version 1.1, 2012/02/21 23:05:52
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version 1.1.1.3, 2012/10/09 09:19:17
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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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The two libraries contain identical sets of functions, except that the |
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names in the 16-bit library start with pcre16_ instead of pcre_. To |
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avoid over-complication and reduce the documentation maintenance load, |
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most of the documentation describes the 8-bit library, with the differ- |
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ences for the 16-bit library described separately in the pcre16 page. |
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References to functions or structures of the form pcre[16]_xxx should |
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be read as meaning "pcre_xxx when using the 8-bit library and |
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pcre16_xxx when using the 16-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 encoded strings and Unicode gen- |
category properties. However, UTF-8 and Unicode support has to be | eral category properties. However, UTF-8/16 and Unicode support has to |
explicitly enabled; it is not the default. The Unicode tables corre- | be explicitly enabled; it is not the default. The Unicode tables corre- |
spond to Unicode release 6.0.0. |
spond to Unicode release 6.0.0. |
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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 |
Line 39 INTRODUCTION
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Line 55 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, |
| which is: |
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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-UNIX-USE 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_", which hopefully will |
any name clashes. In some environments, it is possible to control which | not provoke any name clashes. In some environments, it is possible to |
external symbols are exported when a shared library is built, and in | control which external symbols are exported when a shared library is |
these cases the undocumented symbols are not exported. | built, and in these cases the undocumented symbols are not exported. |
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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 |
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pcre16 details of the 16-bit library |
pcre-config show PCRE installation configuration information |
pcre-config show PCRE installation configuration information |
pcreapi details of PCRE's native C API |
pcreapi details of PCRE's native C API |
pcrebuild options for building PCRE |
pcrebuild options for 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 110 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 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 8-bit C library function, listing its arguments and results. |
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AUTHOR |
AUTHOR |
Line 110 AUTHOR
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Line 128 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: 10 January 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
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PCRE(3) PCRE(3) |
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NAME |
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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 both libraries, as well as definitions of flags, |
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structures, 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 "short int", but checks that it really is a 16-bit data type. If it |
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is not, the build fails with an error message telling the maintainer to |
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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 offsets within subject strings that are returned by the matching |
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functions are in 16-bit units rather than 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 if the PCRE_CONFIG_UTF8 option is |
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given to pcre16_config(), 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 Invalid character 0xfffe |
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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 |
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The pcretest program continues to operate with 8-bit input and output |
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files, but it can be used for testing the 16-bit library. If it is run |
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with the command line option -16, patterns and subject strings are con- |
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verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit |
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library functions are used instead of the 8-bit ones. Returned 16-bit |
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strings are converted to 8-bit for output. If the 8-bit library was not |
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compiled, pcretest defaults to 16-bit and the -16 option is ignored. |
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When PCRE is being built, the RunTest script that is called by "make |
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check" uses the pcretest -C option to discover which of the 8-bit and |
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16-bit libraries has been built, and runs the tests appropriately. |
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NOT SUPPORTED IN 16-BIT MODE |
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Not all the features of the 8-bit library are available with the 16-bit |
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library. The C++ and POSIX wrapper functions support only the 8-bit |
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library, and the pcregrep program is at present 8-bit only. |
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AUTHOR |
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Philip Hazel |
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University Computing Service |
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Cambridge CB2 3QH, England. |
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REVISION |
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Last updated: 14 April 2012 |
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Copyright (c) 1997-2012 University of Cambridge. |
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------------------------------------------------------------------------------ |
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PCREBUILD(3) PCREBUILD(3) |
PCREBUILD(3) PCREBUILD(3) |
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Line 158 PCRE BUILD-TIME OPTIONS
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Line 502 PCRE BUILD-TIME OPTIONS
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is not described. |
is not described. |
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BUILDING 8-BIT and 16-BIT LIBRARIES |
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By default, a library called libpcre is built, containing functions |
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that take string arguments contained in vectors of bytes, either as |
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single-byte characters, or interpreted as UTF-8 strings. You can also |
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build a separate library, called libpcre16, in which strings are con- |
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tained in vectors of 16-bit data units and interpreted either as sin- |
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gle-unit characters or UTF-16 strings, by adding |
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--enable-pcre16 |
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to the configure command. If you do not want the 8-bit library, add |
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--disable-pcre8 |
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as well. At least one of the two libraries must be built. Note that the |
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C++ and POSIX wrappers are for the 8-bit library only, and that pcre- |
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grep is an 8-bit program. None of these are built if you select only |
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the 16-bit library. |
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BUILDING SHARED AND STATIC LIBRARIES |
BUILDING SHARED AND STATIC LIBRARIES |
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The PCRE building process uses libtool to build both shared and static |
The PCRE building process uses libtool to build both shared and static |
Line 172 BUILDING SHARED AND STATIC LIBRARIES
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Line 537 BUILDING SHARED AND STATIC LIBRARIES
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|
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 and UTF-16 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 both 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 and support for UTF-16 to |
have have to set the PCRE_UTF8 option when you call the pcre_compile() | the 16-bit library. There are no separate options for enabling UTF-8 |
or pcre_compile2() functions. | and UTF-16 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 |
| the other without in the same configuration. (For backwards compatibil- |
| ity, --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 or |
expects its input to be either ASCII or UTF-8 (depending on the runtime | UTF-16. As well as compiling PCRE with this option, you also have have |
option). It is not possible to support both EBCDIC and UTF-8 codes in | to set the PCRE_UTF8 or PCRE_UTF16 option when you call one of the pat- |
the same version of the library. Consequently, --enable-utf8 and | tern 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 you have |
not explicitly requested it. |
not explicitly requested it. |
|
|
Including Unicode property support adds around 30K of tables to the |
Including Unicode property support adds around 30K of tables to the |
Line 282 WHAT \R MATCHES
|
Line 657 WHAT \R MATCHES
|
|
|
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 303 HANDLING VERY LARGE PATTERNS
|
Line 678 HANDLING VERY LARGE PATTERNS
|
nation metacharacter). By default, two-byte values are used for these |
nation metacharacter). By default, two-byte values are used for these |
offsets, leading to a maximum size for a compiled pattern of around |
offsets, leading to a maximum size for a compiled pattern of around |
64K. This is sufficient to handle all but the most gigantic patterns. |
64K. This is sufficient to handle all but the most gigantic patterns. |
Nevertheless, some people do want to process truyl enormous patterns, | Nevertheless, some people do want to process truly enormous patterns, |
so it is possible to compile PCRE to use three-byte or four-byte off- |
so it is possible to compile PCRE to use three-byte or four-byte off- |
sets by adding a setting such as |
sets 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. Using longer offsets |
additional bytes when handling them. | slows down the operation of PCRE because it has to load additional data |
| when handling them. |
|
|
|
|
AVOIDING EXCESSIVE STACK USAGE |
AVOIDING EXCESSIVE STACK USAGE |
|
|
When matching with the pcre_exec() function, PCRE implements backtrack- |
When matching with the pcre_exec() function, PCRE implements backtrack- |
ing by making recursive calls to an internal function called match(). | ing by making recursive calls to an internal function called match(). |
In environments where the size of the stack is limited, this can se- | In environments where the size of the stack is limited, this can se- |
verely limit PCRE's operation. (The Unix environment does not usually | verely limit PCRE's operation. (The Unix environment does not usually |
suffer from this problem, but it may sometimes be necessary to increase |
suffer from this problem, but it may sometimes be necessary to increase |
the maximum stack size. There is a discussion in the pcrestack docu- | the maximum stack size. There is a discussion in the pcrestack docu- |
mentation.) An alternative approach to recursion that uses memory from | mentation.) An alternative approach to recursion that uses memory from |
the heap to remember data, instead of using recursive function calls, | the heap to remember data, instead of using recursive function calls, |
has been implemented to work round the problem of limited stack size. | has been implemented to work round the problem of limited stack size. |
If you want to build a version of PCRE that works this way, add |
If you want to build a version of PCRE that works this way, add |
|
|
--disable-stack-for-recursion |
--disable-stack-for-recursion |
|
|
to the configure command. With this configuration, PCRE will use the | to the configure command. With this configuration, PCRE will use the |
pcre_stack_malloc and pcre_stack_free variables to call memory manage- | pcre_stack_malloc and pcre_stack_free variables to call memory manage- |
ment functions. By default these point to malloc() and free(), but you | ment functions. By default these point to malloc() and free(), but you |
can replace the pointers so that your own functions are used instead. |
can replace the pointers so that your own functions are used instead. |
|
|
Separate functions are provided rather than using pcre_malloc and | Separate functions are provided rather than using pcre_malloc and |
pcre_free because the usage is very predictable: the block sizes | pcre_free because the usage is very predictable: the block sizes |
requested are always the same, and the blocks are always freed in | requested are always the same, and the blocks are always freed in |
reverse order. A calling program might be able to implement optimized | reverse order. A calling program might be able to implement optimized |
functions that perform better than malloc() and free(). PCRE runs | functions that perform better than malloc() and free(). PCRE runs |
noticeably more slowly when built in this way. This option affects only |
noticeably more slowly when built in this way. This option affects only |
the pcre_exec() function; it is not relevant for pcre_dfa_exec(). |
the pcre_exec() function; it is not relevant for pcre_dfa_exec(). |
|
|
|
|
LIMITING PCRE RESOURCE USAGE |
LIMITING PCRE RESOURCE USAGE |
|
|
Internally, PCRE has a function called match(), which it calls repeat- | Internally, PCRE has a function called match(), which it calls repeat- |
edly (sometimes recursively) when matching a pattern with the | edly (sometimes recursively) when matching a pattern with the |
pcre_exec() function. By controlling the maximum number of times this | pcre_exec() function. By controlling the maximum number of times this |
function may be called during a single matching operation, a limit can | function may be called during a single matching operation, a limit can |
be placed on the resources used by a single call to pcre_exec(). The | be placed on the resources used by a single call to pcre_exec(). The |
limit can be changed at run time, as described in the pcreapi documen- | limit can be changed at run time, as described in the pcreapi documen- |
tation. The default is 10 million, but this can be changed by adding a | tation. The default is 10 million, but this can be changed by adding a |
setting such as |
setting such as |
|
|
--with-match-limit=500000 |
--with-match-limit=500000 |
|
|
to the configure command. This setting has no effect on the | to the configure command. This setting has no effect on the |
pcre_dfa_exec() matching function. |
pcre_dfa_exec() matching function. |
|
|
In some environments it is desirable to limit the depth of recursive | In some environments it is desirable to limit the depth of recursive |
calls of match() more strictly than the total number of calls, in order |
calls of match() more strictly than the total number of calls, in order |
to restrict the maximum amount of stack (or heap, if --disable-stack- | to restrict the maximum amount of stack (or heap, if --disable-stack- |
for-recursion is specified) that is used. A second limit controls this; |
for-recursion is specified) that is used. A second limit controls this; |
it defaults to the value that is set for --with-match-limit, which | it defaults to the value that is set for --with-match-limit, which |
imposes no additional constraints. However, you can set a lower limit | imposes no additional constraints. However, you can set a lower limit |
by adding, for example, |
by adding, for example, |
|
|
--with-match-limit-recursion=10000 |
--with-match-limit-recursion=10000 |
|
|
to the configure command. This value can also be overridden at run | to the configure command. This value can also be overridden at run |
time. |
time. |
|
|
|
|
CREATING CHARACTER TABLES AT BUILD TIME |
CREATING CHARACTER TABLES AT BUILD TIME |
|
|
PCRE uses fixed tables for processing characters whose code values are | PCRE uses fixed tables for processing characters whose code values are |
less than 256. By default, PCRE is built with a set of tables that are | less than 256. By default, PCRE is built with a set of tables that are |
distributed in the file pcre_chartables.c.dist. These tables are for | distributed in the file pcre_chartables.c.dist. These tables are for |
ASCII codes only. If you add |
ASCII codes only. If you add |
|
|
--enable-rebuild-chartables |
--enable-rebuild-chartables |
|
|
to the configure command, the distributed tables are no longer used. | to the configure command, the distributed tables are no longer used. |
Instead, a program called dftables is compiled and run. This outputs | Instead, a program called dftables is compiled and run. This outputs |
the source for new set of tables, created in the default locale of your |
the source for new set of tables, created in the default locale of your |
C runtime system. (This method of replacing the tables does not work if | C run-time system. (This method of replacing the tables does not work |
you are cross compiling, because dftables is run on the local host. If | if you are cross compiling, because dftables is run on the local host. |
you need to create alternative tables when cross compiling, you will | If you need to create alternative tables when cross compiling, you will |
have to do so "by hand".) |
have to do so "by hand".) |
|
|
|
|
USING EBCDIC CODE |
USING EBCDIC CODE |
|
|
PCRE assumes by default that it will run in an environment where the | PCRE assumes by default that it will run in an environment where the |
character code is ASCII (or Unicode, which is a superset of ASCII). | character code is ASCII (or Unicode, which is a superset of ASCII). |
This is the case for most computer operating systems. PCRE can, how- | This is the case for most computer operating systems. PCRE can, how- |
ever, be compiled to run in an EBCDIC environment by adding |
ever, be compiled to run in an EBCDIC environment by adding |
|
|
--enable-ebcdic |
--enable-ebcdic |
|
|
to the configure command. This setting implies --enable-rebuild-charta- |
to the configure command. This setting implies --enable-rebuild-charta- |
bles. You should only use it if you know that you are in an EBCDIC | bles. You should only use it if you know that you are in an EBCDIC |
environment (for example, an IBM mainframe operating system). The | environment (for example, an IBM mainframe operating system). The |
--enable-ebcdic option is incompatible with --enable-utf8. | --enable-ebcdic option is incompatible with --enable-utf. |
|
|
|
|
PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT |
PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT |
Line 416 PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
|
Line 792 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 818 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 469 PCRETEST OPTION FOR LIBREADLINE SUPPORT
|
Line 845 PCRETEST OPTION FOR LIBREADLINE SUPPORT
|
|
|
SEE ALSO |
SEE ALSO |
|
|
pcreapi(3), pcre_config(3). | pcreapi(3), pcre16, pcre_config(3). |
|
|
|
|
AUTHOR |
AUTHOR |
Line 481 AUTHOR
|
Line 857 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 06 September 2011 | Last updated: 07 January 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 498 PCRE MATCHING ALGORITHMS
|
Line 874 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() and pcre16_exec() functions. These work in the same was as |
function, and provides a Perl-compatible matching operation. | Perl's matching function, and provide a Perl-compatible matching opera- |
| tion. The just-in-time (JIT) optimization that is described in the |
| pcrejit documentation is compatible with these functions. |
|
|
An alternative algorithm is provided by the pcre_dfa_exec() function; | An alternative algorithm is provided by the pcre_dfa_exec() and |
this operates in a different way, and is not Perl-compatible. It has | pcre16_dfa_exec() functions; they operate in a different way, and are |
advantages and disadvantages compared with the standard algorithm, and | not Perl-compatible. This alternative has advantages and disadvantages |
these are described below. | 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 1010 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 or UTF-16 modes, is not sup- |
because the alternative algorithm moves through the subject string one | ported in these modes, because the alternative algorithm moves through |
character at a time, for all active paths through the tree. | 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 1064 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. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 696 PCREAPI(3)
|
Line 1075 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 1098 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 1137 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 |
|
|
|
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 1175 PCRE NATIVE API INDIRECTED FUNCTIONS
|
int (*pcre_callout)(pcre_callout_block *); |
int (*pcre_callout)(pcre_callout_block *); |
|
|
|
|
|
PCRE 8-BIT AND 16-BIT LIBRARIES |
|
|
|
From release 8.30, PCRE can be compiled as a library for handling |
|
16-bit character strings as well as, or instead of, the original |
|
library that handles 8-bit character strings. To avoid too much compli- |
|
cation, this document describes the 8-bit versions of the functions, |
|
with only occasional references to the 16-bit library. |
|
|
|
The 16-bit functions operate in the same way as their 8-bit counter- |
|
parts; they just use different data types for their arguments and |
|
results, and their names start with pcre16_ instead of pcre_. For every |
|
option that has UTF8 in its name (for example, PCRE_UTF8), there is a |
|
corresponding 16-bit name with UTF8 replaced by UTF16. This facility is |
|
in fact just cosmetic; the 16-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 quantities and UTF-16 when using the 16-bit |
|
library, unless specified otherwise. More details of the specific dif- |
|
ferences for the 16-bit library are given in the pcre16 page. |
|
|
|
|
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 |
Line 865 PCRE API OVERVIEW
|
Line 1271 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 1311 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 1359 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. If this option is given to the |
| 16-bit version of this function, pcre16_config(), 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 version of this function, the result is PCRE_ERROR_BADOP- |
|
TION. |
|
|
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 s The output is an integer that is set to one if support for Unicode |
character properties is available; otherwise it is set to zero. |
character properties is available; otherwise it is set to zero. |
|
|
PCRE_CONFIG_JIT |
PCRE_CONFIG_JIT |
Line 989 CHECKING BUILD-TIME OPTIONS
|
Line 1406 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 four values that |
are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, |
are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, |
and -1 for ANY. Though they are derived from ASCII, the same values | and -1 for ANY. Though they are derived from ASCII, the same values |
are returned in EBCDIC environments. The default should normally corre- |
are returned in EBCDIC environments. The default should normally corre- |
spond to the standard sequence for your operating system. |
spond to the standard sequence for your operating system. |
|
|
PCRE_CONFIG_BSR |
PCRE_CONFIG_BSR |
|
|
The output is an integer whose value indicates what character sequences |
The output is an integer whose value indicates what character sequences |
the \R escape sequence matches by default. A value of 0 means that \R | the \R escape sequence matches by default. A value of 0 means that \R |
matches any Unicode line ending sequence; a value of 1 means that \R | matches any Unicode line ending sequence; a value of 1 means that \R |
matches only CR, LF, or CRLF. The default can be overridden when a pat- |
matches only CR, LF, or CRLF. The default can be overridden when a pat- |
tern is compiled or matched. |
tern is compiled or matched. |
|
|
PCRE_CONFIG_LINK_SIZE |
PCRE_CONFIG_LINK_SIZE |
|
|
The output is an integer that contains the number of bytes used for | The output is an integer that contains the number of 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. The default value of 2 |
for all but the most massive patterns, since it allows the compiled | is sufficient for all but the most massive patterns, since it allows |
pattern to be up to 64K in size. | 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 1485 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 byte 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. | string, the offset is that of the first byte of the failing character. |
Also, some errors are not detected until checks are carried out when | |
the whole pattern has been scanned; in these cases the offset passed | |
back is the length of the pattern. | |
|
|
|
Some errors are not detected until the whole pattern has been scanned; |
|
in these cases, the offset passed back is the length of the pattern. |
Note that the offset is in bytes, not characters, even in UTF-8 mode. |
Note that the offset is in bytes, not characters, even in UTF-8 mode. |
It may sometimes point into the middle of a UTF-8 character. |
It may sometimes point into the middle of a UTF-8 character. |
|
|
Line 1199 COMPILING A PATTERN
|
Line 1625 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 1642 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 1301 COMPILING A PATTERN
|
Line 1727 COMPILING A PATTERN
|
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. The Unicode newline sequences are the three just mentioned, |
plus the single characters VT (vertical tab, U+000B), FF (formfeed, | plus the single characters VT (vertical tab, U+000B), FF (form feed, |
U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS |
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 | (paragraph separator, U+2029). For the 8-bit library, the last two are |
UTF-8 mode. | recognized only in UTF-8 mode. |
|
|
The newline setting in the options word uses three bits that are |
The newline setting in the options word uses three bits that are |
treated as a number, giving eight possibilities. Currently only six are |
treated as a number, giving eight possibilities. Currently only six are |
Line 1315 COMPILING A PATTERN
|
Line 1741 COMPILING A PATTERN
|
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 |
Line 1361 COMPILING A PATTERN
|
Line 1787 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. |
|
|
|
|
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 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 1847 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 1859 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 1458 COMPILATION ERROR CODES
|
Line 1885 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 |
|
|
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 1906 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. In that circumstance, if the calling program |
wants to pass any of the other fields to pcre_exec() or | 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. |
|
|
The second argument of pcre_study() contains option bits. There is only | The second argument of pcre_study() contains option bits. There are |
one option: PCRE_STUDY_JIT_COMPILE. If this is set, and the just-in- | three options: |
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 |
| other 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 1979 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 by |
pcre_exec() and pcre_dfa_exec() to avoid wasting time by trying to | pcre_exec() and pcre_dfa_exec() to avoid wasting time by trying to |
match strings that are shorter than the lower bound. You can find out | match strings that are shorter than the lower bound. You can find out |
the value in a calling program via the pcre_fullinfo() function. |
the value in a calling program via the pcre_fullinfo() function. |
|
|
Studying a pattern is also useful for non-anchored patterns that do not |
Studying a pattern is also useful for non-anchored patterns that do not |
have a single fixed starting character. A bitmap of possible starting | have a single fixed starting character. A bitmap of possible starting |
bytes is created. This speeds up finding a position in the subject at | bytes is created. This speeds up finding a position in the subject at |
which to start matching. | which to start matching. (In 16-bit mode, the bitmap is used for 16-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 when |
successful. The optimizations can be disabled by setting the | calling pcre_exec() or pcre_dfa_exec(), but if this is done, JIT execu- |
PCRE_NO_START_OPTIMIZE option when calling pcre_exec() or | tion is also disabled. You might want to do this if your pattern con- |
pcre_dfa_exec(). You might want to do this if your pattern contains | tains callouts or (*MARK) and you want to make use of these facilities |
callouts or (*MARK) (which cannot be handled by the JIT compiler), and | in cases where matching fails. See the discussion of |
you want to make use of these facilities in cases where matching fails. | PCRE_NO_START_OPTIMIZE below. |
See the discussion of PCRE_NO_START_OPTIMIZE below. | |
|
|
|
|
LOCALE SUPPORT |
LOCALE SUPPORT |
|
|
PCRE handles caseless matching, and determines whether characters are | PCRE handles caseless matching, and determines whether characters are |
letters, digits, or whatever, by reference to a set of tables, indexed | letters, digits, or whatever, by reference to a set of tables, indexed |
by character value. When running in UTF-8 mode, this applies only to | by character value. When running in UTF-8 mode, this applies only to |
characters with codes less than 128. By default, higher-valued codes | characters with codes less than 128. By default, higher-valued codes |
never match escapes such as \w or \d, but they can be tested with \p if |
never match escapes such as \w or \d, but they can be tested with \p if |
PCRE is built with Unicode character property support. Alternatively, | PCRE is built with Unicode character property support. Alternatively, |
the PCRE_UCP option can be set at compile time; this causes \w and | the PCRE_UCP option can be set at compile time; this causes \w and |
friends to use Unicode property support instead of built-in tables. The |
friends to use Unicode property support instead of built-in tables. The |
use of locales with Unicode is discouraged. If you are handling charac- |
use of locales with Unicode is discouraged. If you are handling charac- |
