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1 <html>
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>
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">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>
47 This set of functions provides a POSIX-style API for the PCRE regular
48 expression 8-bit library. See the
49 <a href="pcreapi.html"><b>pcreapi</b></a>
50 documentation for a description of PCRE's native API, which contains much
51 additional functionality. There is no POSIX-style wrapper for PCRE's 16-bit
52 library.
53 </P>
54 <P>
55 The functions described here are just wrapper functions that ultimately call
56 the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b>
57 header file, and on Unix systems the library itself is called
58 <b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the
59 command for linking an application that uses them. Because the POSIX functions
60 call the native ones, it is also necessary to add <b>-lpcre</b>.
61 </P>
62 <P>
63 I have implemented only those POSIX option bits that can be reasonably mapped
64 to PCRE native options. In addition, the option REG_EXTENDED is defined with
65 the value zero. This has no effect, but since programs that are written to the
66 POSIX interface often use it, this makes it easier to slot in PCRE as a
67 replacement library. Other POSIX options are not even defined.
68 </P>
69 <P>
70 There are also some other options that are not defined by POSIX. These have
71 been added at the request of users who want to make use of certain
72 PCRE-specific features via the POSIX calling interface.
73 </P>
74 <P>
75 When PCRE is called via these functions, it is only the API that is POSIX-like
76 in style. The syntax and semantics of the regular expressions themselves are
77 still those of Perl, subject to the setting of various PCRE options, as
78 described below. "POSIX-like in style" means that the API approximates to the
79 POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
80 domains it is probably even less compatible.
81 </P>
82 <P>
83 The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
84 potential clash with other POSIX libraries. It can, of course, be renamed or
85 aliased as <b>regex.h</b>, which is the "correct" name. It provides two
86 structure types, <i>regex_t</i> for compiled internal forms, and
87 <i>regmatch_t</i> for returning captured substrings. It also defines some
88 constants whose names start with "REG_"; these are used for setting options and
89 identifying error codes.
90 </P>
91 <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
92 <P>
93 The function <b>regcomp()</b> is called to compile a pattern into an
94 internal form. The pattern is a C string terminated by a binary zero, and
95 is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
96 to a <b>regex_t</b> structure that is used as a base for storing information
97 about the compiled regular expression.
98 </P>
99 <P>
100 The argument <i>cflags</i> is either zero, or contains one or more of the bits
101 defined by the following macros:
102 <pre>
104 </pre>
105 The PCRE_DOTALL option is set when the regular expression is passed for
106 compilation to the native function. Note that REG_DOTALL is not part of the
107 POSIX standard.
108 <pre>
110 </pre>
111 The PCRE_CASELESS option is set when the regular expression is passed for
112 compilation to the native function.
113 <pre>
115 </pre>
116 The PCRE_MULTILINE option is set when the regular expression is passed for
117 compilation to the native function. Note that this does <i>not</i> mimic the
118 defined POSIX behaviour for REG_NEWLINE (see the following section).
119 <pre>
121 </pre>
122 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
123 for compilation to the native function. In addition, when a pattern that is
124 compiled with this flag is passed to <b>regexec()</b> for matching, the
125 <i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings
126 are returned.
127 <pre>
129 </pre>
130 The PCRE_UCP option is set when the regular expression is passed for
131 compilation to the native function. This causes PCRE to use Unicode properties
132 when matchine \d, \w, etc., instead of just recognizing ASCII values. Note
133 that REG_UTF8 is not part of the POSIX standard.
134 <pre>
136 </pre>
137 The PCRE_UNGREEDY option is set when the regular expression is passed for
138 compilation to the native function. Note that REG_UNGREEDY is not part of the
139 POSIX standard.
140 <pre>
141 REG_UTF8
142 </pre>
143 The PCRE_UTF8 option is set when the regular expression is passed for
144 compilation to the native function. This causes the pattern itself and all data
145 strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
146 is not part of the POSIX standard.
147 </P>
148 <P>
149 In the absence of these flags, no options are passed to the native function.
150 This means the the regex is compiled with PCRE default semantics. In
151 particular, the way it handles newline characters in the subject string is the
152 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
153 <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
154 newlines are matched by . (they are not) or by a negative class such as [^a]
155 (they are).
156 </P>
157 <P>
158 The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
159 <i>preg</i> structure is filled in on success, and one member of the structure
160 is public: <i>re_nsub</i> contains the number of capturing subpatterns in
161 the regular expression. Various error codes are defined in the header file.
