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Revision 432 - (hide annotations) (download)
Wed Sep 2 16:02:56 2009 UTC (4 years, 7 months ago) by ph10
File size: 10182 byte(s)
Add REG_UNGREEDY (non-standard) to the POSIX interface.

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 ph10 388 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 nigel 75 .P
48 ph10 432 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 nigel 41 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 nigel 69 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 nigel 75 .P
59     The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
60 nigel 41 potential clash with other POSIX libraries. It can, of course, be renamed or
61 nigel 75 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 nigel 41 constants whose names start with "REG_"; these are used for setting options and
65     identifying error codes.
66 nigel 75 .P
67     .SH "COMPILING A PATTERN"
68 nigel 63 .rs
69     .sp
70 nigel 75 The function \fBregcomp()\fP is called to compile a pattern into an
71 nigel 41 internal form. The pattern is a C string terminated by a binary zero, and
72 nigel 75 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 nigel 87 about the compiled regular expression.
75 nigel 75 .P
76     The argument \fIcflags\fP is either zero, or contains one or more of the bits
77 nigel 41 defined by the following macros:
78 nigel 75 .sp
79 nigel 77 REG_DOTALL
80     .sp
81 nigel 87 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 nigel 77 .sp
85 nigel 41 REG_ICASE
86 nigel 75 .sp
87 nigel 87 The PCRE_CASELESS option is set when the regular expression is passed for
88     compilation to the native function.
89 nigel 75 .sp
90 nigel 41 REG_NEWLINE
91 nigel 75 .sp
92 nigel 87 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 ph10 432 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 nigel 87 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 nigel 75 .P
117 nigel 49 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 nigel 75 \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
122 ph10 432 newlines are matched by . (they are not) or by a negative class such as [^a]
123 nigel 63 (they are).
124 nigel 75 .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 nigel 41 the regular expression. Various error codes are defined in the header file.
129 ph10 424 .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 nigel 75 .
134     .
135     .SH "MATCHING NEWLINE CHARACTERS"
136 nigel 63 .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 nigel 75 .sp
143 nigel 63 Default Change with
144 nigel 75 .sp
145 nigel 63 . matches newline no PCRE_DOTALL
146     newline matches [^a] yes not changeable
147 nigel 75 $ 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 nigel 63 This is the equivalent table for POSIX:
152 nigel 75 .sp
153 nigel 63 Default Change with
154 nigel 75 .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 nigel 63 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
162 nigel 75 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
163 nigel 63 newline from matching [^a].
164 nigel 75 .P
165 nigel 63 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
166 nigel 75 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
167 nigel 63 REG_NEWLINE action.
168 nigel 75 .
169     .
170     .SH "MATCHING A PATTERN"
171 nigel 63 .rs
172     .sp
173 nigel 75 The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
174 ph10 345 against a given \fIstring\fP, which is by default terminated by a zero byte
175 ph10 332 (but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
176     be:
177 nigel 75 .sp
178 nigel 41 REG_NOTBOL
179 nigel 75 .sp
180 nigel 41 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
181     function.
182 nigel 75 .sp
183 ph10 388 REG_NOTEMPTY
184 ph10 392 .sp
185 ph10 388 The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
186 ph10 392 function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
187 ph10 388 setting this option can give more POSIX-like behaviour in some situations.
188     .sp
189 nigel 41 REG_NOTEOL
190 nigel 75 .sp
191 nigel 41 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
192     function.
193 ph10 332 .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 nigel 75 .P
205 nigel 87 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 nigel 75 .P
209 nigel 87 Otherwise,the portion of the string that was matched, and also any captured
210     substrings, are returned via the \fIpmatch\fP argument, which points to an
211     array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
212     members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
213     character of each substring and the offset to the first character after the end
214     of each substring, respectively. The 0th element of the vector relates to the
215     entire portion of \fIstring\fP that was matched; subsequent elements relate to
216     the capturing subpatterns of the regular expression. Unused entries in the
217     array have both structure members set to -1.
218     .P
219 nigel 41 A successful match yields a zero return; various error codes are defined in the
220     header file, of which REG_NOMATCH is the "expected" failure code.
221 nigel 75 .
222     .
223     .SH "ERROR MESSAGES"
224 nigel 63 .rs
225     .sp
226 nigel 75 The \fBregerror()\fP function maps a non-zero errorcode from either
227     \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
228 nigel 41 NULL, the error should have arisen from the use of that structure. A message
229 nigel 75 terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
230     message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
231 nigel 41 function is the size of buffer needed to hold the whole message.
232 nigel 75 .
233     .
234     .SH MEMORY USAGE
235 nigel 63 .rs
236     .sp
237 nigel 41 Compiling a regular expression causes memory to be allocated and associated
238 nigel 75 with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
239     memory, after which \fIpreg\fP may no longer be used as a compiled expression.
240     .
241     .
242 nigel 41 .SH AUTHOR
243 nigel 63 .rs
244     .sp
245 ph10 99 .nf
246 nigel 77 Philip Hazel
247 ph10 99 University Computing Service
248 nigel 93 Cambridge CB2 3QH, England.
249 ph10 99 .fi
250     .
251     .
252     .SH REVISION
253     .rs
254     .sp
255     .nf
256 ph10 432 Last updated: 02 September 2009
257 ph10 388 Copyright (c) 1997-2009 University of Cambridge.
258 ph10 99 .fi

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