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1 .TH PCREPOSIX 3
2 .SH NAME
3 PCRE - Perl-compatible regular expressions.
4 .SH "SYNOPSIS OF POSIX API"
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 .
24 .SH DESCRIPTION
25 .rs
26 .sp
27 This set of functions provides a POSIX-style API to the PCRE regular expression
28 package. See the
29 .\" HREF
30 \fBpcreapi\fP
31 .\"
32 documentation for a description of PCRE's native API, which contains much
33 additional functionality.
34 .P
35 The functions described here are just wrapper functions that ultimately call
36 the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
37 header file, and on Unix systems the library itself is called
38 \fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the
39 command for linking an application that uses them. Because the POSIX functions
40 call the native ones, it is also necessary to add \fB-lpcre\fP.
41 .P
42 I have implemented only those POSIX option bits that can be reasonably mapped
43 to PCRE native options. In addition, the option REG_EXTENDED is defined with
44 the value zero. This has no effect, but since programs that are written to the
45 POSIX interface often use it, this makes it easier to slot in PCRE as a
46 replacement library. Other POSIX options are not even defined.
47 .P
48 There are also some other options that are not defined by POSIX. These have
49 been added at the request of users who want to make use of certain
50 PCRE-specific features via the POSIX calling interface.
51 .P
52 When PCRE is called via these functions, it is only the API that is POSIX-like
53 in style. The syntax and semantics of the regular expressions themselves are
54 still those of Perl, subject to the setting of various PCRE options, as
55 described below. "POSIX-like in style" means that the API approximates to the
56 POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
57 domains it is probably even less compatible.
58 .P
59 The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
60 potential clash with other POSIX libraries. It can, of course, be renamed or
61 aliased as \fBregex.h\fP, which is the "correct" name. It provides two
62 structure types, \fIregex_t\fP for compiled internal forms, and
63 \fIregmatch_t\fP for returning captured substrings. It also defines some
64 constants whose names start with "REG_"; these are used for setting options and
65 identifying error codes.
66 .P
67 .SH "COMPILING A PATTERN"
68 .rs
69 .sp
70 The function \fBregcomp()\fP is called to compile a pattern into an
71 internal form. The pattern is a C string terminated by a binary zero, and
72 is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
73 to a \fBregex_t\fP structure that is used as a base for storing information
74 about the compiled regular expression.
75 .P
76 The argument \fIcflags\fP is either zero, or contains one or more of the bits
77 defined by the following macros:
78 .sp
79 REG_DOTALL
80 .sp
81 The PCRE_DOTALL option is set when the regular expression is passed for
82 compilation to the native function. Note that REG_DOTALL is not part of the
83 POSIX standard.
84 .sp
85 REG_ICASE
86 .sp
87 The PCRE_CASELESS option is set when the regular expression is passed for
88 compilation to the native function.
89 .sp
90 REG_NEWLINE
91 .sp
92 The PCRE_MULTILINE option is set when the regular expression is passed for
93 compilation to the native function. Note that this does \fInot\fP mimic the
94 defined POSIX behaviour for REG_NEWLINE (see the following section).
95 .sp
96 REG_NOSUB
97 .sp
98 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
99 for compilation to the native function. In addition, when a pattern that is
100 compiled with this flag is passed to \fBregexec()\fP for matching, the
101 \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no captured strings
102 are returned.
103 .sp
104 REG_UNGREEDY
105 .sp
106 The PCRE_UNGREEDY option is set when the regular expression is passed for
107 compilation to the native function. Note that REG_UNGREEDY is not part of the
108 POSIX standard.
109 .sp
110 REG_UTF8
111 .sp
112 The PCRE_UTF8 option is set when the regular expression is passed for
113 compilation to the native function. This causes the pattern itself and all data
114 strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
115 is not part of the POSIX standard.
116 .P
117 In the absence of these flags, no options are passed to the native function.
118 This means the the regex is compiled with PCRE default semantics. In
119 particular, the way it handles newline characters in the subject string is the
120 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
121 \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
122 newlines are matched by . (they are not) or by a negative class such as [^a]
123 (they are).