162 </P>
163 <P>
164 NOTE: If the yield of <b>regcomp()</b> is non-zero, you must not attempt to
165 use the contents of the <i>preg</i> structure. If, for example, you pass it to
166 <b>regexec()</b>, the result is undefined and your program is likely to crash.
167 </P>
168 <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
169 <P>
170 This area is not simple, because POSIX and Perl take different views of things.
171 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
172 intended to be a POSIX engine. The following table lists the different
173 possibilities for matching newline characters in PCRE:
174 <pre>
175 Default Change with
177 . matches newline no PCRE_DOTALL
178 newline matches [^a] yes not changeable
179 $ matches \n at end yes PCRE_DOLLARENDONLY
180 $ matches \n in middle no PCRE_MULTILINE
181 ^ matches \n in middle no PCRE_MULTILINE
182 </pre>
183 This is the equivalent table for POSIX:
184 <pre>
185 Default Change with
187 . matches newline yes REG_NEWLINE
188 newline matches [^a] yes REG_NEWLINE
189 $ matches \n at end no REG_NEWLINE
190 $ matches \n in middle no REG_NEWLINE
191 ^ matches \n in middle no REG_NEWLINE
192 </pre>
193 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
194 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
195 newline from matching [^a].
196 </P>
197 <P>
198 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
199 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
200 REG_NEWLINE action.
201 </P>
202 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
203 <P>
204 The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
205 against a given <i>string</i>, which is by default terminated by a zero byte
206 (but see REG_STARTEND below), subject to the options in <i>eflags</i>. These can
207 be:
208 <pre>
210 </pre>
211 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
212 function.
213 <pre>
215 </pre>
216 The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
217 function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
218 setting this option can give more POSIX-like behaviour in some situations.
219 <pre>
221 </pre>
222 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
223 function.
224 <pre>
226 </pre>
227 The string is considered to start at <i>string</i> + <i>pmatch[0].rm_so</i> and
228 to have a terminating NUL located at <i>string</i> + <i>pmatch[0].rm_eo</i>
229 (there need not actually be a NUL at that location), regardless of the value of
230 <i>nmatch</i>. This is a BSD extension, compatible with but not specified by
231 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
232 intended to be portable to other systems. Note that a non-zero <i>rm_so</i> does
233 not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
234 how it is matched.
235 </P>
236 <P>
237 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
238 strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of
239 <b>regexec()</b> are ignored.
240 </P>
241 <P>
242 If the value of <i>nmatch</i> is zero, or if the value <i>pmatch</i> is NULL,
243 no data about any matched strings is returned.
244 </P>
245 <P>
246 Otherwise,the portion of the string that was matched, and also any captured
247 substrings, are returned via the <i>pmatch</i> argument, which points to an
248 array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the
249 members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first
250 character of each substring and the offset to the first character after the end
251 of each substring, respectively. The 0th element of the vector relates to the
252 entire portion of <i>string</i> that was matched; subsequent elements relate to
253 the capturing subpatterns of the regular expression. Unused entries in the
254 array have both structure members set to -1.
255 </P>
256 <P>
257 A successful match yields a zero return; various error codes are defined in the
258 header file, of which REG_NOMATCH is the "expected" failure code.
259 </P>
260 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
261 <P>
262 The <b>regerror()</b> function maps a non-zero errorcode from either
263 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
264 NULL, the error should have arisen from the use of that structure. A message
265 terminated by a binary zero is placed in <i>errbuf</i>. The length of the
266 message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
267 function is the size of buffer needed to hold the whole message.
268 </P>
269 <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
270 <P>
271 Compiling a regular expression causes memory to be allocated and associated
272 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
273 memory, after which <i>preg</i> may no longer be used as a compiled expression.
274 </P>
275 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
276 <P>
277 Philip Hazel
278 <br>
279 University Computing Service
280 <br>
281 Cambridge CB2 3QH, England.
282 <br>
283 </P>
284 <br><a name="SEC9" href="#TOC1">REVISION</a><br>
285 <P>
286 Last updated: 09 January 2012
287 <br>
288 Copyright &copy; 1997-2012 University of Cambridge.
289 <br>
290 <p>
291 Return to the <a href="index.html">PCRE index page</a>.
292 </p>


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