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Documentation and tidies preparatory to 8.37 release.

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 ph10 1548 <li><a name="TOC1" href="#SEC1">PLEASE TAKE NOTE</a>
17     <li><a name="TOC2" href="#SEC2">INTRODUCTION</a>
18     <li><a name="TOC3" href="#SEC3">SECURITY CONSIDERATIONS</a>
19     <li><a name="TOC4" href="#SEC4">USER DOCUMENTATION</a>
20     <li><a name="TOC5" href="#SEC5">AUTHOR</a>
21     <li><a name="TOC6" href="#SEC6">REVISION</a>
22 nigel 63 </ul>
23 ph10 1548 <br><a name="SEC1" href="#TOC1">PLEASE TAKE NOTE</a><br>
24 nigel 63 <P>
25 ph10 1548 This document relates to PCRE releases that use the original API,
26     with library names libpcre, libpcre16, and libpcre32. January 2015 saw the
27     first release of a new API, known as PCRE2, with release numbers starting at
28     10.00 and library names libpcre2-8, libpcre2-16, and libpcre2-32. The old
29     libraries (now called PCRE1) are still being maintained for bug fixes, but
30     there will be no new development. New projects are advised to use the new PCRE2
31     libraries.
32     </P>
33     <br><a name="SEC2" href="#TOC1">INTRODUCTION</a><br>
34     <P>
35 nigel 63 The PCRE library is a set of functions that implement regular expression
36     pattern matching using the same syntax and semantics as Perl, with just a few
37 ph10 461 differences. Some features that appeared in Python and PCRE before they
38     appeared in Perl are also available using the Python syntax, there is some
39     support for one or two .NET and Oniguruma syntax items, and there is an option
40     for requesting some minor changes that give better JavaScript compatibility.
41 nigel 63 </P>
42     <P>
43 ph10 903 Starting with release 8.30, it is possible to compile two separate PCRE
44 ph10 869 libraries: the original, which supports 8-bit character strings (including
45     UTF-8 strings), and a second library that supports 16-bit character strings
46     (including UTF-16 strings). The build process allows either one or both to be
47 ph10 903 built. The majority of the work to make this possible was done by Zoltan
48 ph10 869 Herczeg.
49     </P>
50     <P>
51 ph10 1194 Starting with release 8.32 it is possible to compile a third separate PCRE
52 ph10 1332 library that supports 32-bit character strings (including UTF-32 strings). The
53     build process allows any combination of the 8-, 16- and 32-bit libraries. The
54     work to make this possible was done by Christian Persch.
55 ph10 1194 </P>
56     <P>
57     The three libraries contain identical sets of functions, except that the names
58     in the 16-bit library start with <b>pcre16_</b> instead of <b>pcre_</b>, and the
59     names in the 32-bit library start with <b>pcre32_</b> instead of <b>pcre_</b>. To
60     avoid over-complication and reduce the documentation maintenance load, most of
61     the documentation describes the 8-bit library, with the differences for the
62     16-bit and 32-bit libraries described separately in the
63 ph10 869 <a href="pcre16.html"><b>pcre16</b></a>
64 ph10 1194 and
65     <a href="pcre32.html"><b>pcre32</b></a>
66     pages. References to functions or structures of the form <i>pcre[16|32]_xxx</i>
67     should be read as meaning "<i>pcre_xxx</i> when using the 8-bit library,
68     <i>pcre16_xxx</i> when using the 16-bit library, or <i>pcre32_xxx</i> when using
69     the 32-bit library".
70 ph10 869 </P>
71     <P>
72 ph10 572 The current implementation of PCRE corresponds approximately with Perl 5.12,
73 ph10 1194 including support for UTF-8/16/32 encoded strings and Unicode general category
74     properties. However, UTF-8/16/32 and Unicode support has to be explicitly
75     enabled; it is not the default. The Unicode tables correspond to Unicode
76 ph10 1404 release 6.3.0.
