra block contains the following |
fields (not necessarily in this order): |
fields (not necessarily in this order): |
|
|
unsigned long int flags; |
unsigned long int flags; |
Line 1958 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3043 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
const unsigned char *tables; |
const unsigned char *tables; |
unsigned char **mark; |
unsigned char **mark; |
|
|
The flags field is a bitmap that specifies which of the other fields | In the 16-bit version of this structure, In the 16-bit version of this structure, the mark field has type |
are set. The flag bits are: | "PCRE_UCHAR16 **". |
|
|
PCRE_EXTRA_STUDY_DATA | In the 32-bit version of this structure, the mark field has type |
| "PCRE_UCHAR32 **". |
| |
| The flags field is used to specify which of the other fields are set. |
| The flag bits are: |
| |
| 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 2011 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 2021 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 char * 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 set to NULL. For details of the backtracking control verbs, see | field is set to NULL. For details of the backtracking control verbs, |
the section entitled "Backtracking control" in the pcrepattern documen- | see the section entitled "Backtracking control" in the pcrepattern doc- |
tation. | 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 2083 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 2217 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 section on UTF-8 support in the | points to the start of a UTF-8 character. There is a discussion about |
main pcre page. If an invalid UTF-8 sequence of bytes is found, | the validity of UTF-8 strings in the pcreunicode page. If an invalid |
pcre_exec() returns the error PCRE_ERROR_BADUTF8 or, if PCRE_PAR- | sequence of bytes is found, pcre_exec() returns the error |
TIAL_HARD is set and the problem is a truncated UTF-8 character at the | PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a |
end of the subject, PCRE_ERROR_SHORTUTF8. In both cases, information | truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In |
about the precise nature of the error may also be returned (see the | both cases, information about the precise nature of the error may also |
descriptions of these errors in the section entitled Error return val- | be returned (see the descriptions of these errors in the section enti- |
ues from pcre_exec() below). If startoffset contains a value that does | tled Error return values from pcre_exec() below). If startoffset con- |
not point to the start of a UTF-8 character (or to the end of the sub- | tains a value that does not point to the start of a UTF-8 character (or |
ject), 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 |
Line 2236 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3348 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
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 UTF-8 character (or the end of the subject). | points to the start of a character (or the end of the subject). When |
When PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 | PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a |
string as a subject or an invalid value of startoffset is undefined. | subject or an invalid value of startoffset is undefined. Your program |
Your program may crash. | may crash. |
|
|
PCRE_PARTIAL_HARD |
PCRE_PARTIAL_HARD |
PCRE_PARTIAL_SOFT |
PCRE_PARTIAL_SOFT |
Line 2269 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3381 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
The string to be matched by pcre_exec() |
The string to be matched by pcre_exec() |
|
|
The subject string is passed to pcre_exec() as a pointer in subject, a |
The subject string is passed to pcre_exec() as a pointer in subject, a |
length (in bytes) in length, and a starting byte offset in startoffset. | length in length, and a starting offset in startoffset. The units for |
If this is negative or greater than the length of the subject, | length and startoffset are bytes for the 8-bit library, 16-bit data |
| items for the 16-bit library, and 32-bit data items for the 32-bit |
| library. |
| |
| If startoffset is negative or greater than the length of the subject, |
pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is |
pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is |
zero, the search for a match starts at the beginning of the subject, |
zero, the search for a match starts at the beginning of the subject, |
and this is by far the most common case. In UTF-8 mode, the byte offset | and this is by far the most common case. In UTF-8 or UTF-16 mode, the |
must point to the start of a UTF-8 character (or the end of the sub- | offset must point to the start of a character, or the end of the sub- |
ject). Unlike the pattern string, the subject may contain binary zero | ject (in UTF-32 mode, one data unit equals one character, so all off- |
bytes. | sets are valid). Unlike the pattern string, the subject may contain |
| binary zeroes. |
|
|
A non-zero starting offset is useful when searching for another match | A non-zero starting offset is useful when searching for another match |
in the same subject by calling pcre_exec() again after a previous suc- | in the same subject by calling pcre_exec() again after a previous suc- |
cess. Setting startoffset differs from just passing over a shortened | cess. Setting startoffset differs from just passing over a shortened |
string and setting PCRE_NOTBOL in the case of a pattern that begins | string and setting PCRE_NOTBOL in the case of a pattern that begins |
with any kind of lookbehind. For example, consider the pattern |
with any kind of lookbehind. For example, consider the pattern |
|
|
\Biss\B |
\Biss\B |
|
|
which finds occurrences of "iss" in the middle of words. (\B matches | which finds occurrences of "iss" in the middle of words. (\B matches |
only if the current position in the subject is not a word boundary.) | only if the current position in the subject is not a word boundary.) |
When applied to the string "Mississipi" the first call to pcre_exec() | When applied to the string "Mississipi" the first call to pcre_exec() |
finds the first occurrence. If pcre_exec() is called again with just | finds the first occurrence. If pcre_exec() is called again with just |
the remainder of the subject, namely "issipi", it does not match, | the remainder of the subject, namely "issipi", it does not match, |
because \B is always false at the start of the subject, which is deemed |
because \B is always false at the start of the subject, which is deemed |
to be a word boundary. However, if pcre_exec() is passed the entire | to be a w to be a word boundary. However, if pcre_exec() is passed the entire |
string again, but with startoffset set to 4, it finds the second occur- |
string again, but with startoffset set to 4, it finds the second occur- |
rence of "iss" because it is able to look behind the starting point to | rence of "iss" because it is able to look behind the starting point to |
discover that it is preceded by a letter. |
discover that it is preceded by a letter. |
|
|
Finding all the matches in a subject is tricky when the pattern can | Finding all the matches in a subject is tricky when the pattern can |
match an empty string. It is possible to emulate Perl's /g behaviour by |
match an empty string. It is possible to emulate Perl's /g behaviour by |
first trying the match again at the same offset, with the | first trying the match again at the same offset, with the |
PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that | PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that |
fails, advancing the starting offset and trying an ordinary match | fails, advancing the starting offset and trying an ordinary match |
again. There is some code that demonstrates how to do this in the pcre- |
again. There is some code that demonstrates how to do this in the pcre- |
demo sample program. In the most general case, you have to check to see |
demo sample program. In the most general case, you have to check to see |
if the newline convention recognizes CRLF as a newline, and if so, and | if the newline convention recognizes CRLF as a newline, and if so, and |
the current character is CR followed by LF, advance the starting offset |
the current character is CR followed by LF, advance the starting offset |
by two characters instead of one. |
by two characters instead of one. |
|
|
If a non-zero starting offset is passed when the pattern is anchored, | If a non-zero starting offset is passed when the pattern is anchored, |
one attempt to match at the given offset is made. This can only succeed |
one attempt to match at the given offset is made. This can only succeed |
if the pattern does not require the match to be at the start of the | if the pattern d if the pattern d |
subject. |
subject. |
|
|
How pcre_exec() returns captured substrings |
How pcre_exec() returns captured substrings |
|
|
In general, a pattern matches a certain portion of the subject, and in | In general, a pattern matches a certain portion of the subject, and in |
addition, further substrings from the subject may be picked out by | addition, further substrings from the subject may be picked out by |
parts of the pattern. Following the usage in Jeffrey Friedl's book, | parts of the pattern. Following the usage in Jeffrey Friedl's book, |
this is called "capturing" in what follows, and the phrase "capturing | this is called "capturing" in what follows, and the phrase "capturing |
subpattern" is used for a fragment of a pattern that picks out a sub- | subpattern" is used for a fragment of a pattern that picks out a sub- |
string. PCRE supports several other kinds of parenthesized subpattern | string. PCRE supports several other kinds of parenthesized subpattern |
that do not cause substrings to be captured. |
that do not cause substrings to be captured. |
|
|
Captured substrings are returned to the caller via a vector of integers |
Captured substrings are returned to the caller via a vector of integers |
whose address is passed in ovector. The number of elements in the vec- | whose address is passed in ovector. The number of elements in the vec- |
tor is passed in ovecsize, which must be a non-negative number. Note: | tor is passed in ovecsize, which must be a non-negative number. Note: |
this argument is NOT the size of ovector in bytes. |
this argument is NOT the size of ovector in bytes. |
|
|
The first two-thirds of the vector is used to pass back captured sub- | The first two-thirds of the vector is used to pass back captured sub- |
strings, each substring using a pair of integers. The remaining third | strings, each substring using a pair of integers. The remaining third |
of the vector is used as workspace by pcre_exec() while matching cap- | of the vector is used as workspace by pcre_exec() while matching cap- |
turing subpatterns, and is not available for passing back information. | turing subpatterns, and is not available for passing back information. |
The number passed in ovecsize should always be a multiple of three. If | The number passed in ovecsize should always be a multiple of three. If |
it is not, it is rounded down. |
it is not, it is rounded down. |
|
|
When a match is successful, information about captured substrings is | When a match is successful, information about captured substrings is |
returned in pairs of integers, starting at the beginning of ovector, | returned in pairs of integers, starting at the beginning of ovector, |
and continuing up to two-thirds of its length at the most. The first | and continuing up to two-thirds of its length at the most. The first |
element of each pair is set to the byte offset of the first character | element of each pair is set to the offset of the first character in a |
in a substring, and the second is set to the byte offset of the first | substring, and the second is set to the offset of the first character |
character after the end of a substring. Note: these values are always | after the end of a substring. These values are always data unit off- |
byte offsets, even in UTF-8 mode. They are not character counts. | sets, even in UTF mode. They are byte offsets in the 8-bit library, |
| 16-bit data item offsets in the 16-bit library, and 32-bit data item |
| offsets in the 32-bit library. Note: they are not character counts. |
|
|
The first pair of integers, ovector[0] and ovector[1], identify the | The first pair of integers, ovector[0] and ovector[1], identify the |
portion of the subject string matched by the entire pattern. The next | portion of the subject string matched by the entire pattern. The next |
pair is used for the first capturing subpattern, and so on. The value | pair is used for the first capturing subpattern, and so on. The value |
returned by pcre_exec() is one more than the highest numbered pair that |
returned by pcre_exec() is one more than the highest numbered pair that |
has been set. For example, if two substrings have been captured, the | has been set. For example, if two substrings have been captured, the |
returned value is 3. If there are no capturing subpatterns, the return | returned value is 3. If there are no capturing subpatterns, the return |
value from a successful match is 1, indicating that just the first pair |
value from a successful match is 1, indicating that just the first pair |
of offsets has been set. |
of offsets has been set. |
|
|
If a capturing subpattern is matched repeatedly, it is the last portion |
If a capturing subpattern is matched repeatedly, it is the last portion |
of the string that it matched that is returned. |
of the string that it matched that is returned. |
|
|
If the vector is too small to hold all the captured substring offsets, | If the vector is too small to hold all the captured substring offsets, |
it is used as far as possible (up to two-thirds of its length), and the |
it is used as far as possible (up to two-thirds of its length), and the |
function returns a value of zero. If neither the actual string matched | function returns a value of zero. If neither the actual string matched |
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 |
use during matching. Thus it is usually advisable to supply an ovector | use during matching. Thus it is usually advisable to supply an ovector |
of reasonable size. |
of reasonable size. |
|
|
There are some cases where zero is returned (indicating vector over- | There are some cases where zero is returned (indicating vector over- |
flow) when in fact the vector is exactly the right size for the final | flow) when in fact the vector is exactly the right size for the final |
match. For example, consider the pattern |
match. For example, consider the pattern |
|
|
(a)(?:(b)c|bd) |
(a)(?:(b)c|bd) |
|
|
If a vector of 6 elements (allowing for only 1 captured substring) is | If a vector of 6 elements (allowing for only 1 captured substring) is |
given with subject string "abd", pcre_exec() will try to set the second |
given with subject string "abd", pcre_exec() will try to set the second |
captured string, thereby recording a vector overflow, before failing to |
captured string, thereby recording a vector overflow, before failing to |
match "c" and backing up to try the second alternative. The zero | match "c" and backing up to try the second alternative. The zero |
return, however, does correctly indicate that the maximum number of | return, however, does correctly indicate that the maximum number of |
slots (namely 2) have been filled. In similar cases where there is tem- |
slots (namely 2) have been filled. In similar cases where there is tem- |
porary overflow, but the final number of used slots is actually less | porary overflow, but the final number of used slots is actually less |
than the maximum, a non-zero value is returned. |
than the maximum, a non-zero value is returned. |
|
|
The pcre_fullinfo() function can be used to find out how many capturing |
The pcre_fullinfo() function can be used to find out how many capturing |
subpatterns there are in a compiled pattern. The smallest size for | subpatterns there are in a compiled pattern. The smallest size for |
ovector that will allow for n captured substrings, in addition to the | ovector that will allow for n captured substrings, in addition to the |
offsets of the substring matched by the whole pattern, is (n+1)*3. |
offsets of the substring matched by the whole pattern, is (n+1)*3. |
|
|
It is possible for capturing subpattern number n+1 to match some part | It is possible for capturing subpattern number n+1 to match some part |
of the subject when subpattern n has not been used at all. For example, |
of the subject when subpattern n has not been used at all. For example, |
if the string "abc" is matched against the pattern (a|(z))(bc) the | if the string "abc" is matched against the pattern (a|(z))(bc) the |
return from the function is 4, and subpatterns 1 and 3 are matched, but |
return from the function is 4, and subpatterns 1 and 3 are matched, but |
2 is not. When this happens, both values in the offset pairs corre- | 2 is not. When this happens, both values in the offset pairs corre- |
sponding to unused subpatterns are set to -1. |
sponding to unused subpatterns are set to -1. |
|
|
Offset values that correspond to unused subpatterns at the end of the | Offset values that correspond to unused subpatterns at the end of the |
expression are also set to -1. For example, if the string "abc" is | expression are also set to -1. For example, if the string "abc" is |
matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not | matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not |
matched. The return from the function is 2, because the highest used | matched. The return from the function is 2, because the highest used |
capturing subpattern number is 1, and the offsets for for the second | capturing subpattern number is 1, and the offsets for for the second |
and third capturing subpatterns (assuming the vector is large enough, | and third capturing subpatterns (assuming the vector is large enough, |
of course) are set to -1. |
of course) are set to -1. |
|
|
Note: Elements in the first two-thirds of ovector that do not corre- | Note: Elements in the first two-thirds of ovector that do not corre- |
spond to capturing parentheses in the pattern are never changed. That | spond to capturing parentheses in the pattern are never changed. That |
is, if a pattern contains n capturing parentheses, no more than ovec- | is, if a pattern contains n capturing parentheses, no more than ovec- |
tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in | tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in |
the first two-thirds) retain whatever values they previously had. |
the first two-thirds) retain whatever values they previously had. |
|
|
Some convenience functions are provided for extracting the captured | Some convenience functions are provided for extracting the captured |
substrings as separate strings. These are described below. |
substrings as separate strings. These are described below. |
|
|
Error return values from pcre_exec() |
Error return values from pcre_exec() |
|
|
If pcre_exec() fails, it returns a negative number. The following are | If pcre_exec() fails, it returns a negative number. The following are |
defined in the header file: |
defined in the header file: |
|
|
PCRE_ERROR_NOMATCH (-1) |
PCRE_ERROR_NOMATCH (-1) |
Line 2420 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3539 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
|
|
PCRE_ERROR_NULL (-2) |
PCRE_ERROR_NULL (-2) |
|
|
Either code or subject was passed as NULL, or ovector was NULL and | Either code or subject was passed as NULL, or ovector was NULL and |
ovecsize was not zero. |
ovecsize was not zero. |
|
|
PCRE_ERROR_BADOPTION (-3) |
PCRE_ERROR_BADOPTION (-3) |
Line 2429 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3548 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
|
|
PCRE_ERROR_BADMAGIC (-4) |
PCRE_ERROR_BADMAGIC (-4) |
|
|
PCRE stores a 4-byte "magic number" at the start of the compiled code, | PCRE stores a 4-byte "magic number" at the start of the compiled code, |
to catch the case when it is passed a junk pointer and to detect when a |
to catch the case when it is passed a junk pointer and to detect when a |
pattern that was compiled in an environment of one endianness is run in |
pattern that was compiled in an environment of one endianness is run in |
an environment with the other endianness. This is the error that PCRE | an environment with the other endianness. This is the err an environment with the other endianness. This is the error that PCRE |
gives when the magic number is not present. |
gives when the magic number is not present. |
|
|
PCRE_ERROR_UNKNOWN_OPCODE (-5) |
PCRE_ERROR_UNKNOWN_OPCODE (-5) |
|
|
While running the pattern match, an unknown item was encountered in the |
While running the pattern match, an unknown item was encountered in the |
compiled pattern. This error could be caused by a bug in PCRE or by | compiled pattern. This error could be caused by a bug in PCRE or by |
overwriting of the compiled pattern. |
overwriting of the compiled pattern. |
|
|
PCRE_ERROR_NOMEMORY (-6) |
PCRE_ERROR_NOMEMORY (-6) |
|
|
If a pattern contains back references, but the ovector that is passed | If a pattern contains back references, but the ovector that is passed |
to pcre_exec() is not big enough to remember the referenced substrings, |
to pcre_exec() is not big enough to remember the referenced substrings, |
PCRE gets a block of memory at the start of matching to use for this | PCRE gets a block of memory at the start of matching to use for this |
purpose. If the call via pcre_malloc() fails, this error is given. The | purpose. If the call via pcre_malloc() fails, this error is given. The |
memory is automatically freed at the end of matching. |
memory is automatically freed at the end of matching. |
|
|
This error is also given if pcre_stack_malloc() fails in pcre_exec(). | This error is also given if pcre_stack_malloc() fails in pcre_exec(). |
This can happen only when PCRE has been compiled with --disable-stack- | This can happen only when PCRE has been compiled with --disable-stack- |
for-recursion. |
for-recursion. |
|
|
PCRE_ERROR_NOSUBSTRING (-7) |
PCRE_ERROR_NOSUBSTRING (-7) |
|
|
This error is used by the pcre_copy_substring(), pcre_get_substring(), | This error is used by the pcre_copy_substring(), pcre_get_substring(), |
and pcre_get_substring_list() functions (see below). It is never |
and pcre_get_substring_list() functions (see below). It is never |
returned by pcre_exec(). |
returned by pcre_exec(). |
|
|
PCRE_ERROR_MATCHLIMIT (-8) |
PCRE_ERROR_MATCHLIMIT (-8) |
|
|
The backtracking limit, as specified by the match_limit field in a | The backtracking limit, as specified by the match_limit field in a |
pcre_extra structure (or defaulted) was reached. See the description | pcre_extra structure (or defaulted) was reached. See the description |
above. |
above. |
|
|
PCRE_ERROR_CALLOUT (-9) |
PCRE_ERROR_CALLOUT (-9) |
|
|
This error is never generated by pcre_exec() itself. It is provided for |
This error is never generated by pcre_exec() itself. It is provided for |
use by callout functions that want to yield a distinctive error code. | use by callout functions that want to yield a distinctive error code. |
See the pcrecallout documentation for details. |
See the pcrecallout documentation for details. |
|
|
PCRE_ERROR_BADUTF8 (-10) |
PCRE_ERROR_BADUTF8 (-10) |
|
|
A string that contains an invalid UTF-8 byte sequence was passed as a | A string that contains an invalid UTF-8 byte sequence was passed as a |
subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of | subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of |
the output vector (ovecsize) is at least 2, the byte offset to the | the output vector (ovecsize) is at least 2, the byte offset to the |
start of the the invalid UTF-8 character is placed in the first ele- | start of the the invalid UTF-8 character is placed in the first ele- |
ment, and a reason code is placed in the second element. The reason | ment, and a reason code is placed in the second element. The reason |
codes are listed in the following section. For backward compatibility, |
codes are listed in the following section. For backward compatibility, |
