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Tag code/trunk as code/tags/pcre-6.6.

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 .br
11 .B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,
12 .ti +5n
13 .B int \fIcflags\fP);
14 .PP
15 .br
16 .B int regexec(regex_t *\fIpreg\fP, const char *\fIstring\fP,
17 .ti +5n
18 .B size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);
19 .PP
20 .br
21 .B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
22 .ti +5n
23 .B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
24 .PP
25 .br
26 .B void regfree(regex_t *\fIpreg\fP);
27 .
28 .SH DESCRIPTION
29 .rs
30 .sp
31 This set of functions provides a POSIX-style API to the PCRE regular expression
32 package. See the
33 .\" HREF
34 \fBpcreapi\fP
35 .\"
36 documentation for a description of PCRE's native API, which contains much
37 additional functionality.
38 .P
39 The functions described here are just wrapper functions that ultimately call
40 the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
41 header file, and on Unix systems the library itself is called
42 \fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the
43 command for linking an application that uses them. Because the POSIX functions
44 call the native ones, it is also necessary to add \fB-lpcre\fP.
45 .P
46 I have implemented only those option bits that can be reasonably mapped to PCRE
47 native options. In addition, the option REG_EXTENDED is defined with the value
48 zero. This has no effect, but since programs that are written to the POSIX
49 interface often use it, this makes it easier to slot in PCRE as a replacement
50 library. Other POSIX options are not even defined.
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_UTF8
105 .sp
106 The PCRE_UTF8 option is set when the regular expression is passed for
107 compilation to the native function. This causes the pattern itself and all data
108 strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
109 is not part of the POSIX standard.
110 .P
111 In the absence of these flags, no options are passed to the native function.
112 This means the the regex is compiled with PCRE default semantics. In
113 particular, the way it handles newline characters in the subject string is the
114 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
115 \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
116 newlines are matched by . (they aren't) or by a negative class such as [^a]
117 (they are).
118 .P
119 The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
120 \fIpreg\fP structure is filled in on success, and one member of the structure
121 is public: \fIre_nsub\fP contains the number of capturing subpatterns in
122 the regular expression. Various error codes are defined in the header file.
123 .
124 .
125 .SH "MATCHING NEWLINE CHARACTERS"
126 .rs
127 .sp
128 This area is not simple, because POSIX and Perl take different views of things.
129 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
130 intended to be a POSIX engine. The following table lists the different
131 possibilities for matching newline characters in PCRE:
132 .sp
133 Default Change with
134 .sp
135 . matches newline no PCRE_DOTALL
136 newline matches [^a] yes not changeable
137 $ matches \en at end yes PCRE_DOLLARENDONLY
138 $ matches \en in middle no PCRE_MULTILINE
139 ^ matches \en in middle no PCRE_MULTILINE
140 .sp
141 This is the equivalent table for POSIX:
142 .sp
143 Default Change with
144 .sp
145 . matches newline yes REG_NEWLINE
146 newline matches [^a] yes REG_NEWLINE
147 $ matches \en at end no REG_NEWLINE
148 $ matches \en in middle no REG_NEWLINE
149 ^ matches \en in middle no REG_NEWLINE
150 .sp
151 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
152 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
153 newline from matching [^a].
154 .P
155 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
156 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
157 REG_NEWLINE action.
158 .
159 .
160 .SH "MATCHING A PATTERN"
161 .rs
162 .sp
163 The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
164 against a given \fIstring\fP, which is terminated by a zero byte, subject to
165 the options in \fIeflags\fP. These can be:
166 .sp
167 REG_NOTBOL
168 .sp
169 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
170 function.
171 .sp
172 REG_NOTEOL
173 .sp
174 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
175 function.
176 .P
177 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
178 strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
179 \fBregexec()\fP are ignored.
180 .P
181 Otherwise,the portion of the string that was matched, and also any captured
182 substrings, are returned via the \fIpmatch\fP argument, which points to an
183 array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
184 members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
185 character of each substring and the offset to the first character after the end
186 of each substring, respectively. The 0th element of the vector relates to the
187 entire portion of \fIstring\fP that was matched; subsequent elements relate to
188 the capturing subpatterns of the regular expression. Unused entries in the
189 array have both structure members set to -1.
190 .P
191 A successful match yields a zero return; various error codes are defined in the
192 header file, of which REG_NOMATCH is the "expected" failure code.
193 .
194 .
195 .SH "ERROR MESSAGES"
196 .rs
197 .sp
198 The \fBregerror()\fP function maps a non-zero errorcode from either
199 \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
200 NULL, the error should have arisen from the use of that structure. A message
201 terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
202 message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
203 function is the size of buffer needed to hold the whole message.
204 .
205 .
206 .SH MEMORY USAGE
207 .rs
208 .sp
209 Compiling a regular expression causes memory to be allocated and associated
210 with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
211 memory, after which \fIpreg\fP may no longer be used as a compiled expression.
212 .
213 .
214 .SH AUTHOR
215 .rs
216 .sp
217 Philip Hazel
218 .br
219 University Computing Service,
220 .br
221 Cambridge CB2 3QG, England.
222 .P
223 .in 0
224 Last updated: 16 January 2006
225 .br
226 Copyright (c) 1997-2006 University of Cambridge.

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