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1 nigel 79 .TH PCREPOSIX 3
2 nigel 41 .SH NAME
3 nigel 63 PCRE - Perl-compatible regular expressions.
4 nigel 75 .SH "SYNOPSIS OF POSIX API"
5     .rs
6     .sp
7 nigel 41 .B #include <pcreposix.h>
8     .PP
9     .SM
10 nigel 75 .B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,
11 nigel 41 .ti +5n
12 nigel 75 .B int \fIcflags\fP);
13 nigel 41 .PP
14 nigel 75 .B int regexec(regex_t *\fIpreg\fP, const char *\fIstring\fP,
15 nigel 41 .ti +5n
16 nigel 75 .B size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);
17 nigel 41 .PP
18 nigel 75 .B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
19 nigel 41 .ti +5n
20 nigel 75 .B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
21 nigel 41 .PP
22 nigel 75 .B void regfree(regex_t *\fIpreg\fP);
23     .
24 nigel 41 .SH DESCRIPTION
25 nigel 63 .rs
26     .sp
27 nigel 41 This set of functions provides a POSIX-style API to the PCRE regular expression
28 nigel 63 package. See the
29     .\" HREF
30 nigel 75 \fBpcreapi\fP
31 nigel 63 .\"
32 nigel 77 documentation for a description of PCRE's native API, which contains much
33     additional functionality.
34 nigel 75 .P
35 nigel 41 The functions described here are just wrapper functions that ultimately call
36 nigel 75 the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
37 nigel 63 header file, and on Unix systems the library itself is called
38 nigel 75 \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 nigel 43 I have implemented only those option bits that can be reasonably mapped to PCRE
43 nigel 87 native options. In addition, the option REG_EXTENDED is defined with the value
44     zero. This has no effect, but since programs that are written to the POSIX
45     interface often use it, this makes it easier to slot in PCRE as a replacement
46     library. Other POSIX options are not even defined.
47 nigel 75 .P
48 nigel 41 When PCRE is called via these functions, it is only the API that is POSIX-like
49     in style. The syntax and semantics of the regular expressions themselves are
50     still those of Perl, subject to the setting of various PCRE options, as
51 nigel 69 described below. "POSIX-like in style" means that the API approximates to the
52     POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
53     domains it is probably even less compatible.
54 nigel 75 .P
55     The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
56 nigel 41 potential clash with other POSIX libraries. It can, of course, be renamed or
57 nigel 75 aliased as \fBregex.h\fP, which is the "correct" name. It provides two
58     structure types, \fIregex_t\fP for compiled internal forms, and
59     \fIregmatch_t\fP for returning captured substrings. It also defines some
60 nigel 41 constants whose names start with "REG_"; these are used for setting options and
61     identifying error codes.
62 nigel 75 .P
63     .SH "COMPILING A PATTERN"
64 nigel 63 .rs
65     .sp
66 nigel 75 The function \fBregcomp()\fP is called to compile a pattern into an
67 nigel 41 internal form. The pattern is a C string terminated by a binary zero, and
68 nigel 75 is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
69     to a \fBregex_t\fP structure that is used as a base for storing information
70 nigel 87 about the compiled regular expression.
71 nigel 75 .P
72     The argument \fIcflags\fP is either zero, or contains one or more of the bits
73 nigel 41 defined by the following macros:
74 nigel 75 .sp
75 nigel 77 REG_DOTALL
76     .sp
77 nigel 87 The PCRE_DOTALL option is set when the regular expression is passed for
78     compilation to the native function. Note that REG_DOTALL is not part of the
79     POSIX standard.
80 nigel 77 .sp
81 nigel 41 REG_ICASE
82 nigel 75 .sp
83 nigel 87 The PCRE_CASELESS option is set when the regular expression is passed for
84     compilation to the native function.
85 nigel 75 .sp
86 nigel 41 REG_NEWLINE
87 nigel 75 .sp
88 nigel 87 The PCRE_MULTILINE option is set when the regular expression is passed for
89     compilation to the native function. Note that this does \fInot\fP mimic the
90     defined POSIX behaviour for REG_NEWLINE (see the following section).
91     .sp
92     REG_NOSUB
93     .sp
94     The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
95     for compilation to the native function. In addition, when a pattern that is
96     compiled with this flag is passed to \fBregexec()\fP for matching, the
97     \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no captured strings
98     are returned.
99     .sp
100     REG_UTF8
101     .sp
102     The PCRE_UTF8 option is set when the regular expression is passed for
103     compilation to the native function. This causes the pattern itself and all data
104     strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
105     is not part of the POSIX standard.
106 nigel 75 .P
107 nigel 49 In the absence of these flags, no options are passed to the native function.
