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<title>pcre specification</title>
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<h1>pcre man page</h1>
<p>
Return to the <a href="index.html">PCRE index page</a>.
</p>
<p>
This page is part of the PCRE HTML documentation. It was generated automatically
from the original man page. If there is any nonsense in it, please consult the
man page, in case the conversion went wrong.
<br>
<ul>
<li><a name="TOC1" href="#SEC1">INTRODUCTION</a>
<li><a name="TOC2" href="#SEC2">SECURITY CONSIDERATIONS</a>
<li><a name="TOC3" href="#SEC3">USER DOCUMENTATION</a>
<li><a name="TOC4" href="#SEC4">AUTHOR</a>
<li><a name="TOC5" href="#SEC5">REVISION</a>
</ul>
<br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>
<P>
The PCRE library is a set of functions that implement regular expression
pattern matching using the same syntax and semantics as Perl, with just a few
differences. Some features that appeared in Python and PCRE before they
appeared in Perl are also available using the Python syntax, there is some
support for one or two .NET and Oniguruma syntax items, and there is an option
for requesting some minor changes that give better JavaScript compatibility.
</P>
<P>
Starting with release 8.30, it is possible to compile two separate PCRE
libraries: the original, which supports 8-bit character strings (including
UTF-8 strings), and a second library that supports 16-bit character strings
(including UTF-16 strings). The build process allows either one or both to be
built. The majority of the work to make this possible was done by Zoltan
Herczeg.
</P>
<P>
Starting with release 8.32 it is possible to compile a third separate PCRE
library, which supports 32-bit character strings (including
UTF-32 strings). The build process allows any set of the 8-, 16- and 32-bit
libraries. The work to make this possible was done by Christian Persch.
</P>
<P>
The three libraries contain identical sets of functions, except that the names
in the 16-bit library start with <b>pcre16_</b> instead of <b>pcre_</b>, and the
names in the 32-bit library start with <b>pcre32_</b> instead of <b>pcre_</b>. To
avoid over-complication and reduce the documentation maintenance load, most of
the documentation describes the 8-bit library, with the differences for the
16-bit and 32-bit libraries described separately in the
<a href="pcre16.html"><b>pcre16</b></a>
and
<a href="pcre32.html"><b>pcre32</b></a>
pages. References to functions or structures of the form <i>pcre[16|32]_xxx</i>
should be read as meaning "<i>pcre_xxx</i> when using the 8-bit library,
<i>pcre16_xxx</i> when using the 16-bit library, or <i>pcre32_xxx</i> when using
the 32-bit library".
</P>
<P>
The current implementation of PCRE corresponds approximately with Perl 5.12,
including support for UTF-8/16/32 encoded strings and Unicode general category
properties. However, UTF-8/16/32 and Unicode support has to be explicitly
enabled; it is not the default. The Unicode tables correspond to Unicode
release 6.2.0.
</P>
<P>
In addition to the Perl-compatible matching function, PCRE contains an
alternative function that matches the same compiled patterns in a different
way. In certain circumstances, the alternative function has some advantages.
For a discussion of the two matching algorithms, see the
<a href="pcrematching.html"><b>pcrematching</b></a>
page.
</P>
<P>
PCRE is written in C and released as a C library. A number of people have
written wrappers and interfaces of various kinds. In particular, Google Inc.
have provided a comprehensive C++ wrapper for the 8-bit library. This is now
included as part of the PCRE distribution. The
<a href="pcrecpp.html"><b>pcrecpp</b></a>
page has details of this interface. Other people's contributions can be found
in the <i>Contrib</i> directory at the primary FTP site, which is:
<a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>
</P>
<P>
Details of exactly which Perl regular expression features are and are not
supported by PCRE are given in separate documents. See the
<a href="pcrepattern.html"><b>pcrepattern</b></a>
and
<a href="pcrecompat.html"><b>pcrecompat</b></a>
pages. There is a syntax summary in the
<a href="pcresyntax.html"><b>pcresyntax</b></a>
page.
