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1 <html>
2 <head>
3 <title>pcre specification</title>
4 </head>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 <h1>pcre man page</h1>
7 <p>
8 Return to the <a href="index.html">PCRE index page</a>.
9 </p>
10 <p>
11 This page is part of the PCRE HTML documentation. It was generated automatically
12 from the original man page. If there is any nonsense in it, please consult the
13 man page, in case the conversion went wrong.
14 <br>
15 <ul>
16 <li><a name="TOC1" href="#SEC1">INTRODUCTION</a>
17 <li><a name="TOC2" href="#SEC2">SECURITY CONSIDERATIONS</a>
18 <li><a name="TOC3" href="#SEC3">USER DOCUMENTATION</a>
19 <li><a name="TOC4" href="#SEC4">AUTHOR</a>
20 <li><a name="TOC5" href="#SEC5">REVISION</a>
21 </ul>
22 <br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>
23 <P>
24 The PCRE library is a set of functions that implement regular expression
25 pattern matching using the same syntax and semantics as Perl, with just a few
26 differences. Some features that appeared in Python and PCRE before they
27 appeared in Perl are also available using the Python syntax, there is some
28 support for one or two .NET and Oniguruma syntax items, and there is an option
29 for requesting some minor changes that give better JavaScript compatibility.
30 </P>
31 <P>
32 Starting with release 8.30, it is possible to compile two separate PCRE
33 libraries: the original, which supports 8-bit character strings (including
34 UTF-8 strings), and a second library that supports 16-bit character strings
35 (including UTF-16 strings). The build process allows either one or both to be
36 built. The majority of the work to make this possible was done by Zoltan
37 Herczeg.
38 </P>
39 <P>
40 Starting with release 8.32 it is possible to compile a third separate PCRE
41 library, which supports 32-bit character strings (including
42 UTF-32 strings). The build process allows any set of the 8-, 16- and 32-bit
43 libraries. The work to make this possible was done by Christian Persch.
44 </P>
45 <P>
46 The three libraries contain identical sets of functions, except that the names
47 in the 16-bit library start with <b>pcre16_</b> instead of <b>pcre_</b>, and the
48 names in the 32-bit library start with <b>pcre32_</b> instead of <b>pcre_</b>. To
49 avoid over-complication and reduce the documentation maintenance load, most of
50 the documentation describes the 8-bit library, with the differences for the
51 16-bit and 32-bit libraries described separately in the
52 <a href="pcre16.html"><b>pcre16</b></a>
53 and
54 <a href="pcre32.html"><b>pcre32</b></a>
55 pages. References to functions or structures of the form <i>pcre[16|32]_xxx</i>
56 should be read as meaning "<i>pcre_xxx</i> when using the 8-bit library,
57 <i>pcre16_xxx</i> when using the 16-bit library, or <i>pcre32_xxx</i> when using
58 the 32-bit library".
59 </P>
60 <P>
61 The current implementation of PCRE corresponds approximately with Perl 5.12,
62 including support for UTF-8/16/32 encoded strings and Unicode general category
63 properties. However, UTF-8/16/32 and Unicode support has to be explicitly
64 enabled; it is not the default. The Unicode tables correspond to Unicode
65 release 6.2.0.
66 </P>
67 <P>
68 In addition to the Perl-compatible matching function, PCRE contains an
69 alternative function that matches the same compiled patterns in a different
70 way. In certain circumstances, the alternative function has some advantages.
71 For a discussion of the two matching algorithms, see the
72 <a href="pcrematching.html"><b>pcrematching</b></a>
73 page.
74 </P>
75 <P>
76 PCRE is written in C and released as a C library. A number of people have
77 written wrappers and interfaces of various kinds. In particular, Google Inc.
78 have provided a comprehensive C++ wrapper for the 8-bit library. This is now
79 included as part of the PCRE distribution. The
80 <a href="pcrecpp.html"><b>pcrecpp</b></a>
81 page has details of this interface. Other people's contributions can be found
82 in the <i>Contrib</i> directory at the primary FTP site, which is:
83 <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>
84 </P>
85 <P>
86 Details of exactly which Perl regular expression features are and are not
87 supported by PCRE are given in separate documents. See the
88 <a href="pcrepattern.html"><b>pcrepattern</b></a>
89 and
90 <a href="pcrecompat.html"><b>pcrecompat</b></a>
91 pages. There is a syntax summary in the
92 <a href="pcresyntax.html"><b>pcresyntax</b></a>
93 page.
94 </P>
95 <P>
96 Some features of PCRE can be included, excluded, or changed when the library is
97 built. The
98 <a href="pcre_config.html"><b>pcre_config()</b></a>
99 function makes it possible for a client to discover which features are
100 available. The features themselves are described in the
101 <a href="pcrebuild.html"><b>pcrebuild</b></a>
102 page. Documentation about building PCRE for various operating systems can be
103 found in the <b>README</b> and <b>NON-AUTOTOOLS_BUILD</b> files in the source
104 distribution.