ters with codes greater than 128, you should either use UTF-8 and Uni- | ters with codes greater than 128, you should either use UTF-8 and Uni- |
code, or use locales, but not try to mix the two. |
code, or use locales, but not try to mix the two. |
|
|
PCRE contains an internal set of tables that are used when the final | PCRE contains an internal set of tables that are used when the final |
argument of pcre_compile() is NULL. These are sufficient for many | argument of pcre_compile() is NULL. These are sufficient for many |
applications. Normally, the internal tables recognize only ASCII char- |
applications. Normally, the internal tables recognize only ASCII char- |
acters. However, when PCRE is built, it is possible to cause the inter- |
acters. However, when PCRE is built, it is possible to cause the inter- |
nal tables to be rebuilt in the default "C" locale of the local system, |
nal tables to be rebuilt in the default "C" locale of the local system, |
which may cause them to be different. |
which may cause them to be different. |
|
|
The internal tables can always be overridden by tables supplied by the | The internal tables can always be overridden by tables supplied by the |
application that calls PCRE. These may be created in a different locale |
application that calls PCRE. These may be created in a different locale |
from the default. As more and more applications change to using Uni- | from the default. As more and more applications change to using Uni- |
code, the need for this locale support is expected to die away. |
code, the need for this locale support is expected to die away. |
|
|
External tables are built by calling the pcre_maketables() function, | External tables are built by calling the pcre_maketables() function, |
which has no arguments, in the relevant locale. The result can then be | which has no arguments, in the relevant locale. The result can then be |
passed to pcre_compile() or pcre_exec() as often as necessary. For | passed to pcre_compile() or pcre_exec() as often as necessary. For |
example, to build and use tables that are appropriate for the French | example, to build and use tables that are appropriate for the French |
locale (where accented characters with values greater than 128 are | locale (where accented characters with values greater than 128 are |
treated as letters), the following code could be used: |
treated as letters), the following code could be used: |
|
|
setlocale(LC_CTYPE, "fr_FR"); |
setlocale(LC_CTYPE, "fr_FR"); |
tables = pcre_maketables(); |
tables = pcre_maketables(); |
re = pcre_compile(..., tables); |
re = pcre_compile(..., tables); |
|
|
The locale name "fr_FR" is used on Linux and other Unix-like systems; | The locale name "fr_FR" is used on Linux and other Unix-lik The locale name "fr_FR" is used on Linux and other Unix-lik |
if you are using Windows, the name for the French locale is "french". |
if you are using Windows, the name for the French locale is "french". |
|
|
When pcre_maketables() runs, the tables are built in memory that is | When pcre_maketables() runs, the tables are built in memory that is |
obtained via pcre_malloc. It is the caller's responsibility to ensure | obtained via pcre_malloc. It is the caller's responsibility to ensure |
that the memory containing the tables remains available for as long as | that the memory containing the tables remains available for as long as |
it is needed. |
it is needed. |
|
|
The pointer that is passed to pcre_compile() is saved with the compiled |
The pointer that is passed to pcre_compile() is saved with the compiled |
pattern, and the same tables are used via this pointer by pcre_study() | pattern, and the same tables are used via this pointer by pcre_study() |
and normally also by pcre_exec(). Thus, by default, for any single pat- |
and normally also by pcre_exec(). Thus, by default, for any single pat- |
tern, compilation, studying and matching all happen in the same locale, |
tern, compilation, studying and matching all happen in the same locale, |
but different patterns can be compiled in different locales. |
but different patterns can be compiled in different locales. |
|
|
It is possible to pass a table pointer or NULL (indicating the use of | It is possible to pass a table pointer or NULL (indicating the use of |
the internal tables) to pcre_exec(). Although not intended for this | the internal tables) to pcre_exec(). Although not intended for this |
purpose, this facility could be used to match a pattern in a different | purpose, this facility could be used to match a pattern in a different |
locale from the one in which it was compiled. Passing table pointers at |
locale from the one in which it was compiled. Passing table pointers at |
run time is discussed below in the section on matching a pattern. |
run time is discussed below in the section on matching a pattern. |
|
|
Line 1622 INFORMATION ABOUT A PATTERN
|
Line 2063 INFORMATION ABOUT A PATTERN
|
int pcre_fullinfo(const pcre *code, const pcre_extra *extra, |
int pcre_fullinfo(const pcre *code, const pcre_extra *extra, |
int what, void *where); |
int what, void *where); |
|
|
The pcre_fullinfo() function returns information about a compiled pat- | The pcre_fullinfo() function returns information about a compiled pat- |
tern. It replaces the 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 |
the pattern was not studied. The third argument specifies which piece | the pattern was not studied. The third argument specifies which piece |
of information is required, and the fourth argument is a pointer to a | of information is required, and the fourth argument is a pointer to a |
variable to receive the data. The yield of the function is zero for | variable to receive the data. The yield of the function is zero for |
success, or one of the following negative numbers: |
success, or one of the following negative numbers: |
|
|
PCRE_ERROR_NULL the argument code was NULL | PCRE_ERROR_NULL the argument code was NULL |
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 |
|
|
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 1675 INFORMATION ABOUT A PATTERN
|
Line 2119 INFORMATION ABOUT A PATTERN
|
|
|
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. |
|
|
|
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 1696 INFORMATION ABOUT A PATTERN
|
Line 2144 INFORMATION ABOUT A PATTERN
|
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 |
|
|
Line 1716 INFORMATION ABOUT A PATTERN
|
Line 2164 INFORMATION ABOUT A PATTERN
|
|
|
PCRE_INFO_JIT |
PCRE_INFO_JIT |
|
|
Return 1 if the pattern was studied with the PCRE_STUDY_JIT_COMPILE | Return 1 if the pattern was studied with one of the JIT options, and |
option, and just-in-time compiling was successful. The fourth argument | just-in-time compiling was successful. The fourth argument should point |
should point to an int variable. A return value of 0 means that JIT | to an int variable. A return value of 0 means that JIT support is not |
support is not available in this version of PCRE, or that the pattern | available in this version of PCRE, or that the pattern was not studied |
was not studied with the PCRE_STUDY_JIT_COMPILE option, or that the JIT | with a JIT option, or that the JIT compiler could not handle this par- |
compiler could not handle this particular pattern. See the pcrejit doc- | ticular pattern. See the pcrejit documentation for details of what can |
umentation for details of what can and cannot be handled. | and cannot be handled. |
|
|
PCRE_INFO_JITSIZE |
PCRE_INFO_JITSIZE |
|
|
If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE | If the pattern was successfully studied with a JIT option, return the |
option, return the size of the JIT compiled code, otherwise return | size of the JIT compiled code, otherwise return zero. The fourth argu- |
zero. The fourth argument should point to a size_t variable. | ment should point to a size_t variable. |
|
|
PCRE_INFO_LASTLITERAL |
PCRE_INFO_LASTLITERAL |
|
|
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. |
|
|
|
PCRE_INFO_MAXLOOKBEHIND |
|
|
|
Return the number of characters (NB not bytes) in the longest lookbe- |
|
hind assertion in the pattern. Note that the simple assertions \b and |
|
\B require a one-character lookbehind. This information is useful when |
|
doing multi-segment matching using the partial matching facilities. |
|
|
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-8 mode |
be relevant in UTF-8 mode). The fourth argument should point to an int | may be different from the number of bytes. 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 |
Line 1768 INFORMATION ABOUT A PATTERN
|
Line 2224 INFORMATION ABOUT A PATTERN
|
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. 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 |
Line 1784 INFORMATION ABOUT A PATTERN
|
Line 2242 INFORMATION ABOUT A PATTERN
|
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) ) |
Line 1838 INFORMATION ABOUT A PATTERN
|
Line 2296 INFORMATION ABOUT A PATTERN
|
|
|
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 both libraries). |
point to a size_t variable. This value does not include the size of the | The fourth argument should point to a size_t variable. This value does |
pcre structure that is returned by pcre_compile(). The value that is | not include the size of the pcre structure that is returned by |
passed as the argument to pcre_malloc() when pcre_compile() is getting | pcre_compile(). The value that is passed as the argument to pcre_mal- |
memory in which to place the compiled data is the value returned by | loc() when pcre_compile() is getting memory in which to place the com- |
this option plus the size of the pcre structure. Studying a compiled | piled data is the value returned by this option plus the size of the |
pattern, with or without JIT, does not alter the value returned by this | pcre structure. Studying a compiled pattern, with or without JIT, does |
option. | 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 of the data block pointed to by the study_data |
a pcre_extra block. If pcre_extra is NULL, or there is no study data, | field in a pcre_extra block. If pcre_extra is NULL, or there is no |
zero is returned. The fourth argument should point to a size_t vari- | study data, zero is returned. The fourth argument should point to a |
able. The study_data field is set by pcre_study() to record informa- | size_t variable. The study_data field is set by pcre_study() to record |
tion that will speed up matching (see the section entitled "Studying a | information that will speed up matching (see the section entitled |
pattern" above). The format of the study_data block is private, but its | "Studying a pattern" above). The format of the study_data block is pri- |
length is made available via this option so that it can be saved and | vate, but its length is made available via this option so that it can |
restored (see the pcreprecompile documentation for details). | be saved and restored (see the pcreprecompile documentation for |
| details). |
|
|
|
|
OBSOLETE INFO FUNCTION |
|
|
|
int pcre_info(const pcre *code, int *optptr, int *firstcharptr); |
|
|
|
The pcre_info() function is now obsolete because its interface is too |
|
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 |
|
PCRE_ERROR_BADMAGIC the "magic number" was not found |
|
|
|
If the optptr argument is not NULL, a copy of the options with which |
|
the pattern was compiled is placed in the integer it points to (see |
|
PCRE_INFO_OPTIONS above). |
|
|
|
If the pattern is not anchored and the firstcharptr argument is not |
|
NULL, it is used to pass back information about the first character of |
|
any matched string (see PCRE_INFO_FIRSTBYTE above). |
|
|
|
|
|
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 2346 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 2380 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 2395 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 | 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 |
Line 1989 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 2429 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
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 |
Line 2011 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 2451 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 2036 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 2476 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
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 |
|
|
Line 2183 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 2623 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
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 disables JIT execution; when it is set, 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 2659 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 2678 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 2711 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 bytes in length, and a starting byte offset in startoffset. |
If this is negative or greater than the length of the subject, |
If this 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, |
Line 2358 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 2800 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
If the vector is too small to hold all the captured substring offsets, |
If the vector is too small to hold all the captured substring offsets, |
it is used as far as possible (up to two-thirds of its length), and the |
it is used as far as possible (up to two-thirds of its length), and the |
function returns a value of zero. If neither the actual string matched |
function returns a value of zero. If neither the actual string matched |
not any captured substrings are of interest, pcre_exec() may be called | nor any captured substrings are of interest, pcre_exec() may be called |
with ovector passed as NULL and ovecsize as zero. However, if the pat- |
with ovector passed as NULL and ovecsize as zero. However, if the pat- |
tern contains back references and the ovector is not big enough to |
tern contains back references and the ovector is not big enough to |
remember the related substrings, PCRE has to get additional memory for |
remember the related substrings, PCRE has to get additional memory for |
Line 2549 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 2991 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_ERROR_JIT_STACKLIMIT (-27) |
PCRE_ERROR_JIT_STACKLIMIT (-27) |
|
|
This error is returned when a pattern that was successfully studied |
This error is returned when a pattern that was successfully studied |
using the PCRE_STUDY_JIT_COMPILE option is being matched, but the mem- | using a JIT compile option is being matched, but the memory available |
ory available for the just-in-time processing stack is not large | for the just-in-time processing stack is not large enough. See the |
enough. See the pcrejit documentation for more details. | pcrejit documentation for more details. |
|
|
Error numbers -16 to -20 and -22 are not used by pcre_exec(). | 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 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. |
|
|
|
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 library is given in the pcre16 page. |
|
|
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
|
Line 3027 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_UTF8_ERR4 |
PCRE_UTF8_ERR4 |
PCRE_UTF8_ERR5 |
PCRE_UTF8_ERR5 |
|
|
The string ends with a truncated UTF-8 character; the code specifies | The string ends with a truncated UTF-8 character; the code specifies |
how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 | how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 |
characters to be no longer than 4 bytes, the encoding scheme (origi- | characters to be no longer than 4 bytes, the encoding scheme (origi- |
nally defined by RFC 2279) allows for up to 6 bytes, and this is | nally defined by RFC 2279) allows for up to 6 bytes, and this is |
checked first; hence the possibility of 4 or 5 missing bytes. |
checked first; hence the possibility of 4 or 5 missing bytes. |
|
|
PCRE_UTF8_ERR6 |
PCRE_UTF8_ERR6 |
Line 2583 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3040 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_UTF8_ERR10 |
PCRE_UTF8_ERR10 |
|
|
The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of |
The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of |
the character do not have the binary value 0b10 (that is, either the | the character do not have the binary value 0b10 (that is, either the |
most significant bit is 0, or the next bit is 1). |
most significant bit is 0, or the next bit is 1). |
|
|
PCRE_UTF8_ERR11 |
PCRE_UTF8_ERR11 |
PCRE_UTF8_ERR12 |
PCRE_UTF8_ERR12 |
|
|
A character that is valid by the RFC 2279 rules is either 5 or 6 bytes | A character that is valid by the RFC 2279 rules is either 5 or 6 bytes |
long; these code points are excluded by RFC 3629. |
long; these code points are excluded by RFC 3629. |
|
|
PCRE_UTF8_ERR13 |
PCRE_UTF8_ERR13 |
|
|
A 4-byte character has a value greater than 0x10fff; these code points | A 4-byte character has a value greater than 0x10fff; these code points |
are excluded by RFC 3629. |
are excluded by RFC 3629. |
|
|
PCRE_UTF8_ERR14 |
PCRE_UTF8_ERR14 |
|
|
A 3-byte character has a value in the range 0xd800 to 0xdfff; this | A 3-byte character has a value i A 3-byte character has a value i |
range of code points are reserved by RFC 3629 for use with UTF-16, and | range of code points are reserved by RFC 3629 for use with UTF-16, and |
so are excluded from UTF-8. |
so are excluded from UTF-8. |
|
|
PCRE_UTF8_ERR15 |
PCRE_UTF8_ERR15 |
Line 2609 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
Line 3066 MATCHING A PATTERN: THE TRADITIONAL FUNCTION
|
PCRE_UTF8_ERR18 |
PCRE_UTF8_ERR18 |
PCRE_UTF8_ERR19 |
PCRE_UTF8_ERR19 |
|
|
A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes | A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes |
for a value that can be represented by fewer bytes, which is invalid. | for a value that can be represented by fewer bytes, which is invalid. |
For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor- | For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor- |
rect coding uses just one byte. |
rect coding uses just one byte. |
|
|
PCRE_UTF8_ERR20 |
PCRE_UTF8_ERR20 |
|
|
The two most significant bits of the first byte of a character have the |
The two most significant bits of the first byte of a character have the |
binary value 0b10 (that is, the most significant bit is 1 and the sec- | binary value 0b10 (that is, the most significant bit is 1 and the sec- |
ond is 0). Such a byte can only validly occur as the second or subse- | ond is 0). Such a byte can only validly occur as the second or subse- |
quent byte of a multi-byte character. |
quent byte of a multi-byte character. |
|
|
PCRE_UTF8_ERR21 |
PCRE_UTF8_ERR21 |
|
|
The first byte of a character has the value 0xfe or 0xff. These values | The first byte of a character has the value 0xfe or 0xff. These values |
can never occur in a valid UTF-8 string. |
can never occur in a valid UTF-8 string. |
|
|
|
|
Line 2640 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
|
Line 3097 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
|
int pcre_get_substring_list(const char *subject, |
int pcre_get_substring_list(const char *subject, |
int *ovector, int stringcount, const char ***listptr); |
int *ovector, int stringcount, const char ***listptr); |
|
|
Captured substrings can be accessed directly by using the offsets | Captured substrings can be accessed directly by using the offsets |
returned by pcre_exec() in ovector. For convenience, the functions | returned by pcre_exec() in ovector. For convenience, the functions |
pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub- |
pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub- |
string_list() are provided for extracting captured substrings as new, | string_list() are provided for extracting captured substrings as new, |
separate, zero-terminated strings. These functions identify substrings | separate, zero-terminated strings. These functions identify substrings |
by number. The next section describes functions for extracting named | by number. The next section describes functions for extracting named |
substrings. |
substrings. |
|
|
A substring that contains a binary zero is correctly extracted and has | A substring that contains a binary zero is correctly extracted and has |
a further zero added on the end, but the result is not, of course, a C | a further zero added on the end, but the result is not, of course, a C |
string. However, you can process such a string by referring to the | string. However, you can process such a string by referring to the |
length that is returned by pcre_copy_substring() and pcre_get_sub- | length that is returned by pcre_copy_substring() and pcre_get_sub- |
string(). Unfortunately, the interface to pcre_get_substring_list() is |
string(). Unfortunately, the interface to pcre_get_substring_list() is |
not adequate for handling strings containing binary zeros, because the | not adequate for handling strings containing binary zeros, because the |
end of the final string is not independently indicated. |
end of the final string is not independently indicated. |
|
|
The first three arguments are the same for all three of these func- | The first three arguments are the same for all three of these func- |
tions: subject is the subject string that has just been successfully | tions: subject is the subject string that has just been successfully |
matched, ovector is a pointer to the vector of integer offsets that was |
matched, ovector is a pointer to the vector of integer offsets that was |
passed to pcre_exec(), and stringcount is the number of substrings that |
passed to pcre_exec(), and stringcount is the number of substrings that |
were captured by the match, including the substring that matched the | were captured by the match, including the substring that matched the |
entire regular expression. This is the value returned by pcre_exec() if |
entire regular expression. This is the value returned by pcre_exec() if |
it is greater than zero. If pcre_exec() returned zero, indicating that | it is greater than zero. If pcre_exec() returned zero, indicating that |
it ran out of space in ovector, the value passed as stringcount should | it ran out of space in ovector, the value passed as stringcount should |
be the number of elements in the vector divided by three. |
be the number of elements in the vector divided by three. |
|
|
The functions pcre_copy_substring() and pcre_get_substring() extract a | The functions pcre_copy_substring() and pcre_get_substring() extract a |
single substring, whose number is given as stringnumber. A value of | single substring, whose number is given as stringnumber. A value of |
zero extracts the substring that matched the entire pattern, whereas | zero extracts the substring that matched the entire pattern, whereas |
higher values extract the captured substrings. For pcre_copy_sub- | higher values extract the captured substrings. For pcre_copy_sub- |
string(), the string is placed in buffer, whose length is given by | string(), the string is placed in buffer, whose length is given by |
buffersize, while for pcre_get_substring() a new block of memory is | buffersize, while for pcre_get_substring() a new block of memory is |
obtained via pcre_malloc, and its address is returned via stringptr. | obtained via pcre_malloc, and its address is returned via stringptr. |
The yield of the function is the length of the string, not including | The yield of the function is the length of the string, not including |
the terminating zero, or one of these error codes: |
the terminating zero, or one of these error codes: |
|
|
PCRE_ERROR_NOMEMORY (-6) |
PCRE_ERROR_NOMEMORY (-6) |
|
|
The buffer was too small for pcre_copy_substring(), or the attempt to | The buffer was too small for pcre_copy_substring(), or the attempt to |
get memory failed for pcre_get_substring(). |
get memory failed for pcre_get_substring(). |
|
|
PCRE_ERROR_NOSUBSTRING (-7) |
PCRE_ERROR_NOSUBSTRING (-7) |
|
|
There is no substring whose number is stringnumber. |
There is no substring whose number is stringnumber. |
|
|
The pcre_get_substring_list() function extracts all available sub- | The pcre_get_substring_list() function extracts all available sub- |
strings and builds a list of pointers to them. All this is done in a | strings and builds a list of pointers to them. All this is done in a |
single block of memory that is obtained via pcre_malloc. The address of |
single block of memory that is obtained via pcre_malloc. The address of |
the memory block is returned via listptr, which is also the start of | the memory block is returned via listptr, which is also the start of |
the list of string pointers. The end of the list is marked by a NULL | the list of string pointers. The end of the list is marked by a NULL |
pointer. The yield of the function is zero if all went well, or the | pointer. The yield of the function is zero if all went well, or the |
error code |
error code |
|
|
PCRE_ERROR_NOMEMORY (-6) |
PCRE_ERROR_NOMEMORY (-6) |
|
|
if the attempt to get the memory block failed. |
if the attempt to get the memory block failed. |
|
|
When any of these functions encounter a substring that is unset, which | When any of these functions encounter a substring that is unset, which |
can happen when capturing subpattern number n+1 matches some part of | can happen when capturing subpattern number n+1 matches some part of |
the subject, but subpattern n has not been used at all, they return an | the subject, but subpattern n has not been used at all, they return an |
empty string. This can be distinguished from a genuine zero-length sub- |
empty string. This can be distinguished from a genuine zero-length sub- |
string by inspecting the appropriate offset in ovector, which is nega- | string by inspecting the appropriate offset in ovector, which is nega- |
tive for unset substrings. |
tive for unset substrings. |
|
|
The two convenience functions pcre_free_substring() and pcre_free_sub- | The two convenience functions pcre_free_substring() and pcre_free_sub- |
string_list() can be used to free the memory returned by a previous | string_list() can be used to free the memory returned by a previous |
call of pcre_get_substring() or pcre_get_substring_list(), respec- |
call of pcre_get_substring() or pcre_get_substring_list(), respec- |
tively. They do nothing more than call the function pointed to by | tively. They do nothing more than call the function pointed to by |
pcre_free, which of course could be called directly from a C program. | pcre_free, which of course could be called directly from a C program. |
However, PCRE is used in some situations where it is linked via a spe- | However, PCRE is used in some situations where it is linked via a spe- |
cial interface to another programming language that cannot use | cial interface to another programming language that cannot use |
pcre_free directly; it is for these cases that the functions are pro- | pcre_free directly; it is for these cases that the functions are pro- |
vided. |
vided. |
|
|
|
|
Line 2730 EXTRACTING CAPTURED SUBSTRINGS BY NAME
|
Line 3187 EXTRACTING CAPTURED SUBSTRINGS BY NAME
|
int stringcount, const char *stringname, |
int stringcount, const char *stringname, |
const char **stringptr); |
const char **stringptr); |
|
|
To extract a substring by name, you first have to find associated num- | To extract a substring by name, you first have to find associated num- |
ber. For example, for this pattern |
ber. For example, for this pattern |
|
|
(a+)b(?<xxx>\d+)... |
(a+)b(?<xxx>\d+)... |
Line 2739 EXTRACTING CAPTURED SUBSTRINGS BY NAME
|
Line 3196 EXTRACTING CAPTURED SUBSTRINGS BY NAME
|
be unique (PCRE_DUPNAMES was not set), you can find the number from the |
be unique (PCRE_DUPNAMES was not set), you can find the number from the |
name by calling pcre_get_stringnumber(). The first argument is the com- |
name by calling pcre_get_stringnumber(). The first argument is the com- |
piled pattern, and the second is the name. The yield of the function is |
piled pattern, and the second is the name. The yield of the function is |
the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no | the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) |
subpattern of that name. |
subpattern of that name. |
|
|
Given the number, you can extract the substring directly, or use one of |
Given the number, you can extract the substring directly, or use one of |
the functions described in the previous section. For convenience, there |
the functions described in the previous section. For convenience, there |
are also two functions that do the whole job. |
are also two functions that do the whole job. |
|
|
Most of the arguments of pcre_copy_named_substring() and | Most of the arguments of pcre_copy_named_substring() and |
pcre_get_named_substring() are the same as those for the similarly | pcre_get_named_substring() are the same as those for the similarly |
named functions that extract by number. As these are described in the | named functions that extract by number. As these are described in the |
previous section, they are not re-described here. There are just two | previous section, they are not re-described here. There are just two |
differences: |
differences: |
|
|
First, instead of a substring number, a substring name is given. Sec- | First, instead of a substring number, a substring name is given. Sec- |
ond, there is an extra argument, given at the start, which is a pointer |
ond, there is an extra argument, given at the start, which is a pointer |
to the compiled pattern. This is needed in order to gain access to the | to the compiled pattern. This is needed in order to gain access to the |
name-to-number translation table. |
name-to-number translation table. |
|
|
These functions call pcre_get_stringnumber(), and if it succeeds, they | These functions call pcre_get_stringnumber(), and if it succeeds, they |
then call pcre_copy_substring() or pcre_get_substring(), as appropri- | then call pcre_copy_substring() or pcre_get_substring(), as appropri- |
ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the | ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the |
behaviour may not be what you want (see the next section). |
behaviour may not be what you want (see the next section). |
|
|
Warning: If the pattern uses the (?| feature to set up multiple subpat- |
Warning: If the pattern uses the (?| feature to set up multiple subpat- |
terns with the same number, as described in the section on duplicate | terns with the same number, as described in the section on duplicate |
subpattern numbers in the pcrepattern page, you cannot use names to | subpattern numbers in the pcrepattern page, you cannot use names to |
distinguish the different subpatterns, because names are not included | distinguish the different subpatterns, because names are not included |
in the compiled code. The matching process uses only numbers. For this | in the compiled code. The matching process uses only numbers. For this |
reason, the use of different names for subpatterns of the same number | reason, the use of different names for subpatterns of the same number |
causes an error at compile time. |
causes an error at compile time. |
|
|
|
|
Line 2776 DUPLICATE SUBPATTERN NAMES
|
Line 3233 DUPLICATE SUBPATTERN NAMES
|
int pcre_get_stringtable_entries(const pcre *code, |
int pcre_get_stringtable_entries(const pcre *code, |
const char *name, char **first, char **last); |
const char *name, char **first, char **last); |
|
|
When a pattern is compiled with the PCRE_DUPNAMES option, names for | When a pattern is compiled with the PCRE_DUPNAMES option, names for |
subpatterns are not required to be unique. (Duplicate names are always | subpatterns are not required to be unique. (Duplicate names are always |
allowed for subpatterns with the same number, created by using the (?| | allowed for subpatterns with the same number, created by using the (?| |
feature. Indeed, if such subpatterns are named, they are required to | feature. Indeed, if such subpatterns are named, they are required to |
use the same names.) |
use the same names.) |
|
|
Normally, patterns with duplicate names are such that in any one match, |
Normally, patterns with duplicate names are such that in any one match, |