</P>
<P>
Some features of PCRE can be included, excluded, or changed when the library is
built. The
<a href="pcre_config.html"><b>pcre_config()</b></a>
function makes it possible for a client to discover which features are
available. The features themselves are described in the
<a href="pcrebuild.html"><b>pcrebuild</b></a>
page. Documentation about building PCRE for various operating systems can be
found in the <b>README</b> and <b>NON-AUTOTOOLS_BUILD</b> files in the source
distribution.
</P>
<P>
The libraries contains a number of undocumented internal functions and data
tables that are used by more than one of the exported external functions, but
which are not intended for use by external callers. Their names all begin with
"_pcre_" or "_pcre16_" or "_pcre32_", which hopefully will not provoke any name
clashes. In some environments, it is possible to control which external symbols
are exported when a shared library is built, and in these cases the
undocumented symbols are not exported.
</P>
<br><a name="SEC2" href="#TOC1">SECURITY CONSIDERATIONS</a><br>
<P>
If you are using PCRE in a non-UTF application that permits users to supply
arbitrary patterns for compilation, you should be aware of a feature that
allows users to turn on UTF support from within a pattern, provided that PCRE
was built with UTF support. For example, an 8-bit pattern that begins with
"(*UTF8)" or "(*UTF)" turns on UTF-8 mode, which interprets patterns and
subjects as strings of UTF-8 characters instead of individual 8-bit characters.
This causes both the pattern and any data against which it is matched to be
checked for UTF-8 validity. If the data string is very long, such a check might
use sufficiently many resources as to cause your application to lose
performance.
</P>
<P>
The best way of guarding against this possibility is to use the
<b>pcre_fullinfo()</b> function to check the compiled pattern's options for UTF.
</P>
<P>
If your application is one that supports UTF, be aware that validity checking
can take time. If the same data string is to be matched many times, you can use
the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to
save redundant checks.
</P>
<P>
Another way that performance can be hit is by running a pattern that has a very
large search tree against a string that will never match. Nested unlimited
repeats in a pattern are a common example. PCRE provides some protection
against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the
<a href="pcreapi.html"><b>pcreapi</b></a>
page.
</P>
<br><a name="SEC3" href="#TOC1">USER DOCUMENTATION</a><br>
<P>
The user documentation for PCRE comprises a number of different sections. In
the "man" format, each of these is a separate "man page". In the HTML format,
each is a separate page, linked from the index page. In the plain text format,
all the sections, except the <b>pcredemo</b> section, are concatenated, for ease
of searching. The sections are as follows:
<pre>
  pcre              this document
  pcre16            details of the 16-bit library
  pcre32            details of the 32-bit library
  pcre-config       show PCRE installation configuration information
  pcreapi           details of PCRE's native C API
  pcrebuild         options for building PCRE
  pcrecallout       details of the callout feature
  pcrecompat        discussion of Perl compatibility
  pcrecpp           details of the C++ wrapper for the 8-bit library
  pcredemo          a demonstration C program that uses PCRE
  pcregrep          description of the <b>pcregrep</b> command (8-bit only)
  pcrejit           discussion of the just-in-time optimization support
  pcrelimits        details of size and other limits
  pcrematching      discussion of the two matching algorithms
  pcrepartial       details of the partial matching facility
  pcrepattern       syntax and semantics of supported regular expressions
  pcreperform       discussion of performance issues
  pcreposix         the POSIX-compatible C API for the 8-bit library
  pcreprecompile    details of saving and re-using precompiled patterns
  pcresample        discussion of the pcredemo program
  pcrestack         discussion of stack usage
  pcresyntax        quick syntax reference
  pcretest          description of the <b>pcretest</b> testing command
  pcreunicode       discussion of Unicode and UTF-8/16/32 support
</pre>
In addition, in the "man" and HTML formats, there is a short page for each
C library function, listing its arguments and results.
