1PCRE(3) Library Functions Manual PCRE(3)
2
6 PCRE - Perl-compatible regular expressions
7
9 The PCRE library is a set of functions that implement regular expres‐
11 sion pattern matching using the same syntax and semantics as Perl, with
12 just a few differences. Some features that appeared in Python and PCRE
13 before they appeared in Perl are also available using the Python syn‐
14 tax, there is some support for one or two .NET and Oniguruma syntax
15 items, and there is an option for requesting some minor changes that
16 give better JavaScript compatibility.
17 Starting with release 8.30, it is possible to compile two separate PCRE
19 libraries: the original, which supports 8-bit character strings
20 (including UTF-8 strings), and a second library that supports 16-bit
21 character strings (including UTF-16 strings). The build process allows
22 either one or both to be built. The majority of the work to make this
23 possible was done by Zoltan Herczeg.
24 Starting with release 8.32 it is possible to compile a third separate
26 PCRE library, which supports 32-bit character strings (including UTF-32
27 strings). The build process allows any set of the 8-, 16- and 32-bit
28 libraries. The work to make this possible was done by Christian Persch.
29 The three libraries contain identical sets of functions, except that
31 the names in the 16-bit library start with pcre16_ instead of pcre_,
32 and the names in the 32-bit library start with pcre32_ instead of
33 pcre_. To avoid over-complication and reduce the documentation mainte‐
34 nance load, most of the documentation describes the 8-bit library, with
35 the differences for the 16-bit and 32-bit libraries described sepa‐
36 rately in the pcre16 and pcre32 pages. References to functions or
37 structures of the form pcre[16|32]_xxx should be read as meaning
38 "pcre_xxx when using the 8-bit library, pcre16_xxx when using the
39 16-bit library, or pcre32_xxx when using the 32-bit library".
40 The current implementation of PCRE corresponds approximately with Perl
42 5.12, including support for UTF-8/16/32 encoded strings and Unicode
43 general category properties. However, UTF-8/16/32 and Unicode support
44 has to be explicitly enabled; it is not the default. The Unicode tables
45 correspond to Unicode release 6.2.0.
46 In addition to the Perl-compatible matching function, PCRE contains an
48 alternative function that matches the same compiled patterns in a dif‐
49 ferent way. In certain circumstances, the alternative function has some
50 advantages. For a discussion of the two matching algorithms, see the
51 pcrematching page.
52 PCRE is written in C and released as a C library. A number of people
54 have written wrappers and interfaces of various kinds. In particular,
55 Google Inc. have provided a comprehensive C++ wrapper for the 8-bit
56 library. This is now included as part of the PCRE distribution. The
57 pcrecpp page has details of this interface. Other people's contribu‐
58 tions can be found in the Contrib directory at the primary FTP site,
59 which is:
60 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
62 Details of exactly which Perl regular expression features are and are
64 not supported by PCRE are given in separate documents. See the pcrepat‐
65 tern and pcrecompat pages. There is a syntax summary in the pcresyntax
66 page.
67 Some features of PCRE can be included, excluded, or changed when the
69 library is built. The pcre_config() function makes it possible for a
70 client to discover which features are available. The features them‐
71 selves are described in the pcrebuild page. Documentation about build‐
72 ing PCRE for various operating systems can be found in the README and
73 NON-AUTOTOOLS_BUILD files in the source distribution.
74 The libraries contains a number of undocumented internal functions and
76 data tables that are used by more than one of the exported external
77 functions, but which are not intended for use by external callers.
78 Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which
79 hopefully will not provoke any name clashes. In some environments, it
80 is possible to control which external symbols are exported when a
81 shared library is built, and in these cases the undocumented symbols
82 are not exported.
83
85 If you are using PCRE in a non-UTF application that permits users to
87 supply arbitrary patterns for compilation, you should be aware of a
88 feature that allows users to turn on UTF support from within a pattern,
89 provided that PCRE was built with UTF support. For example, an 8-bit
90 pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode,
91 which interprets patterns and subjects as strings of UTF-8 characters
92 instead of individual 8-bit characters. This causes both the pattern
93 and any data against which it is matched to be checked for UTF-8 valid‐
94 ity. If the data string is very long, such a check might use suffi‐
95 ciently many resources as to cause your application to lose perfor‐
96 mance.
97 The best way of guarding against this possibility is to use the
99 pcre_fullinfo() function to check the compiled pattern's options for
100 UTF.
101 If your application is one that supports UTF, be aware that validity
103 checking can take time. If the same data string is to be matched many
104 times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second
105 and subsequent matches to save redundant checks.
106 Another way that performance can be hit is by running a pattern that
108 has a very large search tree against a string that will never match.
109 Nested unlimited repeats in a pattern are a common example. PCRE pro‐
110 vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea‐
111 ture in the pcreapi page.
112
114 The user documentation for PCRE comprises a number of different sec‐
116 tions. In the "man" format, each of these is a separate "man page". In
117 the HTML format, each is a separate page, linked from the index page.
118 In the plain text format, all the sections, except the pcredemo sec‐
119 tion, are concatenated, for ease of searching. The sections are as fol‐
120 lows:
121 pcre this document
123 pcre16 details of the 16-bit library
124 pcre32 details of the 32-bit library
125 pcre-config show PCRE installation configuration information
126 pcreapi details of PCRE's native C API
127 pcrebuild options for building PCRE
128 pcrecallout details of the callout feature
129 pcrecompat discussion of Perl compatibility
130 pcrecpp details of the C++ wrapper for the 8-bit library
131 pcredemo a demonstration C program that uses PCRE
132 pcregrep description of the pcregrep command (8-bit only)
133 pcrejit discussion of the just-in-time optimization support
134 pcrelimits details of size and other limits
135 pcrematching discussion of the two matching algorithms
136 pcrepartial details of the partial matching facility
137 pcrepattern syntax and semantics of supported
138 regular expressions
139 pcreperform discussion of performance issues
140 pcreposix the POSIX-compatible C API for the 8-bit library
141 pcreprecompile details of saving and re-using precompiled patterns
142 pcresample discussion of the pcredemo program
143 pcrestack discussion of stack usage
144 pcresyntax quick syntax reference
145 pcretest description of the pcretest testing command
146 pcreunicode discussion of Unicode and UTF-8/16/32 support
147 In addition, in the "man" and HTML formats, there is a short page for
149 each C library function, listing its arguments and results.
150
152 Philip Hazel
154 University Computing Service
155 Cambridge CB2 3QH, England.
156 Putting an actual email address here seems to have been a spam magnet,
158 so I've taken it away. If you want to email me, use my two initials,
159 followed by the two digits 10, at the domain cam.ac.uk.
160
162 Last updated: 11 November 2012
164 Copyright (c) 1997-2012 University of Cambridge.
165PCRE 8.32 11 November 2012 PCRE(3)