if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char- | if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char- |
acter at the end of the subject (reason codes 1 to 5), | acter at the end of the subject (reason codes 1 to 5), |
PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8. |
PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8. |
|
|
PCRE_ERROR_BADUTF8_OFFSET (-11) |
PCRE_ERROR_BADUTF8_OFFSET (-11) |
|
|
The UTF-8 byte sequence that was passed as a subject was checked and | The UTF-8 byte sequence that was passed as a subject was checked and |
found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the | found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the |
value of startoffset did not point to the beginning of a UTF-8 charac- | value of startoffset did not point to the beginning of a UTF-8 charac- |
ter or the end of the subject. |
ter or the end of the subject. |
|
|
PCRE_ERROR_PARTIAL (-12) |
PCRE_ERROR_PARTIAL (-12) |
|
|
The subject string did not match, but it did match partially. See the | The subject string did not match, but it did match partiall The subject string did not match, but it did match partially. See the |
pcrepartial documentation for details of partial matching. |
pcrepartial documentation for details of partial matching. |
|
|
PCRE_ERROR_BADPARTIAL (-13) |
PCRE_ERROR_BADPARTIAL (-13) |
|
|
This code is no longer in use. It was formerly returned when the | This code is no longer in use. It was formerly returned when the |
PCRE_PARTIAL option was used with a compiled pattern containing items | PCRE_PARTIAL option was used with a compiled pattern containing items |
that were not supported for partial matching. From release 8.00 | that were not supported for partial matching. From release 8.00 |
onwards, there are no restrictions on partial matching. |
onwards, there are no restrictions on partial matching. |
|
|
PCRE_ERROR_INTERNAL (-14) |
PCRE_ERROR_INTERNAL (-14) |
|
|
An unexpected internal error has occurred. This error could be caused | An unexpected internal error has occurred. This error could be caused |
by a bug in PCRE or by overwriting of the compiled pattern. |
by a bug in PCRE or by overwriting of the compiled pattern. |
|
|
PCRE_ERROR_BADCOUNT (-15) |
PCRE_ERROR_BADCOUNT (-15) |
Line 2514 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3633 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_ERROR_RECURSIONLIMIT (-21) |
PCRE_ERROR_RECURSIONLIMIT (-21) |
|
|
The internal recursion limit, as specified by the match_limit_recursion |
The internal recursion limit, as specified by the match_limit_recursion |
field in a pcre_extra structure (or defaulted) was reached. See the | field in a pcre_extra structure (or defaulted) was reached. See the |
description above. |
description above. |
|
|
PCRE_ERROR_BADNEWLINE (-23) |
PCRE_ERROR_BADNEWLINE (-23) |
Line 2528 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3647 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
|
|
PCRE_ERROR_SHORTUTF8 (-25) |
PCRE_ERROR_SHORTUTF8 (-25) |
|
|
This error is returned instead of PCRE_ERROR_BADUTF8 when the subject | This error is returned instead of PCRE_ERROR_BADUTF8 when the subject |
string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD | string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD |
option is set. Information about the failure is returned as for | option is set. Information about the failure is returned as for |
PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but | PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but |
this special error code for PCRE_PARTIAL_HARD precedes the implementa- | this special error code for PCRE_PARTIAL_HARD precedes the implementa- |
tion of returned information; it is retained for backwards compatibil- | tion of returned information; it is retained for backwards compatibil- |
ity. |
ity. |
|
|
PCRE_ERROR_RECURSELOOP (-26) |
PCRE_ERROR_RECURSELOOP (-26) |
|
|
This error is returned when pcre_exec() detects a recursion loop within |
This error is returned when pcre_exec() detects a recursion loop within |
the pattern. Specifically, it means that either the whole pattern or a | the pattern. Specifically, it means that either the whole pattern or a |
subpattern has been called recursively for the second time at the same | subpattern has been called recursively for the second time at the same |
position in the subject string. Some simple patterns that might do this |
position in the subject string. Some simple patterns that might do this |
are detected and faulted at compile time, but more complicated cases, | are detected and faulted at compile time, but more complicate are detected and faulted at compile time, but more complicate |
in particular mutual recursions between two different subpatterns, can- |
in particular mutual recursions between two different subpatterns, can- |
not be detected until run time. |
not be detected until run time. |
|
|
PCRE_ERROR_JIT_STACKLIMIT (-27) |
PCRE_ERROR_JIT_STACKLIMIT (-27) |
|
|
|
This error is returned when a pattern that was successfully studied |
|
using a JIT compile option is being matched, but the memory available |
|
for the just-in-time processing stack is not large enough. See the |
|
pcrejit documentation for more details. |
|
|
|
PCRE_ERROR_BADMODE (-28) |
|
|
|
This error is given if a pattern that was compiled by the 8-bit library |
|
is passed to a 16-bit or 32-bit library function, or vice versa. |
|
|
|
PCRE_ERROR_BADENDIANNESS (-29) |
|
|
|
This error is given if a pattern that was compiled and saved is |
|
reloaded on a host with different endianness. The utility function |
|
pcre_pattern_to_host_byte_order() can be used to convert such a pattern |
|
so that it runs on the new host. |
|
|
|
PCRE_ERROR_JIT_BADOPTION |
|
|
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 matching mode |
ory available for the just-in-time processing stack is not large | (partial or complete match) does not correspond to any JIT compilation |
enough. See the pcrejit documentation for more details. | 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. |
|
|
Error numbers -16 to -20 and -22 are not used by pcre_exec(). | 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 |
|
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 2570 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
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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. |
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|
PCRE_UTF8_ERR6 |
PCRE_UTF8_ERR6 |
Line 2583 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
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Line 3732 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
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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. |
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|
PCRE_UTF8_ERR13 |
PCRE_UTF8_ERR13 |
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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. |
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PCRE_UTF8_ERR14 |
PCRE_UTF8_ERR14 |
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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. |
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PCRE_UTF8_ERR15 |
PCRE_UTF8_ERR15 |
Line 2609 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
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Line 3758 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
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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. |
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|
PCRE_UTF8_ERR20 |
PCRE_UTF8_ERR20 |
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|
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. |
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|
PCRE_UTF8_ERR21 |
PCRE_UTF8_ERR21 |
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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. |
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PCRE_UTF8_ERR22 |
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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. |
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EXTRACTING CAPTURED SUBSTRINGS BY NUMBER |
EXTRACTING CAPTURED SUBSTRINGS BY NUMBER |
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int pcre_copy_substring(const char *subject, int *ovector, |
int pcre_copy_substring(const char *subject, int *ovector, |
Line 2824 FINDING ALL POSSIBLE MATCHES
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Line 3980 FINDING ALL POSSIBLE MATCHES
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matches, pcre_exec() will yield PCRE_ERROR_NOMATCH. |
matches, pcre_exec() will yield PCRE_ERROR_NOMATCH. |
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OBTAINING AN ESTIMATE OF STACK USAGE |
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|
Matching certain patterns using pcre_exec() can use a lot of process |
|
stack, which in certain environments can be rather limited in size. |
|
Some users find it helpful to have an estimate of the amount of stack |
|
that is used by pcre_exec(), to help them set recursion limits, as |
|
described in the pcrestack documentation. The estimate that is output |
|
by pcretest when called with the -m and -C options is obtained by call- |
|
ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its |
|
first five arguments. |
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|
Normally, if its first argument is NULL, pcre_exec() immediately |
|
returns the negative error code PCRE_ERROR_NULL, but with this special |
|
combination of arguments, it returns instead a negative number whose |
|
absolute value is the approximate stack frame size in bytes. (A nega- |
|
tive number is used so that it is clear that no match has happened.) |
|
The value is approximate because in some cases, recursive calls to |
|
pcre_exec() occur when there are one or two additional variables on the |
|
stack. |
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|
|
If PCRE has been compiled to use the heap instead of the stack for |
|
recursion, the value returned is the size of each block that is |
|
obtained from the heap. |
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|
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MATCHING A PATTERN: THE ALTERNATIVE FUNCTION |
MATCHING A PATTERN: THE ALTERNATIVE FUNCTION |
|
|
int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, |
int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, |
Line 2988 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
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Line 4169 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
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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. |
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|
|
PCRE_ERROR_DFA_BADRESTART (-30) |
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|
|
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. |
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SEE ALSO |
SEE ALSO |
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|
pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar- | pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), |
tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3). | pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre- |
| sample(3), pcrestack(3). |
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AUTHOR |
AUTHOR |
Line 3004 AUTHOR
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Line 4193 AUTHOR
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REVISION |
REVISION |
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|
Last updated: 02 December 2011 | Last updated: 12 May 2013 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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|
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PCRECALLOUT(3) PCRECALLOUT(3) | PCRECALLOUT(3) Library Functions Manual PCRECALLOUT(3) |
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|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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|
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SYNOPSIS |
|
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PCRE CALLOUTS | #include <pcre.h> |
|
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int (*pcre_callout)(pcre_callout_block *); |
int (*pcre_callout)(pcre_callout_block *); |
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int (*pcre16_callout)(pcre16_callout_block *); |
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int (*pcre32_callout)(pcre32_callout_block *); |
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DESCRIPTION |
|
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PCRE provides a feature called "callout", which is a means of temporar- |
PCRE provides a feature called "callout", which is a means of temporar- |
ily passing control to the caller of PCRE in the middle of pattern |
ily passing control to the caller of PCRE in the middle of pattern |
matching. The caller of PCRE provides an external function by putting |
matching. The caller of PCRE provides an external function by putting |
its entry point in the global variable pcre_callout. By default, this | its entry point in the global variable pcre_callout (pcre16_callout for |
variable contains NULL, which disables all calling out. | the 16-bit library, pcre32_callout for the 32-bit library). By default, |
| this variable contains NULL, which disables all calling out. |
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Within a regular expression, (?C) indicates the points at which the | Within a regular expression, (?C) indicates the points at which the |
external function is to be called. Different callout points can be | external function is to be called. Different callout points can be |
identified by putting a number less than 256 after the letter C. The | identified by putting a number less than 256 after the letter C. The |
default value is zero. For example, this pattern has two callout | default value is zero. For example, this pattern has two callout |
points: |
points: |
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|
(?C1)abc(?C2)def |
(?C1)abc(?C2)def |
|
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If the PCRE_AUTO_CALLOUT option bit is set when pcre_compile() or | If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled, |
pcre_compile2() is called, PCRE automatically inserts callouts, all | PCRE automatically inserts callouts, all with number 255, before each |
with number 255, before each item in the pattern. For example, if | item in the pattern. For example, if PCRE_AUTO_CALLOUT is used with the |
PCRE_AUTO_CALLOUT is used with the pattern | pattern |
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A(\d{2}|--) |
A(\d{2}|--) |
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Line 3045 PCRE CALLOUTS
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Line 4244 PCRE CALLOUTS
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(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) |
(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) |
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Notice that there is a callout before and after each parenthesis and | Notice that there is a callout before and after each parenthesis and |
alternation bar. Automatic callouts can be used for tracking the | alternation bar. If the pattern contains a conditional group whose con- |
progress of pattern matching. The pcretest command has an option that | dition is an assertion, an automatic callout is inserted immediately |
sets automatic callouts; when it is used, the output indicates how the | before the condition. Such a callout may also be inserted explicitly, |
pattern is matched. This is useful information when you are trying to | for example: |
optimize the performance of a particular pattern. | |
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The use of callouts in a pattern makes it ineligible for optimization | (?(?C9)(?=a)ab|de) |
by the just-in-time compiler. Studying such a pattern with the | |
PCRE_STUDY_JIT_COMPILE option always fails. | |
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This applies only to assertion conditions (because they are themselves |
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independent groups). |
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Automatic callouts can be used for tracking the progress of pattern |
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matching. The pcretest command has an option that sets automatic call- |
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outs; when it is used, the output indicates how the pattern is matched. |
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This is useful information when you are trying to optimize the perfor- |
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mance of a particular pattern. |
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MISSING CALLOUTS |
MISSING CALLOUTS |
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You should be aware that, because of optimizations in the way PCRE | You should be aware that, because of optimizations in the way PCRE |
matches patterns by default, callouts sometimes do not happen. For | matches patterns by default, callouts sometimes do not happen. For |
example, if the pattern is |
example, if the pattern is |
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ab(?C4)cd |
ab(?C4)cd |
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PCRE knows that any matching string must contain the letter "d". If the |
PCRE knows that any matching string must contain the letter "d". If the |
subject string is "abyz", the lack of "d" means that matching doesn't | subject string is "abyz", the lack of "d" means that matching doesn't |
ever start, and the callout is never reached. However, with "abyd", | ever start, and the callout is never reached. However, with "abyd", |
though the result is still no match, the callout is obeyed. |
though the result is still no match, the callout is obeyed. |
|
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If the pattern is studied, PCRE knows the minimum length of a matching | If the pattern is studied, PCRE knows the minimum length of a matching |
string, and will immediately give a "no match" return without actually | string, and will immediately give a "no match" return without actually |
running a match if the subject is not long enough, or, for unanchored | running a match if the subject is not long enough, or, for unanchored |
patterns, if it has been scanned far enough. |
patterns, if it has been scanned far enough. |
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You can disable these optimizations by passing the PCRE_NO_START_OPTI- | You can disable these optimizations by passing the PCRE_NO_START_OPTI- |
MIZE option to pcre_compile(), pcre_exec(), or pcre_dfa_exec(), or by | MIZE option to the matching function, or by starting the pattern with |
starting the pattern with (*NO_START_OPT). This slows down the matching | (*NO_START_OPT). This slows down the matching process, but does ensure |
process, but does ensure that callouts such as the example above are | that callouts such as the example above are obeyed. |
obeyed. | |
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THE CALLOUT INTERFACE |
THE CALLOUT INTERFACE |
|
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During matching, when PCRE reaches a callout point, the external func- |
During matching, when PCRE reaches a callout point, the external func- |
tion defined by pcre_callout is called (if it is set). This applies to | tion defined by pcre_callout or pcre[16|32]_callout is called (if it is |
both the pcre_exec() and the pcre_dfa_exec() matching functions. The | set). This applies to both normal and DFA matching. The only argument |
only argument to the callout function is a pointer to a pcre_callout | to the callout function is a pointer to a pcre_callout or |
block. This structure 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; | const char *subject; (8-bit version) |
int subject_length; | PCRE_SPTR16 subject; (16-bit version) |
int start_match; | PCRE_SPTR32 subject; (32-bit version) |
int current_position; | int subject_length; |
int capture_top; | int start_match; |
int capture_last; | int current_position; |
void *callout_data; | int capture_top; |
int pattern_position; | int capture_last; |
int next_item_length; | |
const unsigned char *mark; | int pattern_position; |
| int next_item_length; |
| const unsigned char *mark; (8-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). |
|
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The offset_vector field is a pointer to the vector of offsets that was | The offset_vector field is a pointer to the vector of offsets that was |
passed by the caller to pcre_exec() or pcre_dfa_exec(). When | passed by the caller to the matching function. When pcre_exec() or |
pcre_exec() is used, the contents can be inspected in order to extract | pcre[16|32]_exec() is used, the contents can be inspected, in order to |
substrings that have been matched so far, in the same way as for | extract substrings that have been matched so far, in the same way as |
extracting substrings after a match has completed. For pcre_dfa_exec() | for extracting substrings after a match has completed. For the DFA |
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 pcre_exec(). | 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() function is used, the capture_top field contains | When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top |
one more than the number of the highest numbered captured substring so | field contains one more than the number of the highest numbered cap- |
far. If no substrings have been captured, the value of capture_top is | tured substring so far. If no substrings have been captured, the value |
one. This is always the case when pcre_dfa_exec() is used, because it | of capture_top is one. This is always the case when the DFA functions |
does 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 when pcre_dfa_exec() is used. | 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 pcre_exec() | The callout_data field contains a value that is passed to a matching |
or pcre_dfa_exec() specifically so that it can be passed back in call- | function specifically so that it can be passed back in callouts. It is |
outs. It is passed in the pcre_callout field of the pcre_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 |
pcre_callout block is NULL. There is a description of the pcre_extra | in a callout block is NULL. There is a description of the pcre_extra |
structure in the pcreapi documentation. |
structure in the pcreapi documentation. |
|
|
The pattern_position field is present from version 1 of the pcre_call- | The pattern_position field is present from version 1 of the callout |
out structure. It contains the offset to the next item to be matched in | structure. It contains the offset to the next item to be matched in the |
the pattern string. | pattern string. |
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|
The next_item_length field is present from version 1 of the pcre_call- | The next_item_length field is present from version 1 of the callout |
out structure. It contains the length of the next item to be matched in | structure. It contains the length of the next item to be matched in the |
the pattern string. When the callout immediately precedes an alterna- | pattern string. When the callout immediately precedes an alternation |
tion bar, a closing parenthesis, or the end of the pattern, the length | bar, a closing parenthesis, or the end of the pattern, the length is |
is zero. When the callout precedes an opening parenthesis, the length | zero. When the callout precedes an opening parenthesis, the length is |
is that of the entire subpattern. | that of the entire subpattern. |
|
|
The pattern_position and next_item_length fields are intended to help |
The pattern_position and next_item_length fields are intended to help |
in distinguishing between different automatic callouts, which all have |
in distinguishing between different automatic callouts, which all have |
the same callout number. However, they are set for all callouts. |
the same callout number. However, they are set for all callouts. |
|
|
The mark field is present from version 2 of the pcre_callout structure. | The mark field is present from version 2 of the callout structure. In |
