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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 </ul>
25 <br><a name="SEC1" href="#TOC1">SYNOPSIS OF POSIX API</a><br>
26 <P>
27 <b>#include &#60;pcreposix.h&#62;</b>
28 </P>
29 <P>
30 <b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b>
31 <b>int <i>cflags</i>);</b>
32 </P>
33 <P>
34 <b>int regexec(regex_t *<i>preg</i>, const char *<i>string</i>,</b>
35 <b>size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b>
36 </P>
37 <P>
38 <b>size_t regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b>
39 <b>char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b>
40 </P>
41 <P>
42 <b>void regfree(regex_t *<i>preg</i>);</b>
43 </P>
44 <br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
45 <P>
46 This set of functions provides a POSIX-style API to the PCRE regular expression
47 package. See the
48 <a href="pcreapi.html"><b>pcreapi</b></a>
49 documentation for a description of PCRE's native API, which contains much
50 additional functionality.
51 </P>
52 <P>
53 The functions described here are just wrapper functions that ultimately call
54 the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b>
55 header file, and on Unix systems the library itself is called
56 <b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the
57 command for linking an application that uses them. Because the POSIX functions
58 call the native ones, it is also necessary to add <b>-lpcre</b>.
59 </P>
60 <P>
61 I have implemented only those option bits that can be reasonably mapped to PCRE
62 native options. In addition, the option REG_EXTENDED is defined with the value
63 zero. This has no effect, but since programs that are written to the POSIX
64 interface often use it, this makes it easier to slot in PCRE as a replacement
65 library. Other POSIX options are not even defined.
66 </P>
67 <P>
68 When PCRE is called via these functions, it is only the API that is POSIX-like
69 in style. The syntax and semantics of the regular expressions themselves are
70 still those of Perl, subject to the setting of various PCRE options, as
71 described below. "POSIX-like in style" means that the API approximates to the
72 POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
73 domains it is probably even less compatible.
74 </P>
75 <P>
76 The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
77 potential clash with other POSIX libraries. It can, of course, be renamed or
78 aliased as <b>regex.h</b>, which is the "correct" name. It provides two
79 structure types, <i>regex_t</i> for compiled internal forms, and
80 <i>regmatch_t</i> for returning captured substrings. It also defines some
81 constants whose names start with "REG_"; these are used for setting options and
82 identifying error codes.
83 </P>
84 <P>
85 </P>
86 <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
87 <P>
88 The function <b>regcomp()</b> is called to compile a pattern into an
89 internal form. The pattern is a C string terminated by a binary zero, and
90 is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
91 to a <b>regex_t</b> structure that is used as a base for storing information
92 about the compiled regular expression.
93 </P>
94 <P>
95 The argument <i>cflags</i> is either zero, or contains one or more of the bits
96 defined by the following macros:
97 <pre>
99 </pre>
100 The PCRE_DOTALL option is set when the regular expression is passed for
101 compilation to the native function. Note that REG_DOTALL is not part of the
102 POSIX standard.
103 <pre>
105 </pre>
106 The PCRE_CASELESS option is set when the regular expression is passed for
107 compilation to the native function.
108 <pre>
110 </pre>
111 The PCRE_MULTILINE option is set when the regular expression is passed for
112 compilation to the native function. Note that this does <i>not</i> mimic the
113 defined POSIX behaviour for REG_NEWLINE (see the following section).
114 <pre>
116 </pre>
117 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
118 for compilation to the native function. In addition, when a pattern that is
119 compiled with this flag is passed to <b>regexec()</b> for matching, the
120 <i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings
121 are returned.
122 <pre>
123 REG_UTF8
124 </pre>
125 The PCRE_UTF8 option is set when the regular expression is passed for
126 compilation to the native function. This causes the pattern itself and all data
127 strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
128 is not part of the POSIX standard.
129 </P>
130 <P>
131 In the absence of these flags, no options are passed to the native function.
132 This means the the regex is compiled with PCRE default semantics. In
133 particular, the way it handles newline characters in the subject string is the
134 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
135 <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
136 newlines are matched by . (they aren't) or by a negative class such as [^a]
137 (they are).
138 </P>
139 <P>
140 The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
141 <i>preg</i> structure is filled in on success, and one member of the structure
142 is public: <i>re_nsub</i> contains the number of capturing subpatterns in
143 the regular expression. Various error codes are defined in the header file.
144 </P>
145 <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
146 <P>
147 This area is not simple, because POSIX and Perl take different views of things.
148 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
149 intended to be a POSIX engine. The following table lists the different
150 possibilities for matching newline characters in PCRE:
151 <pre>
152 Default Change with
154 . matches newline no PCRE_DOTALL
155 newline matches [^a] yes not changeable
156 $ matches \n at end yes PCRE_DOLLARENDONLY
157 $ matches \n in middle no PCRE_MULTILINE
158 ^ matches \n in middle no PCRE_MULTILINE
159 </pre>
160 This is the equivalent table for POSIX:
161 <pre>
162 Default Change with
164 . matches newline yes REG_NEWLINE
165 newline matches [^a] yes REG_NEWLINE
166 $ matches \n at end no REG_NEWLINE
167 $ matches \n in middle no REG_NEWLINE
168 ^ matches \n in middle no REG_NEWLINE
169 </pre>
170 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
171 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
172 newline from matching [^a].
173 </P>
174 <P>
175 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
176 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
177 REG_NEWLINE action.
178 </P>
179 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
180 <P>
181 The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
182 against a given <i>string</i>, which is terminated by a zero byte, subject to
183 the options in <i>eflags</i>. These can be:
184 <pre>
186 </pre>
187 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
188 function.
189 <pre>
191 </pre>
192 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
193 function.
194 </P>
195 <P>
196 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
197 strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of
198 <b>regexec()</b> are ignored.
199 </P>
200 <P>
201 Otherwise,the portion of the string that was matched, and also any captured
202 substrings, are returned via the <i>pmatch</i> argument, which points to an
203 array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the
204 members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first
205 character of each substring and the offset to the first character after the end
206 of each substring, respectively. The 0th element of the vector relates to the
207 entire portion of <i>string</i> that was matched; subsequent elements relate to
208 the capturing subpatterns of the regular expression. Unused entries in the
209 array have both structure members set to -1.
210 </P>
211 <P>
212 A successful match yields a zero return; various error codes are defined in the
213 header file, of which REG_NOMATCH is the "expected" failure code.
214 </P>
215 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
216 <P>
217 The <b>regerror()</b> function maps a non-zero errorcode from either
218 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
219 NULL, the error should have arisen from the use of that structure. A message
220 terminated by a binary zero is placed in <i>errbuf</i>. The length of the
221 message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
222 function is the size of buffer needed to hold the whole message.
223 </P>
224 <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
225 <P>
226 Compiling a regular expression causes memory to be allocated and associated
227 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
228 memory, after which <i>preg</i> may no longer be used as a compiled expression.
229 </P>
230 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
231 <P>
232 Philip Hazel
233 <br>
234 University Computing Service,
235 <br>
236 Cambridge CB2 3QG, England.
237 </P>
238 <P>
239 Last updated: 16 January 2006
240 <br>
241 Copyright &copy; 1997-2006 University of Cambridge.
242 <p>
243 Return to the <a href="index.html">PCRE index page</a>.
244 </p>

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