</P>
<br><a name="SEC4" href="#TOC1">AUTHOR</a><br>
<P>
Philip Hazel
<br>
University Computing Service
<br>
Cambridge CB2 3QH, England.
<br>
</P>
<P>
Putting an actual email address here seems to have been a spam magnet, so I've
taken it away. If you want to email me, use my two initials, followed by the
two digits 10, at the domain cam.ac.uk.
</P>
<br><a name="SEC5" href="#TOC1">REVISION</a><br>
<P>
Last updated: 11 November 2012
<br>
Copyright &copy; 1997-2012 University of Cambridge.
<br>
<p>
Return to the <a href="index.html">PCRE index page</a>.
</p>
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	The best 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	</P>
132	<P>
133	If your application is one that supports UTF, be aware that validity checking
134	can take time. If the same data string is to be matched many times, you can use
135	the PCRE_NO_UTF[8\|16\|32]_CHECK option for the second and subsequent matches to
136	save redundant checks.
137	</P>
138	<P>
139	Another way that performance can be hit is by running a pattern that has a very
140	large search tree against a string that will never match. Nested unlimited
141	repeats in a pattern are a common example. PCRE provides some protection
142	against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the
143	<a href="pcreapi.html"><b>pcreapi</b></a>
144	page.
145	</P>
146	<br><a name="SEC3" href="#TOC1">USER DOCUMENTATION</a><br>
147	<P>
148	The user documentation for PCRE comprises a number of different sections. In
149	the "man" format, each of these is a separate "man page". In the HTML format,
150	each is a separate page, linked from the index page. In the plain text format,
151	all the sections, except the <b>pcredemo</b> section, are concatenated, for ease
152	of searching. The sections are as follows:
153	<pre>
154	pcre this document
155	pcre16 details of the 16-bit library
156	pcre32 details of the 32-bit library
157	pcre-config show PCRE installation configuration information
158	pcreapi details of PCRE's native C API
159	pcrebuild options for building PCRE
160	pcrecallout details of the callout feature
161	pcrecompat discussion of Perl compatibility
162	pcrecpp details of the C++ wrapper for the 8-bit library
163	pcredemo a demonstration C program that uses PCRE
164	pcregrep description of the <b>pcregrep</b> command (8-bit only)
165	pcrejit discussion of the just-in-time optimization support
166	pcrelimits details of size and other limits
167	pcrematching discussion of the two matching algorithms
168	pcrepartial details of the partial matching facility
169	pcrepattern syntax and semantics of supported regular expressions
170	pcreperform discussion of performance issues
171	pcreposix the POSIX-compatible C API for the 8-bit library
172	pcreprecompile details of saving and re-using precompiled patterns
173	pcresample discussion of the pcredemo program
174	pcrestack discussion of stack usage
175	pcresyntax quick syntax reference
176	pcretest description of the <b>pcretest</b> testing command
177	pcreunicode discussion of Unicode and UTF-8/16/32 support
178	</pre>
179	In addition, in the "man" and HTML formats, there is a short page for each
180	C library function, listing its arguments and results.
181	</P>
182	<br><a name="SEC4" href="#TOC1">AUTHOR</a><br>
183	<P>
184	Philip Hazel
185	<br>
186	University Computing Service
187	<br>
188	Cambridge CB2 3QH, England.
189	<br>
190	</P>
191	<P>
192	Putting an actual email address here seems to have been a spam magnet, so I've
193	taken it away. If you want to email me, use my two initials, followed by the
194	two digits 10, at the domain cam.ac.uk.
195	</P>
196	<br><a name="SEC5" href="#TOC1">REVISION</a><br>
197	<P>
198	Last updated: 11 November 2012
199	<br>
200	Copyright © 1997-2012 University of Cambridge.
201	<br>
202	<p>
203	Return to the <a href="index.html">PCRE index page</a>.
204	</p>
Name	Value
svn:eol-style	native
svn:keywords	"Author Date Id Revision Url"