In callouts from pcre_exec() it contains a pointer to the zero-termi- | callouts from pcre_exec() or pcre[16|32]_exec() it contains a pointer |
nated name of the most recently passed (*MARK), (*PRUNE), or (*THEN) | to the zero-terminated name of the most recently passed (*MARK), |
item in the match, or NULL if no such items have been passed. Instances | (*PRUNE), or (*THEN) item in the match, or NULL if no such items have |
of (*PRUNE) or (*THEN) without a name do not obliterate a previous | been passed. Instances of (*PRUNE) or (*THEN) without a name do not |
(*MARK). In callouts from pcre_dfa_exec() this field always contains | obliterate a previous (*MARK). In callouts from the DFA matching func- |
NULL. | tions this field always contains NULL. |
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RETURN VALUES |
RETURN VALUES |
Line 3180 RETURN VALUES
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Line 4392 RETURN VALUES
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is zero, matching proceeds as normal. If the value is greater than |
is zero, matching proceeds as normal. If the value is greater than |
zero, matching fails at the current point, but the testing of other |
zero, matching fails at the current point, but the testing of other |
matching possibilities goes ahead, just as if a lookahead assertion had |
matching possibilities goes ahead, just as if a lookahead assertion had |
failed. If the value is less than zero, the match is abandoned, and | failed. If the value is less than zero, the match is abandoned, the |
pcre_exec() or pcre_dfa_exec() returns the negative value. | matching function returns the negative value. |
|
|
Negative values should normally be chosen from the set of |
Negative values should normally be chosen from the set of |
PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan- |
PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan- |
Line 3199 AUTHOR
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Line 4411 AUTHOR
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REVISION |
REVISION |
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|
Last updated: 30 November 2011 | Last updated: 03 March 2013 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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PCRECOMPAT(3) PCRECOMPAT(3) | PCRECOMPAT(3) Library Functions Manual PCRECOMPAT(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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|
DIFFERENCES BETWEEN PCRE AND PERL |
DIFFERENCES BETWEEN PCRE AND PERL |
|
|
This document describes the differences in the ways that PCRE and Perl |
This document describes the differences in the ways that PCRE and Perl |
handle regular expressions. The differences described here are with |
handle regular expressions. The differences described here are with |
respect to Perl versions 5.10 and above. |
respect to Perl versions 5.10 and above. |
|
|
1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details | 1. PCRE has only a subset of Perl's Unicode support. Details of what it |
of what it does have are given in the pcreunicode page. | does have are given in the pcreunicode page. |
|
|
2. PCRE allows repeat quantifiers only on parenthesized assertions, but |
2. PCRE allows repeat quantifiers only on parenthesized assertions, but |
they do not mean what you might think. For example, (?!a){3} does not |
they do not mean what you might think. For example, (?!a){3} does not |
Line 3229 DIFFERENCES BETWEEN PCRE AND PERL
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Line 4441 DIFFERENCES BETWEEN PCRE AND PERL
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3. Capturing subpatterns that occur inside negative lookahead asser- |
3. Capturing subpatterns that occur inside negative lookahead asser- |
tions are counted, but their entries in the offsets vector are never |
tions are counted, but their entries in the offsets vector are never |
set. Perl sets its numerical variables from any such patterns that are | set. Perl sometimes (but not always) sets its numerical variables from |
matched before the assertion fails to match something (thereby succeed- | inside negative assertions. |
ing), but only if the negative lookahead assertion contains just one | |
branch. | |
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|
4. Though binary zero characters are supported in the subject string, |
4. Though binary zero characters are supported in the subject string, |
they are not allowed in a pattern string because it is passed as a nor- |
they are not allowed in a pattern string because it is passed as a nor- |
Line 3258 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 3276 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. |
|
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9. Fairly obviously, PCRE does not support the (?{code}) and (??{code}) | 8. Fairly obviously, PCRE does not support the (?{code}) and (??{code}) |
constructions. However, there is support for recursive patterns. This | constructions. However, there is support for recursive patterns. This |
is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE | is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE |
"callout" feature allows an external function to be called during pat- | "callout" feature allows an external function to be called during pat- |
tern matching. See the pcrecallout documentation for details. |
tern matching. See the pcrecallout documentation for details. |
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10. Subpatterns that are called as subroutines (whether or not recur- | 9. Subpatterns that are called as subroutines (whether or not recur- |
sively) are always treated as atomic groups in PCRE. This is like | sively) are always treated as atomic groups in PCRE. This is like |
Python, but unlike Perl. Captured values that are set outside a sub- | Python, but unlike Perl. Captured values that are set outside a sub- |
routine call can be reference from inside in PCRE, but not in Perl. | routine call can be reference from inside in PCRE, but not in Perl. |
There is a discussion that explains these differences in more detail in |
There is a discussion that explains these differences in more detail in |
the section on recursion differences from Perl in the pcrepattern page. |
the section on recursion differences from Perl in the pcrepattern page. |
|
|
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 3356 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 function (pcre_dfa_exec()) matches in a | (k) The alternative matching functions (pcre_dfa_exec(), |
different way and is not Perl-compatible. | pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and |
| 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 |
pattern. |
pattern. |
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Line 3373 AUTHOR
|
Line 4600 AUTHOR
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|
|
REVISION |
REVISION |
|
|
Last updated: 14 November 2011 | Last updated: 19 March 2013 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2013 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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|
|
PCREPATTERN(3) PCREPATTERN(3) | PCREPATTERN(3) Library Functions Manual PCREPATTERN(3) |
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|
|
NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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|
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|
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 3402 PCRE REGULAR EXPRESSION DETAILS
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Line 4629 PCRE REGULAR EXPRESSION DETAILS
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great detail. This description of PCRE's regular expressions is |
great detail. This description of PCRE's regular expressions is |
intended as reference material. |
intended as reference material. |
|
|
|
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 |
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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 |
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pcrematching page. |
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SPECIAL START-OF-PATTERN ITEMS |
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A number of options that can be passed to pcre_compile() can also be |
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set by special items at the start of a pattern. These are not Perl-com- |
|
patible, but are provided to make these options accessible to pattern |
|
writers who are not able to change the program that processes the pat- |
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tern. Any number of these items may appear, but they must all be |
|
together right at the start of the pattern string, and the letters must |
|
be in upper case. |
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|
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 character strings. To use | However, there is now also support for UTF-8 strings in the original |
this, PCRE must be built to include UTF-8 support, and you must call | library, an extra library that supports 16-bit and UTF-16 character |
pcre_compile() or pcre_compile2() with the PCRE_UTF8 option. There is | strings, and a third library that supports 32-bit and UTF-32 character |
also a special sequence that can be given at the start of a pattern: | strings. To use these features, PCRE must be built to include appropri- |
| ate support. When using UTF strings you must either call the compiling |
| function with the PCRE_UTF8, PCRE_UTF16, or PCRE_UTF32 option, or the |
| pattern must start with one of these special sequences: |
|
|
(*UTF8) |
(*UTF8) |
|
(*UTF16) |
|
(*UTF32) |
|
(*UTF) |
|
|
Starting a pattern with this sequence is equivalent to setting the | (*UTF) is a generic sequence that can be used with any of the |
PCRE_UTF8 option. This feature is not Perl-compatible. How setting | libraries. Starting a pattern with such a sequence is equivalent to |
UTF-8 mode affects pattern matching is mentioned in several places | setting the relevant option. How setting a UTF mode affects pattern |
below. There is also a summary of UTF-8 features in the pcreunicode | matching is mentioned in several places below. There is also a summary |
page. | 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) 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 |
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(*UCP) |
(*UCP) |
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|
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 |
sequences such as \d and \w to use Unicode properties to determine | sequences such as \d and \w to use Unicode properties to determine |
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. |
|
|
If a pattern starts with (*NO_START_OPT), it has the same effect as | Disabling start-up optimizations |
| |
| 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 its main matching function, pcre_exec(), is used. | |
From release 6.0, PCRE offers a second matching function, | |
pcre_dfa_exec(), which matches using a different algorithm that is not | |
Perl-compatible. Some of the features discussed below are not available | |
when pcre_dfa_exec() is used. The advantages and disadvantages of the | |
alternative function, and how it differs from the normal function, are | |
discussed in the pcrematching 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 3459 NEWLINE CONVENTIONS
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Line 4712 NEWLINE CONVENTIONS
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(*ANYCRLF) any of the three above |
(*ANYCRLF) any of the three above |
(*ANY) all Unicode newline sequences |
(*ANY) all Unicode newline sequences |
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|
These override the default and the options given to pcre_compile() or | These override the default and the options given to the compiling func- |
pcre_compile2(). For example, on a Unix system where LF is the default | tion. For example, on a Unix system where LF is the default newline |
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. |
|
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|
Setting match and recursion limits |
|
|
|
The caller of pcre_exec() can set a limit on the number of times the |
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internal match() function is called and on the maximum depth of recur- |
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sive calls. These facilities are provided to catch runaway matches that |
|
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 |
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(*LIMIT_MATCH=d) |
|
(*LIMIT_RECURSION=d) |
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|
|
where d is any number of decimal digits. However, the value of the set- |
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ting must be less than the value set by the caller of pcre_exec() for |
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it to have any effect. In other words, the pattern writer can lower the |
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limit set by the programmer, but not raise it. If there is more than |
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one setting of one of these limits, the lower value is used. |
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EBCDIC CHARACTER CODES |
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PCRE can be compiled to run in an environment that uses EBCDIC as its |
|
character code rather than ASCII or Unicode (typically a mainframe sys- |
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tem). In the sections below, character code values are ASCII or Uni- |
|
code; in an EBCDIC environment these characters may have different code |
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values, and there are no code points greater than 255. |
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CHARACTERS AND METACHARACTERS |
CHARACTERS AND METACHARACTERS |
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|
A regular expression is a pattern that is matched against a subject | A regular expression is a pattern that is matched against a subject |
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 UTF-8 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-8 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: |
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|
\ general escape character with several uses |
\ general escape character with several uses |
Line 3525 CHARACTERS AND METACHARACTERS
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Line 4806 CHARACTERS AND METACHARACTERS
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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 3542 BACKSLASH
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Line 4823 BACKSLASH
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|
|
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 UTF-8 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 3575 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 3603 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 both byte mode and UTF-8 mode. (When PCRE | out non-ASCII characters in all modes. |
is compiled in EBCDIC 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 value of the character code | its may appear between \x{ and }, but the character code is constrained |
must be less than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 | as follows: |
mode. That is, the maximum value in hexadecimal is 7FFFFFFF. Note that | |
this is bigger than the largest Unicode code point, which is 10FFFF. | |
|
|
If characters other than hexadecimal digits appear between \x{ and }, | or if there is no terminating }, this form of escape is not recognized. |
| 8-bit UTF-8 mode less than 0x10ffff and a valid codepoint |
| 16-bit non-UTF mode less than 0x10000 |
| 16-bit UTF-16 mode less than 0x10ffff and a valid codepoint |
| 32-bit non-UTF mode less than 0x80000000 |
| 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint |
| |
| Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- |
| called "surrogate" codepoints), and 0xffef. |
| |
| 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. |
Instead, the initial \x will be interpreted as a basic hexadecimal | Instead, the initial \x will be interpreted as a basic hexadecimal |
escape, with no following digits, giving a character whose value is | escape, with no following digits, giving a character whose value is |
zero. |
zero. |
|
|
If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x | If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x |
is as just described only when it is followed by two hexadecimal dig- | is as just described only when it is followed by two hexadecimal dig- |
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- |
ence in the way they are handled. For example, \xdc is exactly the same |
ence in the way they are handled. For example, \xdc is exactly the same |
as \x{dc} (or \u00dc in JavaScript mode). |
as \x{dc} (or \u00dc in JavaScript mode). |
|
|
After \0 up to two further octal digits are read. If there are fewer | After \0 up to two further octal digits are read. If there are fewer |
than two digits, just those that are present are used. Thus the | than two digits, just those that are present are used. Thus the |
sequence \0\x\07 specifies two binary zeros followed by a BEL character |
sequence \0\x\07 specifies two binary zeros followed by a BEL character |
(code value 7). Make sure you supply two digits after the initial zero | (code value 7). Make sure you supply two digits after the initial zero |
if the pattern character that follows is itself an octal digit. |
if the pattern character that follows is itself an octal digit. |
|
|
The handling of a backslash followed by a digit other than 0 is compli- |
The handling of a backslash followed by a digit other than 0 is compli- |
cated. Outside a character class, PCRE reads it and any following dig- |
cated. Outside a character class, PCRE reads it and any following dig- |
its as a decimal number. If the number is less than 10, or if there | its as a decimal number. If the number is less its as a decimal number. If the number is less than 10, or if there |
have been at least that many previous capturing left parentheses in the |
have been at least that many previous capturing left parentheses in the |
expression, the entire sequence is taken as a back reference. A | expression, the entire sequence is taken as a back reference. A |
description of how this works is given later, following the discussion | description of how this works is given later, following the discussion |
of parenthesized subpatterns. |
of parenthesized subpatterns. |
|
|
Inside a character class, or if the decimal number is greater than 9 | Inside a character class, or if the decimal number is greater than 9 |
and there have not been that many capturing subpatterns, PCRE re-reads | and there have not been that many capturing subpatterns, PCRE re-reads |
up to three octal digits following the backslash, and uses them to gen- |
up to three octal digits following the backslash, and uses them to gen- |
erate a data character. Any subsequent digits stand for themselves. In | erate a data character. Any subsequent digits stand for themselves. The |
non-UTF-8 mode, the value of a character specified in octal must be | value of the character is constrained in the same way as characters |
less than \400. In UTF-8 mode, values up to \777 are permitted. For | specified in hexadecimal. For example: |
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 3670 BACKSLASH
|
Line 4969 BACKSLASH
|
\113 might be a back reference, otherwise the |
\113 might be a back reference, otherwise the |
character with octal code 113 |
character with octal code 113 |
\377 might be a back reference, otherwise |
\377 might be a back reference, otherwise |
the byte consisting entirely of 1 bits | the value 255 (decimal) |
\81 is either a back reference, or a binary zero |
\81 is either a back reference, or a binary zero |
followed by the two characters "8" and "1" |
followed by the two characters "8" and "1" |
|
|
Line 3718 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 3755 BACKSLASH
|
Line 5054 BACKSLASH
|
are used for accented letters, and these are then matched by \w. The |
are used for accented letters, and these are then matched by \w. The |
use of locales with Unicode is discouraged. |
use of locales with Unicode is discouraged. |
|
|
By default, in UTF-8 mode, characters with values greater than 128 | By default, in a UTF mode, characters with values greater than 128 |
never match \d, \s, or \w, and always match \D, \S, and \W. These |
never match \d, \s, or \w, and always match \D, \S, and \W. These |
sequences retain their original meanings from before UTF-8 support was | sequences retain their original meanings from before UTF support was |
available, mainly for efficiency reasons. However, if PCRE is compiled |
available, mainly for efficiency reasons. However, if PCRE is compiled |
with Unicode property support, and the PCRE_UCP option is set, the be- |
with Unicode property support, and the PCRE_UCP option is set, the be- |
haviour is changed so that Unicode properties are used to determine |
haviour is changed so that Unicode properties are used to determine |
Line 3776 BACKSLASH
|
Line 5075 BACKSLASH
|
The sequences \h, \H, \v, and \V are features that were added to Perl |
The sequences \h, \H, \v, and \V are features that were added to Perl |
at release 5.10. In contrast to the other sequences, which match only |
at release 5.10. In contrast to the other sequences, which match only |
ASCII characters by default, these always match certain high-valued |
ASCII characters by default, these always match certain high-valued |
codepoints in UTF-8 mode, whether or not PCRE_UCP is set. The horizon- | codepoints, whether or not PCRE_UCP is set. The horizontal space char- |
tal space characters 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 3801 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 |
|
|
|
In 8-bit, non-UTF-8 mode, only the characters with codepoints less than |
|
256 are relevant. |
|
|
Newline sequences |
Newline sequences |
|
|
Outside a character class, by default, the escape sequence \R matches | Outside a character class, by default, the escape sequence \R matches |
any Unicode newline sequence. In non-UTF-8 mode \R is equivalent to the | any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent |
following: | to the following: |
|
|
(?>\r\n|\n|\x0b|\f|\r|\x85) |
(?>\r\n|\n|\x0b|\f|\r|\x85) |
|
|
This is an example of an "atomic group", details of which are given | This is an example of an "atomic group", details of which are given |
below. This particular group matches either the two-character sequence |
below. This particular group matches either the two-character sequence |
CR followed by LF, or one of the single characters LF (linefeed, | CR followed by LF, or one of the single characters LF (linefeed, |
U+000A), VT (vertical tab, U+000B), FF (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 UTF-8 mode, two additional characters whose codepoints are greater | In other modes, two additional characters whose codepoints are greater |
than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa- |
than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa- |
rator, U+2029). Unicode character property support is not needed for | rator, U+2029). Unicode character property support is not needed for |
these characters to be recognized. |
these characters to be recognized. |
|
|
It is possible to restrict \R to match only CR, LF, or CRLF (instead of |
It is possible to restrict \R to match only CR, LF, or CRLF (instead of |
the complete set of Unicode line endings) by setting the option | the complete set of Unicode line endings) by setting the option |
PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched. |
PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched. |
(BSR is an abbrevation for "backslash R".) This can be made the default |
(BSR is an abbrevation for "backslash R".) This can be made the default |
when PCRE is built; if this is the case, the other behaviour can be | when PCRE is built; if this is the case, the other behaviour can be |
requested via the PCRE_BSR_UNICODE option. It is also possible to | requested via the PCRE_BSR_UNICODE option. It is also possible to |
