doc/html/pcre.html

<html>
<head>
<title>pcre specification</title>
</head>
<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
This HTML document has been 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">DESCRIPTION</a>
<li><a name="TOC2" href="#SEC2">USER DOCUMENTATION</a>
<li><a name="TOC3" href="#SEC3">LIMITATIONS</a>
<li><a name="TOC4" href="#SEC4">UTF-8 SUPPORT</a>
<li><a name="TOC5" href="#SEC5">AUTHOR</a>
</ul>
<br><a name="SEC1" href="#TOC1">DESCRIPTION</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. The current implementation of PCRE (release 4.x) corresponds
approximately with Perl 5.8, including support for UTF-8 encoded strings.
However, this support has to be explicitly enabled; it is not the default.
</P>
<P>
PCRE is written in C and released as a C library. However, a number of people
have written wrappers and interfaces of various kinds. A C++ class is included
in these contributions, which can be found in the <i>Contrib</i> directory at
the primary FTP site, which is:
</P>
<a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>
<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.
</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. Documentation about building PCRE for various operating systems can
be found in the <b>README</b> file in the source distribution.
</P>
<br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>
<P>
The user documentation for PCRE has been split up into 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 are concatenated, for ease of searching. The
sections are as follows:
</P>
<P>
<pre>
  pcre              this document
  pcreapi           details of PCRE's native API
  pcrebuild         options for building PCRE
  pcrecallout       details of the callout feature
  pcrecompat        discussion of Perl compatibility
  pcregrep          description of the <b>pcregrep</b> command
  pcrepattern       syntax and semantics of supported
                      regular expressions
  pcreperform       discussion of performance issues
  pcreposix         the POSIX-compatible API
  pcresample        discussion of the sample program
  pcretest          the <b>pcretest</b> testing command
</PRE>
</P>
<P>
In addition, in the "man" and HTML formats, there is a short page for each
library function, listing its arguments and results.
</P>
<br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>
<P>
There are some size limitations in PCRE but it is hoped that they will never in
practice be relevant.
</P>
<P>
The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is
compiled with the default internal linkage size of 2. If you want to process
regular expressions that are truly enormous, you can compile PCRE with an
internal linkage size of 3 or 4 (see the <b>README</b> file in the source
distribution and the
<a href="pcrebuild.html"><b>pcrebuild</b></a>
documentation for details). If these cases the limit is substantially larger.
However, the speed of execution will be slower.
</P>
<P>
All values in repeating quantifiers must be less than 65536.
The maximum number of capturing subpatterns is 65535.
</P>
<P>
There is no limit to the number of non-capturing subpatterns, but the maximum
depth of nesting of all kinds of parenthesized subpattern, including capturing
subpatterns, assertions, and other types of subpattern, is 200.
</P>
<P>
The maximum length of a subject string is the largest positive number that an
integer variable can hold. However, PCRE uses recursion to handle subpatterns
and indefinite repetition. This means that the available stack space may limit
the size of a subject string that can be processed by certain patterns.
</P>
<a name="utf8support"></a><br><a name="SEC4" href="#TOC1">UTF-8 SUPPORT</a><br>
<P>
Starting at release 3.3, PCRE has had some support for character strings
encoded in the UTF-8 format. For release 4.0 this has been greatly extended to
cover most common requirements.
</P>
<P>
In order process UTF-8 strings, you must build PCRE to include UTF-8 support in
the code, and, in addition, you must call
<a href="pcre_compile.html"><b>pcre_compile()</b></a>
with the PCRE_UTF8 option flag. When you do this, both the pattern and any
subject strings that are matched against it are treated as UTF-8 strings
instead of just strings of bytes.
</P>
<P>
If you compile PCRE with UTF-8 support, but do not use it at run time, the
library will be a bit bigger, but the additional run time overhead is limited
to testing the PCRE_UTF8 flag in several places, so should not be very large.
</P>
<P>
The following comments apply when PCRE is running in UTF-8 mode:
</P>
<P>
1. PCRE assumes that the strings it is given contain valid UTF-8 codes. It does
not diagnose invalid UTF-8 strings. If you pass invalid UTF-8 strings to PCRE,
the results are undefined.
</P>
<P>
2. In a pattern, the escape sequence \x{...}, where the contents of the braces
is a string of hexadecimal digits, is interpreted as a UTF-8 character whose
code number is the given hexadecimal number, for example: \x{1234}. If a
non-hexadecimal digit appears between the braces, the item is not recognized.
