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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 option bits that can be reasonably mapped to PCRE
63 native options. In addition, the option REG_EXTENDED is defined with the value
64 zero. This has no effect, but since programs that are written to the POSIX
65 interface often use it, this makes it easier to slot in PCRE as a replacement
66 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 <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
147 <P>
148 This area is not simple, because POSIX and Perl take different views of things.
149 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
150 intended to be a POSIX engine. The following table lists the different
151 possibilities for matching newline characters in PCRE:
152 <pre>
153 Default Change with
154
155 . matches newline no PCRE_DOTALL
156 newline matches [^a] yes not changeable
157 $ matches \n at end yes PCRE_DOLLARENDONLY
158 $ matches \n in middle no PCRE_MULTILINE
159 ^ matches \n in middle no PCRE_MULTILINE
160 </pre>
161 This is the equivalent table for POSIX:
162 <pre>
163 Default Change with
164
165 . matches newline yes REG_NEWLINE
166 newline matches [^a] yes REG_NEWLINE
167 $ matches \n at end no REG_NEWLINE
168 $ matches \n in middle no REG_NEWLINE
169 ^ matches \n in middle no REG_NEWLINE
170 </pre>
171 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
172 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
173 newline from matching [^a].
174 </P>
175 <P>
176 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
177 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
178 REG_NEWLINE action.
179 </P>
180 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
181 <P>
182 The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
183 against a given <i>string</i>, which is terminated by a zero byte, subject to
184 the options in <i>eflags</i>. These can be:
185 <pre>
186 REG_NOTBOL
187 </pre>
188 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
189 function.
190 <pre>
191 REG_NOTEOL
192 </pre>
193 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
194 function.
195 </P>
196 <P>
197 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
198 strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of
199 <b>regexec()</b> are ignored.
200 </P>
201 <P>
202 Otherwise,the portion of the string that was matched, and also any captured
203 substrings, are returned via the <i>pmatch</i> argument, which points to an
204 array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the
205 members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first
206 character of each substring and the offset to the first character after the end
207 of each substring, respectively. The 0th element of the vector relates to the
208 entire portion of <i>string</i> that was matched; subsequent elements relate to
209 the capturing subpatterns of the regular expression. Unused entries in the
210 array have both structure members set to -1.
211 </P>
212 <P>
213 A successful match yields a zero return; various error codes are defined in the
214 header file, of which REG_NOMATCH is the "expected" failure code.
215 </P>
216 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
217 <P>
218 The <b>regerror()</b> function maps a non-zero errorcode from either
219 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
220 NULL, the error should have arisen from the use of that structure. A message
221 terminated by a binary zero is placed in <i>errbuf</i>. The length of the
222 message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
223 function is the size of buffer needed to hold the whole message.
224 </P>
225 <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
226 <P>
227 Compiling a regular expression causes memory to be allocated and associated
228 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
229 memory, after which <i>preg</i> may no longer be used as a compiled expression.
230 </P>
231 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
232 <P>
233 Philip Hazel
234 <br>
235 University Computing Service
236 <br>
237 Cambridge CB2 3QH, England.
238 <br>
239 </P>
240 <br><a name="SEC9" href="#TOC1">REVISION</a><br>
241 <P>
242 Last updated: 06 March 2007
243 <br>
244 Copyright &copy; 1997-2007 University of Cambridge.
245 <br>
246 <p>
247 Return to the <a href="index.html">PCRE index page</a>.
248 </p>

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