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1 .TH PCREPOSIX 3 "09 January 2012" "PCRE 8.30"
3 PCRE - Perl-compatible regular expressions.
5 .rs
6 .sp
7 .B #include <pcreposix.h>
8 .PP
9 .nf
10 .B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,
11 .B " int \fIcflags\fP);"
12 .sp
13 .B int regexec(regex_t *\fIpreg\fP, const char *\fIstring\fP,
14 .B " size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);"
15 .B " size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,"
16 .B " char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);"
17 .sp
18 .B void regfree(regex_t *\fIpreg\fP);
19 .fi
20 .
22 .rs
23 .sp
24 This set of functions provides a POSIX-style API for the PCRE regular
25 expression 8-bit library. See the
26 .\" HREF
27 \fBpcreapi\fP
28 .\"
29 documentation for a description of PCRE's native API, which contains much
30 additional functionality. There is no POSIX-style wrapper for PCRE's 16-bit
31 and 32-bit library.
32 .P
33 The functions described here are just wrapper functions that ultimately call
34 the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
35 header file, and on Unix systems the library itself is called
36 \fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the
37 command for linking an application that uses them. Because the POSIX functions
38 call the native ones, it is also necessary to add \fB-lpcre\fP.
39 .P
40 I have implemented only those POSIX option bits that can be reasonably mapped
41 to PCRE native options. In addition, the option REG_EXTENDED is defined with
42 the value zero. This has no effect, but since programs that are written to the
43 POSIX interface often use it, this makes it easier to slot in PCRE as a
44 replacement library. Other POSIX options are not even defined.
45 .P
46 There are also some other options that are not defined by POSIX. These have
47 been added at the request of users who want to make use of certain
48 PCRE-specific features via the POSIX calling interface.
49 .P
50 When PCRE is called via these functions, it is only the API that is POSIX-like
51 in style. The syntax and semantics of the regular expressions themselves are
52 still those of Perl, subject to the setting of various PCRE options, as
53 described below. "POSIX-like in style" means that the API approximates to the
54 POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
55 domains it is probably even less compatible.
56 .P
57 The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
58 potential clash with other POSIX libraries. It can, of course, be renamed or
59 aliased as \fBregex.h\fP, which is the "correct" name. It provides two
60 structure types, \fIregex_t\fP for compiled internal forms, and
61 \fIregmatch_t\fP for returning captured substrings. It also defines some
62 constants whose names start with "REG_"; these are used for setting options and
63 identifying error codes.
64 .
65 .
67 .rs
68 .sp
69 The function \fBregcomp()\fP is called to compile a pattern into an
70 internal form. The pattern is a C string terminated by a binary zero, and
71 is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
72 to a \fBregex_t\fP structure that is used as a base for storing information
73 about the compiled regular expression.
74 .P
75 The argument \fIcflags\fP is either zero, or contains one or more of the bits
76 defined by the following macros:
77 .sp
79 .sp
80 The PCRE_DOTALL option is set when the regular expression is passed for
81 compilation to the native function. Note that REG_DOTALL is not part of the
82 POSIX standard.
83 .sp
85 .sp
86 The PCRE_CASELESS option is set when the regular expression is passed for
87 compilation to the native function.
88 .sp
90 .sp
91 The PCRE_MULTILINE option is set when the regular expression is passed for
92 compilation to the native function. Note that this does \fInot\fP mimic the
93 defined POSIX behaviour for REG_NEWLINE (see the following section).
94 .sp
96 .sp
97 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
98 for compilation to the native function. In addition, when a pattern that is
99 compiled with this flag is passed to \fBregexec()\fP for matching, the
100 \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no captured strings
101 are returned.
102 .sp
104 .sp
105 The PCRE_UCP option is set when the regular expression is passed for
106 compilation to the native function. This causes PCRE to use Unicode properties
107 when matchine \ed, \ew, etc., instead of just recognizing ASCII values. Note
108 that REG_UTF8 is not part of the POSIX standard.
109 .sp
111 .sp
112 The PCRE_UNGREEDY option is set when the regular expression is passed for
113 compilation to the native function. Note that REG_UNGREEDY is not part of the
114 POSIX standard.
115 .sp
116 REG_UTF8
117 .sp
118 The PCRE_UTF8 option is set when the regular expression is passed for
119 compilation to the native function. This causes the pattern itself and all data
120 strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
121 is not part of the POSIX standard.
