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2<head>
3<title>pcreposix specification</title>
4</head>
5<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6<h1>pcreposix man page</h1>
7<p>
8Return to the <a href="index.html">PCRE index page</a>.
9</p>
10<p>
11This page is part of the PCRE HTML documentation. It was generated automatically
12from the original man page. If there is any nonsense in it, please consult the
13man page, in case the conversion went wrong.
14<br>
15<ul>
16<li><a name="TOC1" href="#SEC1">SYNOPSIS OF POSIX API</a>
17<li><a name="TOC2" href="#SEC2">DESCRIPTION</a>
18<li><a name="TOC3" href="#SEC3">COMPILING A PATTERN</a>
19<li><a name="TOC4" href="#SEC4">MATCHING NEWLINE CHARACTERS</a>
20<li><a name="TOC5" href="#SEC5">MATCHING A PATTERN</a>
21<li><a name="TOC6" href="#SEC6">ERROR MESSAGES</a>
22<li><a name="TOC7" href="#SEC7">MEMORY USAGE</a>
23<li><a name="TOC8" href="#SEC8">AUTHOR</a>
24<li><a name="TOC9" href="#SEC9">REVISION</a>
25</ul>
26<br><a name="SEC1" href="#TOC1">SYNOPSIS OF POSIX API</a><br>
27<P>
28<b>#include &#60;pcreposix.h&#62;</b>
29</P>
30<P>
31<b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b>
32<b>int <i>cflags</i>);</b>
33</P>
34<P>
35<b>int regexec(regex_t *<i>preg</i>, const char *<i>string</i>,</b>
36<b>size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b>
37</P>
38<P>
39<b>size_t regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b>
40<b>char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b>
41</P>
42<P>
43<b>void regfree(regex_t *<i>preg</i>);</b>
44</P>
45<br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
46<P>
47This set of functions provides a POSIX-style API to the PCRE regular expression
48package. See the
49<a href="pcreapi.html"><b>pcreapi</b></a>
50documentation for a description of PCRE's native API, which contains much
51additional functionality.
52</P>
53<P>
54The functions described here are just wrapper functions that ultimately call
55the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b>
56header file, and on Unix systems the library itself is called
57<b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the
58command for linking an application that uses them. Because the POSIX functions
59call the native ones, it is also necessary to add <b>-lpcre</b>.
60</P>
61<P>
62I have implemented only those POSIX option bits that can be reasonably mapped
63to PCRE native options. In addition, the option REG_EXTENDED is defined with
64the value zero. This has no effect, but since programs that are written to the
65POSIX interface often use it, this makes it easier to slot in PCRE as a
66replacement library. Other POSIX options are not even defined.
67</P>
68<P>
69There are also some other options that are not defined by POSIX. These have
70been added at the request of users who want to make use of certain
71PCRE-specific features via the POSIX calling interface.
72</P>
73<P>
74When PCRE is called via these functions, it is only the API that is POSIX-like
75in style. The syntax and semantics of the regular expressions themselves are
76still those of Perl, subject to the setting of various PCRE options, as
77described below. "POSIX-like in style" means that the API approximates to the
78POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
79domains it is probably even less compatible.
80</P>
81<P>
82The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
83potential clash with other POSIX libraries. It can, of course, be renamed or
84aliased as <b>regex.h</b>, which is the "correct" name. It provides two
85structure types, <i>regex_t</i> for compiled internal forms, and
86<i>regmatch_t</i> for returning captured substrings. It also defines some
87constants whose names start with "REG_"; these are used for setting options and
88identifying error codes.
89</P>
90<br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
91<P>
92The function <b>regcomp()</b> is called to compile a pattern into an
93internal form. The pattern is a C string terminated by a binary zero, and
94is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
95to a <b>regex_t</b> structure that is used as a base for storing information
96about the compiled regular expression.
97</P>
98<P>
99The argument <i>cflags</i> is either zero, or contains one or more of the bits
100defined by the following macros:
101<pre>
102 REG_DOTALL
103</pre>
104The PCRE_DOTALL option is set when the regular expression is passed for
105compilation to the native function. Note that REG_DOTALL is not part of the
106POSIX standard.
107<pre>
108 REG_ICASE
109</pre>
110The PCRE_CASELESS option is set when the regular expression is passed for
111compilation to the native function.
112<pre>
113 REG_NEWLINE
114</pre>
115The PCRE_MULTILINE option is set when the regular expression is passed for
116compilation to the native function. Note that this does <i>not</i> mimic the
117defined POSIX behaviour for REG_NEWLINE (see the following section).
118<pre>
119 REG_NOSUB
120</pre>
121The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
122for compilation to the native function. In addition, when a pattern that is
123compiled with this flag is passed to <b>regexec()</b> for matching, the
124<i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings
125are returned.
126<pre>
127 REG_UCP
128</pre>
129The PCRE_UCP option is set when the regular expression is passed for
130compilation to the native function. This causes PCRE to use Unicode properties
131when matchine \d, \w, etc., instead of just recognizing ASCII values. Note
132that REG_UTF8 is not part of the POSIX standard.
133<pre>
134 REG_UNGREEDY
135</pre>
136The PCRE_UNGREEDY option is set when the regular expression is passed for
137compilation to the native function. Note that REG_UNGREEDY is not part of the
138POSIX standard.
