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Documentation update.
1 .TH PCRE 3 "30 October 2012" "PCRE 8.32"
3 PCRE - Perl-compatible regular expressions
5 .rs
6 .sp
7 The PCRE library is a set of functions that implement regular expression
8 pattern matching using the same syntax and semantics as Perl, with just a few
9 differences. Some features that appeared in Python and PCRE before they
10 appeared in Perl are also available using the Python syntax, there is some
11 support for one or two .NET and Oniguruma syntax items, and there is an option
12 for requesting some minor changes that give better JavaScript compatibility.
13 .P
14 Starting with release 8.30, it is possible to compile two separate PCRE
15 libraries: the original, which supports 8-bit character strings (including
16 UTF-8 strings), and a second library that supports 16-bit character strings
17 (including UTF-16 strings). The build process allows either one or both to be
18 built. The majority of the work to make this possible was done by Zoltan
19 Herczeg.
20 .P
21 Starting with release 8.32 it is possible to compile a third separate PCRE
22 library, which supports 32-bit character strings (including
23 UTF-32 strings). The build process allows any set of the 8-, 16- and 32-bit
24 libraries. The work to make this possible was done by Christian Persch.
25 .P
26 The three libraries contain identical sets of functions, except that the names
27 in the 16-bit library start with \fBpcre16_\fP instead of \fBpcre_\fP, and the
28 names in the 32-bit library start with \fBpcre32_\fP instead of \fBpcre_\fP. To
29 avoid over-complication and reduce the documentation maintenance load, most of
30 the documentation describes the 8-bit library, with the differences for the
31 16-bit and 32-bit libraries described separately in the
32 .\" HREF
33 \fBpcre16\fP
34 and
35 .\" HREF
36 \fBpcre32\fP
37 .\"
38 pages. References to functions or structures of the form \fIpcre[16|32]_xxx\fP
39 should be read as meaning "\fIpcre_xxx\fP when using the 8-bit library,
40 \fIpcre16_xxx\fP when using the 16-bit library, or \fIpcre32_xxx\fP when using
41 the 32-bit library".
42 .P
43 The current implementation of PCRE corresponds approximately with Perl 5.12,
44 including support for UTF-8/16/32 encoded strings and Unicode general category
45 properties. However, UTF-8/16/32 and Unicode support has to be explicitly
46 enabled; it is not the default. The Unicode tables correspond to Unicode
47 release 6.2.0.
48 .P
49 In addition to the Perl-compatible matching function, PCRE contains an
50 alternative function that matches the same compiled patterns in a different
51 way. In certain circumstances, the alternative function has some advantages.
52 For a discussion of the two matching algorithms, see the
53 .\" HREF
54 \fBpcrematching\fP
55 .\"
56 page.
57 .P
58 PCRE is written in C and released as a C library. A number of people have
59 written wrappers and interfaces of various kinds. In particular, Google Inc.
60 have provided a comprehensive C++ wrapper for the 8-bit library. This is now
61 included as part of the PCRE distribution. The
62 .\" HREF
63 \fBpcrecpp\fP
64 .\"
65 page has details of this interface. Other people's contributions can be found
66 in the \fIContrib\fP directory at the primary FTP site, which is:
67 .sp
68 .\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">
69 .\" </a>
70 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
71 .P
72 Details of exactly which Perl regular expression features are and are not
73 supported by PCRE are given in separate documents. See the
74 .\" HREF
75 \fBpcrepattern\fP
76 .\"
77 and
78 .\" HREF
79 \fBpcrecompat\fP
80 .\"
81 pages. There is a syntax summary in the
82 .\" HREF
83 \fBpcresyntax\fP
84 .\"
85 page.
86 .P
87 Some features of PCRE can be included, excluded, or changed when the library is
88 built. The
89 .\" HREF
90 \fBpcre_config()\fP
91 .\"
92 function makes it possible for a client to discover which features are
93 available. The features themselves are described in the
94 .\" HREF
95 \fBpcrebuild\fP
96 .\"
97 page. Documentation about building PCRE for various operating systems can be
98 found in the \fBREADME\fP and \fBNON-AUTOTOOLS_BUILD\fP files in the source
99 distribution.