77 nigel 93 </P>
78     <P>
79     In addition to the Perl-compatible matching function, PCRE contains an
80 ph10 461 alternative function that matches the same compiled patterns in a different
81     way. In certain circumstances, the alternative function has some advantages.
82     For a discussion of the two matching algorithms, see the
83 nigel 77 <a href="pcrematching.html"><b>pcrematching</b></a>
84     page.
85     </P>
86     <P>
87 nigel 75 PCRE is written in C and released as a C library. A number of people have
88 nigel 77 written wrappers and interfaces of various kinds. In particular, Google Inc.
89 ph10 869 have provided a comprehensive C++ wrapper for the 8-bit library. This is now
90     included as part of the PCRE distribution. The
91 nigel 77 <a href="pcrecpp.html"><b>pcrecpp</b></a>
92     page has details of this interface. Other people's contributions can be found
93     in the <i>Contrib</i> directory at the primary FTP site, which is:
94 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>
95 nigel 63 </P>
96     <P>
97     Details of exactly which Perl regular expression features are and are not
98     supported by PCRE are given in separate documents. See the
99     <a href="pcrepattern.html"><b>pcrepattern</b></a>
100     and
101     <a href="pcrecompat.html"><b>pcrecompat</b></a>
102 ph10 208 pages. There is a syntax summary in the
103     <a href="pcresyntax.html"><b>pcresyntax</b></a>
104     page.
105 nigel 63 </P>
106     <P>
107     Some features of PCRE can be included, excluded, or changed when the library is
108     built. The
109     <a href="pcre_config.html"><b>pcre_config()</b></a>
110     function makes it possible for a client to discover which features are
111 nigel 75 available. The features themselves are described in the
112     <a href="pcrebuild.html"><b>pcrebuild</b></a>
113     page. Documentation about building PCRE for various operating systems can be
114 ph10 1335 found in the
115 ph10 1332 <a href="README.txt"><b>README</b></a>
116 ph10 1335 and
117 ph10 1332 <a href="NON-AUTOTOOLS-BUILD.txt"><b>NON-AUTOTOOLS_BUILD</b></a>
118     files in the source distribution.
119 nigel 63 </P>
120 nigel 77 <P>
121 ph10 869 The libraries contains a number of undocumented internal functions and data
122 nigel 77 tables that are used by more than one of the exported external functions, but
123     which are not intended for use by external callers. Their names all begin with
124 ph10 1194 "_pcre_" or "_pcre16_" or "_pcre32_", which hopefully will not provoke any name
125     clashes. In some environments, it is possible to control which external symbols
126     are exported when a shared library is built, and in these cases the
127     undocumented symbols are not exported.
128 nigel 77 </P>
129 ph10 1548 <br><a name="SEC3" href="#TOC1">SECURITY CONSIDERATIONS</a><br>
130 nigel 63 <P>
131 ph10 1194 If you are using PCRE in a non-UTF application that permits users to supply
132     arbitrary patterns for compilation, you should be aware of a feature that
133     allows users to turn on UTF support from within a pattern, provided that PCRE
134     was built with UTF support. For example, an 8-bit pattern that begins with
135 ph10 1221 "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, which interprets patterns and
136     subjects as strings of UTF-8 characters instead of individual 8-bit characters.
137     This causes both the pattern and any data against which it is matched to be
138     checked for UTF-8 validity. If the data string is very long, such a check might
139     use sufficiently many resources as to cause your application to lose
140     performance.
141 ph10 1194 </P>
142     <P>
143 ph10 1320 One way of guarding against this possibility is to use the
144 ph10 1194 <b>pcre_fullinfo()</b> function to check the compiled pattern's options for UTF.
145 ph10 1320 Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF option at
146     compile time. This causes an compile time error if a pattern contains a
147     UTF-setting sequence.
148 ph10 1194 </P>
149     <P>
150     If your application is one that supports UTF, be aware that validity checking
151     can take time. If the same data string is to be matched many times, you can use
152 ph10 1221 the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to
153 ph10 1194 save redundant checks.
