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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 This HTML document has been generated automatically from the original man page.
7 If there is any nonsense in it, please consult the man page, in case the
8 conversion went wrong.<br>
9 <ul>
10 <li><a name="TOC1" href="#SEC1">SYNOPSIS OF POSIX API</a>
11 <li><a name="TOC2" href="#SEC2">DESCRIPTION</a>
12 <li><a name="TOC3" href="#SEC3">COMPILING A PATTERN</a>
13 <li><a name="TOC4" href="#SEC4">MATCHING NEWLINE CHARACTERS</a>
14 <li><a name="TOC5" href="#SEC5">MATCHING A PATTERN</a>
15 <li><a name="TOC6" href="#SEC6">ERROR MESSAGES</a>
16 <li><a name="TOC7" href="#SEC7">STORAGE</a>
17 <li><a name="TOC8" href="#SEC8">AUTHOR</a>
18 </ul>
19 <br><a name="SEC1" href="#TOC1">SYNOPSIS OF POSIX API</a><br>
20 <P>
21 <b>#include &#60;pcreposix.h&#62;</b>
22 </P>
23 <P>
24 <b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b>
25 <b>int <i>cflags</i>);</b>
26 </P>
27 <P>
28 <b>int regexec(regex_t *<i>preg</i>, const char *<i>string</i>,</b>
29 <b>size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b>
30 </P>
31 <P>
32 <b>size_t regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b>
33 <b>char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b>
34 </P>
35 <P>
36 <b>void regfree(regex_t *<i>preg</i>);</b>
37 </P>
38 <br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
39 <P>
40 This set of functions provides a POSIX-style API to the PCRE regular expression
41 package. See the
42 <a href="pcreapi.html"><b>pcreapi</b></a>
43 documentation for a description of the native API, which contains additional
44 functionality.
45 </P>
46 <P>
47 The functions described here are just wrapper functions that ultimately call
48 the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b>
49 header file, and on Unix systems the library itself is called
50 <b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the
51 command for linking an application which uses them. Because the POSIX functions
52 call the native ones, it is also necessary to add \fR-lpcre\fR.
53 </P>
54 <P>
55 I have implemented only those option bits that can be reasonably mapped to PCRE
56 native options. In addition, the options REG_EXTENDED and REG_NOSUB are defined
57 with the value zero. They have no effect, but since programs that are written
58 to the POSIX interface often use them, this makes it easier to slot in PCRE as
59 a replacement library. Other POSIX options are not even defined.
60 </P>
61 <P>
62 When PCRE is called via these functions, it is only the API that is POSIX-like
63 in style. The syntax and semantics of the regular expressions themselves are
64 still those of Perl, subject to the setting of various PCRE options, as
65 described below.
66 </P>
67 <P>
68 The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
69 potential clash with other POSIX libraries. It can, of course, be renamed or
70 aliased as <b>regex.h</b>, which is the "correct" name. It provides two
71 structure types, <i>regex_t</i> for compiled internal forms, and
72 <i>regmatch_t</i> for returning captured substrings. It also defines some
73 constants whose names start with "REG_"; these are used for setting options and
74 identifying error codes.
75 </P>
76 <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
77 <P>
78 The function <b>regcomp()</b> is called to compile a pattern into an
79 internal form. The pattern is a C string terminated by a binary zero, and
80 is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
81 to a regex_t structure which is used as a base for storing information about
82 the compiled expression.
83 </P>
84 <P>
85 The argument <i>cflags</i> is either zero, or contains one or more of the bits
86 defined by the following macros:
87 </P>
88 <P>
89 <pre>
91 </PRE>
92 </P>
93 <P>
94 The PCRE_CASELESS option is set when the expression is passed for compilation
95 to the native function.
96 </P>
97 <P>
98 <pre>
100 </PRE>
101 </P>
102 <P>
103 The PCRE_MULTILINE option is set when the expression is passed for compilation
104 to the native function. Note that this does <i>not</i> mimic the defined POSIX
105 behaviour for REG_NEWLINE (see the following section).
