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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 to the PCRE regular expression
48 package. 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.
52 </P>
53 <P>
54 The functions described here are just wrapper functions that ultimately call
55 the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b>
56 header 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
58 command for linking an application that uses them. Because the POSIX functions
59 call the native ones, it is also necessary to add <b>-lpcre</b>.
60 </P>
61 <P>
62 I have implemented only those POSIX option bits that can be reasonably mapped
63 to PCRE native options. In addition, the option REG_EXTENDED is defined with
64 the value zero. This has no effect, but since programs that are written to the
65 POSIX interface often use it, this makes it easier to slot in PCRE as a
66 replacement library. Other POSIX options are not even defined.
67 </P>
68 <P>
69 When PCRE is called via these functions, it is only the API that is POSIX-like
70 in style. The syntax and semantics of the regular expressions themselves are
71 still those of Perl, subject to the setting of various PCRE options, as
72 described below. "POSIX-like in style" means that the API approximates to the
73 POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
74 domains it is probably even less compatible.
75 </P>
76 <P>
77 The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
78 potential clash with other POSIX libraries. It can, of course, be renamed or
79 aliased as <b>regex.h</b>, which is the "correct" name. It provides two
80 structure types, <i>regex_t</i> for compiled internal forms, and
81 <i>regmatch_t</i> for returning captured substrings. It also defines some
82 constants whose names start with "REG_"; these are used for setting options and
83 identifying error codes.
84 </P>
85 <P>
86 </P>
87 <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
88 <P>
89 The function <b>regcomp()</b> is called to compile a pattern into an
90 internal form. The pattern is a C string terminated by a binary zero, and
91 is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
92 to a <b>regex_t</b> structure that is used as a base for storing information
93 about the compiled regular expression.
94 </P>
95 <P>
96 The argument <i>cflags</i> is either zero, or contains one or more of the bits
97 defined by the following macros:
98 <pre>
99 REG_DOTALL
100 </pre>
101 The PCRE_DOTALL option is set when the regular expression is passed for
102 compilation to the native function. Note that REG_DOTALL is not part of the
103 POSIX standard.
104 <pre>
105 REG_ICASE
106 </pre>
107 The PCRE_CASELESS option is set when the regular expression is passed for
108 compilation to the native function.
109 <pre>
110 REG_NEWLINE
111 </pre>
112 The PCRE_MULTILINE option is set when the regular expression is passed for
113 compilation to the native function. Note that this does <i>not</i> mimic the
114 defined POSIX behaviour for REG_NEWLINE (see the following section).
115 <pre>
116 REG_NOSUB
117 </pre>
118 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
119 for compilation to the native function. In addition, when a pattern that is
120 compiled with this flag is passed to <b>regexec()</b> for matching, the
121 <i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings
122 are returned.
123 <pre>
124 REG_UTF8
125 </pre>
126 The PCRE_UTF8 option is set when the regular expression is passed for
127 compilation to the native function. This causes the pattern itself and all data
128 strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
129 is not part of the POSIX standard.
130 </P>
131 <P>
132 In the absence of these flags, no options are passed to the native function.
133 This means the the regex is compiled with PCRE default semantics. In
134 particular, the way it handles newline characters in the subject string is the
135 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
136 <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
137 newlines are matched by . (they aren't) or by a negative class such as [^a]
138 (they are).
139 </P>
140 <P>
141 The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
142 <i>preg</i> structure is filled in on success, and one member of the structure
143 is public: <i>re_nsub</i> contains the number of capturing subpatterns in
144 the regular expression. Various error codes are defined in the header file.
145 </P>
146 <P>
147 NOTE: If the yield of <b>regcomp()</b> is non-zero, you must not attempt to
148 use the contents of the <i>preg</i> structure. If, for example, you pass it to
149 <b>regexec()</b>, the result is undefined and your program is likely to crash.