This escape sequence can be used either as a literal, or within a character
class.
</P>
<P>
3. The original hexadecimal escape sequence, \xhh, matches a two-byte UTF-8
character if the value is greater than 127.
</P>
<P>
4. Repeat quantifiers apply to complete UTF-8 characters, not to individual
bytes, for example: \x{100}{3}.
</P>
<P>
5. The dot metacharacter matches one UTF-8 character instead of a single byte.
</P>
<P>
6. The escape sequence \C can be used to match a single byte in UTF-8 mode,
but its use can lead to some strange effects.
</P>
<P>
7. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
test characters of any code value, but the characters that PCRE recognizes as
digits, spaces, or word characters remain the same set as before, all with
values less than 256.
</P>
<P>
8. Case-insensitive matching applies only to characters whose values are less
than 256. PCRE does not support the notion of "case" for higher-valued
characters.
</P>
<P>
9. PCRE does not support the use of Unicode tables and properties or the Perl
escapes \p, \P, and \X.
</P>
<br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
<P>
Philip Hazel &#60;ph10@cam.ac.uk&#62;
<br>
University Computing Service,
<br>
Cambridge CB2 3QG, England.
<br>
Phone: +44 1223 334714
</P>
<P>
Last updated: 04 February 2003
<br>
Copyright &copy; 1997-2003 University of Cambridge.
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			This HTML document has been generated automatically from the original man page.
7			If there is any nonsense in it, please consult the man page, in case the
8			conversion went wrong.<br>
9			<ul>
10			<li><a name="TOC1" href="#SEC1">DESCRIPTION</a>
11			<li><a name="TOC2" href="#SEC2">USER DOCUMENTATION</a>
12			<li><a name="TOC3" href="#SEC3">LIMITATIONS</a>
13			<li><a name="TOC4" href="#SEC4">UTF-8 SUPPORT</a>
14			<li><a name="TOC5" href="#SEC5">AUTHOR</a>
15			</ul>
16			<br><a name="SEC1" href="#TOC1">DESCRIPTION</a><br>
17			<P>
18			The PCRE library is a set of functions that implement regular expression
19			pattern matching using the same syntax and semantics as Perl, with just a few
20			differences. The current implementation of PCRE (release 4.x) corresponds
21			approximately with Perl 5.8, including support for UTF-8 encoded strings.
22			However, this support has to be explicitly enabled; it is not the default.
23			</P>
24			<P>
25			PCRE is written in C and released as a C library. However, a number of people
26			have written wrappers and interfaces of various kinds. A C++ class is included
27			in these contributions, which can be found in the <i>Contrib</i> directory at
28			the primary FTP site, which is:
29			</P>
30			<a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>
31			<P>
32			Details of exactly which Perl regular expression features are and are not
33			supported by PCRE are given in separate documents. See the
34			<a href="pcrepattern.html"><b>pcrepattern</b></a>
35			and
36			<a href="pcrecompat.html"><b>pcrecompat</b></a>
37			pages.
38			</P>
39			<P>
40			Some features of PCRE can be included, excluded, or changed when the library is
41			built. The
42			<a href="pcre_config.html"><b>pcre_config()</b></a>
43			function makes it possible for a client to discover which features are
44			available. Documentation about building PCRE for various operating systems can
45			be found in the <b>README</b> file in the source distribution.
46			</P>
47			<br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>
48			<P>
49			The user documentation for PCRE has been split up into a number of different
50			sections. In the "man" format, each of these is a separate "man page". In the
51			HTML format, each is a separate page, linked from the index page. In the plain
52			text format, all the sections are concatenated, for ease of searching. The
53			sections are as follows:
54			</P>
55			<P>
56			<pre>
57			pcre this document
58			pcreapi details of PCRE's native API
59			pcrebuild options for building PCRE
60			pcrecallout details of the callout feature
61			pcrecompat discussion of Perl compatibility
62			pcregrep description of the <b>pcregrep</b> command
63			pcrepattern syntax and semantics of supported
64			regular expressions
65			pcreperform discussion of performance issues
66			pcreposix the POSIX-compatible API
67			pcresample discussion of the sample program
68			pcretest the <b>pcretest</b> testing command
69			</PRE>
70			</P>
71			<P>
72			In addition, in the "man" and HTML formats, there is a short page for each
73			library function, listing its arguments and results.