139<pre>
140 REG_UTF8
141</pre>
142The PCRE_UTF8 option is set when the regular expression is passed for
143compilation to the native function. This causes the pattern itself and all data
144strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
145is not part of the POSIX standard.
146</P>
147<P>
148In the absence of these flags, no options are passed to the native function.
149This means the the regex is compiled with PCRE default semantics. In
150particular, the way it handles newline characters in the subject string is the
151Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
152<i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
153newlines are matched by . (they are not) or by a negative class such as [^a]
154(they are).
155</P>
156<P>
157The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
158<i>preg</i> structure is filled in on success, and one member of the structure
159is public: <i>re_nsub</i> contains the number of capturing subpatterns in
160the regular expression. Various error codes are defined in the header file.
161</P>
162<P>
163NOTE: If the yield of <b>regcomp()</b> is non-zero, you must not attempt to
164use the contents of the <i>preg</i> structure. If, for example, you pass it to
165<b>regexec()</b>, the result is undefined and your program is likely to crash.
166</P>
167<br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
168<P>
169This area is not simple, because POSIX and Perl take different views of things.
170It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
171intended to be a POSIX engine. The following table lists the different
172possibilities for matching newline characters in PCRE:
173<pre>
174 Default Change with
175
176 . matches newline no PCRE_DOTALL
177 newline matches [^a] yes not changeable
178 $ matches \n at end yes PCRE_DOLLARENDONLY
179 $ matches \n in middle no PCRE_MULTILINE
180 ^ matches \n in middle no PCRE_MULTILINE
181</pre>
182This is the equivalent table for POSIX:
183<pre>
184 Default Change with
185
186 . matches newline yes REG_NEWLINE
187 newline matches [^a] yes REG_NEWLINE
188 $ matches \n at end no REG_NEWLINE
189 $ matches \n in middle no REG_NEWLINE
190 ^ matches \n in middle no REG_NEWLINE
191</pre>
192PCRE's behaviour is the same as Perl's, except that there is no equivalent for
193PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
194newline from matching [^a].
195</P>
196<P>
197The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
198PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
199REG_NEWLINE action.
200</P>
201<br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
202<P>
203The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
204against a given <i>string</i>, which is by default terminated by a zero byte
205(but see REG_STARTEND below), subject to the options in <i>eflags</i>. These can
206be:
207<pre>
208 REG_NOTBOL
209</pre>
210The PCRE_NOTBOL option is set when calling the underlying PCRE matching
211function.
212<pre>
213 REG_NOTEMPTY
214</pre>
215The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
216function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
217setting this option can give more POSIX-like behaviour in some situations.
218<pre>
219 REG_NOTEOL
220</pre>
221The PCRE_NOTEOL option is set when calling the underlying PCRE matching
222function.
223<pre>
224 REG_STARTEND
225</pre>
226The string is considered to start at <i>string</i> + <i>pmatch[0].rm_so</i> and
227to have a terminating NUL located at <i>string</i> + <i>pmatch[0].rm_eo</i>
228(there need not actually be a NUL at that location), regardless of the value of
229<i>nmatch</i>. This is a BSD extension, compatible with but not specified by
230IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
231intended to be portable to other systems. Note that a non-zero <i>rm_so</i> does
232not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
233how it is matched.
234</P>
235<P>
236If the pattern was compiled with the REG_NOSUB flag, no data about any matched
237strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of
238<b>regexec()</b> are ignored.
239</P>
240<P>
241If the value of <i>nmatch</i> is zero, or if the value <i>pmatch</i> is NULL,
242no data about any matched strings is returned.
243</P>
244<P>
245Otherwise,the portion of the string that was matched, and also any captured
246substrings, are returned via the <i>pmatch</i> argument, which points to an
247array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the
248members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first
249character of each substring and the offset to the first character after the end
250of each substring, respectively. The 0th element of the vector relates to the
251entire portion of <i>string</i> that was matched; subsequent elements relate to
252the capturing subpatterns of the regular expression. Unused entries in the
253array have both structure members set to -1.
254</P>
255<P>
256A successful match yields a zero return; various error codes are defined in the
257header file, of which REG_NOMATCH is the "expected" failure code.
258</P>
259<br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
260<P>
261The <b>regerror()</b> function maps a non-zero errorcode from either
262<b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
263NULL, the error should have arisen from the use of that structure. A message
264terminated by a binary zero is placed in <i>errbuf</i>. The length of the
265message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
266function is the size of buffer needed to hold the whole message.
267</P>
268<br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
269<P>
270Compiling a regular expression causes memory to be allocated and associated
271with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
272memory, after which <i>preg</i> may no longer be used as a compiled expression.
273</P>
274<br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
275<P>
276Philip Hazel
277<br>
278University Computing Service
279<br>
280Cambridge CB2 3QH, England.
281<br>
282</P>
283<br><a name="SEC9" href="#TOC1">REVISION</a><br>
284<P>
285Last updated: 16 May 2010
286<br>
287Copyright &copy; 1997-2010 University of Cambridge.
288<br>
289<p>
290Return to the <a href="index.html">PCRE index page</a>.
291</p>