154     </P>
155     <P>
156 ph10 1221 Another way that performance can be hit is by running a pattern that has a very
157     large search tree against a string that will never match. Nested unlimited
158     repeats in a pattern are a common example. PCRE provides some protection
159 ph10 1194 against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the
160     <a href="pcreapi.html"><b>pcreapi</b></a>
161     page.
162     </P>
163 ph10 1548 <br><a name="SEC4" href="#TOC1">USER DOCUMENTATION</a><br>
164 ph10 1194 <P>
165 nigel 75 The user documentation for PCRE comprises a number of different sections. In
166     the "man" format, each of these is a separate "man page". In the HTML format,
167     each is a separate page, linked from the index page. In the plain text format,
168 ph10 1459 the descriptions of the <b>pcregrep</b> and <b>pcretest</b> programs are in files
169     called <b>pcregrep.txt</b> and <b>pcretest.txt</b>, respectively. The remaining
170     sections, except for the <b>pcredemo</b> section (which is a program listing),
171     are concatenated in <b>pcre.txt</b>, for ease of searching. The sections are as
172     follows:
173 nigel 63 <pre>
174     pcre this document
175 ph10 1332 pcre-config show PCRE installation configuration information
176 ph10 903 pcre16 details of the 16-bit library
177 ph10 1194 pcre32 details of the 32-bit library
178 nigel 77 pcreapi details of PCRE's native C API
179 ph10 1332 pcrebuild building PCRE
180 nigel 63 pcrecallout details of the callout feature
181     pcrecompat discussion of Perl compatibility
182 ph10 869 pcrecpp details of the C++ wrapper for the 8-bit library
183 ph10 429 pcredemo a demonstration C program that uses PCRE
184 ph10 869 pcregrep description of the <b>pcregrep</b> command (8-bit only)
185 ph10 691 pcrejit discussion of the just-in-time optimization support
186     pcrelimits details of size and other limits
187 nigel 77 pcrematching discussion of the two matching algorithms
188 nigel 75 pcrepartial details of the partial matching facility
189     pcrepattern syntax and semantics of supported regular expressions
190 nigel 63 pcreperform discussion of performance issues
191 ph10 869 pcreposix the POSIX-compatible C API for the 8-bit library
192 nigel 75 pcreprecompile details of saving and re-using precompiled patterns
193 ph10 429 pcresample discussion of the pcredemo program
194 nigel 91 pcrestack discussion of stack usage
195 ph10 461 pcresyntax quick syntax reference
196 nigel 75 pcretest description of the <b>pcretest</b> testing command
197 ph10 1194 pcreunicode discussion of Unicode and UTF-8/16/32 support
198 nigel 75 </pre>
199 ph10 1459 In the "man" and HTML formats, there is also a short page for each C library
200     function, listing its arguments and results.
201 nigel 63 </P>
202 ph10 1548 <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
203 nigel 63 <P>
204 nigel 77 Philip Hazel
205 nigel 63 <br>
206 ph10 99 University Computing Service
207 nigel 63 <br>
208 nigel 93 Cambridge CB2 3QH, England.
209 ph10 99 <br>
210 nigel 77 </P>
211     <P>
212     Putting an actual email address here seems to have been a spam magnet, so I've
213 ph10 153 taken it away. If you want to email me, use my two initials, followed by the
214     two digits 10, at the domain cam.ac.uk.
215 ph10 99 </P>
216 ph10 1548 <br><a name="SEC6" href="#TOC1">REVISION</a><br>
217 ph10 99 <P>
218 ph10 1548 Last updated: 10 February 2015
219 nigel 63 <br>
220 ph10 1548 Copyright &copy; 1997-2015 University of Cambridge.
221 ph10 99 <br>
222 nigel 75 <p>
223     Return to the <a href="index.html">PCRE index page</a>.
224     </p>

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