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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 additional
50 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>
99 </pre>
100 The PCRE_CASELESS option is set when the expression is passed for compilation
101 to the native function.
102 <pre>
104 </pre>
105 The PCRE_MULTILINE option is set when the expression is passed for compilation
106 to the native function. Note that this does <i>not</i> mimic the defined POSIX
107 behaviour for REG_NEWLINE (see the following section).
108 </P>
109 <P>
110 In the absence of these flags, no options are passed to the native function.
111 This means the the regex is compiled with PCRE default semantics. In
112 particular, the way it handles newline characters in the subject string is the
113 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
114 <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
115 newlines are matched by . (they aren't) or by a negative class such as [^a]
116 (they are).
117 </P>
118 <P>
119 The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
120 <i>preg</i> structure is filled in on success, and one member of the structure
121 is public: <i>re_nsub</i> contains the number of capturing subpatterns in
122 the regular expression. Various error codes are defined in the header file.
123 </P>
124 <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
125 <P>
126 This area is not simple, because POSIX and Perl take different views of things.
127 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
128 intended to be a POSIX engine. The following table lists the different
129 possibilities for matching newline characters in PCRE:
130 <pre>
131 Default Change with
133 . matches newline no PCRE_DOTALL
134 newline matches [^a] yes not changeable
135 $ matches \n at end yes PCRE_DOLLARENDONLY
136 $ matches \n in middle no PCRE_MULTILINE
137 ^ matches \n in middle no PCRE_MULTILINE
138 </pre>
139 This is the equivalent table for POSIX:
140 <pre>
141 Default Change with
143 . matches newline yes REG_NEWLINE
144 newline matches [^a] yes REG_NEWLINE
145 $ matches \n at end no REG_NEWLINE
146 $ matches \n in middle no REG_NEWLINE
147 ^ matches \n in middle no REG_NEWLINE
148 </pre>
149 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
150 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
151 newline from matching [^a].
152 </P>
153 <P>
154 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
155 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
156 REG_NEWLINE action.
157 </P>
158 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
159 <P>
160 The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
161 against a given <i>string</i>, which is terminated by a zero byte, subject to
162 the options in <i>eflags</i>. These can be:
163 <pre>
165 </pre>
166 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
167 function.
168 <pre>
170 </pre>
171 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
172 function.
173 </P>
174 <P>
175 The portion of the string that was matched, and also any captured substrings,
176 are returned via the <i>pmatch</i> argument, which points to an array of
177 <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the members
178 <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first character of
179 each substring and the offset to the first character after the end of each
180 substring, respectively. The 0th element of the vector relates to the entire
181 portion of <i>string</i> that was matched; subsequent elements relate to the
182 capturing subpatterns of the regular expression. Unused entries in the array
183 have both structure members set to -1.
184 </P>
185 <P>
186 A successful match yields a zero return; various error codes are defined in the
187 header file, of which REG_NOMATCH is the "expected" failure code.
188 </P>
189 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
190 <P>
191 The <b>regerror()</b> function maps a non-zero errorcode from either
192 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
193 NULL, the error should have arisen from the use of that structure. A message
194 terminated by a binary zero is placed in <i>errbuf</i>. The length of the
195 message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
196 function is the size of buffer needed to hold the whole message.
197 </P>
198 <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
199 <P>
200 Compiling a regular expression causes memory to be allocated and associated
201 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
202 memory, after which <i>preg</i> may no longer be used as a compiled expression.
203 </P>
204 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
205 <P>
206 Philip Hazel &#60;ph10@cam.ac.uk&#62;
207 <br>
208 University Computing Service,
209 <br>
210 Cambridge CB2 3QG, England.
211 </P>
212 <P>
213 Last updated: 07 September 2004
214 <br>
215 Copyright &copy; 1997-2004 University of Cambridge.
216 <p>
217 Return to the <a href="index.html">PCRE index page</a>.
218 </p>

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