only one of the named subpatterns participates. An example is shown in | only one of the named subpatterns participates. An example is shown in |
the pcrepattern documentation. |
the pcrepattern documentation. |
|
|
When duplicates are present, pcre_copy_named_substring() and | When duplicates are present, pcre_copy_named_substring() and |
pcre_get_named_substring() return the first substring corresponding to | pcre_get_named_substring() return the first substring corresponding to |
the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING | the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING |
(-7) is returned; no data is returned. The pcre_get_stringnumber() | (-7) is returned; no data is returned. The pcre_get_stringnumber() |
function returns one of the numbers that are associated with the name, | function returns one of the numbers that are associated with the name, |
but it is not defined which it is. |
but it is not defined which it is. |
|
|
If you want to get full details of all captured substrings for a given | If you want to get full details of all captured substrings for a given |
name, you must use the pcre_get_stringtable_entries() function. The | name, you must use the pcre_get_stringtable_entries() function. The |
first argument is the compiled pattern, and the second is the name. The |
first argument is the compiled pattern, and the second is the name. The |
third and fourth are pointers to variables which are updated by the | third and fourth are pointers to variables which are updated by the |
function. After it has run, they point to the first and last entries in |
function. After it has run, they point to the first and last entries in |
the name-to-number table for the given name. The function itself | the name-to-number table for the given name. The function itself |
returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if | returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if |
there are none. The format of the table is described above in the sec- | there are none. The format of the table is described above in the sec- |
tion entitled Information about a pattern above. Given all the rele- | tion entitled Information about a pattern above. Given all the rele- |
vant entries for the name, you can extract each of their numbers, and | vant entries for the name, you can extract each of their numbers, and |
hence the captured data, if any. |
hence the captured data, if any. |
|
|
|
|
FINDING ALL POSSIBLE MATCHES |
FINDING ALL POSSIBLE MATCHES |
|
|
The traditional matching function uses a similar algorithm to Perl, | The traditional matching funct The traditional matching funct |
which stops when it finds the first match, starting at a given point in |
which stops when it finds the first match, starting at a given point in |
the subject. If you want to find all possible matches, or the longest | the subject. If you want to find all possible matches, or the longest |
possible match, consider using the alternative matching function (see | possible match, consider using the alternative matching function (see |
below) instead. If you cannot use the alternative function, but still | below) instead. If you cannot use the alternative function, but still |
need to find all possible matches, you can kludge it up by making use | need to find all possible matches, you can kludge it up by making use |
of the callout facility, which is described in the pcrecallout documen- |
of the callout facility, which is described in the pcrecallout documen- |
tation. |
tation. |
|
|
What you have to do is to insert a callout right at the end of the pat- |
What you have to do is to insert a callout right at the end of the pat- |
tern. When your callout function is called, extract and save the cur- | tern. When your callout function is called, extract and save the cur- |
rent matched substring. Then return 1, which forces pcre_exec() to | rent matched substring. Then return 1, which forces pcre_exec() to |
backtrack and try other alternatives. Ultimately, when it runs out of | backtrack and try other alternatives. Ultimately, when it runs out of |
matches, pcre_exec() will yield PCRE_ERROR_NOMATCH. |
matches, pcre_exec() will yield PCRE_ERROR_NOMATCH. |
|
|
|
|
|
OBTAINING AN ESTIMATE OF STACK USAGE |
|
|
|
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. |
|
|
|
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. |
|
|
|
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. |
|
|
|
|
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 2831 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
Line 3313 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
int options, int *ovector, int ovecsize, |
int options, int *ovector, int ovecsize, |
int *workspace, int wscount); |
int *workspace, int wscount); |
|
|
The function pcre_dfa_exec() is called to match a subject string | The function pcre_dfa_exec() is called to match a subject string |
against a compiled pattern, using a matching algorithm that scans the | against a compiled pattern, using a matching algorithm that scans the |
subject string just once, and does not backtrack. This has different | subject string just once, and does not backtrack. This has different |
characteristics to the normal algorithm, and is not compatible with | characteristics to the normal algorithm, and is not compatible with |
Perl. Some of the features of PCRE patterns are not supported. Never- | Perl. Some of the features of PCRE patterns are not supported. Never- |
theless, there are times when this kind of matching can be useful. For | theless, there are times when this kind of matching can be useful. For |
a discussion of the two matching algorithms, and a list of features | a discussion of the two matching algorithms, and a list of features |
that pcre_dfa_exec() does not support, see the pcrematching documenta- | that pcre_dfa_exec() does not support, see the pcrematching documenta- |
tion. |
tion. |
|
|
The arguments for the pcre_dfa_exec() function are the same as for | The arguments for the pcre_dfa_exec() function are the same as for |
pcre_exec(), plus two extras. The ovector argument is used in a differ- |
pcre_exec(), plus two extras. The ovector argument is used in a differ- |
ent way, and this is described below. The other common arguments are | ent way, and this is described below. The other common arguments are |
used in the same way as for pcre_exec(), so their description is not | used in the same way as for pcre_exec(), so their description is not |
repeated here. |
repeated here. |
|
|
The two additional arguments provide workspace for the function. The | The two additional arguments provide workspace for the function. The |
workspace vector should contain at least 20 elements. It is used for | workspace vector should contain at least 20 elements. It is used for |
keeping track of multiple paths through the pattern tree. More |
keeping track of multiple paths through the pattern tree. More |
workspace will be needed for patterns and subjects where there are a | workspace will be needed for patterns and subjects where there are a |
lot of potential matches. |
lot of potential matches. |
|
|
Here is an example of a simple call to pcre_dfa_exec(): |
Here is an example of a simple call to pcre_dfa_exec(): |
Line 2872 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
Line 3354 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
|
|
Option bits for pcre_dfa_exec() |
Option bits for pcre_dfa_exec() |
|
|
The unused bits of the options argument for pcre_dfa_exec() must be | The unused bits of the options argument for pcre_dfa_exec() must be |
zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW- | zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW- |
LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, |
LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, |
PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, | PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, |
PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR- | PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR- |
TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last | TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last |
four of these are exactly the same as for pcre_exec(), so their | four of these are exactly the same as for pcre_exec(), so their |
description is not repeated here. |
description is not repeated here. |
|
|
PCRE_PARTIAL_HARD |
PCRE_PARTIAL_HARD |
PCRE_PARTIAL_SOFT |
PCRE_PARTIAL_SOFT |
|
|
These have the same general effect as they do for pcre_exec(), but the | These have the same general effect as they do for pcre_exec(), but the |
details are slightly different. When PCRE_PARTIAL_HARD is set for | details are slightly different. When PCRE_PARTIAL_HARD is set for |
pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub- | pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub- |
ject is reached and there is still at least one matching possibility | ject is reached and there is still at least one matching possibility |
that requires additional characters. This happens even if some complete |
that requires additional characters. This happens even if some complete |
matches have also been found. When PCRE_PARTIAL_SOFT is set, the return |
matches have also been found. When PCRE_PARTIAL_SOFT is set, the return |
code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end |
code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end |
of the subject is reached, there have been no complete matches, but | of the subject is reached, there have been no complete matches, but |
there is still at least one matching possibility. The portion of the | there is still at least one matching possibility. The portion of the |
string that was inspected when the longest partial match was found is | string that was inspected when the longest partial match was found is |
set as the first matching string in both cases. There is a more | set as the first matching string in both cases. There is a more |
detailed discussion of partial and multi-segment matching, with exam- | detailed discussion of partial and multi-segment matching, with exam- |
ples, in the pcrepartial documentation. |
ples, in the pcrepartial documentation. |
|
|
PCRE_DFA_SHORTEST |
PCRE_DFA_SHORTEST |
|
|
Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to | Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to |
stop as soon as it has found one match. Because of the way the alterna- |
stop as soon as it has found one match. Because of the way the alterna- |
tive algorithm works, this is necessarily the shortest possible match | tive algorithm works, this is necessarily the shortest possible match |
at the first possible matching point in the subject string. |
at the first possible matching point in the subject string. |
|
|
PCRE_DFA_RESTART |
PCRE_DFA_RESTART |
|
|
When pcre_dfa_exec() returns a partial match, it is possible to call it |
When pcre_dfa_exec() returns a partial match, it is possible to call it |
again, with additional subject characters, and have it continue with | again, with additional subject characters, and have it continue with |
the same match. The PCRE_DFA_RESTART option requests this action; when | the same match. The PCRE_DFA_RESTART option requests this action; when |
it is set, the workspace and wscount options must reference the same | it is set, the workspace and wscount options must reference the same |
vector as before because data about the match so far is left in them | vector as before because data about the match so far is left in them |
after a partial match. There is more discussion of this facility in the |
after a partial match. There is more discussion of this facility in the |
pcrepartial documentation. |
pcrepartial documentation. |
|
|
Successful returns from pcre_dfa_exec() |
Successful returns from pcre_dfa_exec() |
|
|
When pcre_dfa_exec() succeeds, it may have matched more than one sub- | When pcre_dfa_exec() succeeds, it may have matched more than one sub- |
string in the subject. Note, however, that all the matches from one run |
string in the subject. Note, however, that all the matches from one run |
of the function start at the same point in the subject. The shorter | of the function start at the same point in the subject. The shorter |
matches are all initial substrings of the longer matches. For example, | matches are all initial substrings of the longer matches. For example, |
if the pattern |
if the pattern |
|
|
<.*> |
<.*> |
Line 2935 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
Line 3417 MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
|
<something> <something else> |
<something> <something else> |
<something> <something else> <something further> |
<something> <something else> <something further> |
|
|
On success, the yield of the function is a number greater than zero, | On success, the yield of the function is a number greater than zero, |
which is the number of matched substrings. The substrings themselves | which is the number of matched substrings. The substrings themselves |
are returned in ovector. Each string uses two elements; the first is | are returned in ovector. Each string uses two elements; the first is |
the offset to the start, and the second is the offset to the end. In | the offset to the start, and the second is the offset to the end. In |
fact, all the strings have the same start offset. (Space could have | fact, all the strings have the same start offset. (Space could have |
been saved by giving this only once, but it was decided to retain some | been saved by giving this only once, but it was decided to retain some |
compatibility with the way pcre_exec() returns data, even though the | compatibility with the way pcre_exec() returns data, even though the |
meaning of the strings is different.) |
meaning of the strings is different.) |
|
|
The strings are returned in reverse order of length; that is, the long- |
The strings are returned in reverse order of length; that is, the long- |
est matching string is given first. If there were too many matches to | est matching string is given first. If there were too many matches to |
fit into ovector, the yield of the function is zero, and the vector is | fit into ovector, the yield of the function is zero, and the vector is |
filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() | filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() |
can use the entire ovector for returning matched strings. |
can use the entire ovector for returning matched strings. |
|
|
Error returns from pcre_dfa_exec() |
Error returns from pcre_dfa_exec() |
|
|
The pcre_dfa_exec() function returns a negative number when it fails. | The pcre_dfa_exec() function returns a negative number when it fails. |
Many of the errors are the same as for pcre_exec(), and these are | Many of the errors are the same as for pcre_exec(), and these are |
described above. There are in addition the following errors that are | described above. There are in addition the following errors that are |
specific to pcre_dfa_exec(): |
specific to pcre_dfa_exec(): |
|
|
PCRE_ERROR_DFA_UITEM (-16) |
PCRE_ERROR_DFA_UITEM (-16) |
|
|
This return is given if pcre_dfa_exec() encounters an item in the pat- | This return is given if pcre_dfa_exec() encounters an item in the pat- |
tern that it does not support, for instance, the use of \C or a back | tern that it does not support, for instance, the use of \C or a back |
reference. |
reference. |
|
|
PCRE_ERROR_DFA_UCOND (-17) |
PCRE_ERROR_DFA_UCOND (-17) |
|
|
This return is given if pcre_dfa_exec() encounters a condition item | This return is given if pcre_dfa_exec() encounters a condition item |
that uses a back reference for the condition, or a test for recursion | that uses a back reference for the condition, or a test for recursion |
in a specific group. These are not supported. |
in a specific group. These are not supported. |
|
|
PCRE_ERROR_DFA_UMLIMIT (-18) |
PCRE_ERROR_DFA_UMLIMIT (-18) |
|
|
This return is given if pcre_dfa_exec() is called with an extra block | This return is given if pcre_dfa_exec() is called with an extra block |
that contains a setting of the match_limit or match_limit_recursion | that contains a setting of the match_limit or match_limit_recursion |
fields. This is not supported (these fields are meaningless for DFA | fields. This is not supported (these fields are meaningless for DFA |
matching). |
matching). |
|
|
PCRE_ERROR_DFA_WSSIZE (-19) |
PCRE_ERROR_DFA_WSSIZE (-19) |
|
|
This return is given if pcre_dfa_exec() runs out of space in the | This return is given if pcre_dfa_exec() runs out of space in the |
workspace vector. |
workspace vector. |
|
|
PCRE_ERROR_DFA_RECURSE (-20) |
PCRE_ERROR_DFA_RECURSE (-20) |
|
|
When a recursive subpattern is processed, the matching function calls | When a recursive subpattern is processed, the matching function calls |
itself recursively, using private vectors for ovector and workspace. | itself recursively, using private vectors for ovector and workspace. |
This error is given if the output vector is not large enough. This | This error is given if the output vector is not large enough. This |
should be extremely rare, as a vector of size 1000 is used. |
should be extremely rare, as a vector of size 1000 is used. |
|
|
|
PCRE_ERROR_DFA_BADRESTART (-30) |
|
|
|
When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some |
|
plausibility checks are made on the contents of the workspace, which |
|
should contain data about the previous partial match. If any of these |
|
checks fail, this error is given. |
|
|
|
|
SEE ALSO |
SEE ALSO |
|
|
pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar- | pcre16(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematch- |
tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3). | ing(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcresample(3), |
| pcrestack(3). |
|
|
|
|
AUTHOR |
AUTHOR |
Line 3004 AUTHOR
|
Line 3494 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 02 December 2011 | Last updated: 17 June 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 3020 PCRE CALLOUTS
|
Line 3510 PCRE CALLOUTS
|
|
|
int (*pcre_callout)(pcre_callout_block *); |
int (*pcre_callout)(pcre_callout_block *); |
|
|
|
int (*pcre16_callout)(pcre16_callout_block *); |
|
|
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). 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. 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: |
|
|
(?C1)abc(?C2)def |
(?C1)abc(?C2)def |
|
|
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 |
|
|
A(\d{2}|--) |
A(\d{2}|--) |
|
|
Line 3045 PCRE CALLOUTS
|
Line 3538 PCRE CALLOUTS
|
|
|
(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) |
(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) |
|
|
Notice that there is a callout before and after each parenthesis and | Notice that there is a callout before and after each parenthesis and |
alternation bar. Automatic callouts can be used for tracking the | alternation bar. Automatic callouts can be used for tracking the |
progress of pattern matching. The pcretest command has an option that | progress of pattern matching. The pcretest command has an option that |
sets automatic callouts; when it is used, the output indicates how the | sets automatic callouts; when it is used, the output indicates how the |
pattern is matched. This is useful information when you are trying to | pattern is matched. This is useful information when you are trying to |
optimize the performance of a particular pattern. |
optimize the performance of a particular pattern. |
|
|
The use of callouts in a pattern makes it ineligible for optimization | The use of callouts in a pattern makes it ineligible for optimization |
by the just-in-time compiler. Studying such a pattern with the |
by the just-in-time compiler. Studying such a pattern with the |
PCRE_STUDY_JIT_COMPILE option always fails. |
PCRE_STUDY_JIT_COMPILE option always fails. |
|
|
|
|
MISSING CALLOUTS |
MISSING CALLOUTS |
|
|
You should be aware that, because of optimizations in the way PCRE | You should be aware that, because of optimizations in the way PCRE |
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 |
|
|
ab(?C4)cd |
ab(?C4)cd |
|
|
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. |
|
|
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. |
|
|
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. | |
|
|
|
|
THE CALLOUT INTERFACE |
THE CALLOUT INTERFACE |
|
|
During matching, when PCRE reaches a callout point, the external func- |
During matching, when PCRE reaches a callout point, the external func- |
tion defined by pcre_callout is called (if it is set). This applies to | tion defined by pcre_callout or pcre16_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 pcre16_call- |
block. This structure contains the following fields: | out 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; | int subject_length; |
int current_position; | int start_match; |
int capture_top; | int current_position; |
int capture_last; | int capture_top; |
void *callout_data; | int capture_last; |
int pattern_position; | void *callout_data; |
int next_item_length; | |
const unsigned char *mark; | int next_item_length; |
| const unsigned char *mark; (8-bit version) |
| const PCRE_UCHAR16 *mark; (16-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 |
Line 3114 THE CALLOUT INTERFACE
|
Line 3608 THE CALLOUT INTERFACE
|
outs, and 255 for automatically generated callouts). |
outs, and 255 for automatically generated callouts). |
|
|
The offset_vector field is a pointer to the vector of offsets that was |
The offset_vector field is a pointer to the vector of offsets that was |
passed by the caller to 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 | pcre16_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 |
Line 3133 THE CALLOUT INTERFACE
|
Line 3627 THE CALLOUT INTERFACE
|
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 pcre16_exec() is used, the capture_top field |
one more than the number of the highest numbered captured substring so | contains one more than the number of the highest numbered captured sub- |
far. If no substrings have been captured, the value of capture_top is | string so far. If no substrings have been captured, the value of cap- |
one. This is always the case when pcre_dfa_exec() is used, because it | ture_top is one. This is always the case when the DFA functions are |
does not support captured substrings. | 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. If no substrings have been captured, its value is -1. |
This is always the case when pcre_dfa_exec() is used. | This is always the case for the DFA matching functions. |
|
|
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 pcre16_extra data |
structure. If no such data was passed, the value of callout_data in a |
structure. If no such data was passed, the value of callout_data in a |
pcre_callout block is NULL. There is a description of the pcre_extra | callout block is NULL. There is a description of the pcre_extra struc- |
structure in the pcreapi documentation. | ture 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. |
|
|
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 pcre16_exec() it contains a pointer to the |
nated name of the most recently passed (*MARK), (*PRUNE), or (*THEN) | zero-terminated name of the most recently passed (*MARK), (*PRUNE), or |
item in the match, or NULL if no such items have been passed. Instances | (*THEN) item in the match, or NULL if no such items have been passed. |
of (*PRUNE) or (*THEN) without a name do not obliterate a previous | Instances of (*PRUNE) or (*THEN) without a name do not obliterate a |
(*MARK). In callouts from pcre_dfa_exec() this field always contains | previous (*MARK). In callouts from the DFA matching functions this |
NULL. | field always contains NULL. |
|
|
|
|
RETURN VALUES |
RETURN VALUES |
Line 3180 RETURN VALUES
|
Line 3674 RETURN VALUES
|
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
|
Line 3693 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 30 November 2011 | Last updated: 08 Janurary 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 3217 DIFFERENCES BETWEEN PCRE AND PERL
|
Line 3711 DIFFERENCES BETWEEN 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 3292 DIFFERENCES BETWEEN PCRE AND PERL
|
Line 3786 DIFFERENCES BETWEEN PCRE AND 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, | 11. If any of the backtracking control verbs are used in an assertion |
its action is limited to that group, even if the group does not contain | or in a subpattern that is called as a subroutine (whether or not |
any | characters. | recursively), their effect is confined to that subpattern; it does not |
| extend to the surrounding 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. There is one exception to this: the name |
| from a *(MARK), (*PRUNE), or (*THEN) that is encountered in a success- |
| ful positive assertion is passed back when a match succeeds (compare |
| capturing parentheses in assertions). Note that such subpatterns are |
| processed as anchored at the point where they are tested. |
|
|
12. There are some differences that are concerned with the settings of |
12. There are some differences that are concerned with the settings of |
captured strings when part of a pattern is repeated. For example, |
captured strings when part of a pattern is repeated. For example, |
Line 3314 DIFFERENCES BETWEEN PCRE AND PERL
|
Line 3816 DIFFERENCES BETWEEN PCRE AND PERL
|
|
|
14. Perl recognizes comments in some places that PCRE does not, for |
14. 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- |
15. PCRE provides some extensions to the Perl regular expression facil- |
Line 3356 DIFFERENCES BETWEEN PCRE AND PERL
|
Line 3858 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() and |
different way and is not Perl-compatible. | pcre16_dfa_exec()) match in a different way and are not Perl-compati- |
| ble. |
|
|
(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. |
|
|
Line 3373 AUTHOR
|
Line 3876 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 14 November 2011 | Last updated: 01 June 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 3403 PCRE REGULAR EXPRESSION DETAILS
|
Line 3906 PCRE REGULAR EXPRESSION DETAILS
|
intended as reference material. |
intended as reference material. |
|
|
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, and a second library that supports 16-bit and UTF-16 character |
pcre_compile() or pcre_compile2() with the PCRE_UTF8 option. There is | strings. To use these features, PCRE must be built to include appropri- |
also a special sequence that can be given at the start of a pattern: | ate support. When using UTF strings you must either call the compiling |
| function with the PCRE_UTF8 or PCRE_UTF16 option, or the pattern must |
| start with one of these special sequences: |
|
|
(*UTF8) |
(*UTF8) |
|
(*UTF16) |
|
|
Starting a pattern with this sequence is equivalent to setting the | Starting a pattern with such a sequence is equivalent to setting the |
PCRE_UTF8 option. This feature is not Perl-compatible. How setting | relevant option. This feature is not Perl-compatible. How setting a UTF |
UTF-8 mode affects pattern matching is mentioned in several places | mode affects pattern matching is mentioned in several places below. |
below. There is also a summary of UTF-8 features in the pcreunicode | There is also a summary of features in the pcreunicode page. |
page. | |
|
|
Another special sequence that may appear at the start of a pattern or | Another special sequence that may appear at the start of a pattern or |
in combination with (*UTF8) is: | in combination with (*UTF8) or (*UTF16) is: |
|
|
(*UCP) |
(*UCP) |
|
|
This has the same effect as setting the PCRE_UCP option: it causes | This has the same effect as setting the PCRE_UCP option: it causes |
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 | If a pattern sta If a pattern sta |
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. There are also some more of these special sequences that are con- |
cerned with the handling of newlines; they are described below. |
cerned with the handling of newlines; they are described below. |
|
|
The remainder of this document discusses the patterns that are sup- | The remainder of this document discusses the patterns that are sup- |
ported by PCRE when its main matching function, pcre_exec(), is used. | ported by PCRE when one its main matching functions, pcre_exec() |
From release 6.0, PCRE offers a second matching function, | (8-bit) or pcre16_exec() (16-bit), is used. PCRE also has alternative |
pcre_dfa_exec(), which matches using a different algorithm that is not | matching functions, pcre_dfa_exec() and pcre16_dfa_exec(), which match |
Perl-compatible. Some of the features discussed below are not available | using a different algorithm that is not Perl-compatible. Some of the |
when pcre_dfa_exec() is used. The advantages and disadvantages of the | features discussed below are not available when DFA matching is used. |
alternative function, and how it differs from the normal function, are | The advantages and disadvantages of the alternative functions, and how |
discussed in the pcrematching page. | they differ from the normal functions, are discussed in the pcrematch- |
| ing page. |
|
|
|
|
NEWLINE CONVENTIONS |
NEWLINE CONVENTIONS |
Line 3459 NEWLINE CONVENTIONS
|
Line 3965 NEWLINE CONVENTIONS
|
(*ANYCRLF) any of the three above |
(*ANYCRLF) any of the three above |
(*ANY) all Unicode newline sequences |
(*ANY) all Unicode newline sequences |
|
|
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 |
|
|
Line 3491 CHARACTERS AND METACHARACTERS
|
Line 3997 CHARACTERS AND METACHARACTERS
|
|
|
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 |
Line 3552 BACKSLASH
|
Line 4058 BACKSLASH
|
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 space in |
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- |
Line 3594 BACKSLASH
|
Line 4100 BACKSLASH
|
\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 3608 BACKSLASH
|
Line 4114 BACKSLASH
|
inverted. Thus \cz becomes hex 1A (z is 7A), but \c{ becomes hex 3B ({ |
inverted. Thus \cz becomes hex 1A (z is 7A), but \c{ becomes hex 3B ({ |
is 7B), while \c; becomes hex 7B (; is 3B). If the byte following \c |
is 7B), while \c; becomes hex 7B (; is 3B). If the byte 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. (When PCRE is compiled in EBCDIC |
is compiled in EBCDIC mode, all byte values are valid. A lower case | mode, all byte values are valid. A lower case letter is converted to |
letter is converted to upper case, and then the 0xc0 bits are flipped.) | upper case, and then the 0xc0 bits are flipped.) |
|
|
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 |
| |
| Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- |
| called "surrogate" codepoints). |
| |
| If characters other than hexadecimal digits appear between \x{ and }, |
or if there is no terminating }, this form of escape is not recognized. |
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 a space |
\40 is the same, provided there are fewer than 40 |
\40 is the same, provided there are fewer than 40 |
Line 3670 BACKSLASH
|
Line 4183 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 4231 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 4268 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 4289 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 |
U+0020 Space |
U+0020 Space |
Line 3803 BACKSLASH
|
Line 4316 BACKSLASH
|
|
|
U+000A Linefeed |
U+000A Linefeed |
U+000B Vertical tab |
U+000B Vertical tab |
U+000C Formfeed | U+000C Form feed |
U+000D Carriage return |
U+000D Carriage return |
U+0085 Next line |
U+0085 Next line |
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), or (*UCP) special |
Inside a character class, \R is treated as an unrecognized escape | sequences. Inside a character class, \R is treated as an unrecognized |
sequence, and so matches the letter "R" by default, but causes an error | escape sequence, and so matches the letter "R" by default, but causes |
if PCRE_EXTRA is set. | 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 an extended Unicode sequence |
|
|
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 4478 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 and |
