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


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