specify these settings by starting a pattern string with one of the | specify these settings by starting a pattern string with one of the |
following sequences: |
following sequences: |
|
|
(*BSR_ANYCRLF) CR, LF, or CRLF only |
(*BSR_ANYCRLF) CR, LF, or CRLF only |
(*BSR_UNICODE) any Unicode newline sequence |
(*BSR_UNICODE) any Unicode newline sequence |
|
|
These override the default and the options given to pcre_compile() or | These override the default and the options given to the compiling func- |
pcre_compile2(), but they can be overridden by options given to | tion, but they can themselves be overridden by options given to a |
pcre_exec() or pcre_dfa_exec(). Note that these special settings, which | matching function. Note that these special settings, which are not |
are not Perl-compatible, are recognized only at the very start of a | Perl-compatible, are recognized only at the very start of a pattern, |
pattern, and that they must be in upper case. If more than one of them | and that they must be in upper case. If more than one of them is |
is present, the last one is used. They can be combined with a change of | present, the last one is used. They can be combined with a change of |
newline convention; for example, a pattern can start with: |
newline convention; for example, a pattern can start with: |
|
|
(*ANY)(*BSR_ANYCRLF) |
(*ANY)(*BSR_ANYCRLF) |
|
|
They can also be combined with the (*UTF8) or (*UCP) special sequences. | They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF) |
Inside a character class, \R is treated as an unrecognized escape | or (*UCP) special sequences. Inside a character class, \R is treated as |
sequence, and so matches the letter "R" by default, but causes an error | an unrecognized escape sequence, and so matches the letter "R" by |
if PCRE_EXTRA is set. | default, but causes an error if PCRE_EXTRA is set. |
|
|
Unicode character properties |
Unicode character properties |
|
|
When PCRE is built with Unicode character property support, three addi- |
When PCRE is built with Unicode character property support, three addi- |
tional escape sequences that match characters with specific properties | tional escape sequences that match characters with specific properties |
are available. When not in UTF-8 mode, these sequences are of course | are available. When in 8-bit non-UTF-8 mode, these sequences are of |
limited to testing characters whose codepoints are less than 256, but | course limited to testing characters whose codepoints are less than |
they do work in this mode. The extra escape sequences are: | 256, but they do work in this mode. The extra escape sequences are: |
|
|
\p{xx} a character with the xx property |
\p{xx} a character with the xx property |
\P{xx} a character without the xx property |
\P{xx} a character without the xx property |
\X an extended Unicode sequence | \X a Unicode extended grapheme cluster |
|
|
The property names represented by xx above are limited to the Unicode | The property names represented by xx above are limited to the Unicode |
script names, the general category properties, "Any", which matches any |
script names, the general category properties, "Any", which matches any |
character (including newline), and some special PCRE properties | character (including newline), and some special PCRE properties |
(described in the next section). Other Perl properties such as "InMu- | (described in the next section). Other Perl properties such as "InMu- |
sicalSymbols" are not currently supported by PCRE. Note that \P{Any} | sicalSymbols" are not currently supported by PCRE. Note that \P{Any} |
does not match any characters, so always causes a match failure. |
does not match any characters, so always causes a match failure. |
|
|
Sets of Unicode characters are defined as belonging to certain scripts. |
Sets of Unicode characters are defined as belonging to certain scripts. |
A character from one of these sets can be matched using a script name. | A character from one of these sets can be matched using a script name. |
For example: |
For example: |
|
|
\p{Greek} |
\p{Greek} |
\P{Han} |
\P{Han} |
|
|
Those that are not part of an identified script are lumped together as | Those that are not part of an identified script are lumped together as |
"Common". The current list of scripts is: |
"Common". The current list of scripts is: |
|
|
Arabic, Armenian, Avestan, Balinese, Bamum, 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- |
tion can be specified by including a circumflex between the opening | tion can be specified by including a circumflex between the opening |
brace and the property name. For example, \p{^Lu} is the same as | brace and the property name. For example, \p{^Lu} is the same as |
\P{Lu}. |
\P{Lu}. |
|
|
If only one letter is specified with \p or \P, it includes all the gen- |
If only one letter is specified with \p or \P, it includes all the gen- |
eral category properties that start with that letter. In this case, in | eral category properties that start with that letter. In this case, in |
the absence of negation, the curly brackets in the escape sequence are | the absence of negation, the curly brackets in the escape sequence are |
optional; these two examples have the same effect: |
optional; these two examples have the same effect: |
|
|
\p{L} |
\p{L} |
Line 3960 BACKSLASH
|
Line 5264 BACKSLASH
|
Zp Paragraph separator |
Zp Paragraph separator |
Zs Space separator |
Zs Space separator |
|
|
The special property L& is also supported: it matches a character that | The special property L& is also supported: it matches a character that |
has the Lu, Ll, or Lt property, in other words, a letter that is not | has the Lu, Ll, or Lt property, in other words, a letter that is not |
classified as a modifier or "other". |
classified as a modifier or "other". |
|
|
The Cs (Surrogate) property applies only to characters in the range | The Cs (Surrogate) property applies only to characters in the range |
U+D800 to U+DFFF. Such characters are not valid in UTF-8 strings (see | U+D800 to U+DFFF. Such characters are not valid in Unicode strings and |
RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check- | so cannot be tested by PCRE, unless UTF validity checking has been |
ing has been turned off (see the discussion of PCRE_NO_UTF8_CHECK in | turned off (see the discussion of PCRE_NO_UTF8_CHECK, |
the pcreapi page). Perl does not support the Cs property. | PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_CHECK in the pcreapi page). Perl |
| 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 3979 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 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 for pcre_compile() or by | |
starting the pattern 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 4061 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 | string if the first or last character matches \w, respectively. In a |
UTF-8 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 4163 FULL STOP (PERIOD, DOT) AND \N
|
Line 5512 FULL STOP (PERIOD, DOT) AND \N
|
|
|
Outside a character class, a dot in the pattern matches any one charac- |
Outside a character class, a dot in the pattern matches any one charac- |
ter in the subject string except (by default) a character that signi- |
ter in the subject string except (by default) a character that signi- |
fies the end of a line. In UTF-8 mode, the matched character may be | fies the end of a line. |
more than one byte long. | |
|
|
When a line ending is defined as a single character, dot never matches | When a line ending is defined as a single character, dot never matches |
that character; when the two-character sequence CRLF is used, dot does | that character; when the two-character sequence CRLF is used, dot does |
not match CR if it is immediately followed by LF, but otherwise it | not match CR if it is immediately followed by LF, but otherwise it |
matches all characters (including isolated CRs and LFs). When any Uni- | matches all characters (including isolated CRs and LFs). When any Uni- |
code line endings are being recognized, dot does not match CR or LF or | code line endings are being recognized, dot does not match CR or LF or |
any of the other line ending characters. |
any of the other line ending characters. |
|
|
The behaviour of dot with regard to newlines can be changed. If the | The behaviour of dot with regard to newlines can be changed. If the |
PCRE_DOTALL option is set, a dot matches any one character, without | PCRE_DOTALL option is set, a dot matches any one character, without |
exception. If the two-character sequence CRLF is present in the subject |
exception. If the two-character sequence CRLF is present in the subject |
string, it takes two dots to match it. |
string, it takes two dots to match it. |
|
|
The handling of dot is entirely independent of the handling of circum- | The handling of dot is entirely independent of the handling of circum- |
flex and dollar, the only relationship being that they both involve | flex and dollar, the only relationship being that they both involve |
newlines. Dot has no special meaning in a character class. |
newlines. Dot has no special meaning in a character class. |
|
|
The escape sequence \N behaves like a dot, except that it is not | The escape sequence \N behaves like a dot, except that it is not |
affected by the PCRE_DOTALL option. In other words, it matches any | affected by the PCRE_DOTALL option. In other words, it matches any |
character except one that signifies the end of a line. Perl also uses | character except one that signifies the end of a line. Perl also uses |
\N to match characters by name; PCRE does not support this. |
\N to match characters by name; PCRE does not support this. |
|
|
|
|
MATCHING A SINGLE BYTE | MATCHING A SINGLE DATA UNIT |
|
|
Outside a character class, the escape sequence \C matches any one byte, | Outside a character class, the escape sequence \C matches any one data |
both in and out of UTF-8 mode. Unlike a dot, it always matches line- | unit, whether or not a UTF mode is set. In the 8-bit library, one data |
ending characters. The feature is provided in Perl in order to match | unit is one byte; in the 16-bit library it is a 16-bit unit; in the |
individual bytes in UTF-8 mode, but it is unclear how it can usefully | 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches |
be used. Because \C breaks up characters into individual bytes, match- | line-ending characters. The feature is provided in Perl in order to |
ing one byte with \C in UTF-8 mode means that the rest of the string | match individual bytes in UTF-8 mode, but it is unclear how it can use- |
may start with a malformed UTF-8 character. This has undefined results, | fully be used. Because \C breaks up characters into individual data |
because PCRE assumes that it is dealing with valid UTF-8 strings (and | units, matching one unit with \C in a UTF mode means that the rest of |
by default it checks this at the start of processing unless the | the string may start with a malformed UTF character. This has undefined |
PCRE_NO_UTF8_CHECK option is used). | results, because PCRE assumes that it is dealing with valid UTF strings |
| (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 UTF-8 mode, because this would make it impossible to calcu- | below) in a UTF mode, because this would make it impossible to calcu- |
late the length of the lookbehind. |
late the length of the lookbehind. |
|
|
In general, the \C escape sequence is best avoided in UTF-8 mode. How- | In general, the \C escape sequence is best avoided. However, one way of |
ever, one way of using it that avoids the problem of malformed UTF-8 | using it that avoids the problem of malformed UTF characters is to use |
characters is to use a lookahead to check the length of the next char- | a lookahead to check the length of the next character, as in this pat- |
acter, as in this pattern (ignore white space and line breaks): | tern, which could be used with a UTF-8 string (ignore white space and |
| line breaks): |
|
|
(?| (?=[\x00-\x7f])(\C) | |
(?| (?=[\x00-\x7f])(\C) | |
(?=[\x80-\x{7ff}])(\C)(\C) | |
(?=[\x80-\x{7ff}])(\C)(\C) | |
(?=[\x{800}-\x{ffff}])(\C)(\C)(\C) | |
(?=[\x{800}-\x{ffff}])(\C)(\C)(\C) | |
(?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C)) |
(?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C)) |
|
|
A group that starts with (?| resets the capturing parentheses numbers | A group that starts with (?| resets the capturing parentheses numbers |
in each alternative (see "Duplicate Subpattern Numbers" below). The | in each alternative (see "Duplicate Subpattern Numbers" below). The |
assertions at the start of each branch check the next UTF-8 character | assertions at the start of each branch check the next UTF-8 character |
for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The | for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The |
character's individual bytes are then captured by the appropriate num- | character's individual bytes are then captured by the appropriate num- |
ber of groups. |
ber of groups. |
|
|
|
|
Line 4229 SQUARE BRACKETS AND CHARACTER CLASSES
|
Line 5581 SQUARE BRACKETS AND CHARACTER CLASSES
|
closing square bracket. A closing square bracket on its own is not spe- |
closing square bracket. A closing square bracket on its own is not spe- |
cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set, |
cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set, |
a lone closing square bracket causes a compile-time error. If a closing |
a lone closing square bracket causes a compile-time error. If a closing |
square bracket is required as a member of the class, it should be the | square bracket is required as a member of the class, it should be the |
first data character in the class (after an initial circumflex, if | first data character in the class (after an initial circumflex, if |
present) or escaped with a backslash. |
present) or escaped with a backslash. |
|
|
A character class matches a single character in the subject. In UTF-8 | A character class matches a single character in the subject. In a UTF |
mode, the character may be more than one byte long. A matched character | mode, the character may be more than one data unit long. A matched |
must be in the set of characters defined by the class, unless the first | character must be in the set of characters defined by the class, unless |
character in the class definition is a circumflex, in which case the | the first character in the class definition is a circumflex, in which |
subject character must not be in the set defined by the class. If a | case the subject character must not be in the set defined by the class. |
circumflex is actually required as a member of the class, ensure it is | If a circumflex is actually required as a member of the class, ensure |
not the first character, or escape it with a backslash. | it is not the first character, or escape it with a backslash. |
|
|
For example, the character class [aeiou] matches any lower case vowel, | For example, the character class [aeiou] matches any lower case vowel, |
while [^aeiou] matches any character that is not a lower case vowel. | while [^aeiou] matches any character that is not a lower case vowel. |
Note that a circumflex is just a convenient notation for specifying the |
Note that a circumflex is just a convenient notation for specifying the |
characters that are in the class by enumerating those that are not. A | characters that are in the class by enumerating those that are not. A |
class that starts with a circumflex is not an assertion; it still con- | class that starts with a circumflex is not an assertion; it still con- |
sumes a character from the subject string, and therefore it fails if | sumes a character from the subject string, and therefore it fails if |
the current pointer is at the end of the string. |
the current pointer is at the end of the string. |
|
|
In UTF-8 mode, characters with values greater than 255 can be included | In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255 |
in a class as a literal string of bytes, or by using the \x{ escaping | (0xffff) can be included in a class as a literal string of data units, |
mechanism. | or by using the \x{ escaping mechanism. |
|
|
When caseless matching is set, any letters in a class represent both | When caseless matching is set, any letters in a class represent both |
their upper case and lower case versions, so for example, a caseless | their upper case and lower case versions, so for example, a caseless |
[aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not | [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not |
match "A", whereas a caseful version would. In UTF-8 mode, PCRE always | match "A", whereas a caseful version would. In a UTF mode, PCRE always |
understands the concept of case for characters whose values are less | understands the concept of case for characters whose values are less |
than 128, so caseless matching is always possible. For characters with | than 128, so caseless matching is always possible. For characters with |
higher values, the concept of case is supported if PCRE is compiled | higher values, the concept of case is supported if PCRE is compiled |
with Unicode property support, but not otherwise. If you want to use | with Unicode property support, but not otherwise. If you want to use |
caseless matching in UTF8-mode for characters 128 and above, you must | caseless matching in a UTF mode for characters 128 and above, you must |
ensure that PCRE is compiled with Unicode property support as well as | ensure that PCRE is compiled with Unicode property support as well as |
with UTF-8 support. | with UTF support. |
|
|
Characters that might indicate line breaks are never treated in any | Characters that might indicate line breaks are never treated in any |
special way when matching character classes, whatever line-ending | special way when matching character classes, whatever line-ending |
sequence is in use, and whatever setting of the PCRE_DOTALL and | sequence is in use, and whatever setting of the PCRE_DOTALL and |
PCRE_MULTILINE options is used. A class such as [^a] always matches one |
PCRE_MULTILINE options is used. A class such as [^a] always matches one |
of these characters. |
of these characters. |
|
|
The minus (hyphen) character can be used to specify a range of charac- | The minus (hyphen) character can be used to specify a range of charac- |
ters in a character class. For example, [d-m] matches any letter | ters in a character class. For example, [d-m] matches any letter |
between d and m, inclusive. If a minus character is required in a | between d and m, inclusive. If a minus character is required in a |
class, it must be escaped with a backslash or appear in a position | class, it must be escaped with a backslash or appear in a position |
where it cannot be interpreted as indicating a range, typically as the | where it cannot be interpreted as indicating a range, typically as the |
first or last character in the class. |
first or last character in the class. |
|
|
It is not possible to have the literal character "]" as the end charac- |
It is not possible to have the literal character "]" as the end charac- |
ter of a range. A pattern such as [W-]46] is interpreted as a class of | ter of a range. A pattern such as [W-]46] is interpreted as a class of |
two characters ("W" and "-") followed by a literal string "46]", so it | two characters ("W" and "-") followed by a literal string "46]", so it |
would match "W46]" or "-46]". However, if the "]" is escaped with a | would match "W46]" or "-46]". However, if the "]" is escaped with a |
backslash it is interpreted as the end of range, so [W-\]46] is inter- | backslash it is interpreted as the end of range, so [W-\]46] is inter- |
preted as a class containing a range followed by two other characters. | preted as a class containing a range followed by two other characters. |
The octal or hexadecimal representation of "]" can also be used to end | The octal or hexadecimal representation of "]" can also be used to end |
a range. |
a range. |
|
|
Ranges operate in the collating sequence of character values. They can | Ranges operate in the collating sequence of character values. They can |
also be used for characters specified numerically, for example | also be used for characters specified numerically, for example |
[\000-\037]. In UTF-8 mode, ranges can include characters whose values | [\000-\037]. Ranges can include any characters that are valid for the |
are greater than 255, for example [\x{100}-\x{2ff}]. | current mode. |
|
|
If a range that includes letters is used when caseless matching is set, |
If a range that includes letters is used when caseless matching is set, |
it matches the letters in either case. For example, [W-c] is equivalent |
it matches the letters in either case. For example, [W-c] is equivalent |
to [][\\^_`wxyzabc], matched caselessly, and in non-UTF-8 mode, if | to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if |
character tables for a French locale are in use, [\xc8-\xcb] matches | character tables for a French locale are in use, [\xc8-\xcb] matches |
accented E characters in both cases. In UTF-8 mode, PCRE supports the | accented E characters in both cases. In UTF modes, PCRE supports the |
concept of case for characters with values greater than 128 only when | concept of case for characters with values greater than 128 only when |
it is compiled with Unicode property support. |
it is compiled with Unicode property support. |
|
|
The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V, | The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V, |
\w, and \W may appear in a character class, and add the characters that |
\w, and \W may appear in a character class, and add the characters that |
they match to the class. For example, [\dABCDEF] matches any hexadeci- | they match to the class. For example, [\dABCDEF] matches any hexadeci- |
mal digit. In UTF-8 mode, the PCRE_UCP option affects the meanings of | mal digit. In UTF modes, the PCRE_UCP option affects the meanings of |
\d, \s, \w and their upper case partners, just as it does when they | \d, \s, \w and their upper case partners, just as it does when they |
appear outside a character class, as described in the section entitled | appear outside a character class, as described in the section entitled |
"Generic character types" above. The escape sequence \b has a different |
"Generic character types" above. The escape sequence \b has a different |
meaning inside a character class; it matches the backspace character. | meaning inside a character class; it matches the backspace character. |
The sequences \B, \N, \R, and \X are not special inside a character | The sequences \B, \N, \R, and \X are not special inside a character |
class. Like any other unrecognized escape sequences, they are treated | class. Like any other unrecognized escape sequences, they are treated |
as the literal characters "B", "N", "R", and "X" by default, but cause | as the literal characters "B", "N", "R", and "X" by default, but cause |
an error if the PCRE_EXTRA option is set. |
an error if the PCRE_EXTRA option is set. |
|
|
A circumflex can conveniently be used with the upper case character | A circumflex can conveniently be used with the upper case character |
types to specify a more restricted set of characters than the matching | types to specify a more restricted set of characters than the matching |
lower case type. For example, the class [^\W_] matches any letter or | lower case type. For example, the class [^\W_] matches any letter or |
digit, but not underscore, whereas [\w] includes underscore. A positive |
digit, but not underscore, whereas [\w] includes underscore. A positive |
character class should be read as "something OR something OR ..." and a |
character class should be read as "something OR something OR ..." and a |
negative class as "NOT something AND NOT something AND NOT ...". |
negative class as "NOT something AND NOT something AND NOT ...". |
|
|
The only metacharacters that are recognized in character classes are | The only metacharacters that are recognized in character classes are |
backslash, hyphen (only where it can be interpreted as specifying a | backslash, hyphen (only where it can be interpreted as specifying a |
range), circumflex (only at the start), opening square bracket (only | range), circumflex (only at the start), opening square bracket (only |