the pcreapi page). Perl does not support the Cs property. | PCRE_NO_UTF16_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 3990 BACKSLASH
|
Line 4509 BACKSLASH
|
by zero or more characters with the "mark" property, and treats the |
by zero or more characters with the "mark" property, and treats the |
sequence as an atomic group (see below). Characters with the "mark" |
sequence as an atomic group (see below). Characters with the "mark" |
property are typically accents that affect the preceding character. |
property are typically accents that affect the preceding character. |
None of them have codepoints less than 256, so in non-UTF-8 mode \X | None of them have codepoints less than 256, so in 8-bit non-UTF-8 mode |
matches any one character. | \X matches any one character. |
|
|
Note that recent versions of Perl have changed \X to match what Unicode |
Note that recent versions of Perl have changed \X to match what Unicode |
calls an "extended grapheme cluster", which has a more complicated def- |
calls an "extended grapheme cluster", which has a more complicated def- |
Line 4001 BACKSLASH
|
Line 4520 BACKSLASH
|
to search a structure that contains data for over fifteen thousand |
to search a structure that contains data for over fifteen thousand |
characters. That is why the traditional escape sequences such as \d and |
characters. That is why the traditional escape sequences such as \d and |
\w do not use Unicode properties in PCRE by default, though you can |
\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 | make them do so by setting the PCRE_UCP option or by starting the pat- |
starting the pattern with (*UCP). | tern with (*UCP). |
|
|
PCRE's additional properties |
PCRE's additional properties |
|
|
Line 4019 BACKSLASH
|
Line 4538 BACKSLASH
|
|
|
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. |
|
|
Line 4071 BACKSLASH
|
Line 4590 BACKSLASH
|
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. |
Line 4163 FULL STOP (PERIOD, DOT) AND \N
|
Line 4682 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. Unlike a |
individual bytes in UTF-8 mode, but it is unclear how it can usefully | dot, \C always matches line-ending characters. The feature is provided |
be used. Because \C breaks up characters into individual bytes, match- | in Perl in order to match individual bytes in UTF-8 mode, but it is |
ing one byte with \C in UTF-8 mode means that the rest of the string | unclear how it can usefully be used. Because \C breaks up characters |
may start with a malformed UTF-8 character. This has undefined results, | into individual data units, matching one unit with \C in a UTF mode |
because PCRE assumes that it is dealing with valid UTF-8 strings (and | means that the rest of the string may start with a malformed UTF char- |
by default it checks this at the start of processing unless the | acter. This has undefined results, because PCRE assumes that it is |
PCRE_NO_UTF8_CHECK option is used). | dealing with valid UTF strings (and by default it checks this at the |
| start of processing unless the PCRE_NO_UTF8_CHECK or |
| PCRE_NO_UTF16_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) | |
Line 4233 SQUARE BRACKETS AND CHARACTER CLASSES
|
Line 4754 SQUARE BRACKETS AND CHARACTER CLASSES
|
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. |
Line 4249 SQUARE BRACKETS AND CHARACTER CLASSES
|
Line 4770 SQUARE BRACKETS AND CHARACTER CLASSES
|
sumes a character from the subject string, and therefore it fails if |
sumes a character from the subject string, and therefore it fails if |
the current pointer is at the end of the string. |
the current pointer is at the end of the string. |
|
|
In UTF-8 mode, characters with values greater than 255 can be included | In UTF-8 (UTF-16) 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 |
Line 4289 SQUARE BRACKETS AND CHARACTER CLASSES
|
Line 4810 SQUARE BRACKETS AND CHARACTER CLASSES
|
|
|
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 |
Line 4369 POSIX CHARACTER CLASSES
|
Line 4890 POSIX CHARACTER CLASSES
|
POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but |
POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but |
these are not supported, and an error is given if they are encountered. |
these are not supported, and an error is given if they are encountered. |
|
|
By default, in UTF-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- |
Line 4453 INTERNAL OPTION SETTING
|
Line 4974 INTERNAL OPTION SETTING
|
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), and (*UCP) |
used to set UTF-8 and Unicode property modes; they are equivalent to | leading sequences that can be used to set UTF and Unicode property |
setting the PCRE_UTF8 and the PCRE_UCP options, respectively. | modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16, and |
| the PCRE_UCP options, respectively. |
|
|
|
|
SUBPATTERNS |
SUBPATTERNS |
Line 4471 SUBPATTERNS
|
Line 4993 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 5161 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 5193 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 sequences, each of which |
extended sequences, each of which may be several bytes long (and they | may be several data units long (and they may be of different lengths). |
may be of different lengths). | |
|
|
The quantifier {0} is permitted, causing the expression to behave as if |
The quantifier {0} is permitted, causing the expression to behave as if |
the previous item and the quantifier were not present. This may be use- |
the previous item and the quantifier were not present. This may be use- |
ful for subpatterns that are referenced as subroutines from elsewhere | ful for subpatterns that are referenced as subroutines from elsewhere |
in the pattern (but see also the section entitled "Defining subpatterns |
in the pattern (but see also the section entitled "Defining subpatterns |
for use by reference only" below). Items other than subpatterns that | for use by reference only" below). Items other than subpatterns that |
have a {0} quantifier are omitted from the compiled pattern. |
have a {0} quantifier are omitted from the compiled pattern. |
|
|
For convenience, the three most common quantifiers have single-charac- | For convenience, the three most common quantifiers have single-charac- |
ter abbreviations: |
ter abbreviations: |
|
|
* is equivalent to {0,} |
* is equivalent to {0,} |
+ is equivalent to {1,} |
+ is equivalent to {1,} |
? is equivalent to {0,1} |
? is equivalent to {0,1} |
|
|
It is possible to construct infinite loops by following a subpattern | It is possible to construct infinite loops by following a subpattern |
that can match no characters with a quantifier that has no upper limit, |
that can match no characters with a quantifier that has no upper limit, |
for example: |
for example: |
|
|
(a?)* |
(a?)* |
|
|
Earlier versions of Perl and PCRE used to give an error at compile time |
Earlier versions of Perl and PCRE used to give an error at compile time |
for such patterns. However, because there are cases where this can be | for such patterns. However, because there are cases where this can be |
useful, such patterns are now accepted, but if any repetition of the | useful, such patterns are now accepted, but if any repetition of the |
subpattern does in fact match no characters, the loop is forcibly bro- | subpattern does in fact match no characters, the loop is forcibly bro- |
ken. |
ken. |
|
|
By default, the quantifiers are "greedy", that is, they match as much | By default, the quantifiers are "greedy", that is, they match as much |
as possible (up to the maximum number of permitted times), without | as possible (up to the maximum number of permitted times), without |
causing the rest of the pattern to fail. The classic example of where | causing the rest of the pattern to fail. The classic example of where |
this gives problems is in trying to match comments in C programs. These |
this gives problems is in trying to match comments in C programs. These |
appear between /* and */ and within the comment, individual * and / | appear between /* and */ and within the comment, individual * and / |
characters may appear. An attempt to match C comments by applying the | characters may appear. An attempt to match C comments by applying the |
pattern |
pattern |
|
|
/\*.*\*/ |
/\*.*\*/ |
Line 4715 REPETITION
|
Line 5239 REPETITION
|
|
|
/* first comment */ not comment /* second comment */ |
/* first comment */ not comment /* second comment */ |
|
|
fails, because it matches the entire string owing to the greediness of | fails, because it matches the entire string owing to the greediness of |
the .* item. |
the .* item. |
|
|
However, if a quantifier is followed by a question mark, it ceases to | However, if a quantifier is followed by a question mark, it ceases to |
be greedy, and instead matches the minimum number of times possible, so |
be greedy, and instead matches the minimum number of times possible, so |
the pattern |
the pattern |
|
|
/\*.*?\*/ |
/\*.*?\*/ |
|
|
does the right thing with the C comments. The meaning of the various | does the right thing with the C comments. The meaning of the various |
quantifiers is not otherwise changed, just the preferred number of | quantifiers is not otherwise changed, just the preferred number of |
matches. Do not confuse this use of question mark with its use as a | matches. Do not confuse this use of question mark with its use as a |
quantifier in its own right. Because it has two uses, it can sometimes | quantifier in its own right. Because it has two uses, it can sometimes |
appear doubled, as in |
appear doubled, as in |
|
|
\d??\d |
\d??\d |
Line 4735 REPETITION
|
Line 5259 REPETITION
|
which matches one digit by preference, but can match two if that is the |
which matches one digit by preference, but can match two if that is the |
only way the rest of the pattern matches. |
only way the rest of the pattern matches. |
|
|
If the PCRE_UNGREEDY option is set (an option that is not available in | If the PCRE_UNGREEDY option is set (an option that is not available in |
Perl), the quantifiers are not greedy by default, but individual ones | Perl), the quantifiers are not greedy by default, but individual ones |
can be made greedy by following them with a question mark. In other | can be made greedy by following them with a question mark. In other |
words, it inverts the default behaviour. |
words, it inverts the default behaviour. |
|
|
When a parenthesized subpattern is quantified with a minimum repeat | When a parenthesized subpattern is quantified with a minimum repeat |
count that is greater than 1 or with a limited maximum, more memory is | count that is greater than 1 or with a limited maximum, more memory is |
required for the compiled pattern, in proportion to the size of the | required for the compiled pattern, in proportion to the size of the |
minimum or maximum. |
minimum or maximum. |
|
|
If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv- |
If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv- |
alent to Perl's /s) is set, thus allowing the dot to match newlines, | alent to Perl's /s) is set, thus allowing the dot to match newlines, |
the pattern is implicitly anchored, because whatever follows will be | the pattern is implicitly anchored, because whatever follows will be |
tried against every character position in the subject string, so there | tried against every character position in the subject string, so there |
is no point in retrying the overall match at any position after the | is no point in retrying the overall match at any position after the |
first. PCRE normally treats such a pattern as though it were preceded | first. PCRE normally treats such a pattern as though it were preceded |
by \A. |
by \A. |
|
|
In cases where it is known that the subject string contains no new- | In cases where it is known that the subject string contains no new- |
lines, it is worth setting PCRE_DOTALL in order to obtain this opti- | lines, it is worth setting PCRE_DOTALL in order to obtain this opti- |
mization, or alternatively using ^ to indicate anchoring explicitly. |
mization, or alternatively using ^ to indicate anchoring explicitly. |
|
|
However, there is one situation where the optimization cannot be used. | However, there is one situation where the optimization cannot be used. |
When .* is inside capturing parentheses that are the subject of a back |
When .* is inside capturing parentheses that are the subject of a back |
reference elsewhere in the pattern, a match at the start may fail where |
reference elsewhere in the pattern, a match at the start may fail where |
a later one succeeds. Consider, for example: |
a later one succeeds. Consider, for example: |
|
|
(.*)abc\1 |
(.*)abc\1 |
|
|
If the subject is "xyz123abc123" the match point is the fourth charac- | If the subject is "xyz123abc123" the match point is the fourth charac- |
ter. For this reason, such a pattern is not implicitly anchored. |
ter. For this reason, such a pattern is not implicitly anchored. |
|
|
When a capturing subpattern is repeated, the value captured is the sub- |
When a capturing subpattern is repeated, the value captured is the sub- |
Line 4773 REPETITION
|
Line 5297 REPETITION
|
(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 5308 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 5364 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 5414 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 5443 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 5452 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 5486 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, because it does not make sense for negative assertions. |
|
|
For compatibility with Perl, assertion subpatterns may be repeated; | For compatibility with Perl, assertion subpatterns may be repeated; |
though it makes no sense to assert the same thing several times, the | though it makes no sense to assert the same thing several times, the |
side effect of capturing parentheses may occasionally be useful. In | side effect of capturing parentheses may occasionally be useful. In |
practice, there only three cases: |
practice, there only three cases: |
|
|
(1) If the quantifier is {0}, the assertion is never obeyed during | (1) If the quantifier is {0}, the assertion is never obeyed during |
matching. However, it may contain internal capturing parenthesized | matching. However, it may contain internal capturing parenthesized |
groups that are called from elsewhere via the subroutine mechanism. |
groups that are called from elsewhere via the subroutine mechanism. |
|
|
(2) If quantifier is {0,n} where n is greater than zero, it is treated | (2) If quantifier is {0,n} where n is greater than zero, it is treated |
as if it were {0,1}. At run time, the rest of the pattern match is | as if it were {0,1}. At run time, the rest of the pattern match is |
tried with and without the assertion, the order depending on the greed- |
tried with and without the assertion, the order depending on the greed- |
iness of the quantifier. |
iness of the quantifier. |
|
|
(3) If the minimum repetition is greater than zero, the quantifier is | (3) If the minimum repetition is greater than zero, the quantifier is |
ignored. The assertion is obeyed just once when encountered during | ignored. The assertion is obeyed just once when encountered during |
matching. |
matching. |
|
|
Lookahead assertions |
Lookahead assertions |
Line 5048 ASSERTIONS
|
Line 5572 ASSERTIONS
|
|
|
\w+(?=;) |
\w+(?=;) |
|
|
matches a word followed by a semicolon, but does not include the semi- | matches a word followed by a semicolon, but does not include the semi- |
colon in the match, and |
colon in the match, and |
|
|
foo(?!bar) |
foo(?!bar) |
|
|
matches any occurrence of "foo" that is not followed by "bar". Note | matches any occurrence of "foo" that is not followed by "bar". Note |
that the apparently similar pattern |
that the apparently similar pattern |
|
|
(?!foo)bar |
(?!foo)bar |
|
|
does not find an occurrence of "bar" that is preceded by something | does not find an occurrence of "bar" that is preceded by something |
other than "foo"; it finds any occurrence of "bar" whatsoever, because | other than "foo"; it finds any occurrence of "bar" whatsoever, because |
the assertion (?!foo) is always true when the next three characters are |
the assertion (?!foo) is always true when the next three characters are |
"bar". A lookbehind assertion is needed to achieve the other effect. |
"bar". A lookbehind assertion is needed to achieve the other effect. |
|
|
If you want to force a matching failure at some point in a pattern, the |
If you want to force a matching failure at some point in a pattern, the |
most convenient way to do it is with (?!) because an empty string | most convenient way to do it is with (?!) because an empty string |
always matches, so an assertion that requires there not to be an empty | always matches, so an assertion that requires there not to be an empty |
string must always fail. The backtracking control verb (*FAIL) or (*F) |
string must always fail. The backtracking control verb (*FAIL) or (*F) |
is a synonym for (?!). |
is a synonym for (?!). |
|
|
Lookbehind assertions |
Lookbehind assertions |
|
|
Lookbehind assertions start with (?<= for positive assertions and (?<! | Lookbehind assertions start with (?<= for positive assertions and (?<! |
for negative assertions. For example, |
for negative assertions. For example, |
|
|
(?<!foo)bar |
(?<!foo)bar |
|
|
does find an occurrence of "bar" that is not preceded by "foo". The | does find an occurrence of "bar" that is not preceded by "foo". The |
contents of a lookbehind assertion are restricted such that all the | contents of a lookbehind assertion are restricted such that all the |
strings it matches must have a fixed length. However, if there are sev- |
strings it matches must have a fixed length. However, if there are sev- |
eral top-level alternatives, they do not all have to have the same | eral top-level alternatives, they do not all have to have the same |
fixed length. Thus |
fixed length. Thus |
|
|
(?<=bullock|donkey) |
(?<=bullock|donkey) |
Line 5088 ASSERTIONS
|
Line 5612 ASSERTIONS
|
|
|
(?<!dogs?|cats?) |
(?<!dogs?|cats?) |
|
|
causes an error at compile time. Branches that match different length | causes an error at compile time. Branches that match different length |
strings are permitted only at the top level of a lookbehind assertion. | strings are permitted only at the top level of a lookbehind assertion. |
This is an extension compared with Perl, which requires all branches to |
This is an extension compared with Perl, which requires all branches to |
match the same length of string. An assertion such as |
match the same length of string. An assertion such as |
|
|
(?<=ab(c|de)) |
(?<=ab(c|de)) |
|
|
is not permitted, because its single top-level branch can match two | is not permitted, because its single top-level branch can match two |
different lengths, but it is acceptable to PCRE if rewritten to use two |
different lengths, but it is acceptable to PCRE if rewritten to use two |
top-level branches: |
top-level branches: |
|
|
(?<=abc|abde) |
(?<=abc|abde) |
|
|
In some cases, the escape sequence \K (see above) can be used instead | In some cases, the escape sequence \K (see above) can be used instead |
of a lookbehind assertion to get round the fixed-length restriction. |
of a lookbehind assertion to get round the fixed-length restriction. |
|
|
The implementation of lookbehind assertions is, for each alternative, | The implementation of lookbehind assertions is, for each alternative, |
to temporarily move the current position back by the fixed length and | to temporarily move the current position back by the fixed length and |
then try to match. If there are insufficient characters before the cur- |
then try to match. If there are insufficient characters before the cur- |
rent position, the assertion fails. |
rent position, the assertion fails. |
|
|
In 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. |
Recursion, however, is not supported. |
Recursion, however, is not supported. |
|
|
Possessive quantifiers can be used in conjunction with lookbehind | Possessive quantifiers can be used in conjunction with lookbehind |
assertions to specify efficient matching of fixed-length strings at the |
assertions to specify efficient matching of fixed-length strings at the |
end of subject strings. Consider a simple pattern such as |
end of subject strings. Consider a simple pattern such as |
|
|
abcd$ |
abcd$ |
|
|
when applied to a long string that does not match. Because matching | when applied to a long string that does not match. Because matching |
proceeds from left to right, PCRE will look for each "a" in the subject |
proceeds from left to right, PCRE will look for each "a" in the subject |
and then see if what follows matches the rest of the pattern. If the | and then see if what follows matches the rest of the pattern. If the |
pattern is specified as |
pattern is specified as |
|
|
^.*abcd$ |
^.*abcd$ |
|
|
the initial .* matches the entire string at first, but when this fails | the initial .* matches the entire string at first, but when this fails |
(because there is no following "a"), it backtracks to match all but the |
(because there is no following "a"), it backtracks to match all but the |
last character, then all but the last two characters, and so on. Once | last character, then all but the last two characters, and so on. Once |
again the search for "a" covers the entire string, from right to left, | again the search for "a" covers the entire string, from right to left, |
so we are no better off. However, if the pattern is written as |
so we are no better off. However, if the pattern is written as |
|
|
^.*+(?<=abcd) |
^.*+(?<=abcd) |
|
|
there can be no backtracking for the .*+ item; it can match only the | there can be no backtracking for the .*+ item; it can match only the |
entire string. The subsequent lookbehind assertion does a single test | entire string. The subsequent lookbehind assertion does a single test |
on the last four characters. If it fails, the match fails immediately. | on the last four characters. If it fails, the match fails immediately. |
For long strings, this approach makes a significant difference to the | For long strings, this approach makes a significant difference to the |
processing time. |
processing time. |
|
|
Using multiple assertions |
Using multiple assertions |
Line 5152 ASSERTIONS
|
Line 5676 ASSERTIONS
|
|
|
(?<=\d{3})(?<!999)foo |
(?<=\d{3})(?<!999)foo |
|
|
matches "foo" preceded by three digits that are not "999". Notice that | matches "foo" preceded by three digits that are not "999". Notice that |
each of the assertions is applied independently at the same point in | each of the assertions is applied independently at the same point in |
the subject string. First there is a check that the previous three | the subject string. First there is a check that the previous three |
characters are all digits, and then there is a check that the same | characters are all digits, and then there is a check that the same |
three characters are not "999". This pattern does not match "foo" pre- |
three characters are not "999". This pattern does not match "foo" pre- |
ceded by six characters, the first of which are digits and the last | ceded by six characters, the first of which are digits and the last |
three of which are not "999". For example, it doesn't match "123abc- | three of which are not "999". For example, it doesn't match "123abc- |
foo". A pattern to do that is |
foo". A pattern to do that is |
|
|
(?<=\d{3}...)(?<!999)foo |
(?<=\d{3}...)(?<!999)foo |
|
|
This time the first assertion looks at the preceding six characters, | This time the first assertion looks at the preceding six characters, |
checking that the first three are digits, and then the second assertion |
checking that the first three are digits, and then the second assertion |
checks that the preceding three characters are not "999". |
checks that the preceding three characters are not "999". |
|
|
Line 5171 ASSERTIONS
|
Line 5695 ASSERTIONS
|
|
|
(?<=(?<!foo)bar)baz |
(?<=(?<!foo)bar)baz |
|
|
matches an occurrence of "baz" that is preceded by "bar" which in turn | matches an occurrence of "baz" that is preceded by "bar" which in turn |
is not preceded by "foo", while |
is not preceded by "foo", while |
|
|
(?<=\d{3}(?!999)...)foo |
(?<=\d{3}(?!999)...)foo |
|
|
is another pattern that matches "foo" preceded by three digits and any | is another pattern that matches "foo" preceded by three digits and any |
three characters that are not "999". |
three characters that are not "999". |
|
|
|
|
CONDITIONAL SUBPATTERNS |
CONDITIONAL SUBPATTERNS |
|
|
It is possible to cause the matching process to obey a subpattern con- | It is possible to cause the matching process to obey a subpattern con- |
ditionally or to choose between two alternative subpatterns, depending | ditionally or to choose between two alternative subpatterns, depending |
on the result of an assertion, or whether a specific capturing subpat- | on the result of an assertion, or whether a specific capturing subpat- |
tern has already been matched. The two possible forms of conditional | tern has already been matched. The two possible forms of conditional |
subpattern are: |
subpattern are: |
|
|
(?(condition)yes-pattern) |
(?(condition)yes-pattern) |
(?(condition)yes-pattern|no-pattern) |
(?(condition)yes-pattern|no-pattern) |
|
|
If the condition is satisfied, the yes-pattern is used; otherwise the | If the condition is satisfied, the yes-pattern is used; otherwise the |
no-pattern (if present) is used. If there are more than two alterna- | no-pattern (if present) is used. If there are more than two alterna- |
tives in the subpattern, a compile-time error occurs. Each of the two | tives in the subpattern, a compile-time error occurs. Each of the two |
alternatives may itself contain nested subpatterns of any form, includ- |
alternatives may itself contain nested subpatterns of any form, includ- |
ing conditional subpatterns; the restriction to two alternatives |
ing conditional subpatterns; the restriction to two alternatives |
applies only at the level of the condition. This pattern fragment is an |
applies only at the level of the condition. This pattern fragment is an |
Line 5202 CONDITIONAL SUBPATTERNS
|
Line 5726 CONDITIONAL SUBPATTERNS
|
(?(1) (A|B|C) | (D | (?(2)E|F) | E) ) |
(?(1) (A|B|C) | (D | (?(2)E|F) | E) ) |
|
|
|
|
There are four kinds of condition: references to subpatterns, refer- | There are four kinds of condition: references to subpatterns, refer- |
ences to recursion, a pseudo-condition called DEFINE, and assertions. |
ences to recursion, a pseudo-condition called DEFINE, and assertions. |
|
|
Checking for a used subpattern by number |
Checking for a used subpattern by number |
|
|
If the text between the parentheses consists of a sequence of digits, | If the text between the parentheses consists of a sequence of digits, |
the condition is true if a capturing subpattern of that number has pre- |
the condition is true if a capturing subpattern of that number has pre- |
viously matched. If there is more than one capturing subpattern with | viously matched. If there is more than one capturing subpattern with |
the same number (see the earlier section about duplicate subpattern | the same number (see the earlier section about duplicate subpattern |
numbers), the condition is true if any of them have matched. An alter- | numbers), the condition is true if any of them have matched. An alter- |
native notation is to precede the digits with a plus or minus sign. In | native notation is to precede the digits with a plus or minus sign. In |
this case, the subpattern number is relative rather than absolute. The | this case, the subpattern number is relative rather than absolute. The |
most recently opened parentheses can be referenced by (?(-1), the next | most recently opened parentheses can be referenced by (?(-1), the next |
most recent by (?(-2), and so on. Inside loops it can also make sense | most recent by (?(-2), and so on. Inside loops it can also make sense |
to refer to subsequent groups. The next parentheses to be opened can be |
to refer to subsequent groups. The next parentheses to be opened can be |
referenced as (?(+1), and so on. (The value zero in any of these forms | referenced as (?(+1), and so on. (The value zero in any of these forms |
is not used; it provokes a compile-time error.) |
is not used; it provokes a compile-time error.) |
|
|
Consider the following pattern, which contains non-significant white | Consider the following pattern, which contains non-significant white |
space to make it more readable (assume the PCRE_EXTENDED option) and to |
space to make it more readable (assume the PCRE_EXTENDED option) and to |
divide it into three parts for ease of discussion: |
divide it into three parts for ease of discussion: |
|
|
( \( )? [^()]+ (?(1) \) ) |
( \( )? [^()]+ (?(1) \) ) |
|
|
The first part matches an optional opening parenthesis, and if that | The first part matches an optional opening parenthesis, and if that |
character is present, sets it as the first captured substring. The sec- |
character is present, sets it as the first captured substring. The sec- |
ond part matches one or more characters that are not parentheses. The | ond part matches one or more characters that are not parentheses. The |
third part is a conditional subpattern that tests whether or not the | third part is a conditional subpattern that tests whether or not the |
first set of parentheses matched. If they did, that is, if subject | first set of parentheses matched. If they did, that is, if subject |
started with an opening parenthesis, the condition is true, and so the | started with an opening parenthesis, the condition is true, and so the |
yes-pattern is executed and a closing parenthesis is required. Other- | yes-pattern is executed and a closing parenthesis is required. Other- |
wise, since no-pattern is not present, the subpattern matches nothing. | wise, since no-pattern is not present, the subpattern matches nothing. |
In other words, this pattern matches a sequence of non-parentheses, | In other words, this pattern matches a sequence of non-parentheses, |
optionally enclosed in parentheses. |
optionally enclosed in parentheses. |
|
|
If you were embedding this pattern in a larger one, you could use a | If you were embedding this pattern in a larger one, you cou If you were embedding this pattern in a larger one, you cou |
relative reference: |
relative reference: |
|
|
...other stuff... ( \( )? [^()]+ (?(-1) \) ) ... |
...other stuff... ( \( )? [^()]+ (?(-1) \) ) ... |
|
|
This makes the fragment independent of the parentheses in the larger | This makes the fragment independent of the parentheses in the larger |
pattern. |
pattern. |
|
|
Checking for a used subpattern by name |
Checking for a used subpattern by name |
|
|
Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a | Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a |
used subpattern by name. For compatibility with earlier versions of | used subpattern by name. For compatibility with earlier versions of |
PCRE, which had this facility before Perl, the syntax (?(name)...) is | PCRE, which had this facility before Perl, the syntax (?(name)...) is |
also recognized. However, there is a possible ambiguity with this syn- | also recognized. However, there is a possible ambiguity with this syn- |
tax, because subpattern names may consist entirely of digits. PCRE | tax, because subpattern names may consist entirely of digits. PCRE |
looks first for a named subpattern; if it cannot find one and the name | looks first for a named subpattern; if it cannot find one and the name |
consists entirely of digits, PCRE looks for a subpattern of that num- | consists entirely of digits, PCRE looks for a subpattern of that num- |
ber, which must be greater than zero. Using subpattern names that con- | ber, which must be greater than zero. Using subpattern names that con- |
sist entirely of digits is not recommended. |
sist entirely of digits is not recommended. |
|
|
Rewriting the above example to use a named subpattern gives this: |
Rewriting the above example to use a named subpattern gives this: |
|
|
(?<OPEN> \( )? [^()]+ (?(<OPEN>) \) ) |
(?<OPEN> \( )? [^()]+ (?(<OPEN>) \) ) |