122 .P
123 In the absence of these flags, no options are passed to the native function.
124 This means the the regex is compiled with PCRE default semantics. In
125 particular, the way it handles newline characters in the subject string is the
126 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
127 \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
128 newlines are matched by . (they are not) or by a negative class such as [^a]
129 (they are).
130 .P
131 The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
132 \fIpreg\fP structure is filled in on success, and one member of the structure
133 is public: \fIre_nsub\fP contains the number of capturing subpatterns in
134 the regular expression. Various error codes are defined in the header file.
135 .P
136 NOTE: If the yield of \fBregcomp()\fP is non-zero, you must not attempt to
137 use the contents of the \fIpreg\fP structure. If, for example, you pass it to
138 \fBregexec()\fP, the result is undefined and your program is likely to crash.
139 .
140 .
142 .rs
143 .sp
144 This area is not simple, because POSIX and Perl take different views of things.
145 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
146 intended to be a POSIX engine. The following table lists the different
147 possibilities for matching newline characters in PCRE:
148 .sp
149 Default Change with
150 .sp
151 . matches newline no PCRE_DOTALL
152 newline matches [^a] yes not changeable
153 $ matches \en at end yes PCRE_DOLLARENDONLY
154 $ matches \en in middle no PCRE_MULTILINE
155 ^ matches \en in middle no PCRE_MULTILINE
156 .sp
157 This is the equivalent table for POSIX:
158 .sp
159 Default Change with
160 .sp
161 . matches newline yes REG_NEWLINE
162 newline matches [^a] yes REG_NEWLINE
163 $ matches \en at end no REG_NEWLINE
164 $ matches \en in middle no REG_NEWLINE
165 ^ matches \en in middle no REG_NEWLINE
166 .sp
167 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
168 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
169 newline from matching [^a].
170 .P
171 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
172 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
173 REG_NEWLINE action.
174 .
175 .
177 .rs
178 .sp
179 The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
180 against a given \fIstring\fP, which is by default terminated by a zero byte
181 (but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
182 be:
183 .sp
185 .sp
186 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
187 function.
188 .sp
190 .sp
191 The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
192 function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
193 setting this option can give more POSIX-like behaviour in some situations.
194 .sp
196 .sp
197 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
198 function.
199 .sp
201 .sp
202 The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
203 to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
204 (there need not actually be a NUL at that location), regardless of the value of
205 \fInmatch\fP. This is a BSD extension, compatible with but not specified by
206 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
207 intended to be portable to other systems. Note that a non-zero \fIrm_so\fP does
208 not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
209 how it is matched.
210 .P
211 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
212 strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
213 \fBregexec()\fP are ignored.
214 .P
215 If the value of \fInmatch\fP is zero, or if the value \fIpmatch\fP is NULL,
216 no data about any matched strings is returned.
217 .P
218 Otherwise,the portion of the string that was matched, and also any captured
219 substrings, are returned via the \fIpmatch\fP argument, which points to an
220 array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
221 members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
222 character of each substring and the offset to the first character after the end
223 of each substring, respectively. The 0th element of the vector relates to the
224 entire portion of \fIstring\fP that was matched; subsequent elements relate to
225 the capturing subpatterns of the regular expression. Unused entries in the
226 array have both structure members set to -1.
227 .P
228 A successful match yields a zero return; various error codes are defined in the
229 header file, of which REG_NOMATCH is the "expected" failure code.
230 .
231 .
233 .rs
234 .sp
235 The \fBregerror()\fP function maps a non-zero errorcode from either
236 \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
237 NULL, the error should have arisen from the use of that structure. A message
238 terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
239 message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
240 function is the size of buffer needed to hold the whole message.
241 .
242 .
244 .rs
245 .sp
246 Compiling a regular expression causes memory to be allocated and associated
247 with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
248 memory, after which \fIpreg\fP may no longer be used as a compiled expression.
249 .
250 .
252 .rs
253 .sp
254 .nf
255 Philip Hazel
256 University Computing Service
257 Cambridge CB2 3QH, England.
258 .fi
259 .
260 .
262 .rs
263 .sp
264 .nf
265 Last updated: 09 January 2012
266 Copyright (c) 1997-2012 University of Cambridge.
267 .fi


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