100 .P
101 The libraries contains a number of undocumented internal functions and data
102 tables that are used by more than one of the exported external functions, but
103 which are not intended for use by external callers. Their names all begin with
104 "_pcre_" or "_pcre16_" or "_pcre32_", which hopefully will not provoke any name
105 clashes. In some environments, it is possible to control which external symbols
106 are exported when a shared library is built, and in these cases the
107 undocumented symbols are not exported.
108 .
109 .
111 .rs
112 .sp
113 If you are using PCRE in a non-UTF application that permits users to supply
114 arbitrary patterns for compilation, you should be aware of a feature that
115 allows users to turn on UTF support from within a pattern, provided that PCRE
116 was built with UTF support. For example, an 8-bit pattern that begins with
117 "(*UTF8)" turns on UTF-8 mode. This causes both the pattern and any data
118 against which it is matched to be checked for UTF-8 validity. If the data
119 string is very long, such a check might use sufficiently many resources as to
120 cause your application to lose performance.
121 .P
122 The best way of guarding against this possibility is to use the
123 \fBpcre_fullinfo()\fP function to check the compiled pattern's options for UTF.
124 .P
125 If your application is one that supports UTF, be aware that validity checking
126 can take time. If the same data string is to be matched many times, you can use
127 the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to
128 save redundant checks.
129 .P
130 Another way that performance can be hit is by running a pattern that has a very
131 large search tree against a string that will never match. Nested unlimited
132 repeats in a pattern are a common example. PCRE provides some protection
133 against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the
134 .\" HREF
135 \fBpcreapi\fP
136 .\"
137 page.
138 .
139 .
141 .rs
142 .sp
143 The user documentation for PCRE comprises a number of different sections. In
144 the "man" format, each of these is a separate "man page". In the HTML format,
145 each is a separate page, linked from the index page. In the plain text format,
146 all the sections, except the \fBpcredemo\fP section, are concatenated, for ease
147 of searching. The sections are as follows:
148 .sp
149 pcre this document
150 pcre16 details of the 16-bit library
151 pcre32 details of the 32-bit library
152 pcre-config show PCRE installation configuration information
153 pcreapi details of PCRE's native C API
154 pcrebuild options for building PCRE
155 pcrecallout details of the callout feature
156 pcrecompat discussion of Perl compatibility
157 pcrecpp details of the C++ wrapper for the 8-bit library
158 pcredemo a demonstration C program that uses PCRE
159 pcregrep description of the \fBpcregrep\fP command (8-bit only)
160 pcrejit discussion of the just-in-time optimization support
161 pcrelimits details of size and other limits
162 pcrematching discussion of the two matching algorithms
163 pcrepartial details of the partial matching facility
164 .\" JOIN
165 pcrepattern syntax and semantics of supported
166 regular expressions
167 pcreperform discussion of performance issues
168 pcreposix the POSIX-compatible C API for the 8-bit library
169 pcreprecompile details of saving and re-using precompiled patterns
170 pcresample discussion of the pcredemo program
171 pcrestack discussion of stack usage
172 pcresyntax quick syntax reference
173 pcretest description of the \fBpcretest\fP testing command
174 pcreunicode discussion of Unicode and UTF-8/16/32 support
175 .sp
176 In addition, in the "man" and HTML formats, there is a short page for each
177 C library function, listing its arguments and results.
178 .
179 .
181 .rs
182 .sp
183 .nf
184 Philip Hazel
185 University Computing Service
186 Cambridge CB2 3QH, England.
187 .fi
188 .P
189 Putting an actual email address here seems to have been a spam magnet, so I've
190 taken it away. If you want to email me, use my two initials, followed by the
191 two digits 10, at the domain cam.ac.uk.
192 .
193 .
195 .rs
196 .sp
197 .nf
198 Last updated: 30 October 2012
199 Copyright (c) 1997-2012 University of Cambridge.
200 .fi


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