|
|
If the name used in a condition of this kind is a duplicate, the test | If the name used in a condition of this kind is a duplicate, the test |
is applied to all subpatterns of the same name, and is true if any one | is applied to all subpatterns of the same name, and is true if any one |
of them has matched. |
of them has matched. |
|
|
Checking for pattern recursion |
Checking for pattern recursion |
|
|
If the condition is the string (R), and there is no subpattern with the |
If the condition is the string (R), and there is no subpattern with the |
name R, the condition is true if a recursive call to the whole pattern | name R, the condition is true if a recursive call to the whole pattern |
or any subpattern has been made. If digits or a name preceded by amper- |
or any subpattern has been made. If digits or a name preceded by amper- |
sand follow the letter R, for example: |
sand follow the letter R, for example: |
|
|
Line 5276 CONDITIONAL SUBPATTERNS
|
Line 5800 CONDITIONAL SUBPATTERNS
|
|
|
the condition is true if the most recent recursion is into a subpattern |
the condition is true if the most recent recursion is into a subpattern |
whose number or name is given. This condition does not check the entire |
whose number or name is given. This condition does not check the entire |
recursion stack. If the name used in a condition of this kind is a | recursion stack. If the name used in a condition of this kind is a |
duplicate, the test is applied to all subpatterns of the same name, and |
duplicate, the test is applied to all subpatterns of the same name, and |
is true if any one of them is the most recent recursion. |
is true if any one of them is the most recent recursion. |
|
|
At "top level", all these recursion test conditions are false. The | At "top level", all these recursion test conditions are false. The |
syntax for recursive patterns is described below. |
syntax for recursive patterns is described below. |
|
|
Defining subpatterns for use by reference only |
Defining subpatterns for use by reference only |
|
|
If the condition is the string (DEFINE), and there is no subpattern | If the condition is the string (DEFINE), and there is no subpattern |
with the name DEFINE, the condition is always false. In this case, | with the name DEFINE, the condition is always false. In this case, |
there may be only one alternative in the subpattern. It is always | there may be only one alternative in the subpattern. It is always |
skipped if control reaches this point in the pattern; the idea of | skipped if control reaches this point in the pattern; the idea of |
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 |
|
|
The first part of the pattern is a DEFINE group inside which a another | The first part of the pattern is a DEFINE group inside which a another |
group named "byte" is defined. This matches an individual component of | group named "byte" is defined. This matches an individual component of |
an IPv4 address (a number less than 256). When matching takes place, | an IPv4 address (a number less than 256). When matching takes place, |
this part of the pattern is skipped because DEFINE acts like a false | this part of the pattern is skipped because DEFINE acts like a false |
condition. The rest of the pattern uses references to the named group | condition. The rest of the pattern uses references to the named group |
to match the four dot-separated components of an IPv4 address, insist- | to match the four dot-separated components of an IPv4 address, insist- |
ing on a word boundary at each end. |
ing on a word boundary at each end. |
|
|
Assertion conditions |
Assertion conditions |
|
|
If the condition is not in any of the above formats, it must be an | If the condition is not in any of the above formats, it must be an |
assertion. This may be a positive or negative lookahead or lookbehind | assertion. This may be a positive or negative lookahead or lookbehind |
assertion. Consider this pattern, again containing non-significant | assertion. Consider this pattern, again containing non-significant |
white space, and with the two alternatives on the second line: |
white space, and with the two alternatives on the second line: |
|
|
(?(?=[^a-z]*[a-z]) |
(?(?=[^a-z]*[a-z]) |
\d{2}-[a-z]{3}-\d{2} | \d{2}-\d{2}-\d{2} ) |
\d{2}-[a-z]{3}-\d{2} | \d{2}-\d{2}-\d{2} ) |
|
|
The condition is a positive lookahead assertion that matches an | The condition is a positive lookahead assertion that matches an |
optional sequence of non-letters followed by a letter. In other words, | optional sequence of non-letters followed by a letter. In other words, |
it tests for the presence of at least one letter in the subject. If a | it tests for the presence of at least one letter in the subject. If a |
letter is found, the subject is matched against the first alternative; | letter is found, the subject is matched against the first alternative; |
otherwise it is matched against the second. This pattern matches | otherwise it is matched against the second. This pattern matches |
strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are | strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are |
letters and dd are digits. |
letters and dd are digits. |
|
|
|
|
Line 5329 COMMENTS
|
Line 5853 COMMENTS
|
There are two ways of including comments in patterns that are processed |
There are two ways of including comments in patterns that are processed |
by PCRE. In both cases, the start of the comment must not be in a char- |
by PCRE. In both cases, the start of the comment must not be in a char- |
acter class, nor in the middle of any other sequence of related charac- |
acter class, nor in the middle of any other sequence of related charac- |
ters such as (?: or a subpattern name or number. The characters that | ters such as (?: or a subpattern name or number. The characters that |
make up a comment play no part in the pattern matching. |
make up a comment play no part in the pattern matching. |
|
|
The sequence (?# marks the start of a comment that continues up to the | The sequence (?# marks the start of a comment that continues up to the |
next closing parenthesis. Nested parentheses are not permitted. If the | next closing parenthesis. Nested parentheses are not permitted. If the |
PCRE_EXTENDED option is set, an unescaped # character also introduces a |
PCRE_EXTENDED option is set, an unescaped # character also introduces a |
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 |
|
|
On encountering the # character, pcre_compile() skips along, looking | On encountering the # character, pcre_compile() skips along, looking |
for a newline in the pattern. The sequence \n is still literal at this | for a newline in the pattern. The sequence \n is still literal at this |
stage, so it does not terminate the comment. Only an actual character | stage, so it does not terminate the comment. Only an actual character |
with the code value 0x0a (the default newline) does so. |
with the code value 0x0a (the default newline) does so. |
|
|
|
|
RECURSIVE PATTERNS |
RECURSIVE PATTERNS |
|
|
Consider the problem of matching a string in parentheses, allowing for | Consider the problem of matching a string in parentheses, allowing for |
unlimited nested parentheses. Without the use of recursion, the best | unlimited nested parentheses. Without the use of recursion, the best |
that can be done is to use a pattern that matches up to some fixed | that can be done is to use a pattern that matches up to some fixed |
depth of nesting. It is not possible to handle an arbitrary nesting | depth of nesting. It is not possible to handle an arbitrary nesting |
depth. |
depth. |
|
|
For some time, Perl has provided a facility that allows regular expres- |
For some time, Perl has provided a facility that allows regular expres- |
sions to recurse (amongst other things). It does this by interpolating | sions to recurse (amongst other things). It does this by interpolating |
Perl code in the expression at run time, and the code can refer to the | Perl code in the expression at run time, and the code can refer to the |
expression itself. A Perl pattern using code interpolation to solve the |
expression itself. A Perl pattern using code interpolation to solve the |
parentheses problem can be created like this: |
parentheses problem can be created like this: |
|
|
Line 5373 RECURSIVE PATTERNS
|
Line 5897 RECURSIVE PATTERNS
|
refers recursively to the pattern in which it appears. |
refers recursively to the pattern in which it appears. |
|
|
Obviously, PCRE cannot support the interpolation of Perl code. Instead, |
Obviously, PCRE cannot support the interpolation of Perl code. Instead, |
it supports special syntax for recursion of the entire pattern, and | it supports special syntax for recursion of the entire pattern, and |
also for individual subpattern recursion. After its introduction in | also for individual subpattern recursion. After its introduction in |
PCRE and Python, this kind of recursion was subsequently introduced | PCRE and Python, this kind of recursion was subsequently introduced |
into Perl at release 5.10. |
into Perl at release 5.10. |
|
|
A special item that consists of (? followed by a number greater than | A special item that consists of (? followed by a number greater than |
zero and a closing parenthesis is a recursive subroutine call of the | zero and a closing parenthesis is a recursive subroutine call of the |
subpattern of the given number, provided that it occurs inside that | subpattern of the given number, provided that it occurs inside that |
subpattern. (If not, it is a non-recursive subroutine call, which is | subpattern. (If not, it is a non-recursive subroutine call, which is |
described in the next section.) The special item (?R) or (?0) is a | described in the next section.) The special item (?R) or (?0) is a |
recursive call of the entire regular expression. |
recursive call of the entire regular expression. |
|
|
This PCRE pattern solves the nested parentheses problem (assume the | This PCRE pattern solves the nested parentheses problem (assume the |
PCRE_EXTENDED option is set so that white space is ignored): |
PCRE_EXTENDED option is set so that white space is ignored): |
|
|
\( ( [^()]++ | (?R) )* \) |
\( ( [^()]++ | (?R) )* \) |
|
|
First it matches an opening parenthesis. Then it matches any number of | First it matches an opening parenthesis. Then it matches any number of |
substrings which can either be a sequence of non-parentheses, or a | substrings which can either be a sequence of non-parentheses, or a |
recursive match of the pattern itself (that is, a correctly parenthe- | recursive match of the pattern itself (that is, a correctly parenthe- |
sized substring). Finally there is a closing parenthesis. Note the use |
sized substring). Finally there is a closing parenthesis. Note the use |
of a possessive quantifier to avoid backtracking into sequences of non- |
of a possessive quantifier to avoid backtracking into sequences of non- |
parentheses. |
parentheses. |
|
|
If this were part of a larger pattern, you would not want to recurse | If this were part of a larger pattern, you would If this were part of a larger pattern, you would |
the entire pattern, so instead you could use this: |
the entire pattern, so instead you could use this: |
|
|
( \( ( [^()]++ | (?1) )* \) ) |
( \( ( [^()]++ | (?1) )* \) ) |
|
|
We have put the pattern into parentheses, and caused the recursion to | We have put the pattern into parentheses, and caused the recursion to |
refer to them instead of the whole pattern. |
refer to them instead of the whole pattern. |
|
|
In a larger pattern, keeping track of parenthesis numbers can be | In a larger pattern, keeping track of parenthesis numbers can be |
tricky. This is made easier by the use of relative references. Instead | tricky. This is made easier by the use of relative references. Instead |
of (?1) in the pattern above you can write (?-2) to refer to the second |
of (?1) in the pattern above you can write (?-2) to refer to the second |
most recently opened parentheses preceding the recursion. In other | most recently opened parentheses preceding the recursion. In other |
words, a negative number counts capturing parentheses leftwards from | words, a negative number counts capturing parentheses leftwards from |
the point at which it is encountered. |
the point at which it is encountered. |
|
|
It is also possible to refer to subsequently opened parentheses, by | It is also possible to refer to subsequently opened parentheses, by |
writing references such as (?+2). However, these cannot be recursive | writing references such as (?+2). However, these cannot be recursive |
because the reference is not inside the parentheses that are refer- | because the reference is not inside the parentheses that are refer- |
enced. They are always non-recursive subroutine calls, as described in | enced. They are always non-recursive subroutine calls, as described in |
the next section. |
the next section. |
|
|
An alternative approach is to use named parentheses instead. The Perl | An alternative approach is to use named parentheses instead. The Perl |
syntax for this is (?&name); PCRE's earlier syntax (?P>name) is also | syntax for this is (?&name); PCRE's earlier syntax (?P>name) is also |
supported. We could rewrite the above example as follows: |
supported. We could rewrite the above example as follows: |
|
|
(?<pn> \( ( [^()]++ | (?&pn) )* \) ) |
(?<pn> \( ( [^()]++ | (?&pn) )* \) ) |
|
|
If there is more than one subpattern with the same name, the earliest | If there is more than one subpattern with the same name, the earliest |
one is used. |
one is used. |
|
|
This particular example pattern that we have been looking at contains | This particular example pattern that we have been looking at contains |
nested unlimited repeats, and so the use of a possessive quantifier for |
nested unlimited repeats, and so the use of a possessive quantifier for |
matching strings of non-parentheses is important when applying the pat- |
matching strings of non-parentheses is important when applying the pat- |
tern to strings that do not match. For example, when this pattern is | tern to strings that do not match. For example, when this pattern is |
applied to |
applied to |
|
|
(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa() |
(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa() |
|
|
it yields "no match" quickly. However, if a possessive quantifier is | it yields "no match" quickly. However, if a possessive quantifier is |
not used, the match runs for a very long time indeed because there are | not used, the match runs for a very long time indeed because there are |
so many different ways the + and * repeats can carve up the subject, | so many different ways the + and * repeats can carve up the subject, |
and all have to be tested before failure can be reported. |
and all have to be tested before failure can be reported. |
|
|
At the end of a match, the values of capturing parentheses are those | At the end of a match, the values of capturing parentheses are those |
from the outermost level. If you want to obtain intermediate values, a | from the outermost level. If you want to obtain intermediate values, a |
callout function can be used (see below and the pcrecallout documenta- | callout function can be used (see below and the pcrecallout documenta- |
tion). If the pattern above is matched against |
tion). If the pattern above is matched against |
|
|
(ab(cd)ef) |
(ab(cd)ef) |
|
|
the value for the inner capturing parentheses (numbered 2) is "ef", | the value for the inner capturing parentheses (numbered 2) is "ef", |
which is the last value taken on at the top level. If a capturing sub- | which is the last value taken on at the top level. If a capturing sub- |
pattern is not matched at the top level, its final captured value is | pattern is not matched at the top level, its final captured value is |
unset, even if it was (temporarily) set at a deeper level during the | unset, even if it was (temporarily) set at a deeper level during the |
matching process. |
matching process. |
|
|
If there are more than 15 capturing parentheses in a pattern, PCRE has | If there are more than 15 capturing parentheses in a pattern, PCRE has |
to obtain extra memory to store data during a recursion, which it does | to obtain extra memory to store data during a recursion, which it does |
by using pcre_malloc, freeing it via pcre_free afterwards. If no memory |
by using pcre_malloc, freeing it via pcre_free afterwards. If no memory |
can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error. |
can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error. |
|
|
Do not confuse the (?R) item with the condition (R), which tests for | Do not confuse the (?R) item with the condition (R), which tests for |
recursion. Consider this pattern, which matches text in angle brack- | recursion. Consider this pattern, which matches text in angle brack- |
ets, allowing for arbitrary nesting. Only digits are allowed in nested | ets, allowing for arbitrary nesting. Only digits are allowed in nested |
brackets (that is, when recursing), whereas any characters are permit- | brackets (that is, when recursing), whereas any characters are permit- |
ted at the outer level. |
ted at the outer level. |
|
|
< (?: (?(R) \d++ | [^<>]*+) | (?R)) * > |
< (?: (?(R) \d++ | [^<>]*+) | (?R)) * > |
|
|
In this pattern, (?(R) is the start of a conditional subpattern, with | In this pattern, (?(R) is the start of a conditional subpattern, with |
two different alternatives for the recursive and non-recursive cases. | two different alternatives for the recursive and non-recursive cases. |
The (?R) item is the actual recursive call. |
The (?R) item is the actual recursive call. |
|
|
Differences in recursion processing between PCRE and Perl |
Differences in recursion processing between PCRE and Perl |
|
|
Recursion processing in PCRE differs from Perl in two important ways. | Recursion processing in PCRE differs from Perl in two important ways. |
In PCRE (like Python, but unlike Perl), a recursive subpattern call is | In PCRE (like Python, but unlike Perl), a recursive subpattern call is |
always treated as an atomic group. That is, once it has matched some of |
always treated as an atomic group. That is, once it has matched some of |
the subject string, it is never re-entered, even if it contains untried |
the subject string, it is never re-entered, even if it contains untried |
alternatives and there is a subsequent matching failure. This can be | alternatives and there is a subsequent matching failure. This can be |
illustrated by the following pattern, which purports to match a palin- | illustrated by the following pattern, which purports to match a palin- |
dromic string that contains an odd number of characters (for example, | dromic string that contains an odd number of characters (for example, |
"a", "aba", "abcba", "abcdcba"): |
"a", "aba", "abcba", "abcdcba"): |
|
|
^(.|(.)(?1)\2)$ |
^(.|(.)(?1)\2)$ |
|
|
The idea is that it either matches a single character, or two identical |
The idea is that it either matches a single character, or two identical |
characters surrounding a sub-palindrome. In Perl, this pattern works; | characters surrounding a sub-palindrome. In Perl, this pattern works; |
in PCRE it does not if the pattern is longer than three characters. | in PCRE it does not if the pattern is longer than three characters. |
Consider the subject string "abcba": |
Consider the subject string "abcba": |
|
|
At the top level, the first character is matched, but as it is not at | At the top level, the first character is matched, but as it is not at |
the end of the string, the first alternative fails; the second alterna- |
the end of the string, the first alternative fails; the second alterna- |
tive is taken and the recursion kicks in. The recursive call to subpat- |
tive is taken and the recursion kicks in. The recursive call to subpat- |
tern 1 successfully matches the next character ("b"). (Note that the | tern 1 successfully matches the next character ("b"). (Note that the |
beginning and end of line tests are not part of the recursion). |
beginning and end of line tests are not part of the recursion). |
|
|
Back at the top level, the next character ("c") is compared with what | Back at the top level, the next character ("c") is compared with what |
subpattern 2 matched, which was "a". This fails. Because the recursion | subpattern 2 matched, which was "a". This fails. Because the recursion |
is treated as an atomic group, there are now no backtracking points, | is treated as an atomic group, there are now no backtracking points, |
and so the entire match fails. (Perl is able, at this point, to re- | and so the entire match fails. (Perl is able, at this point, to re- |
enter the recursion and try the second alternative.) However, if the | enter the recursion and try the second alternative.) However, if the |
pattern is written with the alternatives in the other order, things are |
pattern is written with the alternatives in the other order, things are |
different: |
different: |
|
|
^((.)(?1)\2|.)$ |
^((.)(?1)\2|.)$ |
|
|
This time, the recursing alternative is tried first, and continues to | This time, the recursing alternative is tried first, and continues to |
recurse until it runs out of characters, at which point the recursion | recurse until it runs out of characters, at which point the recursion |
fails. But this time we do have another alternative to try at the | fails. But this time we do have another alternative to try at the |
higher level. That is the big difference: in the previous case the | higher level. That is the big difference: in the previous case the |
remaining alternative is at a deeper recursion level, which PCRE cannot |
remaining alternative is at a deeper recursion level, which PCRE cannot |
use. |
use. |
|
|
To change the pattern so that it matches all palindromic strings, not | To change the pattern so that it matches all palindromic strings, not |
just those with an odd number of characters, it is tempting to change | just those with an odd number of characters, it is tempting to change |
the pattern to this: |
the pattern to this: |
|
|
^((.)(?1)\2|.?)$ |
^((.)(?1)\2|.?)$ |
|
|
Again, this works in Perl, but not in PCRE, and for the same reason. | Again, this works in Perl, but not in PCRE, and for the same reason. |
When a deeper recursion has matched a single character, it cannot be | When a deeper recursion has matched a single character, it cannot be |
entered again in order to match an empty string. The solution is to | entered again in order to match an empty string. The solution is to |
separate the two cases, and write out the odd and even cases as alter- | separate the two cases, and write out the odd and even cases as alter- |
natives at the higher level: |
natives at the higher level: |
|
|
^(?:((.)(?1)\2|)|((.)(?3)\4|.)) |
^(?:((.)(?1)\2|)|((.)(?3)\4|.)) |
|
|
If you want to match typical palindromic phrases, the pattern has to | If you want to match typical palindromic phrases, the patte If you want to match typical palindromic phrases, the patte |
ignore all non-word characters, which can be done like this: |
ignore all non-word characters, which can be done like this: |
|
|
^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+\4|\W*+.\W*+))\W*+$ |
^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+\4|\W*+.\W*+))\W*+$ |
|
|
If run with the PCRE_CASELESS option, this pattern matches phrases such |
If run with the PCRE_CASELESS option, this pattern matches phrases such |
as "A man, a plan, a canal: Panama!" and it works well in both PCRE and |
as "A man, a plan, a canal: Panama!" and it works well in both PCRE and |
Perl. Note the use of the possessive quantifier *+ to avoid backtrack- | Perl. Note the use of the possessive quantifier *+ to avoid backtrack- |
ing into sequences of non-word characters. Without this, PCRE takes a | ing into sequences of non-word characters. Without this, PCRE takes a |
great deal longer (ten times or more) to match typical phrases, and | great deal longer (ten times or more) to match typical phrases, and |
Perl takes so long that you think it has gone into a loop. |
Perl takes so long that you think it has gone into a loop. |
|
|
WARNING: The palindrome-matching patterns above work only if the sub- | WARNING: The palindrome-matching patterns above work only if the sub- |
ject string does not start with a palindrome that is shorter than the | ject string does not start with a palindrome that is shorter than the |
entire string. For example, although "abcba" is correctly matched, if | entire string. For example, although "abcba" is correctly matched, if |
the subject is "ababa", PCRE finds the palindrome "aba" at the start, | the subject is "ababa", PCRE finds the palindrome "aba" at the start, |
then fails at top level because the end of the string does not follow. | then fails at top level because the end of the string does not follow. |
Once again, it cannot jump back into the recursion to try other alter- | Once again, it cannot jump back into the recursion to try other alter- |
natives, so the entire match fails. |
natives, so the entire match fails. |
|
|
The second way in which PCRE and Perl differ in their recursion pro- | The second way in which PCRE and Perl differ in their recursion pro- |
cessing is in the handling of captured values. In Perl, when a subpat- | cessing is in the handling of captured values. In Perl, when a subpat- |
tern is called recursively or as a subpattern (see the next section), | tern is called recursively or as a subpattern (see the next section), |
it has no access to any values that were captured outside the recur- | it has no access to any values that were captured outside the recur- |
sion, whereas in PCRE these values can be referenced. Consider this | sion, whereas in PCRE these values can be referenced. Consider this |
pattern: |
pattern: |
|
|
^(.)(\1|a(?2)) |
^(.)(\1|a(?2)) |
|
|
In PCRE, this pattern matches "bab". The first capturing parentheses | In PCRE, this pattern matches "bab". The first capturing parentheses |
match "b", then in the second group, when the back reference \1 fails | match "b", then in the second group, when the back reference \1 fails |
to match "b", the second alternative matches "a" and then recurses. In | to match "b", the second alternative matches "a" and then recurses. In |
the recursion, \1 does now match "b" and so the whole match succeeds. | the recursion, \1 does now match "b" and so the whole match succeeds. |
In Perl, the pattern fails to match because inside the recursive call | In Perl, the pattern fails to match because inside the recursive call |
\1 cannot access the externally set value. |
\1 cannot access the externally set value. |
|
|
|
|
SUBPATTERNS AS SUBROUTINES |
SUBPATTERNS AS SUBROUTINES |
|
|
If the syntax for a recursive subpattern call (either by number or by | If the syntax for a recursive subpattern call (either by number or by |
name) is used outside the parentheses to which it refers, it operates | name) is used outside the parentheses to which it refers, it operates |
like a subroutine in a programming language. The called subpattern may | like a subroutine in a programming language. The called subpattern may |
be defined before or after the reference. A numbered reference can be | be defined before or after the reference. A numbered reference can be |
absolute or relative, as in these examples: |
absolute or relative, as in these examples: |
|
|
(...(absolute)...)...(?2)... |
(...(absolute)...)...(?2)... |
Line 5578 SUBPATTERNS AS SUBROUTINES
|
Line 6102 SUBPATTERNS AS SUBROUTINES
|
|
|
(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 instead the pattern |
not "sense and responsibility". If instead the pattern |
|
|
(sens|respons)e and (?1)ibility |
(sens|respons)e and (?1)ibility |
|
|
is used, it does match "sense and responsibility" as well as the other | is used, it does match "sense and responsibility" as well as the other |
two strings. Another example is given in the discussion of DEFINE | two strings. Another example is given in the discussion of DEFINE |
above. |
above. |
|
|
All subroutine calls, whether recursive or not, are always treated as | All subroutine calls, whether recursive or not, are always treated as |
atomic groups. That is, once a subroutine has matched some of the sub- | atomic groups. That is, once a subroutine has matched some of the sub- |
ject string, it is never re-entered, even if it contains untried alter- |
ject string, it is never re-entered, even if it contains untried alter- |
natives and there is a subsequent matching failure. Any capturing | natives and there is a subsequent matching failure. Any capturing |
parentheses that are set during the subroutine call revert to their | parentheses that are set during the subroutine call revert to their |
previous values afterwards. |
previous values afterwards. |
|
|
Processing options such as case-independence are fixed when a subpat- | Processing options such as case-independence are fixed when a subpat- |
tern is defined, so if it is used as a subroutine, such options cannot | tern is defined, so if it is used as a subroutine, such options cannot |
be changed for different calls. For example, consider this pattern: |
be changed for different calls. For example, consider this pattern: |
|
|
(abc)(?i:(?-1)) |
(abc)(?i:(?-1)) |
|
|
It matches "abcabc". It does not match "abcABC" because the change of | It matches "abcabc". It does not match "abcABC" because t It matches "abcabc". It does not match "abcABC" because the change of |
processing option does not affect the called subpattern. |
processing option does not affect the called subpattern. |
|
|
|
|
ONIGURUMA SUBROUTINE SYNTAX |
ONIGURUMA SUBROUTINE SYNTAX |
|
|
For compatibility with Oniguruma, the non-Perl syntax \g followed by a | For compatibility with Oniguruma, the non-Perl syntax \g followed by a |
name or a number enclosed either in angle brackets or single quotes, is |
name or a number enclosed either in angle brackets or single quotes, is |
an alternative syntax for referencing a subpattern as a subroutine, | an alternative syntax for referencing a subpattern as a subroutine, |
possibly recursively. Here are two of the examples used above, rewrit- | possibly recursively. Here are two of the examples used above, rewrit- |
ten using this syntax: |
ten using this syntax: |
|
|
(?<pn> \( ( (?>[^()]+) | \g<pn> )* \) ) |
(?<pn> \( ( (?>[^()]+) | \g<pn> )* \) ) |
(sens|respons)e and \g'1'ibility |
(sens|respons)e and \g'1'ibility |
|
|
PCRE supports an extension to Oniguruma: if a number is preceded by a | PCRE supports an extension to Oniguruma: if a number is preceded by a |
plus or a minus sign it is taken as a relative reference. For example: |
plus or a minus sign it is taken as a relative reference. For example: |
|
|
(abc)(?i:\g<-1>) |
(abc)(?i:\g<-1>) |
|
|
Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not | Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not |
synonymous. The former is a back reference; the latter is a subroutine | synonymous. The former is a back reference; the latter is a subroutine |
call. |
call. |
|
|
|
|
CALLOUTS |
CALLOUTS |
|
|
Perl has a feature whereby using the sequence (?{...}) causes arbitrary |
Perl has a feature whereby using the sequence (?{...}) causes arbitrary |
Perl code to be obeyed in the middle of matching a regular expression. | Perl code to be obeyed in the middle of matching a regular expression. |
This makes it possible, amongst other things, to extract different sub- |
This makes it possible, amongst other things, to extract different sub- |
strings that match the same pair of parentheses when there is a repeti- |
strings that match the same pair of parentheses when there is a repeti- |
tion. |
tion. |
|
|
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 pcre16_callout (16-bit library). By |
all calling out. | 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. |
|
|
During matching, when PCRE reaches a callout point (and pcre_callout is | During matching, when PCRE reaches a callout point, the external func- |
set), the external function is called. It is provided with the number | tion is called. It is provided with the number of the callout, the |
