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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. "POSIX-like in style" means that the API approximates to the
66 POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
67 domains it is probably even less compatible.
68 </P>
69 <P>
70 The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
71 potential clash with other POSIX libraries. It can, of course, be renamed or
72 aliased as <b>regex.h</b>, which is the "correct" name. It provides two
73 structure types, <i>regex_t</i> for compiled internal forms, and
74 <i>regmatch_t</i> for returning captured substrings. It also defines some
75 constants whose names start with "REG_"; these are used for setting options and
76 identifying error codes.
77 </P>
78 <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
79 <P>
80 The function <b>regcomp()</b> is called to compile a pattern into an
81 internal form. The pattern is a C string terminated by a binary zero, and
82 is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
83 to a regex_t structure which is used as a base for storing information about
84 the compiled expression.
85 </P>
86 <P>
87 The argument <i>cflags</i> is either zero, or contains one or more of the bits
88 defined by the following macros:
89 </P>
90 <P>
91 <pre>
92 REG_ICASE
93 </PRE>
94 </P>
95 <P>
96 The PCRE_CASELESS option is set when the expression is passed for compilation
97 to the native function.
98 </P>
99 <P>
100 <pre>
101 REG_NEWLINE
102 </PRE>
103 </P>
104 <P>
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 </P>
131 <P>
132 <pre>
133 Default Change with
134 </PRE>
135 </P>
136 <P>
137 <pre>
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 </P>
145 <P>
146 This is the equivalent table for POSIX:
147 </P>
148 <P>
149 <pre>
150 Default Change with
151 </PRE>
152 </P>
153 <P>
154 <pre>
155 . matches newline yes REG_NEWLINE
156 newline matches [^a] yes REG_NEWLINE
157 $ matches \n at end no REG_NEWLINE
158 $ matches \n in middle no REG_NEWLINE
159 ^ matches \n in middle no REG_NEWLINE
160 </PRE>
161 </P>
162 <P>
163 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
164 PCRE_DOLLARENDONLY in Perl. In both PCRE and Perl, there is no way to stop
165 newline from matching [^a].
166 </P>
167 <P>
168 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
169 PCRE_DOLLARENDONLY, but there is no way to make PCRE behave exactly as for the
170 REG_NEWLINE action.
171 </P>
172 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
173 <P>
174 The function <b>regexec()</b> is called to match a pre-compiled pattern
175 <i>preg</i> against a given <i>string</i>, which is terminated by a zero byte,
176 subject to the options in <i>eflags</i>. These can be:
177 </P>
178 <P>
179 <pre>
180 REG_NOTBOL
181 </PRE>
182 </P>
183 <P>
184 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
185 function.
186 </P>
187 <P>
188 <pre>
189 REG_NOTEOL
190 </PRE>
191 </P>
192 <P>
193 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
194 function.
195 </P>
196 <P>
197 The portion of the string that was matched, and also any captured substrings,
198 are returned via the <i>pmatch</i> argument, which points to an array of
199 <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the members
200 <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first character of
201 each substring and the offset to the first character after the end of each
202 substring, respectively. The 0th element of the vector relates to the entire
203 portion of <i>string</i> that was matched; subsequent elements relate to the
204 capturing subpatterns of the regular expression. Unused entries in the array
205 have both structure members set to -1.
206 </P>
207 <P>
208 A successful match yields a zero return; various error codes are defined in the
209 header file, of which REG_NOMATCH is the "expected" failure code.
210 </P>
211 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
212 <P>
213 The <b>regerror()</b> function maps a non-zero errorcode from either
214 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
215 NULL, the error should have arisen from the use of that structure. A message
216 terminated by a binary zero is placed in <i>errbuf</i>. The length of the
217 message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
218 function is the size of buffer needed to hold the whole message.
219 </P>
220 <br><a name="SEC7" href="#TOC1">STORAGE</a><br>
221 <P>
222 Compiling a regular expression causes memory to be allocated and associated
223 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
224 memory, after which <i>preg</i> may no longer be used as a compiled expression.
225 </P>
226 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
227 <P>
228 Philip Hazel &#60;ph10@cam.ac.uk&#62;
229 <br>
230 University Computing Service,
231 <br>
232 Cambridge CB2 3QG, England.
233 </P>
234 <P>
235 Last updated: 03 February 2003
236 <br>
237 Copyright &copy; 1997-2003 University of Cambridge.

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