when it can be interpreted as introducing a POSIX class name - see the | when it can be interpreted as introducing a POSIX class name - see the |
next section), and the terminating closing square bracket. However, | next section), and the terminating closing square bracket. However, |
escaping other non-alphanumeric characters does no harm. |
escaping other non-alphanumeric characters does no harm. |
|
|
|
|
POSIX CHARACTER CLASSES |
POSIX CHARACTER CLASSES |
|
|
Perl supports the POSIX notation for character classes. This uses names |
Perl supports the POSIX notation for character classes. This uses names |
enclosed by [: and :] within the enclosing square brackets. PCRE also | enclosed by [: and :] within the enclosing square brackets. PCRE also |
supports this notation. For example, |
supports this notation. For example, |
|
|
[01[:alpha:]%] |
[01[:alpha:]%] |
Line 4354 POSIX CHARACTER CLASSES
|
Line 5706 POSIX CHARACTER CLASSES
|
word "word" characters (same as \w) |
word "word" characters (same as \w) |
xdigit hexadecimal digits |
xdigit hexadecimal digits |
|
|
The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), | The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), |
and space (32). Notice that this list includes the VT character (code | and space (32). Notice that this list includes the VT character (code |
11). This makes "space" different to \s, which does not include VT (for |
11). This makes "space" different to \s, which does not include VT (for |
Perl compatibility). |
Perl compatibility). |
|
|
The name "word" is a Perl extension, and "blank" is a GNU extension | The name "word" is a Perl extension, and "blank" is a GNU extension |
from Perl 5.8. Another Perl extension is negation, which is indicated | from Perl 5.8. Another Perl extension is negation, which is indicated |
by a ^ character after the colon. For example, |
by a ^ character after the colon. For example, |
|
|
[12[:^digit:]] |
[12[:^digit:]] |
|
|
matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the | matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the |
POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but |
POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but |
these are not supported, and an error is given if they are encountered. |
these are not supported, and an error is given if they are encountered. |
|
|
By default, in UTF-8 mode, characters with values greater than 128 do | By default, in UTF modes, characters with values greater than 128 do |
not match any of the POSIX character classes. However, if the PCRE_UCP | not match any of the POSIX character classes. However, if the PCRE_UCP |
option is passed to pcre_compile(), some of the classes are changed so | option is passed to pcre_compile(), some of the classes are changed so |
that Unicode character properties are used. This is achieved by replac- |
that Unicode character properties are used. This is achieved by replac- |
ing the POSIX classes by other sequences, as follows: |
ing the POSIX classes by other sequences, as follows: |
|
|
Line 4384 POSIX CHARACTER CLASSES
|
Line 5736 POSIX CHARACTER CLASSES
|
[:upper:] becomes \p{Lu} |
[:upper:] becomes \p{Lu} |
[:word:] becomes \p{Xwd} |
[:word:] becomes \p{Xwd} |
|
|
Negated versions, such as [:^alpha:] use \P instead of \p. The other | Negated versions, such as [:^alpha:] use \P instead of \p. The other |
POSIX classes are unchanged, and match only characters with code points |
POSIX classes are unchanged, and match only characters with code points |
less than 128. |
less than 128. |
|
|
|
|
VERTICAL BAR |
VERTICAL BAR |
|
|
Vertical bar characters are used to separate alternative patterns. For | Vertical bar characters are used to separate alternative patterns. For |
example, the pattern |
example, the pattern |
|
|
gilbert|sullivan |
gilbert|sullivan |
|
|
matches either "gilbert" or "sullivan". Any number of alternatives may | matches either "gilbert" or "sullivan". Any number of alternatives may |
appear, and an empty alternative is permitted (matching the empty | appear, and an empty alternative is permitted (matching the empty |
string). The matching process tries each alternative in turn, from left |
string). The matching process tries each alternative in turn, from left |
to right, and the first one that succeeds is used. If the alternatives | to right, and the first one that succeeds is used. If the alternatives |
are within a subpattern (defined below), "succeeds" means matching the | are within a subpattern (defined below), "succeeds" means matching the |
rest of the main pattern as well as the alternative in the subpattern. |
rest of the main pattern as well as the alternative in the subpattern. |
|
|
|
|
INTERNAL OPTION SETTING |
INTERNAL OPTION SETTING |
|
|
The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and | The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and |
PCRE_EXTENDED options (which are Perl-compatible) can be changed from | PCRE_EXTENDED options (which are Perl-compatible) can be changed from |
within the pattern by a sequence of Perl option letters enclosed | within the pattern by a sequence of Perl option letters enclosed |
between "(?" and ")". The option letters are |
between "(?" and ")". The option letters are |
|
|
i for PCRE_CASELESS |
i for PCRE_CASELESS |
Line 4418 INTERNAL OPTION SETTING
|
Line 5770 INTERNAL OPTION SETTING
|
|
|
For example, (?im) sets caseless, multiline matching. It is also possi- |
For example, (?im) sets caseless, multiline matching. It is also possi- |
ble to unset these options by preceding the letter with a hyphen, and a |
ble to unset these options by preceding the letter with a hyphen, and a |
combined setting and unsetting such as (?im-sx), which sets PCRE_CASE- | combined setting and unsetting such as (?im-sx), which sets PCRE_CASE- |
LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED, | LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED, |
is also permitted. If a letter appears both before and after the | is also permitted. If a letter appears both before and after the |
hyphen, the option is unset. |
hyphen, the option is unset. |
|
|
The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA | The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA |
can be changed in the same way as the Perl-compatible options by using | can be changed in the same way as the Perl-compatible options by using |
the characters J, U and X respectively. |
the characters J, U and X respectively. |
|
|
When one of these option changes occurs at top level (that is, not | When one of these option changes occurs at top level (that is, not |
inside subpattern parentheses), the change applies to the remainder of | inside subpattern parentheses), the change applies to the remainder of |
the pattern that follows. If the change is placed right at the start of |
the pattern that follows. If the change is placed right at the start of |
a pattern, PCRE extracts it into the global options (and it will there- |
a pattern, PCRE extracts it into the global options (and it will there- |
fore show up in data extracted by the pcre_fullinfo() function). |
fore show up in data extracted by the pcre_fullinfo() function). |
|
|
An option change within a subpattern (see below for a description of | An option change within a subpattern (see below for a description of |
subpatterns) affects only that part of the subpattern that follows it, | subpatterns) affects only that part of the subpattern that follows it, |
so |
so |
|
|
(a(?i)b)c |
(a(?i)b)c |
|
|
matches abc and aBc and no other strings (assuming PCRE_CASELESS is not |
matches abc and aBc and no other strings (assuming PCRE_CASELESS is not |
used). By this means, options can be made to have different settings | used). By this means, options can be made to have different settings |
in different parts of the pattern. Any changes made in one alternative | in different parts of the pattern. Any changes made in one alternative |
do carry on into subsequent branches within the same subpattern. For | do carry on into subsequent branches within the same subpattern. For |
example, |
example, |
|
|
(a(?i)b|c) |
(a(?i)b|c) |
|
|
matches "ab", "aB", "c", and "C", even though when matching "C" the | matches "ab", "aB", "c", and "C", even though when matching "C" the |
first branch is abandoned before the option setting. This is because | first branch is abandoned before the option setting. This is because |
the effects of option settings happen at compile time. There would be | the effects of option settings happen at compile time. There would be |
some very weird behaviour otherwise. |
some very weird behaviour otherwise. |
|
|
Note: There are other PCRE-specific options that can be set by the | Note: There are other PCRE-specific options that can be set by the |
application when the compile or match functions are called. In some | application when the compiling or matching functions are called. In |
cases the pattern can contain special leading sequences such as (*CRLF) | some cases the pattern can contain special leading sequences such as |
to override what the application has set or what has been defaulted. | (*CRLF) to override what the application has set or what has been |
Details are given in the section entitled "Newline sequences" above. | defaulted. Details are given in the section entitled "Newline |
There are also the (*UTF8) and (*UCP) leading sequences that can be | sequences" above. There are also the (*UTF8), (*UTF16),(*UTF32), and |
used to set UTF-8 and Unicode property modes; they are equivalent to | (*UCP) leading sequences that can be used to set UTF and Unicode prop- |
setting the PCRE_UTF8 and the PCRE_UCP options, respectively. | erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16, |
| 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 4471 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 pcre_exec(). Opening parentheses are counted from | ovector argument of the matching function. (This applies only to the |
left to right (starting from 1) to obtain numbers for the capturing | traditional matching functions; the DFA matching functions do not sup- |
subpatterns. For example, if the string "the red king" is matched | port capturing.) |
against the pattern | |
|
|
|
Opening parentheses are counted from left to right (starting from 1) to |
|
obtain numbers for the capturing subpatterns. For example, if the |
|
string "the red king" is matched against the pattern |
|
|
the ((red|white) (king|queen)) |
the ((red|white) (king|queen)) |
|
|
the captured substrings are "red king", "red", and "king", and are num- |
the captured substrings are "red king", "red", and "king", and are num- |
Line 4636 REPETITION
|
Line 5995 REPETITION
|
a literal data character |
a literal data character |
the dot metacharacter |
the dot metacharacter |
the \C escape sequence |
the \C escape sequence |
the \X escape sequence (in UTF-8 mode with Unicode properties) | the \X escape sequence |
the \R escape sequence |
the \R escape sequence |
an escape such as \d or \pL that matches a single character |
an escape such as \d or \pL that matches a single character |
a character class |
a character class |
Line 4668 REPETITION
|
Line 6027 REPETITION
|
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-8 mode, quantifiers apply to UTF-8 characters rather than to | In UTF modes, quantifiers apply to characters rather than to individual |
individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char- | data units. Thus, for example, \x{100}{2} matches two characters, each |
acters, each of which is represented by a two-byte sequence. Similarly, | of which is represented by a two-byte sequence in a UTF-8 string. Simi- |
when Unicode property support is available, \X{3} matches three Unicode | larly, \X{3} matches three Unicode extended grapheme clusters, each of |
extended sequences, each of which may be several bytes long (and they | which may be several data units long (and they may be of different |
may be of different lengths). | 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 4757 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 4767 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 4784 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 4840 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 4890 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 4919 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 4928 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 4962 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 5109 ASSERTIONS
|
Line 6478 ASSERTIONS
|
then try to match. If there are insufficient characters before the cur- |
then try to match. If there are insufficient characters before the cur- |
rent position, the assertion fails. |
rent position, the assertion fails. |
|
|
In UTF-8 mode, PCRE does not allow the \C escape (which matches a sin- | In a UTF mode, PCRE does not allow the \C escape (which matches a sin- |
gle byte, even in UTF-8 mode) to appear in lookbehind assertions, | gle data unit even in a UTF mode) to appear in lookbehind assertions, |
because it makes it impossible to calculate the length of the lookbe- |
because it makes it impossible to calculate the length of the lookbe- |
hind. The \X and \R escapes, which can match different numbers of | hind. The \X and \R escapes, which can match different numbers of data |
bytes, are also not permitted. | units, are also not permitted. |
|
|
"Subroutine" calls (see below) such as (?2) or (?&X) are permitted in |
"Subroutine" calls (see below) such as (?2) or (?&X) are permitted in |
lookbehinds, as long as the subpattern matches a fixed-length string. |
lookbehinds, as long as the subpattern matches a fixed-length string. |
Line 5292 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 5338 COMMENTS
|
Line 6707 COMMENTS
|
comment, which in this case continues to immediately after the next |
comment, which in this case continues to immediately after the next |
newline character or character sequence in the pattern. Which charac- |
newline character or character sequence in the pattern. Which charac- |
ters are interpreted as newlines is controlled by the options passed to |
ters are interpreted as newlines is controlled by the options passed to |
pcre_compile() or by a special sequence at the start of the pattern, as | a compiling function or by a special sequence at the start of the pat- |
described in the section entitled "Newline conventions" above. Note | tern, as described in the section entitled "Newline conventions" above. |
that the end of this type of comment is a literal newline sequence in | Note that the end of this type of comment is a literal newline sequence |
the pattern; escape sequences that happen to represent a newline do not | in the pattern; escape sequences that happen to represent a newline do |
count. For example, consider this pattern when PCRE_EXTENDED is set, | not count. For example, consider this pattern when PCRE_EXTENDED is |
and the default newline convention is in force: | set, and the default newline convention is in force: |
|
|
abc #comment \n still comment |
abc #comment \n still comment |
|
|
Line 5636 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. By default, this variable contains NULL, which disables | pcre_callout (8-bit library) or pcre[16|32]_callout (16-bit or 32-bit |
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 pcre_compile(), callouts are | If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, call- |
automatically installed before each item in the pattern. They are all | outs are automatically installed before each item in the pattern. They |
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 (and pcre_callout is | (?(?C9)(?=a)abc|def) |
set), the external function 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 pcre_exec(). The callout | |
function may cause matching to proceed, to backtrack, or to fail alto- | |
gether. A complete description of the interface to the callout function | |
is given in the pcrecallout documentation. | |
|
|
|
Note that this applies only to assertion conditions, not to other types |
|
of condition. |
|
|
BACKTRACKING CONTROL | During matching, when PCRE reaches a callout point, the external func- |
| tion is called. It is provided with the number of the callout, the |
| position in the pattern, and, optionally, one item of data originally |
| supplied by the caller of the matching function. The callout function |
| may cause matching to proceed, to backtrack, or to fail altogether. A |
| complete description of the interface to the callout function is given |
| in the pcrecallout documentation. |
|
|
Perl 5.10 introduced a number of "Special Backtracking Control Verbs", |
|
which are described in the Perl documentation as "experimental and sub- |
|
ject to change or removal in a future version of Perl". It goes on to |
|
say: "Their usage in production code should be noted to avoid problems |
|
during upgrades." The same remarks apply to the PCRE features described |
|
in this section. |
|
|
|
Since these verbs are specifically related to backtracking, most of | BACKTRACKING CONTROL |
them can be used only when the pattern is to be matched using | |
pcre_exec(), which uses a backtracking algorithm. With the exception of | |
(*FAIL), which behaves like a failing negative assertion, they cause an | |
error if encountered by pcre_dfa_exec(). | |
|
|
If any of these verbs are used in an assertion or in a subpattern that | Perl 5.10 introduced a number of "Special Backtracking Control Verbs", |
is called as a subroutine (whether or not recursively), their effect is | which are still described in the Perl documentation as "experimental |
confined to that subpattern; it does not extend to the surrounding pat- | and subject to change or removal in a future version of Perl". It goes |
tern, with one exception: the name from a *(MARK), (*PRUNE), or (*THEN) | on to say: "Their usage in production code should be noted to avoid |
that is encountered in a successful positive assertion is passed back | problems during upgrades." The same remarks apply to the PCRE features |
when a match succeeds (compare capturing parentheses in assertions). | described in this section. |
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- | The new verbs make use of what was previously invalid syntax: an open- |
ing parenthesis followed by an asterisk. They are generally of the form |
ing parenthesis followed by an asterisk. They are generally of the form |
(*VERB) or (*VERB:NAME). Some may take either form, with differing be- | (*VERB) or (*VERB:NAME). Some may take either form, possibly behaving |
haviour, depending on whether or not an argument is present. A name is | differently depending on whether or not a name is present. A name is |
any sequence of characters that does not include a closing parenthesis. |
any sequence of characters that does not include a closing parenthesis. |
If the name is empty, that is, if the closing parenthesis immediately | The maximum length of name is 255 in the 8-bit library and 65535 in the |
follows the colon, the effect is as if the colon were not there. Any | 16-bit and 32-bit libraries. If the name is empty, that is, if the |
number of these verbs may occur in a pattern. | 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 |
|
them can be used only when the pattern is to be matched using one of |
|
the traditional matching functions, because these use a backtracking |
|
algorithm. With the exception of (*FAIL), which behaves like a failing |
|
negative assertion, the backtracking control verbs cause an error if |
|
encountered by a DFA matching function. |
|
|
|
The behaviour of these verbs in repeated groups, assertions, and in |
|
subpatterns called as subroutines (whether or not recursively) is docu- |
|
mented below. |
|
|
|
Optimizations that affect backtracking verbs |
|
|
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. |
Line 5716 BACKTRACKING CONTROL
|
Line 7095 BACKTRACKING CONTROL
|
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- |
Line 5750 BACKTRACKING CONTROL
|
Line 7133 BACKTRACKING CONTROL
|
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 via the pcre_extra data | (*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to |
structure, as described in the section on pcre_extra in the pcreapi | the caller as described in the section entitled "Extra data for |
documentation. Here is an example of pcretest output, where the /K mod- | pcre_exec()" in the pcreapi documentation. Here is an example of |
ifier requests 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 5765 BACKTRACKING CONTROL
|
Line 7149 BACKTRACKING CONTROL
|
MK: B |
MK: B |
|
|
The (*MARK) name is tagged with "MK:" in this output, and in this exam- |
The (*MARK) name is tagged with "MK:" in this output, and in this exam- |
ple it indicates which of the two alternatives matched. This is a more | ple it indicates which of the two alternatives matched. This is a more |
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 |
|
|
Line 5816 BACKTRACKING CONTROL
|
Line 7209 BACKTRACKING CONTROL
|
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. |
|
|
Note that (*COMMIT) at the start of a pattern is not the same as an | If there is more than one backtracking verb in a pattern, a different |
anchor, unless PCRE's start-of-match optimizations are turned off, as | one that follows (*COMMIT) may be triggered first, so merely 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 |
| anchor, unless PCRE's start-of-match optimizations are turned off, as |
shown in this pcretest example: |
shown in this pcretest example: |
|
|
re> /(*COMMIT)abc/ |
re> /(*COMMIT)abc/ |
Line 5826 BACKTRACKING CONTROL
|
Line 7224 BACKTRACKING CONTROL
|
xyzabc\Y |
xyzabc\Y |
No match |
No match |
|
|
PCRE knows that any match must start with "a", so the optimization | PCRE knows that any match must start with "a", so the optimization |
skips along the subject to "a" before running the first match attempt, | skips along the subject to "a" before running the first match attempt, |
which succeeds. When the optimization is disabled by the \Y escape in | which succeeds. When the optimization is disabled by the \Y escape in |
the second subject, the match starts at "x" and so the (*COMMIT) causes |
the second subject, the match starts at "x" and so the (*COMMIT) causes |
it to fail without trying any other starting points. |
it to fail without trying any other starting points. |
|
|
(*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 |
Line 5866 BACKTRACKING CONTROL
|
Line 7269 BACKTRACKING CONTROL
|
|
|
(*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 |
backtrack into A; instead it moves to the next alternative, that is, D. |
backtrack into A; instead it moves to the next alternative, that is, D. |
However, if the subpattern containing (*THEN) is given an alternative, | However, if the subpattern containing (*THEN) is given an alternative, |
it behaves differently: |
it behaves differently: |
|
|
A (B(*THEN)C | (*FAIL)) | D |
A (B(*THEN)C | (*FAIL)) | D |
|
|
The effect of (*THEN) is now confined to the inner subpattern. After a | The effect of (*THEN) is now confined to the inner subpattern. After a |
failure in C, matching moves to (*FAIL), which causes the whole subpat- |
failure in C, matching moves to (*FAIL), which causes the whole subpat- |
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: |
|
|
^.*? (?(?=a) a | b(*THEN)c ) |
^.*? (?(?=a) a | b(*THEN)c ) |
|
|
If the subject is "ba", this pattern does not match. Because .*? is | If the subject is "ba", this pattern does not match. Because .*? is |
ungreedy, it initially matches zero characters. The condition (?=a) | ungreedy, it initially matches zero characters. The condition (?=a) |
then fails, the character "b" is matched, but "c" is not. At this | then fails, the character "b" is matched, but "c" is not. At this |
point, matching does not backtrack to .*? as might perhaps be expected | point, matching does not backtrack to .*? as might perhaps be expected |
from the presence of the | character. The conditional subpattern is | from the presence of the | character. The conditional subpattern is |
part of the single alternative that comprises the whole pattern, and so |
part of the single alternative that comprises the whole pattern, and so |
the match fails. (If there was a backtrack into .*?, allowing it to | the match fails. (If there was a backtrack into .*?, allowing it to |