105 </P>
106 <P>
107 The libraries contains a number of undocumented internal functions and data
108 tables that are used by more than one of the exported external functions, but
109 which are not intended for use by external callers. Their names all begin with
110 "_pcre_" or "_pcre16_" or "_pcre32_", which hopefully will not provoke any name
111 clashes. In some environments, it is possible to control which external symbols
112 are exported when a shared library is built, and in these cases the
113 undocumented symbols are not exported.
114 </P>
115 <br><a name="SEC2" href="#TOC1">SECURITY CONSIDERATIONS</a><br>
116 <P>
117 If you are using PCRE in a non-UTF application that permits users to supply
118 arbitrary patterns for compilation, you should be aware of a feature that
119 allows users to turn on UTF support from within a pattern, provided that PCRE
120 was built with UTF support. For example, an 8-bit pattern that begins with
121 "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, which interprets patterns and
122 subjects as strings of UTF-8 characters instead of individual 8-bit characters.
123 This causes both the pattern and any data against which it is matched to be
124 checked for UTF-8 validity. If the data string is very long, such a check might
125 use sufficiently many resources as to cause your application to lose
126 performance.
127 </P>
128 <P>
129 One way of guarding against this possibility is to use the
130 <b>pcre_fullinfo()</b> function to check the compiled pattern's options for UTF.
131 Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF option at
132 compile time. This causes an compile time error if a pattern contains a
133 UTF-setting sequence.
134 </P>
135 <P>
136 If your application is one that supports UTF, be aware that validity checking
137 can take time. If the same data string is to be matched many times, you can use
138 the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to
139 save redundant checks.
140 </P>
141 <P>
142 Another way that performance can be hit is by running a pattern that has a very
143 large search tree against a string that will never match. Nested unlimited
144 repeats in a pattern are a common example. PCRE provides some protection
145 against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the
146 <a href="pcreapi.html"><b>pcreapi</b></a>
147 page.
148 </P>
149 <br><a name="SEC3" href="#TOC1">USER DOCUMENTATION</a><br>
150 <P>
151 The user documentation for PCRE comprises a number of different sections. In
152 the "man" format, each of these is a separate "man page". In the HTML format,
153 each is a separate page, linked from the index page. In the plain text format,
154 all the sections, except the <b>pcredemo</b> section, are concatenated, for ease
155 of searching. The sections are as follows:
156 <pre>
157 pcre this document
158 pcre16 details of the 16-bit library
159 pcre32 details of the 32-bit library
160 pcre-config show PCRE installation configuration information
161 pcreapi details of PCRE's native C API
162 pcrebuild options for building PCRE
163 pcrecallout details of the callout feature
164 pcrecompat discussion of Perl compatibility
165 pcrecpp details of the C++ wrapper for the 8-bit library
166 pcredemo a demonstration C program that uses PCRE
167 pcregrep description of the <b>pcregrep</b> command (8-bit only)
168 pcrejit discussion of the just-in-time optimization support
169 pcrelimits details of size and other limits
170 pcrematching discussion of the two matching algorithms
171 pcrepartial details of the partial matching facility
172 pcrepattern syntax and semantics of supported regular expressions
173 pcreperform discussion of performance issues
174 pcreposix the POSIX-compatible C API for the 8-bit library
175 pcreprecompile details of saving and re-using precompiled patterns
176 pcresample discussion of the pcredemo program
177 pcrestack discussion of stack usage
178 pcresyntax quick syntax reference
179 pcretest description of the <b>pcretest</b> testing command
180 pcreunicode discussion of Unicode and UTF-8/16/32 support
181 </pre>
182 In addition, in the "man" and HTML formats, there is a short page for each
183 C library function, listing its arguments and results.
184 </P>
185 <br><a name="SEC4" href="#TOC1">AUTHOR</a><br>
186 <P>
187 Philip Hazel
188 <br>
189 University Computing Service
190 <br>
191 Cambridge CB2 3QH, England.
192 <br>
193 </P>
194 <P>
195 Putting an actual email address here seems to have been a spam magnet, so I've
196 taken it away. If you want to email me, use my two initials, followed by the
197 two digits 10, at the domain cam.ac.uk.
198 </P>
199 <br><a name="SEC5" href="#TOC1">REVISION</a><br>
200 <P>
201 Last updated: 26 April 2013
202 <br>
203 Copyright &copy; 1997-2013 University of Cambridge.
204 <br>
205 <p>
206 Return to the <a href="index.html">PCRE index page</a>.
207 </p>

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