74			</P>
75			<br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>
76			<P>
77			There are some size limitations in PCRE but it is hoped that they will never in
78			practice be relevant.
79			</P>
80			<P>
81			The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is
82			compiled with the default internal linkage size of 2. If you want to process
83			regular expressions that are truly enormous, you can compile PCRE with an
84			internal linkage size of 3 or 4 (see the <b>README</b> file in the source
85			distribution and the
86			<a href="pcrebuild.html"><b>pcrebuild</b></a>
87			documentation for details). If these cases the limit is substantially larger.
88			However, the speed of execution will be slower.
89			</P>
90			<P>
91			All values in repeating quantifiers must be less than 65536.
92			The maximum number of capturing subpatterns is 65535.
93			</P>
94			<P>
95			There is no limit to the number of non-capturing subpatterns, but the maximum
96			depth of nesting of all kinds of parenthesized subpattern, including capturing
97			subpatterns, assertions, and other types of subpattern, is 200.
98			</P>
99			<P>
100			The maximum length of a subject string is the largest positive number that an
101			integer variable can hold. However, PCRE uses recursion to handle subpatterns
102			and indefinite repetition. This means that the available stack space may limit
103			the size of a subject string that can be processed by certain patterns.
104			</P>
105			<a name="utf8support"></a><br><a name="SEC4" href="#TOC1">UTF-8 SUPPORT</a><br>
106			<P>
107			Starting at release 3.3, PCRE has had some support for character strings
108			encoded in the UTF-8 format. For release 4.0 this has been greatly extended to
109			cover most common requirements.
110			</P>
111			<P>
112			In order process UTF-8 strings, you must build PCRE to include UTF-8 support in
113			the code, and, in addition, you must call
114			<a href="pcre_compile.html"><b>pcre_compile()</b></a>
115			with the PCRE_UTF8 option flag. When you do this, both the pattern and any
116			subject strings that are matched against it are treated as UTF-8 strings
117			instead of just strings of bytes.
118			</P>
119			<P>
120			If you compile PCRE with UTF-8 support, but do not use it at run time, the
121			library will be a bit bigger, but the additional run time overhead is limited
122			to testing the PCRE_UTF8 flag in several places, so should not be very large.
123			</P>
124			<P>
125			The following comments apply when PCRE is running in UTF-8 mode:
126			</P>
127			<P>
128			1. PCRE assumes that the strings it is given contain valid UTF-8 codes. It does
129			not diagnose invalid UTF-8 strings. If you pass invalid UTF-8 strings to PCRE,
130			the results are undefined.
131			</P>
132			<P>
133			2. In a pattern, the escape sequence \x{...}, where the contents of the braces
134			is a string of hexadecimal digits, is interpreted as a UTF-8 character whose
135			code number is the given hexadecimal number, for example: \x{1234}. If a
136			non-hexadecimal digit appears between the braces, the item is not recognized.
137			This escape sequence can be used either as a literal, or within a character
138			class.
139			</P>
140			<P>
141			3. The original hexadecimal escape sequence, \xhh, matches a two-byte UTF-8
142			character if the value is greater than 127.
143			</P>
144			<P>
145			4. Repeat quantifiers apply to complete UTF-8 characters, not to individual
146			bytes, for example: \x{100}{3}.
147			</P>
148			<P>
149			5. The dot metacharacter matches one UTF-8 character instead of a single byte.
150			</P>
151			<P>
152			6. The escape sequence \C can be used to match a single byte in UTF-8 mode,
153			but its use can lead to some strange effects.
154			</P>
155			<P>
156			7. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
157			test characters of any code value, but the characters that PCRE recognizes as
158			digits, spaces, or word characters remain the same set as before, all with
159			values less than 256.
160			</P>
161			<P>
162			8. Case-insensitive matching applies only to characters whose values are less
163			than 256. PCRE does not support the notion of "case" for higher-valued
164			characters.
165			</P>
166			<P>
167			9. PCRE does not support the use of Unicode tables and properties or the Perl
168			escapes \p, \P, and \X.
169			</P>
170			<br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
171			<P>
172			Philip Hazel <ph10@cam.ac.uk>
173			<br>
174			University Computing Service,
175			<br>
176			Cambridge CB2 3QG, England.
177			<br>
178			Phone: +44 1223 334714
179			</P>
180			<P>
181			Last updated: 04 February 2003
182			<br>
183			Copyright © 1997-2003 University of Cambridge.