of the callout, the position in the pattern, and, optionally, one item | position in the pattern, and, optionally, one item of data originally |
of data originally supplied by the caller of pcre_exec(). The callout | supplied by the caller of the matching function. The callout function |
function may cause matching to proceed, to backtrack, or to fail alto- | may cause matching to proceed, to backtrack, or to fail altogether. A |
gether. A complete description of the interface to the callout function | complete description of the interface to the callout function is given |
is given in the pcrecallout documentation. | in the pcrecallout documentation. |
|
|
|
|
BACKTRACKING CONTROL |
BACKTRACKING CONTROL |
|
|
Perl 5.10 introduced a number of "Special Backtracking Control Verbs", | Perl 5.10 introduced a number of "Special Backtracking Control Verbs", |
which are described in the Perl documentation as "experimental and sub- |
which are described in the Perl documentation as "experimental and sub- |
ject to change or removal in a future version of Perl". It goes on to | 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 | say: "Their usage in production code should be noted to avoid problems |
during upgrades." The same remarks apply to the PCRE features described |
during upgrades." The same remarks apply to the PCRE features described |
in this section. |
in this section. |
|
|
Since these verbs are specifically related to backtracking, most of | Since these verbs are specifically related to backtracking, most of |
them can be used only when the pattern is to be matched using | them can be used only when the pattern is to be matched using one of |
pcre_exec(), which uses a backtracking algorithm. With the exception of | the traditional matching functions, which use a backtracking algorithm. |
(*FAIL), which behaves like a failing negative assertion, they cause an | With the exception of (*FAIL), which behaves like a failing negative |
error if encountered by pcre_dfa_exec(). | assertion, they cause an error if encountered by a DFA matching func- |
| tion. |
|
|
If any of these verbs are used in an assertion or in a subpattern that |
If any of these verbs are used in an assertion or in a subpattern that |
is called as a subroutine (whether or not recursively), their effect is |
is called as a subroutine (whether or not recursively), their effect is |
Line 5682 BACKTRACKING CONTROL
|
Line 6207 BACKTRACKING CONTROL
|
that is encountered in a successful positive assertion is passed back |
that is encountered in a successful positive assertion is passed back |
when a match succeeds (compare capturing parentheses in assertions). |
when a match succeeds (compare capturing parentheses in assertions). |
Note that such subpatterns are processed as anchored at the point where |
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- | they are tested. Note also that Perl's treatment of subroutines and |
ferent in some cases. | assertions is different 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, with differing be- |
haviour, depending on whether or not an argument is present. A name is |
haviour, depending on whether or not an argument 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 library. If the name is empty, that is, if the closing parenthe- |
number of these verbs may occur in a pattern. | sis immediately follows the colon, the effect is as if the colon were |
| not there. Any number of these verbs may occur in a pattern. |
|
|
PCRE contains some optimizations that are used to speed up matching by | Optimizations that affect backtracking verbs |
| |
| 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 suppresses |
the running of a match, any included backtracking verbs will not, of | the 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 opt by setting the PCRE_NO_START_OPTIMIZE option when calling pcre_com- |
pile() or pcre_exec(), or by starting the pattern with (*NO_START_OPT). |
pile() or pcre_exec(), or by starting the pattern with (*NO_START_OPT). |
|
There is more discussion of this option in the section entitled "Option |
|
bits for pcre_exec()" in the pcreapi documentation. |
|
|
Experiments with Perl suggest that it too has similar optimizations, | Experiments with Perl suggest that it too has similar optimizations, |
sometimes leading to anomalous results. |
sometimes leading to anomalous results. |
|
|
Verbs that act immediately |
Verbs that act immediately |
|
|
The following verbs act as soon as they are encountered. They may not | The following verbs act as soon as they are encountered. Th The following verbs act as soon as they are encountered. They may not |
be followed by a name. |
be followed by a name. |
|
|
(*ACCEPT) |
(*ACCEPT) |
|
|
This verb causes the match to end successfully, skipping the remainder | This verb causes the match to end successfully, skipping the remainder |
of the pattern. However, when it is inside a subpattern that is called | of the pattern. However, when it is inside a subpattern that is called |
as a subroutine, only that subpattern is ended successfully. Matching | as a subroutine, only that subpattern is ended successfully. Matching |
then continues at the outer level. If (*ACCEPT) is inside capturing | then continues at the outer level. If (*ACCEPT) is inside capturing |
parentheses, the data so far is captured. For example: |
parentheses, the data so far is captured. For example: |
|
|
A((?:A|B(*ACCEPT)|C)D) |
A((?:A|B(*ACCEPT)|C)D) |
|
|
This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap- | This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap- |
tured by the outer parentheses. |
tured by the outer parentheses. |
|
|
(*FAIL) or (*F) |
(*FAIL) or (*F) |
|
|
This verb causes a matching failure, forcing backtracking to occur. It | This verb causes a matching failure, forcing backtracking to occur. It |
is equivalent to (?!) but easier to read. The Perl documentation notes | is equivalent to (?!) but easier to read. The Perl documentation notes |
that it is probably useful only when combined with (?{}) or (??{}). | that it is probably useful only when combined with (?{}) or (??{}). |
Those are, of course, Perl features that are not present in PCRE. The | Those are, of course, Perl features that are not present in PCRE. The |
nearest equivalent is the callout feature, as for example in this pat- | nearest equivalent is the callout feature, as for example in this pat- |
tern: |
tern: |
|
|
a+(?C)(*FAIL) |
a+(?C)(*FAIL) |
|
|
A match with the string "aaaa" always fails, but the callout is taken | A match with the string "aaaa" always fails, but the callout is taken |
before each backtrack happens (in this example, 10 times). |
before each backtrack happens (in this example, 10 times). |
|
|
Recording which path was taken |
Recording which path was taken |
|
|
There is one verb whose main purpose is to track how a match was | There is one verb whose main purpose is to track how a match was |
arrived at, though it also has a secondary use in conjunction with | arrived at, though it also has a secondary use in conjunction with |
advancing the match starting point (see (*SKIP) below). |
advancing the match starting point (see (*SKIP) below). |
|
|
(*MARK:NAME) or (*:NAME) |
(*MARK:NAME) or (*:NAME) |
|
|
A name is always required with this verb. There may be as many | A name is always required with this verb. There may be as many |
instances of (*MARK) as you like in a pattern, and their names do not | instances of (*MARK) as you like in a pattern, and their names do not |
have to be unique. |
have to be unique. |
|
|
When a match succeeds, the name of the last-encountered (*MARK) on the | When a match succeeds, the name of the last-encountered (*MARK) on the |
matching path is passed back to the caller via the pcre_extra data | matching path is passed back to the caller as described in the section |
structure, as described in the section on pcre_extra in the pcreapi | entitled "Extra data for pcre_exec()" in the pcreapi documentation. |
documentation. Here is an example of pcretest output, where the /K mod- | Here is an example of pcretest output, where the /K modifier requests |
ifier requests the retrieval and outputting of (*MARK) data: | the retrieval and outputting 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 6295 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 (*MARK) is encountered in a positive assertion, its name is recorded |
and passed back if it is the last-encountered. This does not happen for |
and passed back if it is the last-encountered. This does not happen for |
negative assertions. |
negative assertions. |
|
|
After a partial match or a failed match, the name of the last encoun- | After a partial match or a failed match, the name of the last encoun- |
tered (*MARK) in the entire match process is returned. For example: |
tered (*MARK) in 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, its effect is confined to that group, |
because once the group has been matched, there is never any backtrack- | because once the group has been matched, there is never any backtrack- |
ing into it. In this situation, backtracking can "jump back" to the | ing into it. In this situation, backtracking can "jump back" to the |
left of the entire atomic group. (Remember also, as stated above, that | left of the entire atomic group. (Remember also, as stated above, that |
this localization also applies in subroutine calls and assertions.) |
this localization also applies in subroutine calls and assertions.) |
|
|
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. |
|
|
(*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 the rest of the pattern does not match. Even if the |
pattern is unanchored, no further attempts to find a match by advancing |
pattern is unanchored, no further attempts to find a match by advancing |
the starting point take place. Once (*COMMIT) has been passed, |
the starting point take place. Once (*COMMIT) has been passed, |
pcre_exec() is committed to finding a match at the current starting | pcre_exec() is committed to finding a match at the current starting |
point, or not at all. For example: |
point, or not at all. For example: |
|
|
a+(*COMMIT)b |
a+(*COMMIT)b |
|
|
This matches "xxaab" but not "aacaab". It can be thought of as a kind | This matches "xxaab" but not "aacaab". It can be thought of as a kind |
of dynamic anchor, or "I've started, so I must finish." The name of the |
of dynamic anchor, or "I've started, so I must finish." The name of the |
most recently passed (*MARK) in the path is passed back when (*COMMIT) | most recently passed (*MARK) in the path is passed back when (*COMMIT) |
forces a match failure. |
forces a match failure. |
|
|
Note that (*COMMIT) at the start of a pattern is not the same as an | Note that (*COMMIT) at the start of a pattern is not the same as an |
anchor, unless PCRE's start-of-match optimizations are turned off, as | anchor, unless PCRE's start-of-match optimizations are turned off, as |
shown in this pcretest example: |
shown in this pcretest example: |
|
|
re> /(*COMMIT)abc/ |
re> /(*COMMIT)abc/ |
Line 5826 BACKTRACKING CONTROL
|
Line 6360 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 the rest of the pattern does not match. If the pattern |
is unanchored, the normal "bumpalong" advance to the next starting | is unanchored, the normal "bumpalong" advance to the next starting |
character then happens. Backtracking can occur as usual to the left of | character then happens. Backtracking can occur as usual to the left of |
(*PRUNE), before it is reached, or when matching to the right of | (*PRUNE), before it is reached, or when matching to the right of |
(*PRUNE), but if there is no match to the right, backtracking cannot | (*PRUNE), but if there is no match to the right, backtracking cannot |
cross (*PRUNE). In simple cases, the use of (*PRUNE) is just an alter- | cross (*PRUNE). In simple cases, the use of (*PRUNE) is just an alter- |
native to an atomic group or possessive quantifier, but there are some | native to an atomic group or possessive quantifier, but there are some |
uses of (*PRUNE) that cannot be expressed in any other way. The behav- |
uses of (*PRUNE) that cannot be expressed in any other way. The behav- |
iour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE). In an | iour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE). In an |
anchored pattern (*PRUNE) has the same effect as (*COMMIT). |
anchored pattern (*PRUNE) has the same effect as (*COMMIT). |
|
|
(*SKIP) |
(*SKIP) |
|
|
This verb, when given without a name, is like (*PRUNE), except that if | This verb, when given without a name, is like (*PRUNE), except that if |
the pattern is unanchored, the "bumpalong" advance is not to the next | the pattern is unanchored, the "bumpalong" advance is not to the next |
character, but to the position in the subject where (*SKIP) was encoun- |
character, but to the position in the subject where (*SKIP) was encoun- |
tered. (*SKIP) signifies that whatever text was matched leading up to | tered. (*SKIP) signifies that whatever text was matched leading up to |
it cannot be part of a successful match. Consider: |
it cannot be part of a successful match. Consider: |
|
|
a+(*SKIP)b |
a+(*SKIP)b |
|
|
If the subject is "aaaac...", after the first match attempt fails | If the subject is "aaaac...", after the first match attempt fails |
(starting at the first character in the string), the starting point | (starting at the first character in the string), the starting point |
skips on to start the next attempt at "c". Note that a possessive quan- |
skips on to start the next attempt at "c". Note that a possessive quan- |
tifer does not have the same effect as this example; although it would | tifer does not have the same effect as this example; although it would |
suppress backtracking during the first match attempt, the second | suppress backtracking during the first match attempt, the second |
attempt would start at the second character instead of skipping on to | attempt would start at the second character instead of skipping on to |
"c". |
"c". |
|
|
(*SKIP:NAME) |
(*SKIP:NAME) |
|
|
When (*SKIP) has an associated name, its behaviour is modified. If the | When (*SKIP) has an associated name, its behaviour is modified. If the |
following pattern fails to match, the previous path through the pattern |
following pattern fails to match, the previous path through the pattern |
is searched for the most recent (*MARK) that has the same name. If one | is searched for the most recent (*MARK) that has the same name. If one |
is found, the "bumpalong" advance is to the subject position that cor- | is found, the "bumpalong" advance is to the subject position that cor- |
responds to that (*MARK) instead of to where (*SKIP) was encountered. | responds to that (*MARK) instead of to where (*SKIP) was encountered. |
If no (*MARK) with a matching name is found, the (*SKIP) is ignored. |
If no (*MARK) with a matching name is found, the (*SKIP) is ignored. |
|
|
(*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 if the rest |
of the pattern does not match. That is, it cancels pending backtrack- | of the pattern does not match. That is, it cancels pending backtrack- |
ing, but only within the current alternative. Its name comes from the | ing, but only within the current alternative. Its name comes from the |
observation that it can be used for a pattern-based if-then-else block: |
observation 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. The behaviour of (*THEN:NAME) is exactly the same as |
(*MARK:NAME)(*THEN). If (*THEN) is not inside an alternation, it acts | (*MARK:NAME)(*THEN). If (*THEN) is not inside an alternation, it acts |
like (*PRUNE). |
like (*PRUNE). |
|
|
Note that a subpattern that does not contain a | character is just a | Note that a subpattern that does not contain a | character is just a |
part of the enclosing alternative; it is not a nested alternation with | part of the enclosing alternative; it is not a nested alternation with |
only one alternative. The effect of (*THEN) extends beyond such a sub- | only one alternative. The effect of (*THEN) extends beyond such a sub- |
pattern to the enclosing alternative. Consider this pattern, where A, | pattern to the enclosing alternative. Consider this pattern, where A, |
B, etc. are complex pattern fragments that do not contain any | charac- |
B, etc. are complex pattern fragments that do not contain any | charac- |
ters at this level: |
ters 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 also 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. |
|
|
Line 5940 BACKTRACKING CONTROL
|
Line 6474 BACKTRACKING CONTROL
|
|
|
(A(*COMMIT)B(*THEN)C|D) |
(A(*COMMIT)B(*THEN)C|D) |
|
|
Once A has matched, PCRE is committed to this match, at the current | Once A has matched, PCRE is committed to this match, at the current |
starting position. If subsequently B matches, but C does not, the nor- | 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 |
mal (*THEN) action of trying the next alternative (that is, D) does not |
happen because (*COMMIT) overrides. |
happen because (*COMMIT) overrides. |
|
|
|
|
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). |
|
|
|
|
AUTHOR |
AUTHOR |
Line 5960 AUTHOR
|
Line 6495 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 29 November 2011 | Last updated: 17 June 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 5976 PCRE REGULAR EXPRESSION SYNTAX SUMMARY
|
Line 6511 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 6525 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 6538 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 an extended Unicode sequence |
|
|
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 6083 PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P
|
Line 6618 PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P
|
|
|
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 6654 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 6208 OPTION SETTING
|
Line 6745 OPTION SETTING
|
one of the newline-setting options with similar syntax: |
one of the newline-setting options with similar syntax: |
|
|
(*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) |
(*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 6815 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 6824 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) or (*UCP) option. |
|
|
(*CR) carriage return only |
(*CR) carriage return only |
(*LF) linefeed only |
(*LF) linefeed only |
Line 6304 NEWLINE CONVENTIONS
|
Line 6847 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 6873 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 21 November 2010 | Last updated: 10 January 2012 |
Copyright (c) 1997-2010 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 6342 NAME
|
Line 6885 NAME
|
PCRE - Perl-compatible regular expressions |
PCRE - Perl-compatible regular expressions |
|
|
|
|
UTF-8 AND UNICODE PROPERTY SUPPORT | UTF-8, UTF-16, AND UNICODE PROPERTY SUPPORT |
|
|
In order process UTF-8 strings, you must build PCRE to include UTF-8 | From Release 8.30, in addition to its previous UTF-8 support, PCRE also |
support in the code, and, in addition, you must call pcre_compile() | supports UTF-16 by means of a separate 16-bit library. This can be |
with the PCRE_UTF8 option flag, or the pattern must start with the | built as well as, or instead of, the 8-bit library. |
sequence (*UTF8). When either of these is the case, both the pattern | |
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 | |
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, | |
| UTF-8 SUPPORT |
| |
| 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). When either of these is the case, both the pattern and any |
| subject strings that are matched against it are treated as UTF-8 |
| strings instead of strings of 1-byte characters. |
| |
| |
| UTF-16 SUPPORT |
| |
| In order process UTF-16 strings, you must build PCRE's 16-bit library |
| with UTF support, and, in addition, you must call pcre16_compile() with |
| the PCRE_UTF16 option flag, or the pattern must start with the sequence |
| (*UTF16). When either of these is the case, both the pattern and any |
| subject strings that are matched against it are treated as UTF-16 |
| strings instead of strings of 16-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 |
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 | is limited to testing the PCRE_UTF8/16 flag occasionally, so should not |
very big. | 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&. A full list is given in the pcrepattern |
pcrepattern documentation. Only the short names for properties are sup- | documentation. Only the short names for properties are supported. For |
ported. For example, \p{L} matches a letter. Its Perl synonym, \p{Let- | example, \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not |
ter}, is not supported. Furthermore, in Perl, many properties may | supported. Furthermore, in Perl, many properties may optionally be |
optionally be prefixed by "Is", for compatibility with Perl 5.6. PCRE | prefixed by "Is", for compatibility with Perl 5.6. PCRE does not sup- |
does not support this. | port 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 U+D800 to U+DFFF. |
|
|
The excluded code points are the "Low Surrogate Area" of Unicode, of | The excluded code points are the "Surrogate Area" of Unicode. They are |
which the Unicode Standard says this: "The Low Surrogate Area does not | reserved for use by UTF-16, where they are used in pairs to encode |
contain any character assignments, consequently no character code | codepoints with values greater than 0xFFFF. The code points that are |
charts or namelists are provided for this area. Surrogates are reserved | encoded by UTF-16 pairs are available independently in the UTF-8 encod- |
for use with UTF-16 and then must be used in pairs." The code points | ing. (In other words, the whole surrogate thing is a fudge for UTF-16 |
that are encoded by UTF-16 pairs are available as independent code | which unfortunately messes up UTF-8.) |
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 with different patterns. If you set the |
tively) contains only valid UTF-8 codes. In this case, it does not | PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE assumes |
diagnose an invalid UTF-8 string. | that the pattern or subject it is 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, | If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, |
what happens depends on why the string is invalid. If the string con- | what happens depends on why the string is invalid. If the string con- |
forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a |
forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a |
string of characters in the range 0 to 0x7FFFFFFF by pcre_dfa_exec() | 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 | and the interpreted version of pcre_exec(). In other words, apart from |
the initial validity test, these functions (when in UTF-8 mode) handle | the initial validity test, these functions (when in UTF-8 mode) handle |
strings according to the more liberal rules of RFC 2279. However, the | strings according to the more liberal rules of RFC 2279. However, the |
just-in-time (JIT) optimization for pcre_exec() supports only RFC 3629. |
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- | 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. |
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 want to process strings of values in the full range 0 to |
0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you can | 0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you can |
set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in |
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 | this situation, you will have to apply your own validity check, and |
avoid the use of JIT optimization. |
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. |
|
|
4. The dot metacharacter matches one UTF-8 character instead of a sin- | General comments about UTF modes |
gle byte. | |
|
|
|
1. Codepoints less than 256 can be specified 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 |
5. The escape sequence \C can be used to match a single byte in UTF-8 |
mode, but its use can lead to some strange effects because it breaks up | mode, or a single 16-bit data unit in UTF-16 mode, but its use can lead |
multibyte characters (see the description of \C in the pcrepattern doc- | to some strange effects because it breaks up multi-unit characters (see |
umentation). The use of \C is not supported in the alternative matching | the description of \C in the pcrepattern documentation). The use of \C |
function pcre_dfa_exec(), nor is it supported in UTF-8 mode by the JIT | is not supported in the alternative matching function |
optimization of pcre_exec(). If JIT optimization is requested for a | pcre[16]_dfa_exec(), nor is it supported in UTF mode by the JIT opti- |
UTF-8 pattern that contains \C, it will not succeed, and so the match- | mization of pcre[16]_exec(). If JIT optimization is requested for a UTF |
ing will be carried out by the normal interpretive function. | 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 | 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 | Even when Unicode property support is available, PCRE still uses its |
own character tables when checking the case of low-valued characters, | own character tables when checking the case of low-valued characters, |
so as not to degrade performance. The Unicode property information is | so as not to degrade performance. The Unicode property information is |
used only for characters with higher values. Furthermore, PCRE supports |
used only for characters with higher values. Furthermore, PCRE supports |
case-insensitive matching only when there is a one-to-one mapping | case-insensitive matching only when there is a one-to-one mapping |
between a letter's cases. There are a small number of many-to-one map- | between a letter's cases. There are a small number of many-to-one map- |
pings in Unicode; these are not supported by PCRE. |
pings in Unicode; these are not supported by PCRE. |
|
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|
Line 6484 AUTHOR
|
Line 7074 AUTHOR
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|
|
REVISION |
REVISION |
|
|
Last updated: 19 October 2011 | Last updated: 14 April 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 6502 PCRE JUST-IN-TIME COMPILER SUPPORT
|
Line 7092 PCRE JUST-IN-TIME COMPILER SUPPORT
|
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 and 16-BIT SUPPORT |
|
|
|
JIT support is available for both the 8-bit and 16-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, substi- |
|
tute the 16-bit functions and 16-bit structures (for example, |
|
pcre16_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 7122 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 |
|
|
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 API is implemented in a way that falls back to the interpretive |
code if JIT is not available. |
code if JIT is not available. |
|
|
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 |
Line 6552 SIMPLE USE OF JIT
|
Line 7149 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 |
Line 6571 SIMPLE USE OF JIT
|
Line 7168 SIMPLE USE OF JIT
|
pcre_free(study_ptr); |
pcre_free(study_ptr); |
#endif |
#endif |
|
|
In some circumstances you may need to call additional functions. These | PCRE_STUDY_JIT_COMPILE requests the JIT compiler to generate code for |
are described in the section entitled "Controlling the JIT stack" | 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 |
| 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 6603 SIMPLE USE OF JIT
|
Line 7221 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_NOTBOL, PCRE_NOTEOL, |
PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not | PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PAR- |
supported. | TIAL_SOFT. |
|
|
The unsupported pattern items are: |
The unsupported pattern items are: |
|
|
\C match a single byte; not supported in UTF-8 mode |
\C match a single byte; not supported in UTF-8 mode |
(?Cn) callouts |
(?Cn) callouts |
(*COMMIT) ) | (*PRUNE) ) |
(*MARK) ) | (*SKIP) ) backtracking control verbs |
(*PRUNE) ) the backtracking control verbs | |
(*SKIP) ) | |
(*THEN) ) |
(*THEN) ) |
|
|
Support for some of these may be added in future. |
Support for some of these may be added in future. |
Line 6681 CONTROLLING THE JIT STACK
|
Line 7297 CONTROLLING THE JIT STACK
|
void *data |
void *data |
|
|
The extra argument must be the result of studying a pattern with |
The extra argument must be the result of studying a pattern with |
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 7306 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 6719 CONTROLLING THE JIT STACK
|
Line 7347 CONTROLLING THE JIT STACK
|
Use a one-line callback function |
Use a one-line callback function |
return thread_local_var |
return thread_local_var |
|
|
All the functions described in this section do nothing if JIT is not | All the functions described in this section do nothing if JIT is not |
available, and pcre_assign_jit_stack() does nothing unless the extra | available, and pcre_assign_jit_stack() does nothing unless the extra |
argument is non-NULL and points to a pcre_extra block that is the | argument is non-NULL and points to a pcre_extra block that is the |
result of a successful study with PCRE_STUDY_JIT_COMPILE. | result of a successful study with PCRE_STUDY_JIT_COMPILE etc. |
|
|
|
|
JIT STACK FAQ |
JIT STACK FAQ |
|
|
(1) Why do we need JIT stacks? |
(1) Why do we need JIT stacks? |
|
|
PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack | PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack |
where the local data of the current node is pushed before checking its | where the local data of the current node is pushed before checking its |
child nodes. Allocating real machine stack on some platforms is diffi- |
child nodes. Allocating real machine stack on some platforms is diffi- |
cult. For example, the stack chain needs to be updated every time if we |
cult. For example, the stack chain needs to be updated every time if we |
extend the stack on PowerPC. Although it is possible, its updating | extend the stack on PowerPC. Although it is possible, its updating |
time overhead decreases performance. So we do the recursion in memory. |
time overhead decreases performance. So we do the recursion in memory. |
|
|
(2) Why don't we simply allocate blocks of memory with malloc()? |
(2) Why don't we simply allocate blocks of memory with malloc()? |
|
|
Modern operating systems have a nice feature: they can reserve an | Modern operating systems have a nice feature: they can reserve an |
address space instead of allocating memory. We can safely allocate mem- |
address space instead of allocating memory. We can safely allocate mem- |
ory pages inside this address space, so the stack could grow without | ory pages inside this address space, so the stack cou ory pages inside this address space, so the stack cou |
moving memory data (this is important because of pointers). Thus we can |
moving memory data (this is important because of pointers). Thus we can |
allocate 1M address space, and use only a single memory page (usually | allocate 1M address space, and use only a single memory page (usually |
4K) if that is enough. However, we can still grow up to 1M anytime if | 4K) if that is enough. However, we can still grow up to 1M anytime if |
needed. |
needed. |
|
|
(3) Who "owns" a JIT stack? |
(3) Who "owns" a JIT stack? |
|
|
The owner of the stack is the user program, not the JIT studied pattern |
The owner of the stack is the user program, not the JIT studied pattern |
or anything else. The user program must ensure that if a stack is used | or anything else. The user program must ensure that if a stack is used |
by pcre_exec(), (that is, it is assigned to the pattern currently run- | by pcre_exec(), (that is, it is assigned to the pattern currently run- |
ning), that stack must not be used by any other threads (to avoid over- |
ning), that stack must not be used by any other threads (to avoid over- |
writing the same memory area). The best practice for multithreaded pro- |
writing the same memory area). The best practice for multithreaded pro- |
grams is to allocate a stack for each thread, and return this stack | grams is to allocate a stack for each thread, and return this stack |
