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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 options REG_EXTENDED and REG_NOSUB are defined
63 with the value zero. They have no effect, but since programs that are written
64 to the POSIX interface often use them, this makes it easier to slot in PCRE as
65 a replacement 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 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>
98 REG_DOTALL
99 </pre>
100 The PCRE_DOTALL option is set when the expression is passed for compilation to
101 the native function. Note that REG_DOTALL is not part of the POSIX standard.
102 <pre>
103 REG_ICASE
104 </pre>
105 The PCRE_CASELESS option is set when the expression is passed for compilation
106 to the native function.
107 <pre>
108 REG_NEWLINE
109 </pre>
110 The PCRE_MULTILINE option is set when the expression is passed for compilation
111 to the native function. Note that this does <i>not</i> mimic the defined POSIX
112 behaviour for REG_NEWLINE (see the following section).
113 </P>
114 <P>
115 In the absence of these flags, no options are passed to the native function.
116 This means the the regex is compiled with PCRE default semantics. In
117 particular, the way it handles newline characters in the subject string is the
118 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
119 <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
120 newlines are matched by . (they aren't) or by a negative class such as [^a]
121 (they are).
122 </P>
123 <P>
124 The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
125 <i>preg</i> structure is filled in on success, and one member of the structure
126 is public: <i>re_nsub</i> contains the number of capturing subpatterns in
127 the regular expression. Various error codes are defined in the header file.
128 </P>
129 <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
130 <P>
131 This area is not simple, because POSIX and Perl take different views of things.
132 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
133 intended to be a POSIX engine. The following table lists the different
134 possibilities for matching newline characters in PCRE:
135 <pre>
136 Default Change with
137
138 . matches newline no PCRE_DOTALL
139 newline matches [^a] yes not changeable
140 $ matches \n at end yes PCRE_DOLLARENDONLY
141 $ matches \n in middle no PCRE_MULTILINE
142 ^ matches \n in middle no PCRE_MULTILINE
143 </pre>
144 This is the equivalent table for POSIX:
145 <pre>
146 Default Change with
147
148 . matches newline yes REG_NEWLINE
149 newline matches [^a] yes REG_NEWLINE
150 $ matches \n at end no REG_NEWLINE
151 $ matches \n in middle no REG_NEWLINE
152 ^ matches \n in middle no REG_NEWLINE
153 </pre>
154 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
155 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
156 newline from matching [^a].
157 </P>
158 <P>
159 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
160 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
161 REG_NEWLINE action.
162 </P>
163 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
164 <P>
165 The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
166 against a given <i>string</i>, which is terminated by a zero byte, subject to
167 the options in <i>eflags</i>. These can be:
168 <pre>
169 REG_NOTBOL
170 </pre>
171 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
172 function.
173 <pre>
174 REG_NOTEOL
175 </pre>
176 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
177 function.
178 </P>
179 <P>
180 The portion of the string that was matched, and also any captured substrings,
181 are returned via the <i>pmatch</i> argument, which points to an array of
182 <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the members
183 <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first character of
184 each substring and the offset to the first character after the end of each
185 substring, respectively. The 0th element of the vector relates to the entire
186 portion of <i>string</i> that was matched; subsequent elements relate to the
187 capturing subpatterns of the regular expression. Unused entries in the array
188 have both structure members set to -1.
189 </P>
190 <P>
191 A successful match yields a zero return; various error codes are defined in the
192 header file, of which REG_NOMATCH is the "expected" failure code.
193 </P>
194 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
195 <P>
196 The <b>regerror()</b> function maps a non-zero errorcode from either
197 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
198 NULL, the error should have arisen from the use of that structure. A message
199 terminated by a binary zero is placed in <i>errbuf</i>. The length of the
200 message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
201 function is the size of buffer needed to hold the whole message.
202 </P>
203 <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
204 <P>
205 Compiling a regular expression causes memory to be allocated and associated
206 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
207 memory, after which <i>preg</i> may no longer be used as a compiled expression.
208 </P>
209 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
210 <P>
211 Philip Hazel
212 <br>
213 University Computing Service,
214 <br>
215 Cambridge CB2 3QG, England.
216 </P>
217 <P>
218 Last updated: 28 February 2005
219 <br>
220 Copyright &copy; 1997-2005 University of Cambridge.
221 <p>
222 Return to the <a href="index.html">PCRE index page</a>.
223 </p>

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