match "b", the match would succeed.) |
match "b", the match would succeed.) |
|
|
The verbs just described provide four different "strengths" of control | The verbs just described provide four different "strengths" of control |
when subsequent matching fails. (*THEN) is the weakest, carrying on the |
when subsequent matching fails. (*THEN) is the weakest, carrying on the |
match at the next alternative. (*PRUNE) comes next, failing the match | match at the next alternative. (*PRUNE) comes next, failing the match |
at the current starting position, but allowing an advance to the next | at the current starting position, but allowing an advance to the next |
character (for an unanchored pattern). (*SKIP) is similar, except that | character (for an unanchored pattern). (*SKIP) is similar, except that |
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), pcre32(3). |
|
|
|
|
AUTHOR |
AUTHOR |
Line 5960 AUTHOR
|
Line 7435 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 29 November 2011 | Last updated: 26 April 2013 |
Copyright (c) 1997-2011 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- |
ported by PCRE are described in the pcrepattern documentation. This |
ported by PCRE are described in the pcrepattern documentation. This |
document contains just a quick-reference summary of the syntax. | document contains a quick-reference summary of the syntax. |
|
|
|
|
QUOTING |
QUOTING |
Line 5990 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 6003 CHARACTER TYPES
|
Line 7478 CHARACTER TYPES
|
|
|
. any character except newline; |
. any character except newline; |
in dotall mode, any character whatsoever |
in dotall mode, any character whatsoever |
\C one byte, even in UTF-8 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 UTF-8 mode. However, this can be changed by setting | characters, even in a UTF mode. However, this can be changed by setting |
the PCRE_UCP option. |
the PCRE_UCP option. |
|
|
|
|
Line 6078 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 6117 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 6207 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 (PCRE_UTF8) | (*UTF8) set UTF-8 mode: 8-bit library (PCRE_UTF8) |
| (*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 6277 BACKTRACKING CONTROL
|
Line 7761 BACKTRACKING CONTROL
|
|
|
(*ACCEPT) force successful match |
(*ACCEPT) force successful match |
(*FAIL) force backtrack; synonym (*F) |
(*FAIL) force backtrack; synonym (*F) |
|
(*MARK:NAME) set name to be passed back; synonym (*:NAME) |
|
|
The following act only when a subsequent match failure causes a back- |
The following act only when a subsequent match failure causes a back- |
track to reach them. They all force a match failure, but they differ in |
track to reach them. They all force a match failure, but they differ in |
Line 6285 BACKTRACKING CONTROL
|
Line 7770 BACKTRACKING CONTROL
|
|
|
(*COMMIT) overall failure, no advance of starting point |
(*COMMIT) overall failure, no advance of starting point |
(*PRUNE) advance to next starting character |
(*PRUNE) advance to next starting character |
(*SKIP) advance start to current matching position | (*PRUNE:NAME) equivalent to (*MARK:NAME)(*PRUNE) |
| (*SKIP) advance to current matching position |
| (*SKIP:NAME) advance to position corresponding to an earlier |
| (*MARK:NAME); if not found, the (*SKIP) is ignored |
(*THEN) local failure, backtrack to next alternation |
(*THEN) local failure, backtrack to next alternation |
|
(*THEN:NAME) equivalent to (*MARK:NAME)(*THEN) |
|
|
|
|
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_...) or (*UTF8) 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 6304 NEWLINE CONVENTIONS
|
Line 7793 NEWLINE CONVENTIONS
|
WHAT \R MATCHES |
WHAT \R MATCHES |
|
|
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 |
(*...) option that sets the newline convention or UTF-8 or UCP mode. | (*...) option that sets the newline convention or a UTF or UCP mode. |
|
|
(*BSR_ANYCRLF) CR, LF, or CRLF |
(*BSR_ANYCRLF) CR, LF, or CRLF |
(*BSR_UNICODE) any Unicode newline sequence |
(*BSR_UNICODE) any Unicode newline sequence |
Line 6330 AUTHOR
|
Line 7819 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 21 November 2010 | Last updated: 26 April 2013 |
Copyright (c) 1997-2010 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 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. |
|
|
In order process UTF-8 strings, you must build PCRE to include UTF-8 | |
support in the code, and, in addition, you must call pcre_compile() | UTF-8 SUPPORT |
with the PCRE_UTF8 option flag, or the pattern must start with the | |
sequence (*UTF8). When either of these is the case, both the pattern | 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 |
| the PCRE_UTF8 option flag, or the pattern must start with the sequence |
| (*UTF8) or (*UTF). When either of these is the case, both the pattern |
and any subject strings that are matched against it are treated as |
and any subject strings that are matched against it are treated as |
UTF-8 strings instead of strings of 1-byte characters. PCRE does not | UTF-8 strings instead of strings of individual 1-byte characters. |
support any other formats (in particular, it does not support UTF-16). | |
|
|
If you compile PCRE with UTF-8 support, but do not use it at run time, |
|
the library will be a bit bigger, but the additional run time overhead |
|
is limited to testing the PCRE_UTF8 flag occasionally, so should not be |
|
very big. |
|
|
|
|
UTF-16 AND UTF-32 SUPPORT |
|
|
|
In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit |
|
or 32-bit library with UTF support, and, in addition, you must call |
|
pcre16_compile() or pcre32_compile() with the PCRE_UTF16 or PCRE_UTF32 |
|
option flag, as appropriate. Alternatively, the pattern must start with |
|
the sequence (*UTF16), (*UTF32), as appropriate, or (*UTF), which can |
|
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 |
|
|
|
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 |
|
is limited to testing the PCRE_UTF[8|16|32] flag occasionally, so |
|
should not be very big. |
|
|
|
|
|
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-8 support), the escape sequences \p{..}, \P{..}, and \X are sup- | UTF support), the escape sequences \p{..}, \P{..}, and \X can be used. |
ported. The available properties that can be tested are limited to the | The available properties that can be tested are limited to the general |
general category properties such as Lu for an upper case letter or Nd | category properties such as Lu for an upper case letter or Nd for a |
for a decimal number, the Unicode script names such as Arabic or Han, | decimal number, the Unicode script names such as Arabic or Han, and the |
and the derived properties Any and L&. A full list is given in the | derived properties Any and L&. Full lists is given in the pcrepattern |
pcrepattern documentation. Only the short names for properties are sup- | and pcresyntax documentation. Only the short names for properties are |
ported. For example, \p{L} matches a letter. Its Perl synonym, \p{Let- | supported. For example, \p{L} matches a letter. Its Perl synonym, |
ter}, is not supported. Furthermore, in Perl, many properties may | \p{Letter}, is not supported. Furthermore, in Perl, many properties |
optionally be prefixed by "Is", for compatibility with Perl 5.6. PCRE | may optionally be prefixed by "Is", for compatibility with Perl 5.6. |
does not support this. | PCRE does not support this. |
|
|
Validity of UTF-8 strings |
Validity of UTF-8 strings |
|
|
When you set the PCRE_UTF8 flag, the strings passed as patterns and | When you set the PCRE_UTF8 flag, the byte strings passed as patterns |
subjects are (by default) checked for validity on entry to the relevant | and subjects are (by default) checked for validity on entry to the rel- |
functions. From release 7.3 of PCRE, the check is according the rules | evant functions. The entire string is checked before any other process- |
of RFC 3629, which are themselves derived from the Unicode specifica- | ing takes place. From release 7.3 of PCRE, the check is according the |
tion. Earlier releases of PCRE followed the rules of RFC 2279, which | rules of RFC 3629, which are themselves derived from the Unicode speci- |
allows the full range of 31-bit values (0 to 0x7FFFFFFF). The current | fication. Earlier releases of PCRE followed the rules of RFC 2279, |
check allows only values in the range U+0 to U+10FFFF, excluding U+D800 | which allows the full range of 31-bit values (0 to 0x7FFFFFFF). The |
to U+DFFF. | current check allows only values in the range U+0 to U+10FFFF, exclud- |
| 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 "Low Surrogate Area" of Unicode, of | Characters in the "Surrogate Area" of Unicode are reserved for use by |
which the Unicode Standard says this: "The Low Surrogate Area does not | UTF-16, where they are used in pairs to encode codepoints with values |
contain any character assignments, consequently no character code | greater than 0xFFFF. The code points that are encoded by UTF-16 pairs |
charts or namelists are provided for this area. Surrogates are reserved | are available independently in the UTF-8 and UTF-32 encodings. (In |
for use with UTF-16 and then must be used in pairs." The code points | other words, the whole surrogate thing is a fudge for UTF-16 which |
that are encoded by UTF-16 pairs are available as independent code | unfortunately messes up UTF-8 and UTF-32.) |
points in the UTF-8 encoding. (In other words, the whole surrogate | |
thing is a fudge for UTF-16 which unfortunately messes up UTF-8.) | |
|
|
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. | |
|
|
General comments about UTF-8 mode | Validity of UTF-16 strings |
|
|
1. An unbraced hexadecimal escape sequence (such as \xb3) matches a | When you set the PCRE_UTF16 flag, the strings of 16-bit data units that |
two-byte UTF-8 character if the value is greater than 127. | are passed as patterns and subjects are (by default) checked for valid- |
| ity on entry to the relevant functions. Values other than those in the |
| surrogate range U+D800 to U+DFFF are independent code points. Values in |
| the surrogate range must be used in pairs in the correct manner. |
|
|
2. Octal numbers up to \777 are recognized, and match two-byte UTF-8 | If an invalid UTF-16 string is passed to PCRE, an error return is |
characters for values greater than \177. | given. At compile time, the only additional information is the offset |
| 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 |
| well as a more detailed reason code if the caller has provided memory |
| in which to do this. |
|
|
3. Repeat quantifiers apply to complete UTF-8 characters, not to indi- | In some situations, you may already know that your strings are valid, |
vidual bytes, for example: \x{100}{3}. | and therefore want to skip these checks in order to improve perfor- |
| mance. If you set the PCRE_NO_UTF16_CHECK flag at compile time or at |
| 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 |
| diagnose an invalid UTF-16 string. However, if an invalid string is |
| passed, the result is undefined. |
|
|
4. The dot metacharacter matches one UTF-8 character instead of a sin- | Validity of UTF-32 strings |
gle byte. | |
|
|
5. The escape sequence \C can be used to match a single byte in UTF-8 | When you set the PCRE_UTF32 flag, the strings of 32-bit data units that |
mode, but its use can lead to some strange effects because it breaks up | are passed as patterns and subjects are (by default) checked for valid- |
multibyte characters (see the description of \C in the pcrepattern doc- | ity on entry to the relevant functions. This check allows only values |
umentation). The use of \C is not supported in the alternative matching | in the range U+0 to U+10FFFF, excluding the surrogate area U+D800 to |
function pcre_dfa_exec(), nor is it supported in UTF-8 mode by the JIT | U+DFFF. |
optimization of pcre_exec(). If JIT optimization is requested for a | |
UTF-8 pattern that contains \C, it will not succeed, and so the match- | |
ing will be carried out by the normal interpretive function. | |
|
|
6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly | 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 |
| |
| 1. Codepoints less than 256 can be specified in patterns by either |
| braced or unbraced hexadecimal escape sequences (for example, \x{b3} or |
| \xb3). Larger values have to use braced sequences. |
| |
| 2. Octal numbers up to \777 are recognized, and in UTF-8 mode they |
| match two-byte characters for values greater than \177. |
| |
| 3. Repeat quantifiers apply to complete UTF characters, not to individ- |
| ual data units, for example: \x{100}{3}. |
| |
| 4. The dot metacharacter matches one UTF character instead of a single |
| data unit. |
| |
| 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, or a single 32-bit |
| data unit in UTF-32 mode, but its use can lead to some strange effects |
| because it breaks up multi-unit characters (see the description of \C |
| in the pcrepattern documentation). The use of \C is not supported in |
| the alternative matching function pcre[16|32]_dfa_exec(), nor is it |
| supported in UTF mode by the JIT optimization of pcre[16|32]_exec(). If |
| JIT optimization is requested for a UTF pattern that contains \C, it |
| 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 |
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 before, all with values less than 256. This remains true even | set as in non-UTF mode, all with values less than 256. This remains |
when PCRE is built to include Unicode property support, because to do | true even when PCRE is built to include Unicode property support, |
otherwise would slow down PCRE in many common cases. Note in particular | because to do otherwise would slow down PCRE in many common cases. Note |
that this applies to \b and \B, because they are defined in terms of \w | in particular that this applies to \b and \B, because they are defined |
and \W. If you really want to test for a wider sense of, say, "digit", | in terms of \w and \W. If you really want to test for a wider sense of, |
you can use explicit Unicode property tests such as \p{Nd}. Alterna- | say, "digit", you can use explicit Unicode property tests such as |
tively, if you set the PCRE_UCP option, the way that the character | \p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that the |
escapes work is changed so that Unicode properties are used to deter- | character escapes work is changed so that Unicode properties are used |
mine which characters match. There are more details in the section on | to determine which characters match. There are more details in the sec- |
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 6484 AUTHOR
|
Line 8038 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 19 October 2011 | Last updated: 27 February 2013 |
Copyright (c) 1997-2011 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 |
speed up pattern matching. However, it comes at the cost of extra pro- |
speed up pattern matching. However, it comes at the cost of extra pro- |
cessing before the match is performed. Therefore, it is of most benefit |
cessing before the match is performed. Therefore, it is of most benefit |
when the same pattern is going to be matched many times. This does not |
when the same pattern is going to be matched many times. This does not |
necessarily mean many calls of pcre_exec(); if the pattern is not | necessarily mean many calls of a matching function; if the pattern is |
anchored, matching attempts may take place many times at various posi- | not anchored, matching attempts may take place many times at various |
tions in the subject, even for a single call to pcre_exec(). If the | positions in the subject, even for a single call. Therefore, if the |
subject string is very long, it may still pay to use JIT for one-off |
subject string is very long, it may still pay to use JIT for one-off |
matches. |
matches. |
|
|
JIT support applies only to the traditional matching function, | JIT support applies only to the traditional Perl-compatible matching |
pcre_exec(). It does not apply when pcre_dfa_exec() is being used. The | function. It does not apply when the DFA matching function is being |
code for this support was written by Zoltan Herczeg. | used. The code for this support was written by Zoltan Herczeg. |
|
|
|
|
|
8-BIT, 16-BIT AND 32-BIT SUPPORT |
|
|
|
JIT support is available for all of the 8-bit, 16-bit and 32-bit PCRE |
|
libraries. To keep this documentation simple, only the 8-bit interface |
|
is described in what follows. If you are using the 16-bit library, sub- |
|
stitute the 16-bit functions and 16-bit structures (for example, |
|
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 |
|
|
JIT support is an optional feature of PCRE. The "configure" option |
JIT support is an optional feature of PCRE. The "configure" option |
Line 6523 AVAILABILITY OF JIT SUPPORT
|
Line 8088 AVAILABILITY OF JIT SUPPORT
|
ARM v5, v7, and Thumb2 |
ARM v5, v7, and Thumb2 |
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 (experimental) | 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 6552 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 6571 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 6602 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 6690 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 6722 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 6773 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 6782 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 6817 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 6831 AUTHOR
|
Line 8451 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 26 November 2011 | Last updated: 17 March 2013 |
Copyright (c) 1997-2011 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 | In normal use of PCRE, if the subject string that is passed to a match- |
pcre_exec() or pcre_dfa_exec() matches as far as it goes, but is too | ing function matches as far as it goes, but is too short to match the |
short to match the entire pattern, PCRE_ERROR_NOMATCH is returned. | entire pattern, PCRE_ERROR_NOMATCH is returned. There are circumstances |
There are circumstances where it might be helpful to distinguish this | where it might be helpful to distinguish this case from other cases in |
case from other cases in which there is no match. | which there is no match. |
|
|
Consider, for example, an application where a human is required to type |
Consider, for example, an application where a human is required to type |
in data for a field with specific formatting requirements. An example |
in data for a field with specific formatting requirements. An example |
Line 6867 PARTIAL MATCHING IN PCRE
|
Line 8487 PARTIAL MATCHING IN PCRE
|
available at once. |
available at once. |
|
|
PCRE supports partial matching by means of the PCRE_PARTIAL_SOFT and |
PCRE supports partial matching by means of the PCRE_PARTIAL_SOFT and |
PCRE_PARTIAL_HARD options, which can be set when calling pcre_exec() or | PCRE_PARTIAL_HARD options, which can be set when calling any of the |
pcre_dfa_exec(). For backwards compatibility, PCRE_PARTIAL is a synonym | matching functions. For backwards compatibility, PCRE_PARTIAL is a syn- |
for PCRE_PARTIAL_SOFT. The essential difference between the two options | onym for PCRE_PARTIAL_SOFT. The essential difference between the two |
is whether or not a partial match is preferred to an alternative com- | options is whether or not a partial match is preferred to an alterna- |
plete match, though the details differ between the two matching func- | tive complete match, though the details differ between the two types of |
tions. If both options are set, PCRE_PARTIAL_HARD takes precedence. | matching function. If both options are set, PCRE_PARTIAL_HARD takes |
| precedence. |
|
|
Setting a partial matching option for pcre_exec() disables the use of | If you want to use partial matching with just-in-time optimized code, |
any just-in-time code that was set up by calling pcre_study() 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 byte in a pattern, and | |
abandons matching immediately if such a byte is not present in the sub- | PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE |
ject string. This optimization cannot be used for a subject string that | PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE |
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 | PCRE_STUDY_JIT_COMPILE should also be set if you are going to run non- |
matching function on shorter strings. This optimization is also dis- | 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 |
| 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 |
| matching function on shorter strings. This optimization is also dis- |
abled for partial matching. |
abled for partial matching. |
|
|
|
|
PARTIAL MATCHING USING pcre_exec() | PARTIAL MATCHING USING pcre_exec() OR pcre[16|32]_exec() |
|
|
A partial match occurs during a call to pcre_exec() when the end of the | A partial match occurs during a call to pcre_exec() or |
subject string is reached successfully, but matching cannot continue | pcre[16|32]_exec() when the end of the subject string is reached suc- |
because more characters are needed. However, at least one character in | cessfully, but matching cannot continue because more characters are |
the subject must have been inspected. This character need not form part | needed. However, at least one character in the subject must have been |
of the final matched string; lookbehind assertions and the \K escape | inspected. This character need not form part of the final matched |
sequence provide ways of inspecting characters before the start of a | string; lookbehind assertions and the \K escape sequence provide ways |
matched substring. The requirement for inspecting at least one charac- | of inspecting characters before the start of a matched substring. The |
ter exists because an empty string can always be matched; without such | requirement for inspecting at least one character exists because an |
a restriction there would always be a partial match of an empty string | empty string can always be matched; without such a restriction there |
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 pcre_exec() | If there are at least two slots in the offsets vector when a partial |
returns with a partial match, the first slot is set to the offset of | match is returned, the first slot is set to the offset of the earliest |
the earliest character that was inspected when the partial match was | character that was inspected. For convenience, the second offset points |
found. For convenience, the second offset points to the end of the sub- | to the end of the subject so that a substring can easily be identified. |
ject 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() | PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre[16|32]_exec() |
|
|
If PCRE_PARTIAL_SOFT is set when pcre_exec() identifies a partial | If PCRE_PARTIAL_SOFT is set when pcre_exec() or pcre[16|32]_exec() |
match, the partial match is remembered, but matching continues as nor- | identifies a partial match, the partial match is remembered, but match- |
mal, and other alternatives in the pattern are tried. If no complete | ing continues as normal, and other alternatives in the pattern are |
match can be found, pcre_exec() returns PCRE_ERROR_PARTIAL instead of | tried. If no complete match can be found, PCRE_ERROR_PARTIAL is |
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() | PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre[16|32]_exec() |
|
|
If PCRE_PARTIAL_HARD is set for pcre_exec(), it returns PCRE_ERROR_PAR- | If PCRE_PARTIAL_HARD is set for pcre_exec() or pcre[16|32]_exec(), |
TIAL as soon as a partial match is found, without continuing to search | PCRE_ERROR_PARTIAL is returned as soon as a partial match is found, |
for possible complete matches. This option is "hard" because it prefers | without continuing to search for possible complete matches. This option |
an earlier partial match over a later complete match. For this reason, | is "hard" because it prefers an earlier partial match over a later com- |
the assumption is made that the end of the supplied subject string may | plete match. For this reason, the assumption is made that the end of |
not be the true end of the available data, and so, if \z, \Z, \b, \B, | the supplied subject string may not be the true end of the available |
