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1 nigel 63 <html>
2     <head>
3     <title>pcre specification</title>
4     </head>
5     <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 nigel 75 <h1>pcre man page</h1>
7     <p>
8     Return to the <a href="index.html">PCRE index page</a>.
9     </p>
10 ph10 111 <p>
11 nigel 75 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 ph10 111 <br>
15 nigel 63 <ul>
16 nigel 75 <li><a name="TOC1" href="#SEC1">INTRODUCTION</a>
17 ph10 1194 <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 nigel 63 </ul>
22 nigel 75 <br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>
23 nigel 63 <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 ph10 461 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 nigel 63 </P>
31     <P>
32 ph10 903 Starting with release 8.30, it is possible to compile two separate PCRE
33 ph10 869 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 ph10 903 built. The majority of the work to make this possible was done by Zoltan
37 ph10 869 Herczeg.
38     </P>
39     <P>
40 ph10 1194 Starting with release 8.32 it is possible to compile a third separate PCRE
41 ph10 1332 library that supports 32-bit character strings (including UTF-32 strings). The
42     build process allows any combination of the 8-, 16- and 32-bit libraries. The
43     work to make this possible was done by Christian Persch.
44 ph10 1194 </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 ph10 869 <a href="pcre16.html"><b>pcre16</b></a>
53 ph10 1194 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 ph10 869 </P>
60     <P>
61 ph10 572 The current implementation of PCRE corresponds approximately with Perl 5.12,
62 ph10 1194 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 ph10 1404 release 6.3.0.
66 nigel 93 </P>
67     <P>
68     In addition to the Perl-compatible matching function, PCRE contains an
69 ph10 461 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 nigel 77 <a href="pcrematching.html"><b>pcrematching</b></a>
73     page.
74     </P>
75     <P>
76 nigel 75 PCRE is written in C and released as a C library. A number of people have
77 nigel 77 written wrappers and interfaces of various kinds. In particular, Google Inc.
78 ph10 869 have provided a comprehensive C++ wrapper for the 8-bit library. This is now
79     included as part of the PCRE distribution. The
80 nigel 77 <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 nigel 75 <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>
84 nigel 63 </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 ph10 208 pages. There is a syntax summary in the
92     <a href="pcresyntax.html"><b>pcresyntax</b></a>
93     page.
94 nigel 63 </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 nigel 75 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 ph10 1335 found in the
104 ph10 1332 <a href="README.txt"><b>README</b></a>
105 ph10 1335 and
106 ph10 1332 <a href="NON-AUTOTOOLS-BUILD.txt"><b>NON-AUTOTOOLS_BUILD</b></a>
107     files in the source distribution.
108 nigel 63 </P>
109 nigel 77 <P>
110 ph10 869 The libraries contains a number of undocumented internal functions and data
111 nigel 77 tables that are used by more than one of the exported external functions, but
112     which are not intended for use by external callers. Their names all begin with
113 ph10 1194 "_pcre_" or "_pcre16_" or "_pcre32_", which hopefully will not provoke any name
114     clashes. In some environments, it is possible to control which external symbols
115     are exported when a shared library is built, and in these cases the
116     undocumented symbols are not exported.
117 nigel 77 </P>
118 ph10 1194 <br><a name="SEC2" href="#TOC1">SECURITY CONSIDERATIONS</a><br>
119 nigel 63 <P>
120 ph10 1194 If you are using PCRE in a non-UTF application that permits users to supply
121     arbitrary patterns for compilation, you should be aware of a feature that
122     allows users to turn on UTF support from within a pattern, provided that PCRE
123     was built with UTF support. For example, an 8-bit pattern that begins with
124 ph10 1221 "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, which interprets patterns and
125     subjects as strings of UTF-8 characters instead of individual 8-bit characters.
126     This causes both the pattern and any data against which it is matched to be
127     checked for UTF-8 validity. If the data string is very long, such a check might
128     use sufficiently many resources as to cause your application to lose
129     performance.
130 ph10 1194 </P>
131     <P>
132 ph10 1320 One way of guarding against this possibility is to use the
133 ph10 1194 <b>pcre_fullinfo()</b> function to check the compiled pattern's options for UTF.