106 </P>
107 <P>
108 In the absence of these flags, no options are passed to the native function.
109 This means the the regex is compiled with PCRE default semantics. In
110 particular, the way it handles newline characters in the subject string is the
111 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
112 <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
113 newlines are matched by . (they aren't) or by a negative class such as [^a]
114 (they are).
115 </P>
116 <P>
117 The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
118 <i>preg</i> structure is filled in on success, and one member of the structure
119 is public: <i>re_nsub</i> contains the number of capturing subpatterns in
120 the regular expression. Various error codes are defined in the header file.
121 </P>
122 <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
123 <P>
124 This area is not simple, because POSIX and Perl take different views of things.
125 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
126 intended to be a POSIX engine. The following table lists the different
127 possibilities for matching newline characters in PCRE:
128 </P>
129 <P>
130 <pre>
131 Default Change with
132 </PRE>
133 </P>
134 <P>
135 <pre>
136 . matches newline no PCRE_DOTALL
137 newline matches [^a] yes not changeable
138 $ matches \n at end yes PCRE_DOLLARENDONLY
139 $ matches \n in middle no PCRE_MULTILINE
140 ^ matches \n in middle no PCRE_MULTILINE
141 </PRE>
142 </P>
143 <P>
144 This is the equivalent table for POSIX:
145 </P>
146 <P>
147 <pre>
148 Default Change with
149 </PRE>
150 </P>
151 <P>
152 <pre>
153 . matches newline yes REG_NEWLINE
154 newline matches [^a] yes REG_NEWLINE
155 $ matches \n at end no REG_NEWLINE
156 $ matches \n in middle no REG_NEWLINE
157 ^ matches \n in middle no REG_NEWLINE
158 </PRE>
159 </P>
160 <P>
161 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
162 PCRE_DOLLARENDONLY in Perl. In both PCRE and Perl, there is no way to stop
163 newline from matching [^a].
164 </P>
165 <P>
166 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
167 PCRE_DOLLARENDONLY, but there is no way to make PCRE behave exactly as for the
168 REG_NEWLINE action.
169 </P>
170 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
171 <P>
172 The function <b>regexec()</b> is called to match a pre-compiled pattern
173 <i>preg</i> against a given <i>string</i>, which is terminated by a zero byte,
174 subject to the options in <i>eflags</i>. These can be:
175 </P>
176 <P>
177 <pre>
179 </PRE>
180 </P>
181 <P>
182 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
183 function.
184 </P>
185 <P>
186 <pre>
188 </PRE>
189 </P>
190 <P>
191 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
192 function.
193 </P>
194 <P>
195 The portion of the string that was matched, and also any captured substrings,
196 are returned via the <i>pmatch</i> argument, which points to an array of
197 <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the members
198 <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first character of
199 each substring and the offset to the first character after the end of each
200 substring, respectively. The 0th element of the vector relates to the entire
201 portion of <i>string</i> that was matched; subsequent elements relate to the
202 capturing subpatterns of the regular expression. Unused entries in the array
203 have both structure members set to -1.
204 </P>
205 <P>
206 A successful match yields a zero return; various error codes are defined in the
207 header file, of which REG_NOMATCH is the "expected" failure code.
208 </P>
209 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
210 <P>
211 The <b>regerror()</b> function maps a non-zero errorcode from either
212 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
213 NULL, the error should have arisen from the use of that structure. A message
214 terminated by a binary zero is placed in <i>errbuf</i>. The length of the
215 message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
216 function is the size of buffer needed to hold the whole message.
217 </P>
218 <br><a name="SEC7" href="#TOC1">STORAGE</a><br>
219 <P>
220 Compiling a regular expression causes memory to be allocated and associated
221 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
222 memory, after which <i>preg</i> may no longer be used as a compiled expression.
223 </P>
224 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
225 <P>
226 Philip Hazel &#60;ph10@cam.ac.uk&#62;
227 <br>
228 University Computing Service,
229 <br>
230 Cambridge CB2 3QG, England.
231 </P>
232 <P>
233 Last updated: 03 February 2003
234 <br>
235 Copyright &copy; 1997-2003 University of Cambridge.

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