doc/html/pcre.html

<html>
<head>
<title>pcre specification</title>
</head>
<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
<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 that supports 32-bit character strings (including UTF-32 strings). The
build process allows any combination 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 
<a href="README.txt"><b>README</b></a>
and 
<a href="NON-AUTOTOOLS-BUILD.txt"><b>NON-AUTOTOOLS_BUILD</b></a>
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>
One way of guarding against this possibility is to use the
<b>pcre_fullinfo()</b> function to check the compiled pattern's options for UTF.
Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF option at
compile time. This causes an compile time error if a pattern contains a
UTF-setting sequence.
</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
  pcre-config       show PCRE installation configuration information
  pcre16            details of the 16-bit library
  pcre32            details of the 32-bit library
  pcreapi           details of PCRE's native C API
  pcrebuild         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: 13 May 2013
<br>
Copyright &copy; 1997-2013 University of Cambridge.
<br>
<p>
Return to the <a href="index.html">PCRE index page</a>.
</p>
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			release 6.2.0.
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	1332	found in the
104			<a href="README.txt"><b>README</b></a>
105			and
106			<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	429	all the sections, except the <b>pcredemo</b> section, are concatenated, for ease
158			of searching. The sections are as follows:
159	nigel	63	<pre>
160			pcre this document
161	ph10	1332	pcre-config show PCRE installation configuration information
162	ph10	903	pcre16 details of the 16-bit library
163	ph10	1194	pcre32 details of the 32-bit library
164	nigel	77	pcreapi details of PCRE's native C API
165	ph10	1332	pcrebuild building PCRE
166	nigel	63	pcrecallout details of the callout feature
167			pcrecompat discussion of Perl compatibility
168	ph10	869	pcrecpp details of the C++ wrapper for the 8-bit library
169	ph10	429	pcredemo a demonstration C program that uses PCRE
170	ph10	869	pcregrep description of the <b>pcregrep</b> command (8-bit only)
171	ph10	691	pcrejit discussion of the just-in-time optimization support
172			pcrelimits details of size and other limits
173	nigel	77	pcrematching discussion of the two matching algorithms
174	nigel	75	pcrepartial details of the partial matching facility
175			pcrepattern syntax and semantics of supported regular expressions
176	nigel	63	pcreperform discussion of performance issues
177	ph10	869	pcreposix the POSIX-compatible C API for the 8-bit library
178	nigel	75	pcreprecompile details of saving and re-using precompiled patterns
179	ph10	429	pcresample discussion of the pcredemo program
180	nigel	91	pcrestack discussion of stack usage
181	ph10	461	pcresyntax quick syntax reference
182	nigel	75	pcretest description of the <b>pcretest</b> testing command
183	ph10	1194	pcreunicode discussion of Unicode and UTF-8/16/32 support
184	nigel	75	</pre>
185	nigel	63	In addition, in the "man" and HTML formats, there is a short page for each
186	ph10	1194	C library function, listing its arguments and results.
187	nigel	63	</P>
188	ph10	1194	<br><a name="SEC4" href="#TOC1">AUTHOR</a><br>
189	nigel	63	<P>
190	nigel	77	Philip Hazel
191	nigel	63	<br>
192	ph10	99	University Computing Service
193	nigel	63	<br>
194	nigel	93	Cambridge CB2 3QH, England.
195	ph10	99	<br>
196	nigel	77	</P>
197			<P>
198			Putting an actual email address here seems to have been a spam magnet, so I've
199	ph10	153	taken it away. If you want to email me, use my two initials, followed by the
200			two digits 10, at the domain cam.ac.uk.
201	ph10	99	</P>
202	ph10	1194	<br><a name="SEC5" href="#TOC1">REVISION</a><br>
203	ph10	99	<P>
204	ph10	1332	Last updated: 13 May 2013
205	nigel	63	<br>
206	ph10	1320	Copyright © 1997-2013 University of Cambridge.
207	ph10	99	<br>
208	nigel	75	<p>
209			Return to the <a href="index.html">PCRE index page</a>.
210			</p>
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svn:keywords	"Author Date Id Revision Url"