124 .P
125 The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
126 \fIpreg\fP structure is filled in on success, and one member of the structure
127 is public: \fIre_nsub\fP contains the number of capturing subpatterns in
128 the regular expression. Various error codes are defined in the header file.
129 .P
130 NOTE: If the yield of \fBregcomp()\fP is non-zero, you must not attempt to
131 use the contents of the \fIpreg\fP structure. If, for example, you pass it to
132 \fBregexec()\fP, the result is undefined and your program is likely to crash.
133 .
134 .
135 .SH "MATCHING NEWLINE CHARACTERS"
136 .rs
137 .sp
138 This area is not simple, because POSIX and Perl take different views of things.
139 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
140 intended to be a POSIX engine. The following table lists the different
141 possibilities for matching newline characters in PCRE:
142 .sp
143 Default Change with
144 .sp
145 . matches newline no PCRE_DOTALL
146 newline matches [^a] yes not changeable
147 $ matches \en at end yes PCRE_DOLLARENDONLY
148 $ matches \en in middle no PCRE_MULTILINE
149 ^ matches \en in middle no PCRE_MULTILINE
150 .sp
151 This is the equivalent table for POSIX:
152 .sp
153 Default Change with
154 .sp
155 . matches newline yes REG_NEWLINE
156 newline matches [^a] yes REG_NEWLINE
157 $ matches \en at end no REG_NEWLINE
158 $ matches \en in middle no REG_NEWLINE
159 ^ matches \en in middle no REG_NEWLINE
160 .sp
161 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
162 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
163 newline from matching [^a].
164 .P
165 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
166 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
167 REG_NEWLINE action.
168 .
169 .
170 .SH "MATCHING A PATTERN"
171 .rs
172 .sp
173 The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
174 against a given \fIstring\fP, which is by default terminated by a zero byte
175 (but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
176 be:
177 .sp
178 REG_NOTBOL
179 .sp
180 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
181 function.
182 .sp
183 REG_NOTEMPTY
184 .sp
185 The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
186 function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
187 setting this option can give more POSIX-like behaviour in some situations.
188 .sp
189 REG_NOTEOL
190 .sp
191 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
192 function.
193 .sp
194 REG_STARTEND
195 .sp
196 The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
197 to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
198 (there need not actually be a NUL at that location), regardless of the value of
199 \fInmatch\fP. This is a BSD extension, compatible with but not specified by
200 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
201 intended to be portable to other systems. Note that a non-zero \fIrm_so\fP does
202 not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
203 how it is matched.
204 .P
205 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
206 strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
207 \fBregexec()\fP are ignored.
208 .P
209 If the value of \fInmatch\fP is zero, or if the value \fIpmatch\fP is NULL,
210 no data about any matched strings is returned.
211 .P
212 Otherwise,the portion of the string that was matched, and also any captured
213 substrings, are returned via the \fIpmatch\fP argument, which points to an
214 array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
215 members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
216 character of each substring and the offset to the first character after the end
217 of each substring, respectively. The 0th element of the vector relates to the
218 entire portion of \fIstring\fP that was matched; subsequent elements relate to
219 the capturing subpatterns of the regular expression. Unused entries in the
220 array have both structure members set to -1.
221 .P
222 A successful match yields a zero return; various error codes are defined in the
223 header file, of which REG_NOMATCH is the "expected" failure code.
224 .
225 .
226 .SH "ERROR MESSAGES"
227 .rs
228 .sp
229 The \fBregerror()\fP function maps a non-zero errorcode from either
230 \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
231 NULL, the error should have arisen from the use of that structure. A message
232 terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
233 message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
234 function is the size of buffer needed to hold the whole message.
235 .
236 .
237 .SH MEMORY USAGE
238 .rs
239 .sp
240 Compiling a regular expression causes memory to be allocated and associated
241 with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
242 memory, after which \fIpreg\fP may no longer be used as a compiled expression.
243 .
244 .
245 .SH AUTHOR
246 .rs
247 .sp
248 .nf
249 Philip Hazel
250 University Computing Service
251 Cambridge CB2 3QH, England.
252 .fi
253 .
254 .
255 .SH REVISION
256 .rs
257 .sp
258 .nf
259 Last updated: 02 September 2009
260 Copyright (c) 1997-2009 University of Cambridge.
261 .fi

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