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Add more explanation about recursive subpatterns, and make it possible to 
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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 There are also some other options that are not defined by POSIX. These have
70 been added at the request of users who want to make use of certain
71 PCRE-specific features via the POSIX calling interface.
72 </P>
73 <P>
74 When PCRE is called via these functions, it is only the API that is POSIX-like
75 in style. The syntax and semantics of the regular expressions themselves are
76 still those of Perl, subject to the setting of various PCRE options, as
77 described below. "POSIX-like in style" means that the API approximates to the
78 POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
79 domains it is probably even less compatible.
80 </P>
81 <P>
82 The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
83 potential clash with other POSIX libraries. It can, of course, be renamed or
84 aliased as <b>regex.h</b>, which is the "correct" name. It provides two
85 structure types, <i>regex_t</i> for compiled internal forms, and
86 <i>regmatch_t</i> for returning captured substrings. It also defines some
87 constants whose names start with "REG_"; these are used for setting options and
88 identifying error codes.
89 </P>
90 <P>
91 </P>
92 <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
93 <P>
94 The function <b>regcomp()</b> is called to compile a pattern into an
95 internal form. The pattern is a C string terminated by a binary zero, and
96 is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
97 to a <b>regex_t</b> structure that is used as a base for storing information
98 about the compiled regular expression.
99 </P>
100 <P>
101 The argument <i>cflags</i> is either zero, or contains one or more of the bits
102 defined by the following macros:
103 <pre>
104 REG_DOTALL
105 </pre>
106 The PCRE_DOTALL option is set when the regular expression is passed for
107 compilation to the native function. Note that REG_DOTALL is not part of the
108 POSIX standard.
109 <pre>
110 REG_ICASE
111 </pre>
112 The PCRE_CASELESS option is set when the regular expression is passed for
113 compilation to the native function.
114 <pre>
115 REG_NEWLINE
116 </pre>
117 The PCRE_MULTILINE option is set when the regular expression is passed for
118 compilation to the native function. Note that this does <i>not</i> mimic the
119 defined POSIX behaviour for REG_NEWLINE (see the following section).
120 <pre>
121 REG_NOSUB
122 </pre>
123 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
124 for compilation to the native function. In addition, when a pattern that is
125 compiled with this flag is passed to <b>regexec()</b> for matching, the
126 <i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings
127 are returned.
128 <pre>
129 REG_UNGREEDY
130 </pre>
131 The PCRE_UNGREEDY option is set when the regular expression is passed for
132 compilation to the native function. Note that REG_UNGREEDY is not part of the
133 POSIX standard.
134 <pre>
135 REG_UTF8
136 </pre>
137 The PCRE_UTF8 option is set when the regular expression is passed for
138 compilation to the native function. This causes the pattern itself and all data
139 strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
140 is not part of the POSIX standard.
141 </P>
142 <P>
143 In the absence of these flags, no options are passed to the native function.
144 This means the the regex is compiled with PCRE default semantics. In
145 particular, the way it handles newline characters in the subject string is the
146 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
147 <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
148 newlines are matched by . (they are not) or by a negative class such as [^a]
149 (they are).
150 </P>
151 <P>
152 The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
153 <i>preg</i> structure is filled in on success, and one member of the structure
154 is public: <i>re_nsub</i> contains the number of capturing subpatterns in
155 the regular expression. Various error codes are defined in the header file.
156 </P>
157 <P>
158 NOTE: If the yield of <b>regcomp()</b> is non-zero, you must not attempt to
159 use the contents of the <i>preg</i> structure. If, for example, you pass it to
160 <b>regexec()</b>, the result is undefined and your program is likely to crash.
161 </P>
162 <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
163 <P>
164 This area is not simple, because POSIX and Perl take different views of things.
165 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
166 intended to be a POSIX engine. The following table lists the different
167 possibilities for matching newline characters in PCRE:
168 <pre>
169 Default Change with
170
171 . matches newline no PCRE_DOTALL
172 newline matches [^a] yes not changeable
173 $ matches \n at end yes PCRE_DOLLARENDONLY
174 $ matches \n in middle no PCRE_MULTILINE
175 ^ matches \n in middle no PCRE_MULTILINE
176 </pre>
177 This is the equivalent table for POSIX:
178 <pre>
179 Default Change with
180
181 . matches newline yes REG_NEWLINE
182 newline matches [^a] yes REG_NEWLINE
183 $ matches \n at end no REG_NEWLINE
184 $ matches \n in middle no REG_NEWLINE
185 ^ matches \n in middle no REG_NEWLINE
186 </pre>
187 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
188 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
189 newline from matching [^a].
190 </P>
191 <P>
192 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
193 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
194 REG_NEWLINE action.
195 </P>
196 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
197 <P>
198 The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
199 against a given <i>string</i>, which is by default terminated by a zero byte
200 (but see REG_STARTEND below), subject to the options in <i>eflags</i>. These can
201 be:
202 <pre>
203 REG_NOTBOL
204 </pre>
205 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
206 function.
207 <pre>
208 REG_NOTEMPTY
209 </pre>
210 The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
211 function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
212 setting this option can give more POSIX-like behaviour in some situations.
213 <pre>
214 REG_NOTEOL
215 </pre>
216 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
217 function.
218 <pre>
219 REG_STARTEND
220 </pre>
221 The string is considered to start at <i>string</i> + <i>pmatch[0].rm_so</i> and
222 to have a terminating NUL located at <i>string</i> + <i>pmatch[0].rm_eo</i>
223 (there need not actually be a NUL at that location), regardless of the value of
224 <i>nmatch</i>. This is a BSD extension, compatible with but not specified by
225 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
226 intended to be portable to other systems. Note that a non-zero <i>rm_so</i> does
227 not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
228 how it is matched.
229 </P>
230 <P>
231 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
232 strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of
233 <b>regexec()</b> are ignored.
234 </P>
235 <P>
236 If the value of <i>nmatch</i> is zero, or if the value <i>pmatch</i> is NULL,
237 no data about any matched strings is returned.
238 </P>
239 <P>
240 Otherwise,the portion of the string that was matched, and also any captured
241 substrings, are returned via the <i>pmatch</i> argument, which points to an
242 array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the
243 members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first
244 character of each substring and the offset to the first character after the end
245 of each substring, respectively. The 0th element of the vector relates to the
246 entire portion of <i>string</i> that was matched; subsequent elements relate to
247 the capturing subpatterns of the regular expression. Unused entries in the
248 array have both structure members set to -1.
249 </P>
250 <P>
251 A successful match yields a zero return; various error codes are defined in the
252 header file, of which REG_NOMATCH is the "expected" failure code.
253 </P>
254 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
255 <P>
256 The <b>regerror()</b> function maps a non-zero errorcode from either
257 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
258 NULL, the error should have arisen from the use of that structure. A message
259 terminated by a binary zero is placed in <i>errbuf</i>. The length of the
260 message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
261 function is the size of buffer needed to hold the whole message.
262 </P>
263 <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
264 <P>
265 Compiling a regular expression causes memory to be allocated and associated
266 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
267 memory, after which <i>preg</i> may no longer be used as a compiled expression.
268 </P>
269 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
270 <P>
271 Philip Hazel
272 <br>
273 University Computing Service
274 <br>
275 Cambridge CB2 3QH, England.
276 <br>
277 </P>
278 <br><a name="SEC9" href="#TOC1">REVISION</a><br>
279 <P>
280 Last updated: 02 September 2009
281 <br>
282 Copyright &copy; 1997-2009 University of Cambridge.
283 <br>
284 <p>
285 Return to the <a href="index.html">PCRE index page</a>.
286 </p>

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