134 ph10 1320 Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF option at
135     compile time. This causes an compile time error if a pattern contains a
136     UTF-setting sequence.
137 ph10 1194 </P>
138     <P>
139     If your application is one that supports UTF, be aware that validity checking
140     can take time. If the same data string is to be matched many times, you can use
141 ph10 1221 the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to
142 ph10 1194 save redundant checks.
143     </P>
144     <P>
145 ph10 1221 Another way that performance can be hit is by running a pattern that has a very
146     large search tree against a string that will never match. Nested unlimited
147     repeats in a pattern are a common example. PCRE provides some protection
148 ph10 1194 against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the
149     <a href="pcreapi.html"><b>pcreapi</b></a>
150     page.
151     </P>
152     <br><a name="SEC3" href="#TOC1">USER DOCUMENTATION</a><br>
153     <P>
154 nigel 75 The user documentation for PCRE comprises a number of different sections. In
155     the "man" format, each of these is a separate "man page". In the HTML format,
156     each is a separate page, linked from the index page. In the plain text format,
157 ph10 1459 the descriptions of the <b>pcregrep</b> and <b>pcretest</b> programs are in files
158     called <b>pcregrep.txt</b> and <b>pcretest.txt</b>, respectively. The remaining
159     sections, except for the <b>pcredemo</b> section (which is a program listing),
160     are concatenated in <b>pcre.txt</b>, for ease of searching. The sections are as
161     follows:
162 nigel 63 <pre>
163     pcre this document
164 ph10 1332 pcre-config show PCRE installation configuration information
165 ph10 903 pcre16 details of the 16-bit library
166 ph10 1194 pcre32 details of the 32-bit library
167 nigel 77 pcreapi details of PCRE's native C API
168 ph10 1332 pcrebuild building PCRE
169 nigel 63 pcrecallout details of the callout feature
170     pcrecompat discussion of Perl compatibility
171 ph10 869 pcrecpp details of the C++ wrapper for the 8-bit library
172 ph10 429 pcredemo a demonstration C program that uses PCRE
173 ph10 869 pcregrep description of the <b>pcregrep</b> command (8-bit only)
174 ph10 691 pcrejit discussion of the just-in-time optimization support
175     pcrelimits details of size and other limits
176 nigel 77 pcrematching discussion of the two matching algorithms
177 nigel 75 pcrepartial details of the partial matching facility
178     pcrepattern syntax and semantics of supported regular expressions
179 nigel 63 pcreperform discussion of performance issues
180 ph10 869 pcreposix the POSIX-compatible C API for the 8-bit library
181 nigel 75 pcreprecompile details of saving and re-using precompiled patterns
182 ph10 429 pcresample discussion of the pcredemo program
183 nigel 91 pcrestack discussion of stack usage
184 ph10 461 pcresyntax quick syntax reference
185 nigel 75 pcretest description of the <b>pcretest</b> testing command
186 ph10 1194 pcreunicode discussion of Unicode and UTF-8/16/32 support
187 nigel 75 </pre>
188 ph10 1459 In the "man" and HTML formats, there is also a short page for each C library
189     function, listing its arguments and results.
190 nigel 63 </P>
191 ph10 1194 <br><a name="SEC4" href="#TOC1">AUTHOR</a><br>
192 nigel 63 <P>
193 nigel 77 Philip Hazel
194 nigel 63 <br>
195 ph10 99 University Computing Service
196 nigel 63 <br>
197 nigel 93 Cambridge CB2 3QH, England.
198 ph10 99 <br>
199 nigel 77 </P>
200     <P>
201     Putting an actual email address here seems to have been a spam magnet, so I've
202 ph10 153 taken it away. If you want to email me, use my two initials, followed by the
203     two digits 10, at the domain cam.ac.uk.
204 ph10 99 </P>
205 ph10 1194 <br><a name="SEC5" href="#TOC1">REVISION</a><br>
206 ph10 99 <P>
207 ph10 1459 Last updated: 08 January 2014
208 nigel 63 <br>
209 ph10 1459 Copyright &copy; 1997-2014 University of Cambridge.
210 ph10 99 <br>
211 nigel 75 <p>
212     Return to the <a href="index.html">PCRE index page</a>.
213     </p>

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