or $ are encountered at the end of the subject, the result is | data, and so, if \z, \Z, \b, \B, or $ are encountered at the end of the |
PCRE_ERROR_PARTIAL. | subject, the result is PCRE_ERROR_PARTIAL, provided that at least one |
| character in the subject has been inspected. |
|
|
Setting PCRE_PARTIAL_HARD also affects the way pcre_exec() checks UTF-8 | Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16 subject |
subject strings for validity. Normally, an invalid UTF-8 sequence | strings are checked for validity. Normally, an invalid sequence causes |
causes the error PCRE_ERROR_BADUTF8. However, in the special case of a | the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the |
truncated UTF-8 character at the end of the subject, PCRE_ERROR_SHORT- | special case of a truncated character at the end of the subject, |
UTF8 is returned when PCRE_PARTIAL_HARD is set. | PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when |
| 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 pcre_exec() | In this case the result is always a complete match because that is |
finds that first, and it never continues after finding a match. It | found first, and matching never continues after finding a complete |
might be easier to follow this explanation by thinking of the two pat- | match. It might be easier to follow this explanation by thinking of the |
terns 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" when pcre_exec() is | The second pattern will never match "dogsbody", because it will always |
used, because it will always find the shorter match first. | find the shorter match first. |
|
|
|
|
PARTIAL MATCHING USING pcre_dfa_exec() | PARTIAL MATCHING USING pcre_dfa_exec() OR pcre[16|32]_dfa_exec() |
|
|
The pcre_dfa_exec() function moves along the subject string character | The DFA functions move along the subject string character by character, |
by character, without backtracking, searching for all possible matches | without backtracking, searching for all possible matches simultane- |
simultaneously. If the end of the subject is reached before the end of | ously. If the end of the subject is reached before the end of the pat- |
the pattern, there is the possibility of a partial match, again pro- | tern, there is the possibility of a partial match, again provided that |
vided 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 pcre_dfa_exec() always searches 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, its be- | there is no difference between greedy and ungreedy repetition, their |
haviour is different from pcre_exec when PCRE_PARTIAL_HARD is set. Con- | behaviour is different from the standard functions when PCRE_PAR- |
sider the string "dog" matched against the ungreedy pattern shown | TIAL_HARD is set. Consider the string "dog" matched against the |
above: | ungreedy pattern shown above: |
|
|
/dog(sbody)??/ |
/dog(sbody)??/ |
|
|
Whereas pcre_exec() stops as soon as it finds the complete match for | Whereas the standard functions stop as soon as they find the complete |
"dog", pcre_dfa_exec() also finds the partial match for "dogsbody", and | match for "dog", the DFA functions also find the partial match for |
so returns 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, pcre_exec() carries on with normal matching, which matches \b | However, normal matching carries on, and \b matches at the end of the |
at the end of the subject when the last character is a letter, thus | subject when the last character is a letter, so a complete match is |
finding a complete match. The result, therefore, is not PCRE_ERROR_PAR- | found. The result, therefore, is not PCRE_ERROR_PARTIAL. Using |
TIAL. The same thing happens with pcre_dfa_exec(), because it also | PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because |
finds the complete match. | then the partial match takes precedence. |
|
|
Using PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, |
|
because 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 pcre_exec() can be requested | longer apply, and partial matching with can be requested for any pat- |
for any pattern. | 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 |
Line 7080 EXAMPLE OF PARTIAL MATCHING USING PCRETEST
|
Line 8713 EXAMPLE OF PARTIAL MATCHING USING PCRETEST
|
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 when pcre_dfa_exec() 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() | MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre[16|32]_dfa_exec() |
|
|
When a partial match has been found using pcre_dfa_exec(), it is possi- | When a partial match has been found using a DFA matching function, it |
ble to continue the match by providing additional subject data and | is possible to continue the match by providing additional subject data |
calling pcre_dfa_exec() 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 pcre_dfa_exec()): | 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$/ |
re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ |
data> 23ja\P\D |
data> 23ja\P\D |
Line 7112 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()
|
Line 8745 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()
|
|
|
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 | This facility can be used to pass very long subject strings to the DFA |
pcre_dfa_exec(). | matching functions. |
|
|
|
|
MULTI-SEGMENT MATCHING WITH pcre_exec() | MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre[16|32]_exec() |
|
|
From release 8.00, pcre_exec() can also be used to do multi-segment | From release 8.00, the standard matching functions can also be used to |
matching. Unlike pcre_dfa_exec(), it is not possible to restart the | do multi-segment matching. Unlike the DFA functions, it is not possible |
previous match with a new segment of data. Instead, new data must be | to restart the previous match with a new segment of data. Instead, new |
added to the previous subject string, and the entire match re-run, | data must be added to the previous subject string, and the entire match |
starting from the point where the partial match occurred. Earlier data | re-run, starting from the point where the partial match occurred. Ear- |
can be discarded. It is best to use PCRE_PARTIAL_HARD in this situa- | lier data can be discarded. |
tion, because it does 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 dates: | |
|
|
|
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 |
|
\z, \Z, \b, \B, and $. Consider an unanchored pattern that matches |
|
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 pcre_exec() again. Unlike | add on text from the next segment, and call the matching function |
pcre_dfa_exec(), the entire matching string must always be available, | again. Unlike the DFA matching functions, the entire matching string |
and the complete matching process occurs for each call, so more memory | must always be available, and the complete matching process occurs for |
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 will | with \b or \B, the string that is returned for a partial match includes |
include characters that precede the partially matched string itself, | characters that precede the start of what would be returned for a com- |
because these must be retained when adding on more characters for a | plete match, because it contains all the characters that were inspected |
subsequent matching attempt. | during the partial match. |
|
|
|
|
ISSUES WITH MULTI-SEGMENT MATCHING |
ISSUES WITH MULTI-SEGMENT MATCHING |
Line 7156 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 8791 ISSUES WITH MULTI-SEGMENT MATCHING
|
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- |
| acters to retain. Instead of subtracting the length of the longest |
| lookbehind from the earliest inspected character (offsets[0]), the |
| match start position (offsets[2]) should be used, and the next match |
| attempt started at the offsets[2] character by setting the startoffset |
| argument of pcre_exec() or pcre_dfa_exec(). |
| |
| For example, if the pattern "(?<=123)abc" is partially matched against |
| the string "xx123a", the three offset values returned are 2, 6, and 5. |
| This indicates that the matching process that gave a partial match |
| started at offset 5, but the characters "123a" were all inspected. The |
| maximum lookbehind for that pattern is 3, so taking that away from 5 |
| shows that we need only keep "123a", and the next match attempt can be |
| started at offset 3 (that is, at "a") when further characters have been |
| added. When the match start is not the earliest inspected character, |
| pcretest shows it explicitly: |
| |
| re> "(?<=123)abc" |
| data> xx123a\P\P |
| Partial match at offset 5: 123a |
| |
| 3. Because a partial match must always contain at least one character, |
| what might be considered a partial match of an empty string actually |
| gives a "no match" result. For example: |
| |
| 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 |
not always produce exactly the same result as matching over one single |
long string, especially when PCRE_PARTIAL_SOFT is used. The section |
long string, especially when PCRE_PARTIAL_SOFT is used. The section |
"Partial Matching and Word Boundaries" above describes an issue that |
"Partial Matching and Word Boundaries" above describes an issue that |
Line 7186 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 pcre_exec(), setting | The first data line passes the string "dogsb" to a standard matching |
the PCRE_PARTIAL_SOFT option. Although the string is a partial match | function, setting the PCRE_PARTIAL_SOFT option. Although the string is |
for "dogsbody", the result is not PCRE_ERROR_PARTIAL, because the | a partial match for "dogsbody", the result is not PCRE_ERROR_PARTIAL, |
shorter string "dog" is a complete match. Similarly, when the subject | because the shorter string "dog" is a complete match. Similarly, when |
is presented to pcre_dfa_exec() in several parts ("do" and "gsb" being | the subject is presented to a DFA matching function in several parts |
the first two) the match stops when "dog" has been found, and it is not | ("do" and "gsb" being the first two) the match stops when "dog" has |
possible to continue. On the other hand, if "dogsbody" is presented as | been found, and it is not possible to continue. On the other hand, if |
a single string, pcre_dfa_exec() finds both matches. | "dogsbody" is presented as a single string, a DFA matching function |
| 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 7207 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 with pcre_dfa_exec(). For example, consider | PCRE_DFA_RESTART is used. For example, consider this pattern: |
this pattern: | |
|
|
1234|3789 |
1234|3789 |
|
|
Line 7227 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 8900 ISSUES WITH MULTI-SEGMENT MATCHING
|
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 pcre_exec() is used, because the entire match has to | not a problem if a standard matching function is used, because the |
be rerun each time: | entire match has to be rerun each time: |
|
|
re> /1234|3789/ |
re> /1234|3789/ |
data> ABC123\P\P |
data> ABC123\P\P |
Line 7237 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 pcre_dfa_exec(). Another | running the entire match can also be used with the DFA matching func- |
possibility is to work with two buffers. If a partial match at offset n | tions. Another possibility is to work with two buffers. If a partial |
in the first buffer is followed by "no match" when PCRE_DFA_RESTART is | match at offset n in the first buffer is followed by "no match" when |
used on the second buffer, you can then try a new match starting at | PCRE_DFA_RESTART is used on the second buffer, you can then try a new |
offset n+1 in the first buffer. | match starting at offset n+1 in the first buffer. |
|
|
|
|
AUTHOR |
AUTHOR |
Line 7253 AUTHOR
|
Line 8926 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 26 August 2011 | Last updated: 20 February 2013 |
Copyright (c) 1997-2011 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 7273 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
|
Line 8946 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
|
run. If you are not using any private character tables (see the |
run. If you are not using any private character tables (see the |
pcre_maketables() documentation), this is relatively straightforward. |
pcre_maketables() documentation), this is relatively straightforward. |
If you are using private tables, it is a little bit more complicated. |
If you are using private tables, it is a little bit more complicated. |
However, if you are using the just-in-time optimization feature of | However, if you are using the just-in-time optimization feature, it is |
pcre_study(), it is not possible to save and reload the JIT data. | not possible to save and reload the JIT data. |
|
|
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. This works even if the new host has the | ent host and run them there. If the two hosts have different endianness |
opposite endianness to the one on which the patterns were compiled. | (byte order), you should run the pcre[16|32]_pat- |
There may be a small performance penalty, but it should be insignifi- | tern_to_host_byte_order() function on the new host before trying to |
cant. However, compiling regular expressions with one version of PCRE | match the pattern. The matching functions return PCRE_ERROR_BADENDIAN- |
for use with a different version is not guaranteed to work and may | NESS if they detect a pattern with the wrong endianness. |
cause crashes, and saving and restoring a compiled pattern loses any | |
JIT optimization data. | |
|
|
|
Compiling regular expressions with one version of PCRE for use with a |
|
different version is not guaranteed to work and may cause crashes, and |
|
saving and restoring a compiled pattern loses any JIT optimization |
|
data. |
|
|
|
|
SAVING A COMPILED PATTERN |
SAVING A COMPILED PATTERN |
|
|
The value returned by pcre_compile() points to a single block of memory | The value returned by pcre[16|32]_compile() points to a single block of |
that holds the compiled pattern and associated data. You can find the | memory that holds the compiled pattern and associated data. You can |
length of this block in bytes by calling pcre_fullinfo() with an argu- | find the length of this block in bytes by calling |
ment of PCRE_INFO_SIZE. You can then save the data in any appropriate | pcre[16|32]_fullinfo() with an argument of PCRE_INFO_SIZE. You can then |
manner. Here is sample code that compiles a pattern and writes it to a | save the data in any appropriate manner. Here is sample code for the |
file. It assumes that the variable fd refers to a file that is open for | 8-bit library that compiles a pattern and writes it to a file. It |
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 7307 SAVING A COMPILED PATTERN
|
Line 8983 SAVING A COMPILED PATTERN
|
rc = fwrite(re, 1, size, fd); |
rc = fwrite(re, 1, size, fd); |
if (rc != size) { ... handle errors ... } |
if (rc != size) { ... handle errors ... } |
|
|
In this example, the bytes that comprise the compiled pattern are | In this example, the bytes that comprise the compiled pattern are |
copied exactly. Note that this is binary data that may contain any of | copied exactly. Note that this is binary data that may contain any of |
the 256 possible byte values. On systems that make a distinction | the 256 possible byte values. On systems that make a distinction |
between binary and non-binary data, be sure that the file is opened for |
between binary and non-binary data, be sure that the file is opened for |
binary output. |
binary output. |
|
|
If you want to write more than one pattern to a file, you will have to | If you want to write more than one pattern to a file, you will have to |
devise a way of separating them. For binary data, preceding each pat- | devise a way of separating them. For binary data, preceding each pat- |
tern with its length is probably the most straightforward approach. | tern with its length is probably the most straightforward approach. |
Another possibility is to write out the data in hexadecimal instead of | Another possibility is to write out the data in hexadecimal instead of |
binary, one pattern to a line. |
binary, one pattern to a line. |
|
|
Saving compiled patterns in a file is only one possible way of storing | Saving compiled patterns in a file is only one possible way of storing |
them for later use. They could equally well be saved in a database, or | them for later use. They could equally well be saved in a database, or |
in the memory of some daemon process that passes them via sockets to | in the memory of some daemon process that passes them via sockets to |
the processes that want them. |
the processes that want them. |
|
|
If the pattern has been studied, it is also possible to save the normal |
If the pattern has been studied, it is also possible to save the normal |
study data in a similar way to the compiled pattern itself. However, if |
study data in a similar way to the compiled pattern itself. However, if |
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, pcre_study() | ronment. When studying generates additional information, |
returns a pointer to a pcre_extra data block. Its format is defined in | pcre[16|32]_study() returns a pointer to a pcre[16|32]_extra data |
the section on matching a pattern in the pcreapi documentation. The | block. Its format is defined in the section on matching a pattern in |
study_data field points to the binary study data, and this is what you | the pcreapi documentation. The study_data field points to the binary |
must save (not the pcre_extra block itself). The length of the study | study data, and this is what you must save (not the pcre[16|32]_extra |
data can be obtained by calling pcre_fullinfo() with an argument of | block itself). The length of the study data can be obtained by calling |
PCRE_INFO_STUDYSIZE. Remember to check that pcre_study() did return a | pcre[16|32]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remem- |
non-NULL value before trying to save the study data. | ber to check that pcre[16|32]_study() did return a non-NULL value |
| 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, you pass its pointer to pcre_exec() or | into main memory, called pcre[16|32]_pattern_to_host_byte_order() if |
pcre_dfa_exec() in the usual way. This should work even on another | necessary, you pass its pointer to pcre[16|32]_exec() or |
host, and even if that host has the opposite endianness to the one | pcre[16|32]_dfa_exec() in the usual way. |
where the pattern was compiled. | |
|
|
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_compile()), you | pattern was compiled (the tableptr argument of pcre[16|32]_compile()), |
must now pass a similar pointer to pcre_exec() or pcre_dfa_exec(), | you must now pass a similar pointer to pcre[16|32]_exec() or |
because the value saved with the compiled pattern will obviously be | pcre[16|32]_dfa_exec(), because the value saved with the compiled pat- |
nonsense. A field in a pcre_extra() block is used to pass this data, as | tern will obviously be nonsense. A field in a pcre[16|32]_extra() block |
described in the section on matching a pattern in the pcreapi documen- | is used to pass this data, as described in the section on matching a |
tation. | 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 | compiled, the pointer in the compiled pattern is NULL, which causes the |
pcre_exec() to use PCRE's internal tables. Thus, you do not need to | matching functions to use PCRE's internal tables. Thus, you do not need |
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_extra data block and set the study_data field to point to | your own pcre[16|32]_extra data block and set the study_data field to |
the reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA | point to the reloaded study data. You must also set the |
bit in the flags field to indicate that study data is present. Then | PCRE_EXTRA_STUDY_DATA bit in the flags field to indicate that study |
pass the pcre_extra block to pcre_exec() or pcre_dfa_exec() in the | data is present. Then pass the pcre[16|32]_extra block to the matching |
usual way. If the pattern was studied for just-in-time optimization, | function in the usual way. If the pattern was studied for just-in-time |
that data cannot be saved, and so is lost by a save/restore cycle. | optimization, that data cannot be saved, and so is lost by a |
| save/restore cycle. |
|
|
|
|
COMPATIBILITY WITH DIFFERENT PCRE RELEASES |
COMPATIBILITY WITH DIFFERENT PCRE RELEASES |
Line 7384 AUTHOR
|
Line 9061 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 26 August 2011 | Last updated: 24 June 2012 |
Copyright (c) 1997-2011 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 7405 PCRE PERFORMANCE
|
Line 9082 PCRE PERFORMANCE
|
|
|
COMPILED PATTERN MEMORY USAGE |
COMPILED PATTERN MEMORY USAGE |
|
|
Patterns are compiled by PCRE into a reasonably efficient byte code, so | Patterns are compiled by PCRE into a reasonably efficient interpretive |
that most simple patterns do not use much memory. However, there is one | code, so that most simple patterns do not use much memory. However, |
case where the memory usage of a compiled pattern can be unexpectedly | there is one case where the memory usage of a compiled pattern can be |
large. If a parenthesized subpattern has a quantifier with a minimum | unexpectedly large. If a parenthesized subpattern has a quantifier with |
greater than 1 and/or a limited maximum, the whole subpattern is | a minimum greater than 1 and/or a limited maximum, the whole subpattern |
repeated in the compiled code. For example, the pattern | is repeated in the compiled code. For example, the pattern |
|
|
(abc|def){2,4} |
(abc|def){2,4} |
|
|
Line 7428 COMPILED PATTERN MEMORY USAGE
|
Line 9105 COMPILED PATTERN MEMORY USAGE
|
|
|
((ab){1,1000}c){1,3} |
((ab){1,1000}c){1,3} |
|
|
uses 51K bytes when compiled. When PCRE is compiled with its default | uses 51K bytes when compiled using the 8-bit library. When PCRE is com- |
internal pointer size of two bytes, the size limit on a compiled pat- | piled with its default internal pointer size of two bytes, the size |
tern is 64K, and this is reached with the above pattern if the outer | limit on a compiled pattern is 64K data units, and this is reached with |
repetition is increased from 3 to 4. PCRE can be compiled to use larger | the above pattern if the outer repetition is increased from 3 to 4. |
internal pointers and thus handle larger compiled patterns, but it is | PCRE can be compiled to use larger internal pointers and thus handle |
better to try to rewrite your pattern to use less memory if you can. | larger compiled patterns, but it is better to try to rewrite your pat- |
| tern to use less memory if you can. |
|
|
One way of reducing the memory usage for such patterns is to make use | One way of reducing the memory usage for such patterns is to make use |
of PCRE's "subroutine" facility. Re-writing the above pattern as |
of PCRE's "subroutine" facility. Re-writing the above pattern as |
|
|
((ab)(?2){0,999}c)(?1){0,2} |
((ab)(?2){0,999}c)(?1){0,2} |
|
|
reduces the memory requirements to 18K, and indeed it remains under 20K |
reduces the memory requirements to 18K, and indeed it remains under 20K |
even with the outer repetition increased to 100. However, this pattern | even with the outer repetition increased to 100. However, this pattern |
is not exactly equivalent, because the "subroutine" calls are treated | is not exactly equivalent, because the "subroutine" calls are treated |
as atomic groups into which there can be no backtracking if there is a | as atomic groups into which there can be no backtracking if there is a |
subsequent matching failure. Therefore, PCRE cannot do this kind of | subsequent matching failure. Therefore, PCRE cannot do this kind of |
rewriting automatically. Furthermore, there is a noticeable loss of | rewriting automatically. Furthermore, there is a noticeable loss of |
speed when executing the modified pattern. Nevertheless, if the atomic | speed when executing the modified pattern. Nevertheless, if the atomic |
grouping is not a problem and the loss of speed is acceptable, this | grouping is not a problem and the loss of speed is acceptable, this |
kind of rewriting will allow you to process patterns that PCRE cannot | kind of rewriting will allow you to process patterns that PCRE cannot |
otherwise handle. |