150 </P>
151 <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
152 <P>
153 This area is not simple, because POSIX and Perl take different views of things.
154 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
155 intended to be a POSIX engine. The following table lists the different
156 possibilities for matching newline characters in PCRE:
157 <pre>
158 Default Change with
159
160 . matches newline no PCRE_DOTALL
161 newline matches [^a] yes not changeable
162 $ matches \n at end yes PCRE_DOLLARENDONLY
163 $ matches \n in middle no PCRE_MULTILINE
164 ^ matches \n in middle no PCRE_MULTILINE
165 </pre>
166 This is the equivalent table for POSIX:
167 <pre>
168 Default Change with
169
170 . matches newline yes REG_NEWLINE
171 newline matches [^a] yes REG_NEWLINE
172 $ matches \n at end no REG_NEWLINE
173 $ matches \n in middle no REG_NEWLINE
174 ^ matches \n in middle no REG_NEWLINE
175 </pre>
176 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
177 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
178 newline from matching [^a].
179 </P>
180 <P>
181 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
182 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
183 REG_NEWLINE action.
184 </P>
185 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
186 <P>
187 The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
188 against a given <i>string</i>, which is by default terminated by a zero byte
189 (but see REG_STARTEND below), subject to the options in <i>eflags</i>. These can
190 be:
191 <pre>
192 REG_NOTBOL
193 </pre>
194 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
195 function.
196 <pre>
197 REG_NOTEMPTY
198 </pre>
199 The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
200 function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
201 setting this option can give more POSIX-like behaviour in some situations.
202 <pre>
203 REG_NOTEOL
204 </pre>
205 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
206 function.
207 <pre>
208 REG_STARTEND
209 </pre>
210 The string is considered to start at <i>string</i> + <i>pmatch[0].rm_so</i> and
211 to have a terminating NUL located at <i>string</i> + <i>pmatch[0].rm_eo</i>
212 (there need not actually be a NUL at that location), regardless of the value of
213 <i>nmatch</i>. This is a BSD extension, compatible with but not specified by
214 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
215 intended to be portable to other systems. Note that a non-zero <i>rm_so</i> does
216 not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
217 how it is matched.
218 </P>
219 <P>
220 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
221 strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of
222 <b>regexec()</b> are ignored.
223 </P>
224 <P>
225 Otherwise,the portion of the string that was matched, and also any captured
226 substrings, are returned via the <i>pmatch</i> argument, which points to an
227 array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the
228 members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first
229 character of each substring and the offset to the first character after the end
230 of each substring, respectively. The 0th element of the vector relates to the
231 entire portion of <i>string</i> that was matched; subsequent elements relate to
232 the capturing subpatterns of the regular expression. Unused entries in the
233 array have both structure members set to -1.
234 </P>
235 <P>
236 A successful match yields a zero return; various error codes are defined in the
237 header file, of which REG_NOMATCH is the "expected" failure code.
238 </P>
239 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
240 <P>
241 The <b>regerror()</b> function maps a non-zero errorcode from either
242 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
243 NULL, the error should have arisen from the use of that structure. A message
244 terminated by a binary zero is placed in <i>errbuf</i>. The length of the
245 message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
246 function is the size of buffer needed to hold the whole message.
247 </P>
248 <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
249 <P>
250 Compiling a regular expression causes memory to be allocated and associated
251 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
252 memory, after which <i>preg</i> may no longer be used as a compiled expression.
253 </P>
254 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
255 <P>
256 Philip Hazel
257 <br>
258 University Computing Service
259 <br>
260 Cambridge CB2 3QH, England.
261 <br>
262 </P>
263 <br><a name="SEC9" href="#TOC1">REVISION</a><br>
264 <P>
265 Last updated: 15 August 2009
266 <br>
267 Copyright &copy; 1997-2009 University of Cambridge.
268 <br>
269 <p>
270 Return to the <a href="index.html">PCRE index page</a>.
271 </p>

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