through the JIT callback function. |
through the JIT callback function. |
|
|
(4) When should a JIT stack be freed? |
(4) When should a JIT stack be freed? |
|
|
You can free a JIT stack at any time, as long as it will not be used by |
You can free a JIT stack at any time, as long as it will not be used by |
pcre_exec() again. When you assign the stack to a pattern, only a | pcre_exec() again. When you assign the stack to a pattern, only a |
pointer is set. There is no reference counting or any other magic. You | pointer is set. There is no reference counting or any other magic. You |
can free the patterns and stacks in any order, anytime. Just do not | can free the patterns and stacks in any order, anytime. Just do not |
call pcre_exec() with a pattern pointing to an already freed stack, as | call pcre_exec() with a pattern pointing to an already freed stack, as |
that will cause SEGFAULT. (Also, do not free a stack currently used by | that will cause SEGFAULT. (Also, do not free a stack currently used by |
pcre_exec() in another thread). You can also replace the stack for a | pcre_exec() in another thread). You can also replace the stack for a |
pattern at any time. You can even free the previous stack before | pattern at any time. You can even free the previous stack before |
assigning a replacement. |
assigning a replacement. |
|
|
(5) Should I allocate/free a stack every time before/after calling | (5) Should I allocate/free a stack every time before/afte (5) Should I allocate/free a stack every time before/afte |
pcre_exec()? |
pcre_exec()? |
|
|
No, because this is too costly in terms of resources. However, you | No, because this is too costly in terms of resources. However, you |
could implement some clever idea which release the stack if it is not | could implement some clever idea which release the stack if it is not |
used in let's say two minutes. The JIT callback can help to achive this |
used in let's say two minutes. The JIT callback can help to achive this |
without keeping a list of the currently JIT studied patterns. |
without keeping a list of the currently JIT studied patterns. |
|
|
(6) OK, the stack is for long term memory allocation. But what happens | (6) OK, the stack is for long term memory allocation. But what happens |
if a pattern causes stack overflow with a stack of 1M? Is that 1M kept | if a pattern causes stack overflow with a stack of 1M? Is that 1M kept |
until the stack is freed? |
until the stack is freed? |
|
|
Especially on embedded sytems, it might be a good idea to release mem- | Especially on embedded sytems, it might be a good idea to release mem- |
ory sometimes without freeing the stack. There is no API for this at | ory sometimes without freeing the stack. There is no API for this at |
the moment. Probably a function call which returns with the currently | the moment. Probably a function call which returns with the currently |
allocated memory for any stack and another which allows releasing mem- | allocated memory for any stack and another which allows releasing mem- |
ory (shrinking the stack) would be a good idea if someone needs this. |
ory (shrinking the stack) would be a good idea if someone needs this. |
|
|
(7) This is too much of a headache. Isn't there any better solution for |
(7) This is too much of a headache. Isn't there any better solution for |
JIT stack handling? |
JIT stack handling? |
|
|
No, thanks to Windows. If POSIX threads were used everywhere, we could | No, thanks to Windows. If POSIX threads were used everywhere, we could |
throw out this complicated API. |
throw out this complicated API. |
|
|
|
|
EXAMPLE CODE |
EXAMPLE CODE |
|
|
This is a single-threaded example that specifies a JIT stack without | This is a single-threaded example that specifies a JIT stack without |
using a callback. |
using a callback. |
|
|
int rc; |
int rc; |
Line 6831 AUTHOR
|
Line 7459 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 26 November 2011 | Last updated: 04 May 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 6845 NAME
|
Line 7473 NAME
|
|
|
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 7495 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() or pcre16_study() with one or both of these |
PCRE_STUDY_JIT_COMPILE option. It also disables two of PCRE's standard | 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 pcre16_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 pcre16_exec() |
subject string is reached successfully, but matching cannot continue | when the end of the subject string is reached successfully, but match- |
because more characters are needed. However, at least one character in | ing cannot continue because more characters are needed. However, at |
the subject must have been inspected. This character need not form part | least one character in the subject must have been inspected. This char- |
of the final matched string; lookbehind assertions and the \K escape | acter need not form part of the final matched string; lookbehind asser- |
sequence provide ways of inspecting characters before the start of a | tions and the \K escape sequence provide ways of inspecting characters |
matched substring. The requirement for inspecting at least one charac- | before the start of a matched substring. The requirement for inspecting |
ter exists because an empty string can always be matched; without such | at least one character exists because an empty string can always be |
a restriction there would always be a partial match of an empty string | matched; without such a restriction there would always be a partial |
at the end of the subject. | 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. | |
|
|
For the majority of patterns, the first offset identifies the start of |
For the majority of patterns, the first offset identifies the start of |
the partially matched string. However, for patterns that contain look- |
the partially matched string. However, for patterns that contain look- |
Line 6920 PARTIAL MATCHING USING pcre_exec()
|
Line 7557 PARTIAL MATCHING USING pcre_exec()
|
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 pcre16_exec() |
|
|
If PCRE_PARTIAL_SOFT is set when pcre_exec() identifies a partial | If PCRE_PARTIAL_SOFT is set when pcre_exec() or pcre16_exec() identi- |
match, the partial match is remembered, but matching continues as nor- | fies a partial match, the partial match is remembered, but matching |
mal, and other alternatives in the pattern are tried. If no complete | continues as normal, and other alternatives in the pattern are tried. |
match can be found, pcre_exec() returns PCRE_ERROR_PARTIAL instead of | If no complete match can be found, PCRE_ERROR_PARTIAL is returned |
PCRE_ERROR_NOMATCH. | 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 |
Line 6946 PARTIAL MATCHING USING pcre_exec()
|
Line 7583 PARTIAL MATCHING USING pcre_exec()
|
(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 pcre16_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 pcre16_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 |
|
|
Line 6979 PARTIAL MATCHING USING pcre_exec()
|
Line 7618 PARTIAL MATCHING USING pcre_exec()
|
|
|
/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 pcre16_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 |
Line 7007 PARTIAL MATCHING USING pcre_dfa_exec()
|
Line 7646 PARTIAL MATCHING USING pcre_dfa_exec()
|
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 |
Line 7031 PARTIAL MATCHING AND WORD BOUNDARIES
|
Line 7670 PARTIAL MATCHING AND WORD BOUNDARIES
|
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 |
not conform to the restrictions, pcre_exec() returned the error code | not conform to the restrictions, pcre_exec() returned the error code |
PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The | PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The |
PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if a compiled | PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if a compiled |
pattern can be used for partial matching now always returns 1. |
pattern can be used for partial matching now always returns 1. |
|
|
|
|
EXAMPLE OF PARTIAL MATCHING USING PCRETEST |
EXAMPLE OF PARTIAL MATCHING USING PCRETEST |
|
|
If the escape sequence \P is present in a pcretest data line, the | If the escape sequence \P is present in a pcretest data line, the |
PCRE_PARTIAL_SOFT option is used for the match. Here is a run of | PCRE_PARTIAL_SOFT option is used for the match. Here is a run of |
pcretest that uses the date example quoted above: |
pcretest that uses the date example quoted above: |
|
|
re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ |
re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ |
Line 7077 EXAMPLE OF PARTIAL MATCHING USING PCRETEST
|
Line 7713 EXAMPLE OF PARTIAL MATCHING USING PCRETEST
|
data> j\P |
data> j\P |
No match |
No match |
|
|
The first data string is matched completely, so pcretest shows the | The first data string is matched completely, so pcretest shows the |
matched substrings. The remaining four strings do not match the com- | matched substrings. The remaining four strings do not match the com- |
plete pattern, but the first two are partial matches. Similar output is |
plete pattern, but the first two are partial matches. Similar output is |
obtained 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 pcre16_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 7103 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()
|
Line 7739 MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()
|
data> n05\R\D |
data> n05\R\D |
0: n05 |
0: n05 |
|
|
The first call has "23ja" as the subject, and requests partial match- | The first call has "23ja" as the subject, and requests partial match- |
ing; the second call has "n05" as the subject for the continued | ing; the second call has "n05" as the subject for the continued |
(restarted) match. Notice that when the match is complete, only the | (restarted) match. Notice that when the match is complete, only the |
last part is shown; PCRE does not retain the previously partially- | last part is shown; PCRE does not retain the previously partially- |
matched string. It is up to the calling program to do that if it needs | matched string. It is up to the calling program to do that if it needs |
to. |
to. |
|
|
You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with | You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with |
PCRE_DFA_RESTART to continue partial matching over multiple segments. | PCRE_DFA_RESTART to continue partial matching over multiple segments. |
This facility can be used to pass very long subject strings to | 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 pcre16_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 partially matched string itself, because |
because these must be retained when adding on more characters for a | these must be retained when adding on more characters for a subsequent |
subsequent matching attempt. | matching attempt. However, in some cases you may need to retain even |
| earlier characters, as discussed in the next section. |
|
|
|
|
ISSUES WITH MULTI-SEGMENT MATCHING |
ISSUES WITH MULTI-SEGMENT MATCHING |
Line 7156 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 7795 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 | pcre16_fullinfo() functions to obtain the length of the largest lookbe- |
characters at the start. | hind 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 | 3. Because a partial match must always contain at least one character, |
not always produce exactly the same result as matching over one single | what might be considered a partial match of an empty string actually |
long string, especially when PCRE_PARTIAL_SOFT is used. The section | gives a "no match" result. For example: |
"Partial Matching and Word Boundaries" above describes an issue that | |
arises if the pattern ends with \b or \B. Another kind of difference | re> /c(?<=abc)x/ |
may occur when there are multiple matching possibilities, because (for | data> ab\P |
PCRE_PARTIAL_SOFT) a partial match result is given only when there are | no completed matches. This means that as soon as the shortest match has |
| |
| If the next segment begins "cx", a match should be found, but this will |
| only happen if characters from the previous segment are retained. For |
| this reason, a "no match" result should be interpreted as "partial |
| match of an empty string" when the pattern contains lookbehinds. |
| |
| 4. Matching a subject string that is split into multiple segments may |
| not always produce exactly the same result as matching over one single |
| long string, especially when PCRE_PARTIAL_SOFT is used. The section |
| "Partial Matching and Word Boundaries" above describes an issue that |
| arises if the pattern ends with \b or \B. Another kind of difference |
| may occur when there are multiple matching possibilities, because (for |
| PCRE_PARTIAL_SOFT) a partial match result is given only when there are |
no completed matches. This means that as soon as the shortest match has |
no completed matches. This means that as soon as the shortest match has |
been found, continuation to a new subject segment is no longer possi- | been found, continuation to a new subject segment is no longer possi- |
ble. Consider again this pcretest example: |
ble. Consider again this pcretest example: |
|
|
re> /dog(sbody)?/ |
re> /dog(sbody)?/ |
Line 7186 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 7842 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- |
Line 7207 ISSUES WITH MULTI-SEGMENT MATCHING
|
Line 7864 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 |
|
|
If the first part of the subject is "ABC123", a partial match of the | If the first part of the subject is "ABC123", a partial match of the |
first alternative is found at offset 3. There is no partial match for | first alternative is found at offset 3. There is no partial match for |
the second alternative, because such a match does not start at the same |
the second alternative, because such a match does not start at the same |
point in the subject string. Attempting to continue with the string | point in the subject string. Attempting to continue with the string |
"7890" does not yield a match because only those alternatives that | "7890" does not yield a match because only those alternatives that |
match at one point in the subject are remembered. The problem arises | match at one point in the subject are remembered. The problem arises |
because the start of the second alternative matches within the first | because the start of the second alternative matches within the first |
alternative. There is no problem with anchored patterns or patterns | alternative. There is no problem with anchored patterns or patterns |
such as: |
such as: |
|
|
1234|ABCD |
1234|ABCD |
|
|
where no string can be a partial match for both alternatives. This is | where no string can be a partial match for both alternatives. This is |
not a problem if 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 7893 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 7909 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 26 August 2011 | Last updated: 24 February 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 7273 SAVING AND RE-USING PRECOMPILED PCRE PATTERNS
|
Line 7929 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]_pattern_to_host_byte_order() |
There may be a small performance penalty, but it should be insignifi- | function on the new host before trying to match the pattern. The match- |
cant. However, compiling regular expressions with one version of PCRE | ing functions return PCRE_ERROR_BADENDIANNESS if they detect a pattern |
for use with a different version is not guaranteed to work and may | 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]_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 pcre[16]_fullinfo() |
ment of PCRE_INFO_SIZE. You can then save the data in any appropriate | with an argument of PCRE_INFO_SIZE. You can then save the data in any |
manner. Here is sample code that compiles a pattern and writes it to a | appropriate manner. Here is sample code for the 8-bit library that com- |
file. It assumes that the variable fd refers to a file that is open for | piles a pattern and writes it to a file. It assumes that the variable |
output: | 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 7966 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]_study() returns a pointer to a pcre[16]_extra data block. Its |
the section on matching a pattern in the pcreapi documentation. The | format is defined in the section on matching a pattern in the pcreapi |
study_data field points to the binary study data, and this is what you | documentation. The study_data field points to the binary study data, |
must save (not the pcre_extra block itself). The length of the study | and this is what you must save (not the pcre[16]_extra block itself). |
data can be obtained by calling pcre_fullinfo() with an argument of | 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]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remember |
non-NULL value before trying to save the study data. | to check that pcre[16]_study() did return a non-NULL value before try- |
| ing 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]_pattern_to_host_byte_order() if nec- |
pcre_dfa_exec() in the usual way. This should work even on another | essary, you pass its pointer to pcre[16]_exec() or pcre[16]_dfa_exec() |
host, and even if that host has the opposite endianness to the one | 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]_compile()), you |
must now pass a similar pointer to pcre_exec() or pcre_dfa_exec(), | must now pass a similar pointer to pcre[16]_exec() or |
because the value saved with the compiled pattern will obviously be | pcre[16]_dfa_exec(), because the value saved with the compiled pattern |
nonsense. A field in a pcre_extra() block is used to pass this data, as | will obviously be nonsense. A field in a pcre[16]_extra() block is used |
described in the section on matching a pattern in the pcreapi documen- | to pass this data, as described in the section on matching a pattern in |
tation. | 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]_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]_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 8044 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 26 August 2011 | Last updated: 10 January 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 7405 PCRE PERFORMANCE
|
Line 8065 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 8088 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 pcre16_exec() is used for matching, certain kinds |
cause it to use large amounts of the process stack. In some environ- | of pattern can cause it to use large amounts of the process stack. In |
ments the default process stack is quite small, and if it runs out the | some environments the default process stack is quite small, and if it |
result is often SIGSEGV. This issue is probably the most frequently | runs out the result is often SIGSEGV. This issue is probably the most |
raised problem with PCRE. Rewriting your pattern can often help. The | frequently raised problem with PCRE. Rewriting your pattern can often |
pcrestack documentation discusses this issue in detail. | help. The pcrestack documentation discusses this issue in detail. |
|
|
|
|
PROCESSING TIME |
PROCESSING TIME |
|
|
Certain items in regular expression patterns are processed more effi- | Certain items in regular expression patterns are processed more effi- |
ciently than others. It is more efficient to use a character class like |
ciently than others. It is more efficient to use a character class like |
[aeiou] than a set of single-character alternatives such as | [aeiou] than a set of single-character alternatives such as |
(a|e|i|o|u). In general, the simplest construction that provides the | (a|e|i|o|u). In general, the simplest construction that provides the |
required behaviour is usually the most efficient. Jeffrey Friedl's book |
required behaviour is usually the most efficient. Jeffrey Friedl's book |
contains a lot of useful general discussion about optimizing regular | contains a lot of useful general discussion about optimizing regular |
expressions for efficient performance. This document contains a few | expressions for efficient performance. This document contains a few |
observations about PCRE. |
observations about PCRE. |
|
|
Using Unicode character properties (the \p, \P, and \X escapes) is | Using Unicode character properties (the \p, \P, and \X escapes) is |
slow, because PCRE has to scan a structure that contains data for over | slow, because PCRE has to scan a structure that contains data for over |
fifteen thousand characters whenever it needs a character's property. | fifteen thousand characters whenever it needs a character's property. |
If you can find an alternative pattern that does not use character | If you can find an alternative pattern 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 8214 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. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 7582 SYNOPSIS OF POSIX API
|
Line 8244 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 library. |
|
|
The functions described here are just wrapper functions that ultimately |
The functions described here are just wrapper functions that ultimately |
call the PCRE native API. Their prototypes are defined in the |
call the PCRE native API. Their prototypes are defined in the |
pcreposix.h header file, and on Unix systems the library itself is | pcreposix.h header file, and on Unix systems the library itself is |
called pcreposix.a, so can be accessed by adding -lpcreposix to the | called pcreposix.a, so can be accessed by adding -lpcreposix to the |
command for linking an application that uses them. Because the POSIX | command for linking an application that uses them. Because the POSIX |
functions call the native ones, it is also necessary to add -lpcre. |
functions call the native ones, it is also necessary to add -lpcre. |
|
|
I have implemented only those POSIX option bits that can be reasonably | I have implemented only those POSIX option bits that can be reasonably |
mapped to PCRE native options. In addition, the option REG_EXTENDED is | mapped to PCRE native options. In addition, the option REG_EXTENDED is |
defined with the value zero. This has no effect, but since programs | defined with the value zero. This has no effect, but since programs |
that are written to the POSIX interface often use it, this makes it | that are written to the POSIX interface often use it, this makes it |
easier to slot in PCRE as a replacement library. Other POSIX options | easier to slot in PCRE as a replacement library. Other POSIX options |
are not even defined. |
are not even defined. |
|
|
There are also some other options that are not defined by POSIX. These | There are also some other options that are not defined by POSIX. These |
have been added at the request of users who want to make use of certain |
have been added at the request of users who want to make use of certain |
PCRE-specific features via the POSIX calling interface. |
PCRE-specific features via the POSIX calling interface. |
|
|
When PCRE is called via these functions, it is only the API that is | When PCRE is called via these functions, it is only the API that is |
POSIX-like in style. The syntax and semantics of the regular expres- | POSIX-like in style. The syntax and semantics of the regular expres- |
sions themselves are still those of Perl, subject to the setting of | sions themselves are still those of Perl, subject to the setting of |
various PCRE options, as described below. "POSIX-like in style" means | various PCRE options, as described below. "POSIX-like in style" means |
that the API approximates to the POSIX definition; it is not fully | that the API approximates to the POSIX definition; it is not fully |
POSIX-compatible, and in multi-byte encoding domains it is probably | POSIX-compatible, and in multi-byte encoding domains it is probably |
even less compatible. |
even less compatible. |
|
|
The header for these functions is supplied as pcreposix.h to avoid any | The header for these functions is supplied as pcreposix.h to avoid any |
potential clash with other POSIX libraries. It can, of course, be | potential clash with other POSIX libraries. It can, of course, be |
renamed or aliased as regex.h, which is the "correct" name. It provides |
renamed or aliased as regex.h, which is the "correct" name. It provides |
two structure types, regex_t for compiled internal forms, and reg- | two structure types, regex_t for compiled internal forms, and reg- |
match_t for returning captured substrings. It also defines some con- | match_t for returning captured substrings. It also defines some con- |
stants whose names start with "REG_"; these are used for setting | stants whose names start with "REG_"; these are used for setting |
options and identifying error codes. |
options and identifying error codes. |
|
|
|
|
COMPILING A PATTERN |
COMPILING A PATTERN |
|
|
The function regcomp() is called to compile a pattern into an internal | The function regcomp() is called to compile a pattern into an internal |
form. The pattern is a C string terminated by a binary zero, and is | form. The pattern is a C string terminated by a binary zero, and is |
passed in the argument pattern. The preg argument is a pointer to a | passed in the argument pattern. The preg argument is a pointer to a |
regex_t structure that is used as a base for storing information about | regex_t structure that is used as a base for storing information about |
the compiled regular expression. |
the compiled regular expression. |
|
|
The argument cflags is either zero, or contains one or more of the bits |
The argument cflags is either zero, or contains one or more of the bits |
Line 7640 COMPILING A PATTERN
|
Line 8303 COMPILING A PATTERN
|
|
|
REG_ICASE |
REG_ICASE |
|
|
The PCRE_CASELESS option is set when the regular expression is passed | The PCRE_CASELESS option is set when the regular expression is passed |
for compilation to the native function. |
for compilation to the native function. |
|
|
REG_NEWLINE |
REG_NEWLINE |
|
|
The PCRE_MULTILINE option is set when the regular expression is passed | The PCRE_MULTILINE option is set when the regular expression is passed |
for compilation to the native function. Note that this does not mimic | for compilation to the native function. Note that this does not mimic |
the defined POSIX behaviour for REG_NEWLINE (see the following sec- | the defined POSIX behaviour for REG_NEWLINE (see the following sec- |
tion). |
tion). |
|
|
REG_NOSUB |
REG_NOSUB |
|
|
The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is | The PCRE_NO_AUTO_CAPTURE option is set when the regul The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is |
passed for compilation to the native function. In addition, when a pat- |
passed for compilation to the native function. In addition, when a pat- |
tern that is compiled with this flag is passed to regexec() for match- | tern that is compiled with this flag is passed to regexec() for match- |
ing, the nmatch and pmatch arguments are ignored, and no captured | ing, the nmatch and pmatch arguments are ignored, and no captured |
strings are returned. |
strings are returned. |
|
|
REG_UCP |
REG_UCP |
|
|
The PCRE_UCP option is set when the regular expression is passed for | The PCRE_UCP option is set when the regular expression is passed for |
compilation to the native function. This causes PCRE to use Unicode | compilation to the native function. This causes PCRE to use Unicode |
properties when matchine \d, \w, etc., instead of just recognizing | properties when matchine \d, \w, etc., instead of just recognizing |
ASCII values. Note that REG_UTF8 is not part of the POSIX standard. |
ASCII values. Note that REG_UTF8 is not part of the POSIX standard. |
|
|
REG_UNGREEDY |
REG_UNGREEDY |
|
|
The PCRE_UNGREEDY option is set when the regular expression is passed | The PCRE_UNGREEDY option is set when the regular expression is passed |
for compilation to the native function. Note that REG_UNGREEDY is not | for compilation to the native function. Note that REG_UNGREEDY is not |
part of the POSIX standard. |
part of the POSIX standard. |
|
|
REG_UTF8 |
REG_UTF8 |
|
|
The PCRE_UTF8 option is set when the regular expression is passed for | The PCRE_UTF8 option is set when the regular expression is passed for |
compilation to the native function. This causes the pattern itself and | compilation to the native function. This causes the pattern itself and |
all data strings used for matching it to be treated as UTF-8 strings. | all data strings used for matching it to be treated as UTF-8 strings. |
Note that REG_UTF8 is not part of the POSIX standard. |
Note that REG_UTF8 is not part of the POSIX standard. |
|
|
In the absence of these flags, no options are passed to the native | In the absence of these flags, no options are passed to the native |
function. This means the the regex is compiled with PCRE default | function. This means the the regex is compiled with PCRE default |
semantics. In particular, the way it handles newline characters in the | semantics. In particular, the way it handles newline characters in the |
subject string is the Perl way, not the POSIX way. Note that setting | subject string is the Perl way, not the POSIX way. Note that setting |
PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE. | PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE. |
It does not affect the way newlines are matched by . (they are not) or | It does not affect the way newlines are matched by . (they are not) or |
by a negative class such as [^a] (they are). |
by a negative class such as [^a] (they are). |
|
|
The yield of regcomp() is zero on success, and non-zero otherwise. The | The yield of regcomp() is zero on success, and non-zero otherwise. The |
preg structure is filled in on success, and one member of the structure |
preg structure is filled in on success, and one member of the structure |
is public: re_nsub contains the number of capturing subpatterns in the | is public: re_nsub contains the number of capturing subpatterns in the |
regular expression. Various error codes are defined in the header file. |
regular expression. Various error codes are defined in the header file. |
|
|
NOTE: If the yield of regcomp() is non-zero, you must not attempt to | NOTE: If the yield of regcomp() is non-zero, you must not attempt to |
use the contents of the preg structure. If, for example, you pass it to |
use the contents of the preg structure. If, for example, you pass it to |
regexec(), the result is undefined and your program is likely to crash. |
regexec(), the result is undefined and your program is likely to crash. |
|
|
Line 7699 COMPILING A PATTERN
|
Line 8362 COMPILING A PATTERN
|
MATCHING NEWLINE CHARACTERS |
MATCHING NEWLINE CHARACTERS |
|
|
This area is not simple, because POSIX and Perl take different views of |
This area is not simple, because POSIX and Perl take different views of |
things. It is not possible to get PCRE to obey POSIX semantics, but | things. It is not possible to get PCRE to obey POSIX semantics, but |
then PCRE was never intended to be a POSIX engine. The following table | then PCRE was never intended to be a POSIX engine. The following table |
lists the different possibilities for matching newline characters in | lists the different possibilities for matching newline characters in |
PCRE: |
PCRE: |
|
|
Default Change with |
Default Change with |
Line 7723 MATCHING NEWLINE CHARACTERS
|
Line 8386 MATCHING NEWLINE CHARACTERS
|
^ matches \n in middle no REG_NEWLINE |
^ matches \n in middle no REG_NEWLINE |
|
|
PCRE's behaviour is the same as Perl's, except that there is no equiva- |
PCRE's behaviour is the same as Perl's, except that there is no equiva- |
lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is | lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is |
no way to stop newline from matching [^a]. |
no way to stop newline from matching [^a]. |
|
|
The default POSIX newline handling can be obtained by setting | The default POSIX newline handling can be obtained by setting |
PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE | PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE |
behave exactly as for the REG_NEWLINE action. |
behave exactly as for the REG_NEWLINE action. |
|
|
|
|
MATCHING A PATTERN |
MATCHING A PATTERN |
|
|
The function regexec() is called to match a compiled pattern preg | The function regexec() is called to match a compiled pattern preg |
against a given string, which is by default terminated by a zero byte | against a given string, which is by default terminated by a zero byte |
(but see REG_STARTEND below), subject to the options in eflags. These | (but see REG_STARTEND below), subject to the options in eflags. These |
can be: |
can be: |
|
|
REG_NOTBOL |
REG_NOTBOL |
Line 7757 MATCHING A PATTERN
|
Line 8420 MATCHING A PATTERN
|
|
|
REG_STARTEND |
REG_STARTEND |
|
|
The string is considered to start at string + pmatch[0].rm_so and to | The string is considered to start at string + pmatch[0].rm_so and to |
have a terminating NUL located at string + pmatch[0].rm_eo (there need | have a terminating NUL located at string + pmatch[0].rm_eo (there need |
not actually be a NUL at that location), regardless of the value of | not actually be a NUL at that location), regardless of the value of |
nmatch. This is a BSD extension, compatible with but not specified by | nmatch. This is a BSD extension, compatible with but not specified by |
IEEE Standard 1003.2 (POSIX.2), and should be used with caution in | IEEE Standard 1003.2 (POSIX.2), and should be used with caution in |
software intended to be portable to other systems. Note that a non-zero |
software intended to be portable to other systems. Note that a non-zero |
rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location |
rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location |
of the string, not how it is matched. |
of the string, not how it is matched. |
|
|
If the pattern was compiled with the REG_NOSUB flag, no data about any | If the pattern was compiled with the REG_NOSUB flag, no data about any |
matched strings is returned. The nmatch and pmatch arguments of | matched strings is returned. The nmatch and pmatch arguments of |
regexec() are ignored. |
regexec() are ignored. |
|
|
If the value of nmatch is zero, or if the value pmatch is NULL, no data |
If the value of nmatch is zero, or if the value pmatch is NULL, no data |
Line 7775 MATCHING A PATTERN
|
Line 8438 MATCHING A PATTERN
|
|
|
Otherwise,the portion of the string that was matched, and also any cap- |
Otherwise,the portion of the string that was matched, and also any cap- |
tured substrings, are returned via the pmatch argument, which points to |
tured substrings, are returned via the pmatch argument, which points to |
an array of nmatch structures of type regmatch_t, containing the mem- | an array of nmatch structures of type regmatch_t, containing the mem- |
bers rm_so and rm_eo. These contain the offset to the first character | bers rm_so and rm_eo. These contain the offset to the first character |
of each substring and the offset to the first character after the end | of each substring and the offset to the first character after the end |
of each substring, respectively. The 0th element of the vector relates | of each substring, respectively. The 0th element of the vector relates |
to the entire portion of string that was matched; subsequent elements | to the entire portion of string that was matched; subsequent elements |
relate to the capturing subpatterns of the regular expression. Unused | relate to the capturing subpatterns of the regular expression. Unused |
entries in the array have both structure members set to -1. |
entries in the array have both structure members set to -1. |
|
|
A successful match yields a zero return; various error codes are | A successful match yields a zero return; various error codes are |
defined in the header file, of which REG_NOMATCH is the "expected" | defined in the header file, of which REG_NOMATCH is the "expected" |
failure code. |
failure code. |
|
|
|
|
ERROR MESSAGES |
ERROR MESSAGES |
|
|
The regerror() function maps a non-zero errorcode from either regcomp() |
The regerror() function maps a non-zero errorcode from either regcomp() |
or regexec() to a printable message. If preg is not NULL, the error | or regexec() to or regexec() to a printable message. If preg is not NULL, the error |
should have arisen from the use of that structure. A message terminated |
should have arisen from the use of that structure. A message terminated |
by a binary zero is placed in errbuf. The length of the message, | by a binary zero is placed in errbuf. The length of the message, |
including the zero, is limited to errbuf_size. The yield of the func- | including the zero, is limited to errbuf_size. The yield of the func- |
tion is the size of buffer needed to hold the whole message. |
tion is the size of buffer needed to hold the whole message. |
|
|
|
|
MEMORY USAGE |
MEMORY USAGE |
|
|
Compiling a regular expression causes memory to be allocated and asso- | Compiling a regular expression causes memory to be allocated and asso- |
ciated with the preg structure. The function regfree() frees all such | ciated with the preg structure. The function regfree() frees all such |
memory, after which preg may no longer be used as a compiled expres- | memory, after which preg may no longer be used as a compiled expres- |
sion. |
sion. |
|
|
|
|
Line 7815 AUTHOR
|
Line 8478 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. |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 7837 DESCRIPTION
|
Line 8500 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 support at present. |
|
|
|
|
MATCHING INTERFACE |
MATCHING INTERFACE |
|
|
The "FullMatch" operation checks that supplied text matches a supplied | The "FullMatch" operation checks that supplied text matches a supplied |
pattern exactly. If pointer arguments are supplied, it copies matched | pattern exactly. If pointer arguments are supplied, it copies matched |
sub-strings that match sub-patterns into them. |
sub-strings that match sub-patterns into them. |
|
|
Example: successful match |
Example: successful match |
Line 7857 MATCHING INTERFACE
|
Line 8521 MATCHING INTERFACE
|
Example: creating a temporary RE object: |
Example: creating a temporary RE object: |
pcrecpp::RE("h.*o").FullMatch("hello"); |
pcrecpp::RE("h.*o").FullMatch("hello"); |
|
|
You can pass in a "const char*" or a "string" for "text". The examples | You can pass in a "const char*" or a "string" for "text". The examples |
below tend to use a const char*. You can, as in the different examples | below tend to use a const char*. You can, as in the different examples |
above, store the RE object explicitly in a variable or use a temporary | above, store the RE object explicitly in a variable or use a temporary |
RE object. The examples below use one mode or the other arbitrarily. | RE object. The examples below use one mode or the other arbitrarily. |
Either could correctly be used for any of these examples. |
Either could correctly be used for any of these examples. |
|
|
You must supply extra pointer arguments to extract matched subpieces. |
You must supply extra pointer arguments to extract matched subpieces. |
Line 7886 MATCHING INTERFACE
|
Line 8550 MATCHING INTERFACE
|
Example: fails because string cannot be stored in integer |
Example: fails because string cannot be stored in integer |
!pcrecpp::RE("(.*)").FullMatch("ruby", &i); |
!pcrecpp::RE("(.*)").FullMatch("ruby", &i); |
|
|
The provided pointer arguments can be pointers to any scalar numeric | The provided point The provided point |
type, or one of: |
type, or one of: |
|
|
string (matched piece is copied to string) |
string (matched piece is copied to string) |
Line 7894 MATCHING INTERFACE
|
Line 8558 MATCHING INTERFACE
|
T (where "bool T::ParseFrom(const char*, int)" exists) |
T (where "bool T::ParseFrom(const char*, int)" exists) |
NULL (the corresponding matched sub-pattern is not copied) |
NULL (the corresponding matched sub-pattern is not copied) |
|
|
The function returns true iff all of the following conditions are sat- | The function returns true iff all of the following conditions are sat- |
isfied: |
isfied: |
|
|
a. "text" matches "pattern" exactly; |
a. "text" matches "pattern" exactly; |
Line 7909 MATCHING INTERFACE
|
Line 8573 MATCHING INTERFACE
|
number of sub-patterns, "i"th captured sub-pattern is |
number of sub-patterns, "i"th captured sub-pattern is |
ignored. |
ignored. |
|
|
CAVEAT: An optional sub-pattern that does not exist in the matched | CAVEAT: An optional sub-pattern that does not exist in the matched |
string is assigned the empty string. Therefore, the following will | string is assigned the empty string. Therefore, the following will |
return false (because the empty string is not a valid number): |
return false (because the empty string is not a valid number): |
|
|
int number; |
int number; |
pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number); |
pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number); |
|
|
The matching interface supports at most 16 arguments per call. If you | The matching interface supports at most 16 arguments per call. If you |
need more, consider using the more general interface | need more, consider using the more general interface |
pcrecpp::RE::DoMatch. See pcrecpp.h for the signature for DoMatch. |
pcrecpp::RE::DoMatch. See pcrecpp.h for the signature for DoMatch. |
|
|
NOTE: Do not use no_arg, which is used internally to mark the end of a | NOTE: Do not use no_arg, which is used internally to mark the end of a |
list of optional arguments, as a placeholder for missing arguments, as | list of optional arguments, as a placeholder for missing arguments, as |
this can lead to segfaults. |
this can lead to segfaults. |
|
|
|
|
QUOTING METACHARACTERS |
QUOTING METACHARACTERS |
|
|
You can use the "QuoteMeta" operation to insert backslashes before all | You can use the "QuoteMeta" operation to insert backslashes before all |
potentially meaningful characters in a string. The returned string, | potentially meaningful characters in a string. The returned string, |
used as a regular expression, will exactly match the original string. |
used as a regular expression, will exactly match the original string. |
|
|
Example: |
Example: |
string quoted = RE::QuoteMeta(unquoted); |
string quoted = RE::QuoteMeta(unquoted); |
|
|
Note that it's legal to escape a character even if it has no special | Note that it's legal to escape a character even if it has no special |
meaning in a regular expression -- so this function does that. (This | meaning in a regular expression -- so this function does that. (This |
also makes it identical to the perl function of the same name; see | also makes it identical to the perl function of the same name; see |
"perldoc -f quotemeta".) For example, "1.5-2.0?" becomes | "perldoc -f quotemeta".) For example, "1.5-2.0?" becomes |
"1\.5\-2\.0\?". |
"1\.5\-2\.0\?". |
|
|
|
|
PARTIAL MATCHES |
PARTIAL MATCHES |
|
|
You can use the "PartialMatch" operation when you want the pattern to | You can use the "PartialMatch" operation when you want t You can use the "PartialMatch" operation when you want the pattern to |
match any substring of the text. |
match any substring of the text. |
|
|
Example: simple search for a string: |
Example: simple search for a string: |
Line 7958 PARTIAL MATCHES
|
Line 8622 PARTIAL MATCHES
|
|
|
UTF-8 AND THE MATCHING INTERFACE |
UTF-8 AND THE MATCHING INTERFACE |
|
|
By default, pattern and text are plain text, one byte per character. | By default, pattern and text are plain text, one byte per character. |
The UTF8 flag, passed to the constructor, causes both pattern and | The UTF8 flag, passed to the constructor, causes both pattern and |
string to be treated as UTF-8 text, still a byte stream but potentially |
string to be treated as UTF-8 text, still a byte stream but potentially |
multiple bytes per character. In practice, the text is likelier to be | multiple bytes per character. In practice, the text is likelier to be |
UTF-8 than the pattern, but the match returned may depend on the UTF8 | UTF-8 than the pattern, but the match returned may depend on the UTF8 |
flag, so always use it when matching UTF8 text. For example, "." will | flag, so always use it when matching UTF8 text. For example, "." will |
match one byte normally but with UTF8 set may match up to three bytes | match one byte normally but with UTF8 set may match up to three bytes |
of a multi-byte character. |
of a multi-byte character. |
|
|
Example: |
Example: |
Line 7983 UTF-8 AND THE MATCHING INTERFACE
|
Line 8647 UTF-8 AND THE MATCHING INTERFACE
|
|
|
PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE |
PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE |
|
|
PCRE defines some modifiers to change the behavior of the regular | PCRE defines some modifiers to change the behavior of the regular |
expression engine. The C++ wrapper defines an auxiliary class, | expression engine. The C++ wrapper defines an auxiliary class, |
RE_Options, as a vehicle to pass such modifiers to a RE class. Cur- | RE_Options, as a vehicle to pass such modifiers to a RE class. Cur- |
rently, the following modifiers are supported: |
rently, the following modifiers are supported: |
|
|
modifier description Perl corresponding |
modifier description Perl corresponding |
Line 7995 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 8659 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
PCRE_DOTALL dot matches newlines /s |
PCRE_DOTALL dot matches newlines /s |
PCRE_DOLLAR_ENDONLY $ matches only at end N/A |
PCRE_DOLLAR_ENDONLY $ matches only at end N/A |
PCRE_EXTRA strict escape parsing N/A |
PCRE_EXTRA strict escape parsing N/A |
PCRE_EXTENDED ignore whitespaces /x | PCRE_EXTENDED ignore white spaces /x |
PCRE_UTF8 handles UTF8 chars built-in |
PCRE_UTF8 handles UTF8 chars built-in |
PCRE_UNGREEDY reverses * and *? N/A |
PCRE_UNGREEDY reverses * and *? N/A |
PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*) |
PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*) |
|
|
(*) Both Perl and PCRE allow non capturing parentheses by means of the | (*) Both Perl and PCRE allow non capturing parentheses by means of the |
"?:" modifier within the pattern itself. e.g. (?:ab|cd) does not cap- | "?:" modifier within the pattern itself. e.g. (?:ab|cd) does not cap- |
ture, while (ab|cd) does. |
ture, while (ab|cd) does. |
|
|
For a full account on how each modifier works, please check the PCRE | For a full account on how each modifier works, please check the PCRE |
API reference page. |
API reference page. |
|
|
For each modifier, there are two member functions whose name is made | For each modifier, there are two member functions whose name is made |
out of the modifier in lowercase, without the "PCRE_" prefix. For | out of the modifier in lowercase, without the "PCRE_" prefix. For |
instance, PCRE_CASELESS is handled by |
instance, PCRE_CASELESS is handled by |
|
|
bool caseless() |
bool caseless() |
Line 8018 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 8682 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
RE_Options & set_caseless(bool) |
RE_Options & set_caseless(bool) |
|
|
which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can |
which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can |
be accessed through the set_match_limit() and match_limit() member | be accessed through the set_match_limit() and match_limit() member |
functions. Setting match_limit to a non-zero value will limit the exe- | functions. Setting match_limit to a non-zero value will limit the exe- |
cution of pcre to keep it from doing bad things like blowing the stack | cution of pcre to keep it from doing bad things like blowing the stack |
or taking an eternity to return a result. A value of 5000 is good | or taking an eternity to return a result. A value of 5000 is good |
enough to stop stack blowup in a 2MB thread stack. Setting match_limit | enough to stop stack blowup in a 2MB thread stack. Setting match_limit |
to zero disables match limiting. Alternatively, you can call | to zero disables match limiting. Alternatively, you can call |
match_limit_recursion() which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to | match_limit_recursion() which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to |
limit how much PCRE recurses. match_limit() limits the number of | limit how much PCRE recurses. match_limit() limits the number of |
matches PCRE does; match_limit_recursion() limits the depth of internal |
matches PCRE does; match_limit_recursion() limits the depth of internal |
recursion, and therefore the amount of stack that is used. |
recursion, and therefore the amount of stack that is used. |
|
|
Normally, to pass one or more modifiers to a RE class, you declare a | Normally, to pass one or more modifiers to a RE class, you declare a |
RE_Options object, set the appropriate options, and pass this object to |
RE_Options object, set the appropriate options, and pass this object to |
a RE constructor. Example: |
a RE constructor. Example: |
|
|
Line 8038 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 8702 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
if (RE("HELLO", opt).PartialMatch("hello world")) ... |
if (RE("HELLO", opt).PartialMatch("hello world")) ... |
|
|
RE_options has two constructors. The default constructor takes no argu- |
RE_options has two constructors. The default constructor takes no argu- |
ments and creates a set of flags that are off by default. The optional | ments and creates a set of flags that are off by default. The optional |
parameter option_flags is to facilitate transfer of legacy code from C | parameter option_flags is to facilitate transfer of legacy code from C |
programs. This lets you do |
programs. This lets you do |
|
|
RE(pattern, |
RE(pattern, |
Line 8053 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 8717 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
|
|
If you are going to pass one of the most used modifiers, there are some |
If you are going to pass one of the most used modifiers, there are some |
convenience functions that return a RE_Options class with the appropri- |
convenience functions that return a RE_Options class with the appropri- |
ate modifier already set: CASELESS(), UTF8(), MULTILINE(), DOTALL(), | ate modifier already set: CASELESS(), UTF8(), MULTILINE(), DOTALL(), |
and EXTENDED(). |
and EXTENDED(). |
|
|
If you need to set several options at once, and you don't want to go | If you need to set several options at once, and you don't want to go |
through the pains of declaring a RE_Options object and setting several | through the pains of declaring a RE_Options object and setting several |
options, there is a parallel method that give you such ability on the | options, there is a parallel method that give you such ability on the |
fly. You can concatenate several set_xxxxx() member functions, since | fly. You can concatenate several set_xxxxx() member functions, since |
each of them returns a reference to its class object. For example, to | each of them returns a reference to its class object. For example, to |
pass PCRE_CASELESS, PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one | pass PCRE_CASELESS, PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one |
statement, you may write: |
statement, you may write: |
|
|
RE(" ^ xyz \\s+ .* blah$", |
RE(" ^ xyz \\s+ .* blah$", |
Line 8073 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
Line 8737 PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE
|
|
|
SCANNING TEXT INCREMENTALLY |
SCANNING TEXT INCREMENTALLY |
|
|
The "Consume" operation may be useful if you want to repeatedly match | The "Consume" operation may be useful if you want to repeatedl The "Consume" operation may be useful if you want to repeatedl |
regular expressions at the front of a string and skip over them as they |
regular expressions at the front of a string and skip over them as they |
match. This requires use of the "StringPiece" type, which represents a | match. This requires use of the "StringPiece" type, which represents a |
sub-range of a real string. Like RE, StringPiece is defined in the | sub-range of a real string. Like RE, StringPiece is defined in the |
pcrecpp namespace. |
pcrecpp namespace. |
|
|
Example: read lines of the form "var = value" from a string. |
Example: read lines of the form "var = value" from a string. |
Line 8090 SCANNING TEXT INCREMENTALLY
|
Line 8754 SCANNING TEXT INCREMENTALLY
|
...; |
...; |
} |
} |
|
|
Each successful call to "Consume" will set "var/value", and also | Each successful call to "Consume" will set "var/value", and also |
advance "input" so it points past the matched text. |
advance "input" so it points past the matched text. |
|
|
The "FindAndConsume" operation is similar to "Consume" but does not | The "FindAndConsume" operation is similar to "Consume" but does not |
anchor your match at the beginning of the string. For example, you | anchor your match at the beginning of the string. For example, you |
could extract all words from a string by repeatedly calling |
could extract all words from a string by repeatedly calling |
|
|
pcrecpp::RE("(\\w+)").FindAndConsume(&input, &word) |
pcrecpp::RE("(\\w+)").FindAndConsume(&input, &word) |
Line 8103 SCANNING TEXT INCREMENTALLY
|
Line 8767 SCANNING TEXT INCREMENTALLY
|
PARSING HEX/OCTAL/C-RADIX NUMBERS |
PARSING HEX/OCTAL/C-RADIX NUMBERS |
|
|
By default, if you pass a pointer to a numeric value, the corresponding |
By default, if you pass a pointer to a numeric value, the corresponding |
text is interpreted as a base-10 number. You can instead wrap the | text is interpreted as a base-10 number. You can instead wrap the |
pointer with a call to one of the operators Hex(), Octal(), or CRadix() |
pointer with a call to one of the operators Hex(), Octal(), or CRadix() |
to interpret the text in another base. The CRadix operator interprets | to interpret the text in another base. The CRadix operator interprets |
C-style "0" (base-8) and "0x" (base-16) prefixes, but defaults to | C-style "0" (base-8) and "0x" (base-16) prefixes, but defaults to |
base-10. |
base-10. |
|
|
Example: |
Example: |
Line 8121 PARSING HEX/OCTAL/C-RADIX NUMBERS
|
Line 8785 PARSING HEX/OCTAL/C-RADIX NUMBERS
|
|
|
REPLACING PARTS OF STRINGS |
REPLACING PARTS OF STRINGS |
|
|
You can replace the first match of "pattern" in "str" with "rewrite". | You can replace the first match of "pattern" in "str" with "rewrite". |
Within "rewrite", backslash-escaped digits (\1 to \9) can be used to | Within "rewrite", backslash-escaped digits (\1 to \9) can be used to |
insert text matching corresponding parenthesized group from the pat- | insert text matching corresponding parenthesized group from the pat- |
tern. \0 in "rewrite" refers to the entire matching text. For example: |
tern. \0 in "rewrite" refers to the entire matching text. For example: |
|
|
string s = "yabba dabba doo"; |
string s = "yabba dabba doo"; |
pcrecpp::RE("b+").Replace("d", &s); |
pcrecpp::RE("b+").Replace("d", &s); |
|
|
will leave "s" containing "yada dabba doo". The result is true if the | will leave "s" containing "yada dabba doo". The result is true if the |
pattern matches and a replacement occurs, false otherwise. |
pattern matches and a replacement occurs, false otherwise. |
|
|
GlobalReplace is like Replace except that it replaces all occurrences | GlobalReplace is like Replace except that it replaces all occurrences |
of the pattern in the string with the rewrite. Replacements are not | of the pattern in the string with the rewrite. Replacements are not |
subject to re-matching. For example: |
subject to re-matching. For example: |
|
|
string s = "yabba dabba doo"; |
string s = "yabba dabba doo"; |
pcrecpp::RE("b+").GlobalReplace("d", &s); |
pcrecpp::RE("b+").GlobalReplace("d", &s); |
|
|
will leave "s" containing "yada dada doo". It returns the number of | will leave "s" containing "yada dada doo". It returns the number of |
replacements made. |
replacements made. |
|
|
Extract is like Replace, except that if the pattern matches, "rewrite" | Extract is like Replace, except that if the pattern matches, "rewrite" |
is copied into "out" (an additional argument) with substitutions. The | is copied into "out" (an additional argument) with substitutions. The |
non-matching portions of "text" are ignored. Returns true iff a match | non-matching portions of "text" are ignored. Returns true iff a match |
occurred and the extraction happened successfully; if no match occurs, |
occurred and the extraction happened successfully; if no match occurs, |
the string is left unaffected. |
the string is left unaffected. |
|
|
Line 8157 AUTHOR
|
Line 8821 AUTHOR
|
|
|
REVISION |
REVISION |
|
|
Last updated: 17 March 2009 | Last updated: 08 January 2012 |
Minor typo fixed: 25 July 2011 | |
------------------------------------------------------------------------------ |
------------------------------------------------------------------------------ |
|
|
|
|
Line 8177 PCRE SAMPLE PROGRAM
|
Line 8840 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 8908 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) PCRELIMITS(3) |
|
|
Line 8259 SIZE AND OTHER LIMITATIONS
|
Line 8923 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, 16-bit units for the 16-bit |
process regular expressions that are truly enormous, you can compile | library) if PCRE is compiled with the default internal linkage size of |
PCRE with an internal linkage size of 3 or 4 (see the README file in | 2 bytes. If you want to process regular expressions that are truly |
the source distribution and the pcrebuild documentation for details). | enormous, you can compile PCRE with an internal linkage size of 3 or 4 |
In these cases the limit is substantially larger. However, the speed | (when building the 16-bit library, 3 is rounded up to 4). See the |
of execution is slower. | README file in the source distribution and the pcrebuild documentation |
| for details. In these cases the limit is substantially larger. How- |
| ever, the speed of execution is slower. |
|
|
All values in repeating quantifiers must be less than 65536. |
All values in repeating quantifiers must be less than 65536. |
|
|
Line 8281 SIZE AND OTHER LIMITATIONS
|
Line 8947 SIZE AND OTHER LIMITATIONS
|
The maximum length of name for a named subpattern is 32 characters, and |
The maximum length of name for a named subpattern is 32 characters, and |
the maximum number of named subpatterns is 10000. |
the maximum number of named subpatterns is 10000. |
|
|
|
The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or |
|
(*THEN) verb is 255 for the 8-bit library and 65535 for the 16-bit |
|
library. |
|
|
The maximum length of a subject string is the largest positive number |
The maximum length of a subject string is the largest positive number |
that an integer variable can hold. However, when using the traditional |
that an integer variable can hold. However, when using the traditional |
matching function, PCRE uses recursion to handle subpatterns and indef- |
matching function, PCRE uses recursion to handle subpatterns and indef- |
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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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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]_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 |
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Line 8998 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]_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]_exec() were not incompatible, |
the JIT-compiled code instead of the match() function. In this case, | the matching process uses the JIT-compiled code instead of the match() |
the memory requirements are handled entirely differently. See the pcre- | function. In this case, the memory requirements are handled entirely |
jit documentation for details. | 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]_dfa_exec() function operates in an entirely different way, |
uses recursion only when there is a regular expression recursion or | and uses recursion only when there is a regular expression recursion or |
subroutine call in the pattern. This includes the processing of asser- |
subroutine call in the pattern. This includes the processing of asser- |
tion and "once-only" subpatterns, which are handled like subroutine |
tion and "once-only" subpatterns, which are handled like subroutine |
calls. Normally, these are never very deep, and the limit on the com- |
calls. Normally, these are never very deep, and the limit on the com- |
plexity of pcre_dfa_exec() is controlled by the amount of workspace it | plexity of pcre[16]_dfa_exec() is controlled by the amount of workspace |
is given. However, it is possible to write patterns with runaway infi- | it is given. However, it is possible to write patterns with runaway |
nite recursions; such patterns will cause pcre_dfa_exec() to run out of | infinite recursions; such patterns will cause pcre[16]_dfa_exec() to |
stack. At present, there is no protection against this. | 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]_dfa_exec(); they are |
evant only for pcre_exec() without the JIT optimization. | relevant only for pcre[16]_exec() without the JIT optimization. |
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Reducing pcre_exec()'s stack usage | Reducing pcre[16]_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 |
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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]_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]_exec() is running. This makes it run a lot more |
slowly, however. Details of how to do this are given in the pcrebuild |
slowly, however. Details of how to do this are given in the pcrebuild |
documentation. When built in this way, instead of using the stack, PCRE |
documentation. When built in this way, instead of using the stack, PCRE |
obtains and frees memory by calling the functions that are pointed to |
obtains and frees memory by calling the functions that are pointed to |
by the pcre_stack_malloc and pcre_stack_free variables. By default, | by the pcre[16]_stack_malloc and pcre[16]_stack_free variables. By |
these point to malloc() and free(), but you can replace the pointers to | default, these point to malloc() and free(), but you can replace the |
cause PCRE to use your own functions. Since the block sizes are always | pointers to cause PCRE to use your own functions. Since the block sizes |
the same, and are always freed in reverse order, it may be possible to | are always the same, and are always freed in reverse order, it may be |
implement customized memory handlers that are more efficient than the | possible to implement customized memory handlers that are more effi- |
standard functions. | cient than the standard functions. |
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Limiting pcre_exec()'s stack usage | Limiting pcre[16]_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]_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]_exec() is called. For details of |
interfaces, see the pcrebuild documentation and the section on extra | these interfaces, see the pcrebuild documentation and the section on |
data for pcre_exec() in the pcreapi documentation. | extra data for pcre[16]_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 |
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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]_exec() repeatedly with |
different limits. |
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 |
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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]_exec(). |
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Changing stack size in Mac OS X |
Changing stack size in Mac OS X |
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Line 8459 AUTHOR
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Line 9153 AUTHOR
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REVISION |
REVISION |
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Last updated: 26 August 2011 | Last updated: 21 January 2012 |
Copyright (c) 1997-2011 University of Cambridge. | Copyright (c) 1997-2012 University of Cambridge. |
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