otherwise handle. |
|
|
|
|
STACK USAGE AT RUN TIME |
STACK USAGE AT RUN TIME |
|
|
When pcre_exec() is used for matching, certain kinds of pattern can | When pcre_exec() or pcre[16|32]_exec() is used for matching, certain |
cause it to use large amounts of the process stack. In some environ- | kinds of pattern can cause it to use large amounts of the process |
ments the default process stack is quite small, and if it runs out the | stack. In some environments the default process stack is quite small, |
result is often SIGSEGV. This issue is probably the most frequently | and if it runs out the result is often SIGSEGV. This issue is probably |
raised problem with PCRE. Rewriting your pattern can often help. The | the most frequently raised problem with PCRE. Rewriting your pattern |
pcrestack documentation discusses this issue in detail. | can often help. The pcrestack documentation discusses this issue in |
| detail. |
|
|
|
|
PROCESSING TIME |
PROCESSING TIME |
Line 7474 PROCESSING TIME
|
Line 9153 PROCESSING TIME
|
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, |
partly for backwards compatibility, and partly for performance reasons. |
partly for backwards compatibility, and partly for performance reasons. |
However, you can set PCRE_UCP if you want Unicode character properties | However, you can set PCRE_UCP if you want Unicode character properties |
to be used. This can double the matching time for items such as \d, | to be used. This can double the matching time for items such as \d, |
when matched with pcre_exec(); the performance loss is less with | when matched with a traditional matching function; the performance loss |
pcre_dfa_exec(), and in both cases there is not much difference for \b. | is less with a DFA matching function, and in both cases there is not |
| much difference for \b. |
|
|
When a pattern begins with .* not in parentheses, or in parentheses |
When a pattern begins with .* not in parentheses, or in parentheses |
that are not the subject of a backreference, and the PCRE_DOTALL option |
that are not the subject of a backreference, and the PCRE_DOTALL option |
Line 7552 AUTHOR
|
Line 9231 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 16 May 2010 | Last updated: 25 August 2012 |
Copyright (c) 1997-2010 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 7582 SYNOPSIS OF POSIX API
|
Line 9261 SYNOPSIS OF POSIX API
|
|
|
DESCRIPTION |
DESCRIPTION |
|
|
This set of functions provides a POSIX-style API to the PCRE regular | This set of functions provides a POSIX-style API for the PCRE regular |
expression package. See the pcreapi documentation for a description of | expression 8-bit library. See the pcreapi documentation for a descrip- |
PCRE's native API, which contains much additional functionality. | tion of PCRE's native API, which contains much additional functional- |
| 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 |
Line 7815 AUTHOR
|
Line 9496 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 16 May 2010 | Last updated: 09 January 2012 |
Copyright (c) 1997-2010 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
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 7837 DESCRIPTION
|
Line 9518 DESCRIPTION
|
The C++ wrapper for PCRE was provided by Google Inc. Some additional |
The C++ wrapper for PCRE was provided by Google Inc. Some additional |
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. | sulted for further details. Note that the C++ wrapper supports only the |
| original 8-bit PCRE library. There is no 16-bit or 32-bit support at |
| present. |
|
|
|
|
MATCHING INTERFACE |
MATCHING INTERFACE |
Line 7995 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 (*) |
Line 8157 AUTHOR
|
Line 9840 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 17 March 2009 | Last updated: 08 January 2012 |
Minor typo fixed: 25 July 2011 | |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
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 8177 PCRE SAMPLE PROGRAM
|
Line 9859 PCRE SAMPLE PROGRAM
|
do not have a copy of the PCRE distribution, you can save this listing |
do not have a copy of the PCRE distribution, you can save this listing |
to re-create pcredemo.c. |
to re-create pcredemo.c. |
|
|
The program compiles the regular expression that is its first argument, | The demonstration program, which uses the original PCRE 8-bit library, |
and matches it against the subject string in its second argument. No | compiles the regular expression that is its first argument, and matches |
PCRE options are set, and default character tables are used. If match- | it against the subject string in its second argument. No PCRE options |
ing succeeds, the program outputs the portion of the subject that | are set, and default character tables are used. If matching succeeds, |
matched, together with the contents of any captured substrings. | the program outputs the portion of the subject that matched, together |
| with the contents of any captured substrings. |
|
|
If the -g option is given on the command line, the program then goes on |
If the -g option is given on the command line, the program then goes on |
to check for further matches of the same regular expression in the same |
to check for further matches of the same regular expression in the same |
subject string. The logic is a little bit tricky because of the possi- | subject string. The logic is a little bit tricky because of the possi- |
bility of matching an empty string. Comments in the code explain what | bility of matching an empty string. Comments in the code explain what |
is going on. |
is going on. |
|
|
If PCRE is installed in the standard include and library directories | If PCRE is installed in the standard include and library directories |
for your operating system, you should be able to compile the demonstra- |
for your operating system, you should be able to compile the demonstra- |
tion program using this command: |
tion program using this command: |
|
|
gcc -o pcredemo pcredemo.c -lpcre |
gcc -o pcredemo pcredemo.c -lpcre |
|
|
If PCRE is installed elsewhere, you may need to add additional options | If PCRE is installed elsewhere, you may need to add additional options |
to the command line. For example, on a Unix-like system that has PCRE | to the command line. For example, on a Unix-like system that has PCRE |
installed in /usr/local, you can compile the demonstration program | installed in /usr/local, you can compile the demonstration program |
using a command like this: |
using a command like this: |
|
|
gcc -o pcredemo -I/usr/local/include pcredemo.c \ |
gcc -o pcredemo -I/usr/local/include pcredemo.c \ |
-L/usr/local/lib -lpcre |
-L/usr/local/lib -lpcre |
|
|
In a Windows environment, if you want to statically link the program | In a Windows environment, if you want to statica In a Windows environment, if you want to statically link the program |
against a non-dll pcre.a file, you must uncomment the line that defines |
against a non-dll pcre.a file, you must uncomment the line that defines |
PCRE_STATIC before including pcre.h, because otherwise the pcre_mal- | PCRE_STATIC before including pcre.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. |
|
|
Once you have compiled and linked the demonstration program, you can | Once you have compiled and linked the demonstration program, you can |
run simple tests like this: |
run simple tests like this: |
|
|
./pcredemo 'cat|dog' 'the cat sat on the mat' |
./pcredemo 'cat|dog' 'the cat sat on the mat' |
./pcredemo -g 'cat|dog' 'the dog sat on the cat' |
./pcredemo -g 'cat|dog' 'the dog sat on the cat' |
|
|
Note that there is a much more comprehensive test program, called | Note that there is a much more comprehensive test program, called |
pcretest, which supports many more facilities for testing regular | pcretest, which supports many more facilities for testing regular |
expressions and the PCRE library. The pcredemo program is provided as a | expressions and both PCRE libraries. The pcredemo program is provided |
simple coding example. | as a simple coding example. |
|
|
If you try to run pcredemo when PCRE is not installed in the standard | If you try to run pcredemo when PCRE is not installed in the standard |
library directory, you may get an error like this on some operating | library directory, you may get an error like this on some operating |
systems (e.g. Solaris): |
systems (e.g. Solaris): |
|
|
ld.so.1: a.out: fatal: libpcre.so.0: open failed: No such file or | ld.so.1: a.out: fatal: libpcre.so.0: open failed: No such file or |
directory |
directory |
|
|
This is caused by the way shared library support works on those sys- | This is caused by the way shared library support works on those sys- |
tems. You need to add |
tems. You need to add |
|
|
-R/usr/local/lib |
-R/usr/local/lib |
Line 8244 AUTHOR
|
Line 9927 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 17 November 2010 | Last updated: 10 January 2012 |
Copyright (c) 1997-2010 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 65539 (sic) bytes if PCRE | The maximum length of a compiled pattern is approximately 64K data |
is compiled with the default internal linkage size of 2. If you want to | units (bytes for the 8-bit library, 32-bit units for the 32-bit |
| library, and 32-bit units for the 32-bit library) if PCRE is compiled |
| with the default internal linkage size of 2 bytes. If you want to |
process regular expressions that are truly enormous, you can compile |
process regular expressions that are truly enormous, you can compile |
PCRE with an internal linkage size of 3 or 4 (see the README file in | PCRE with an internal linkage size of 3 or 4 (when building the 16-bit |
the source distribution and the pcrebuild documentation for details). | or 32-bit library, 3 is rounded up to 4). See the README file in the |
In these cases the limit is substantially larger. However, the speed | source distribution and the pcrebuild documentation for details. In |
of execution is slower. | these cases the limit is substantially larger. However, the speed of |
| execution is slower. |
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All values in repeating quantifiers must be less than 65536. |
All values in repeating quantifiers must be less than 65536. |
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Line 8273 SIZE AND OTHER LIMITATIONS
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Line 9959 SIZE AND OTHER LIMITATIONS
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can be no more than 65535 capturing subpatterns. |
can be no more than 65535 capturing subpatterns. |
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There is a limit to the number of forward references to subsequent sub- |
There is a limit to the number of forward references to subsequent sub- |
patterns of around 200,000. Repeated forward references with fixed | patterns of around 200,000. Repeated forward references with fixed |
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. |
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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. |
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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. |
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Line 8298 AUTHOR
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Line 9988 AUTHOR
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REVISION |
REVISION |
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Last updated: 30 November 2011 | Last updated: 04 May 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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PCRESTACK(3) PCRESTACK(3) | PCRESTACK(3) Library Functions Manual PCRESTACK(3) |
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NAME |
NAME |
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
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PCRE DISCUSSION OF STACK USAGE |
PCRE DISCUSSION OF STACK USAGE |
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When you call pcre_exec(), it makes use of an internal function called | When you call pcre[16|32]_exec(), it makes use of an internal function |
match(). This calls itself recursively at branch points in the pattern, | called match(). This calls itself recursively at branch points in the |
in order to remember the state of the match so that it can back up and | pattern, in order to remember the state of the match so that it can |
try a different alternative if the first one fails. As matching pro- | back up and try a different alternative if the first one fails. As |
ceeds deeper and deeper into the tree of possibilities, the recursion | matching proceeds deeper and deeper into the tree of possibilities, the |
depth increases. The match() function is also called in other circum- | recursion depth increases. The match() function is also called in other |
stances, for example, whenever a parenthesized sub-pattern is entered, | circumstances, for example, whenever a parenthesized sub-pattern is |
and in certain cases of repetition. | entered, and in certain cases of repetition. |
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Not all calls of match() increase the recursion depth; for an item such |
Not all calls of match() increase the recursion depth; for an item such |
as a* it may be called several times at the same level, after matching |
as a* it may be called several times at the same level, after matching |
Line 8328 PCRE DISCUSSION OF STACK USAGE
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Line 10018 PCRE DISCUSSION OF STACK USAGE
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result of the current call (a "tail recursion"), the function is just |
result of the current call (a "tail recursion"), the function is just |
restarted instead. |
restarted instead. |
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The above comments apply when pcre_exec() is run in its normal inter- | The above comments apply when pcre[16|32]_exec() is run in its normal |
pretive manner. If the pattern was studied with the PCRE_STUDY_JIT_COM- | interpretive manner. If the pattern was studied with the |
PILE option, and just-in-time compiling was successful, and the options | PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was success- |
passed to pcre_exec() were not incompatible, the matching process uses | ful, and the options passed to pcre[16|32]_exec() were not incompati- |
the JIT-compiled code instead of the match() function. In this case, | ble, the matching process uses the JIT-compiled code instead of the |
the memory requirements are handled entirely differently. See the pcre- | match() function. In this case, the memory requirements are handled |
jit documentation for details. | entirely differently. See the pcrejit documentation for details. |
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The pcre_dfa_exec() function operates in an entirely different way, and | The pcre[16|32]_dfa_exec() function operates in an entirely different |
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_dfa_exec() is controlled by the amount of workspace it | complexity of pcre[16|32]_dfa_exec() is controlled by the amount of |
is given. However, it is possible to write patterns with runaway infi- | workspace it is given. However, it is possible to write patterns with |
nite recursions; such patterns will cause pcre_dfa_exec() to run out of | runaway infinite recursions; such patterns will cause |
stack. At present, there is no protection against this. | pcre[16|32]_dfa_exec() to run out of stack. At present, there is no |
| protection against this. |
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The comments that follow do NOT apply to pcre_dfa_exec(); they are rel- | The comments that follow do NOT apply to pcre[16|32]_dfa_exec(); they |
evant only for pcre_exec() without the JIT optimization. | are relevant only for pcre[16|32]_exec() without the JIT optimization. |
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Reducing pcre_exec()'s stack usage | Reducing pcre[16|32]_exec()'s stack usage |
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Each time that match() is actually called recursively, it uses memory | Each time that match() is actually called recursively, it uses memory |
from the process stack. For certain kinds of pattern and data, very | from the process stack. For certain kinds of pattern and data, very |
large amounts of stack may be needed, despite the recognition of "tail | large amounts of stack may be needed, despite the recognition of "tail |
recursion". You can often reduce the amount of recursion, and there- | recursion". You can often reduce the amount of recursion, and there- |
fore the amount of stack used, by modifying the pattern that is being | fore the amount of stack used, by modifying the pattern that is being |
matched. Consider, for example, this pattern: |
matched. Consider, for example, this pattern: |
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([^<]|<(?!inet))+ |
([^<]|<(?!inet))+ |
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It matches from wherever it starts until it encounters "<inet" or the | It matches from wherever it starts until it encounters "<inet" or the |
end of the data, and is the kind of pattern that might be used when | end of the data, and is the kind of pattern that might be used when |
processing an XML file. Each iteration of the outer parentheses matches |
processing an XML file. Each iteration of the outer parentheses matches |
either one character that is not "<" or a "<" that is not followed by | either one character that is not "<" or a "<" that is not followed by |
"inet". However, each time a parenthesis is processed, a recursion | "inet". However, each time a parenthesis is processed, a recursion |
occurs, so this formulation uses a stack frame for each matched charac- |
occurs, so this formulation uses a stack frame for each matched charac- |
ter. For a long string, a lot of stack is required. Consider now this | ter. For a long string, a lot of stack is required. Consider now this |
rewritten pattern, which matches exactly the same strings: |
rewritten pattern, which matches exactly the same strings: |
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([^<]++|<(?!inet))+ |
([^<]++|<(?!inet))+ |
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This uses very much less stack, because runs of characters that do not | This uses very much less stack, because runs of characters that do not |
contain "<" are "swallowed" in one item inside the parentheses. Recur- | contain "<" are "swallowed" in one item inside the parentheses. Recur- |
sion happens only when a "<" character that is not followed by "inet" | sion happens only when a "<" character that is not followed by "inet" |
is encountered (and we assume this is relatively rare). A possessive | is encountered (and we assume this is relatively rare). A possessive |
quantifier is used to stop any backtracking into the runs of non-"<" | quantifier is used to stop any backtracking into the runs of non-"<" |
characters, but that is not related to stack usage. |
characters, but that is not related to stack usage. |
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This example shows that one way of avoiding stack problems when match- | This example shows that one way of avoiding stack problems when match- |
ing long subject strings is to write repeated parenthesized subpatterns |
ing long subject strings is to write repeated parenthesized subpatterns |
to match more than one character whenever possible. |
to match more than one character whenever possible. |
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Compiling PCRE to use heap instead of stack for pcre_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_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_stack_malloc and pcre_stack_free variables. By default, | pointed to by the pcre[16|32]_stack_malloc and pcre[16|32]_stack_free |
these point to malloc() and free(), but you can replace the pointers to | variables. By default, these point to malloc() and free(), but you can |
cause PCRE to use your own functions. Since the block sizes are always | replace the pointers to cause PCRE to use your own functions. Since the |
the same, and are always freed in reverse order, it may be possible to | block sizes are always the same, and are always freed in reverse order, |
implement customized memory handlers that are more efficient than the | it may be possible to implement customized memory handlers that are |
standard functions. | more efficient than the standard functions. |
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Limiting pcre_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_exec() returns | in total and recursively. If a limit is exceeded, pcre[16|32]_exec() |
an error code. Setting suitable limits should prevent it from running | returns an error code. Setting suitable limits should prevent it from |
out of stack. The default values of the limits are very large, and | running out of stack. The default values of the limits are very large, |
unlikely ever to operate. They can be changed when PCRE is built, and | and unlikely ever to operate. They can be changed when PCRE is built, |
they can also be set when pcre_exec() is called. For details of these | and they can also be set when pcre[16|32]_exec() is called. For details |
interfaces, see the pcrebuild documentation and the section on extra | of these interfaces, see the pcrebuild documentation and the section on |
data for pcre_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_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 |
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The actual amount of stack used per recursion can vary quite a lot, |
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depending on the compiler that was used to build PCRE and the optimiza- |
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tion or debugging options that were set for it. The rule of thumb value |
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of 500 bytes mentioned above may be larger or smaller than what is |
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actually needed. A better approximation can be obtained by running this |
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command: |
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pcretest -m -C |
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The -C option causes pcretest to output information about the options |
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with which PCRE was compiled. When -m is also given (before -C), infor- |
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mation about stack use is given in a line like this: |
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Match recursion uses stack: approximate frame size = 640 bytes |
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The value is approximate because some recursions need a bit more (up to |
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perhaps 16 more bytes). |
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If the above command is given when PCRE is compiled to use the heap |
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instead of the stack for recursion, the value that is output is the |
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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 8438 PCRE DISCUSSION OF STACK USAGE
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Line 10153 PCRE DISCUSSION OF STACK USAGE
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rlim.rlim_cur = 100*1024*1024; |
rlim.rlim_cur = 100*1024*1024; |
setrlimit(RLIMIT_STACK, &rlim); |
setrlimit(RLIMIT_STACK, &rlim); |
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This reads the current limits (soft and hard) using getrlimit(), then | This reads the current limits (soft and hard) using getrlimit(), then |
attempts to increase the soft limit to 100Mb using setrlimit(). You | attempts to increase the soft limit to 100Mb using setrlimit(). You |
must do this before calling pcre_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 8459 AUTHOR
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Line 10174 AUTHOR
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REVISION |
REVISION |
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Last updated: 26 August 2011 | Last updated: 24 June 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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