108     This means the the regex is compiled with PCRE default semantics. In
109     particular, the way it handles newline characters in the subject string is the
110     Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
111 nigel 75 \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
112 nigel 63 newlines are matched by . (they aren't) or by a negative class such as [^a]
113     (they are).
114 nigel 75 .P
115     The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
116     \fIpreg\fP structure is filled in on success, and one member of the structure
117     is public: \fIre_nsub\fP contains the number of capturing subpatterns in
118 nigel 41 the regular expression. Various error codes are defined in the header file.
119 nigel 75 .
120     .
121     .SH "MATCHING NEWLINE CHARACTERS"
122 nigel 63 .rs
123     .sp
124     This area is not simple, because POSIX and Perl take different views of things.
125     It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
126     intended to be a POSIX engine. The following table lists the different
127     possibilities for matching newline characters in PCRE:
128 nigel 75 .sp
129 nigel 63 Default Change with
130 nigel 75 .sp
131 nigel 63 . matches newline no PCRE_DOTALL
132     newline matches [^a] yes not changeable
133 nigel 75 $ matches \en at end yes PCRE_DOLLARENDONLY
134     $ matches \en in middle no PCRE_MULTILINE
135     ^ matches \en in middle no PCRE_MULTILINE
136     .sp
137 nigel 63 This is the equivalent table for POSIX:
138 nigel 75 .sp
139 nigel 63 Default Change with
140 nigel 75 .sp
141     . matches newline yes REG_NEWLINE
142     newline matches [^a] yes REG_NEWLINE
143     $ matches \en at end no REG_NEWLINE
144     $ matches \en in middle no REG_NEWLINE
145     ^ matches \en in middle no REG_NEWLINE
146     .sp
147 nigel 63 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
148 nigel 75 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
149 nigel 63 newline from matching [^a].
150 nigel 75 .P
151 nigel 63 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
152 nigel 75 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
153 nigel 63 REG_NEWLINE action.
154 nigel 75 .
155     .
156     .SH "MATCHING A PATTERN"
157 nigel 63 .rs
158     .sp
159 nigel 75 The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
160 ph10 345 against a given \fIstring\fP, which is by default terminated by a zero byte
161 ph10 332 (but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
162     be:
163 nigel 75 .sp
164 nigel 41 REG_NOTBOL
165 nigel 75 .sp
166 nigel 41 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
167     function.
168 nigel 75 .sp
169 nigel 41 REG_NOTEOL
170 nigel 75 .sp
171 nigel 41 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
172     function.
173 ph10 332 .sp
174     REG_STARTEND
175     .sp
176     The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
177     to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
178     (there need not actually be a NUL at that location), regardless of the value of
179     \fInmatch\fP. This is a BSD extension, compatible with but not specified by
180     IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
181     intended to be portable to other systems. Note that a non-zero \fIrm_so\fP does
182     not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
183     how it is matched.
184 nigel 75 .P
185 nigel 87 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
186     strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
187     \fBregexec()\fP are ignored.
188 nigel 75 .P
189 nigel 87 Otherwise,the portion of the string that was matched, and also any captured
190     substrings, are returned via the \fIpmatch\fP argument, which points to an
191     array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
192     members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
193     character of each substring and the offset to the first character after the end
194     of each substring, respectively. The 0th element of the vector relates to the
195     entire portion of \fIstring\fP that was matched; subsequent elements relate to
196     the capturing subpatterns of the regular expression. Unused entries in the
197     array have both structure members set to -1.
198     .P
199 nigel 41 A successful match yields a zero return; various error codes are defined in the
200     header file, of which REG_NOMATCH is the "expected" failure code.
201 nigel 75 .
202     .
203     .SH "ERROR MESSAGES"
204 nigel 63 .rs
205     .sp
206 nigel 75 The \fBregerror()\fP function maps a non-zero errorcode from either
207     \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
208 nigel 41 NULL, the error should have arisen from the use of that structure. A message
209 nigel 75 terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
210     message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
211 nigel 41 function is the size of buffer needed to hold the whole message.
212 nigel 75 .
213     .
214     .SH MEMORY USAGE
215 nigel 63 .rs
216     .sp
217 nigel 41 Compiling a regular expression causes memory to be allocated and associated
218 nigel 75 with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
219     memory, after which \fIpreg\fP may no longer be used as a compiled expression.
220     .
221     .
222 nigel 41 .SH AUTHOR
223 nigel 63 .rs
224     .sp
225 ph10 99 .nf
226 nigel 77 Philip Hazel
227 ph10 99 University Computing Service
228 nigel 93 Cambridge CB2 3QH, England.
229 ph10 99 .fi
230     .
231     .
232     .SH REVISION
233     .rs
234     .sp
235     .nf
236 ph10 332 Last updated: 05 April 2008
237     Copyright (c) 1997-2008 University of Cambridge.
238 ph10 99 .fi

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