1PCREPOSIX(3) Library Functions Manual PCREPOSIX(3)
2
6 PCRE - Perl-compatible regular expressions.
7
9 #include <pcreposix.h>
11 int regcomp(regex_t *preg, const char *pattern,
13 int cflags);
14 int regexec(regex_t *preg, const char *string,
16 size_t nmatch, regmatch_t pmatch[], int eflags);
17 size_t regerror(int errcode, const regex_t *preg,
19 char *errbuf, size_t errbuf_size);
20 void regfree(regex_t *preg);
22
24 This set of functions provides a POSIX-style API to the PCRE regular
26 expression package. See the pcreapi documentation for a description of
27 PCRE's native API, which contains much additional functionality.
28 The functions described here are just wrapper functions that ultimately
30 call the PCRE native API. Their prototypes are defined in the
31 pcreposix.h header file, and on Unix systems the library itself is
32 called pcreposix.a, so can be accessed by adding -lpcreposix to the
33 command for linking an application that uses them. Because the POSIX
34 functions call the native ones, it is also necessary to add -lpcre.
35 I have implemented only those POSIX option bits that can be reasonably
37 mapped to PCRE native options. In addition, the option REG_EXTENDED is
38 defined with the value zero. This has no effect, but since programs
39 that are written to the POSIX interface often use it, this makes it
40 easier to slot in PCRE as a replacement library. Other POSIX options
41 are not even defined.
42 There are also some other options that are not defined by POSIX. These
44 have been added at the request of users who want to make use of certain
45 PCRE-specific features via the POSIX calling interface.
46 When PCRE is called via these functions, it is only the API that is
48 POSIX-like in style. The syntax and semantics of the regular expres‐
49 sions themselves are still those of Perl, subject to the setting of
50 various PCRE options, as described below. "POSIX-like in style" means
51 that the API approximates to the POSIX definition; it is not fully
52 POSIX-compatible, and in multi-byte encoding domains it is probably
53 even less compatible.
54 The header for these functions is supplied as pcreposix.h to avoid any
56 potential clash with other POSIX libraries. It can, of course, be
57 renamed or aliased as regex.h, which is the "correct" name. It provides
58 two structure types, regex_t for compiled internal forms, and reg‐
59 match_t for returning captured substrings. It also defines some con‐
60 stants whose names start with "REG_"; these are used for setting
61 options and identifying error codes.
62
64 The function regcomp() is called to compile a pattern into an internal
66 form. The pattern is a C string terminated by a binary zero, and is
67 passed in the argument pattern. The preg argument is a pointer to a
68 regex_t structure that is used as a base for storing information about
69 the compiled regular expression.
70 The argument cflags is either zero, or contains one or more of the bits
72 defined by the following macros:
73 REG_DOTALL
75 The PCRE_DOTALL option is set when the regular expression is passed for
77 compilation to the native function. Note that REG_DOTALL is not part of
78 the POSIX standard.
79 REG_ICASE
81 The PCRE_CASELESS option is set when the regular expression is passed
83 for compilation to the native function.
84 REG_NEWLINE
86 The PCRE_MULTILINE option is set when the regular expression is passed
88 for compilation to the native function. Note that this does not mimic
89 the defined POSIX behaviour for REG_NEWLINE (see the following sec‐
90 tion).
91 REG_NOSUB
93 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is
95 passed for compilation to the native function. In addition, when a pat‐
96 tern that is compiled with this flag is passed to regexec() for match‐
97 ing, the nmatch and pmatch arguments are ignored, and no captured
98 strings are returned.
99 REG_UCP
101 The PCRE_UCP option is set when the regular expression is passed for
103 compilation to the native function. This causes PCRE to use Unicode
104 properties when matchine \d, \w, etc., instead of just recognizing
105 ASCII values. Note that REG_UTF8 is not part of the POSIX standard.
106 REG_UNGREEDY
108 The PCRE_UNGREEDY option is set when the regular expression is passed
110 for compilation to the native function. Note that REG_UNGREEDY is not
111 part of the POSIX standard.
112 REG_UTF8
114 The PCRE_UTF8 option is set when the regular expression is passed for
116 compilation to the native function. This causes the pattern itself and
117 all data strings used for matching it to be treated as UTF-8 strings.
118 Note that REG_UTF8 is not part of the POSIX standard.
119 In the absence of these flags, no options are passed to the native
121 function. This means the the regex is compiled with PCRE default
122 semantics. In particular, the way it handles newline characters in the
123 subject string is the Perl way, not the POSIX way. Note that setting
124 PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE.
125 It does not affect the way newlines are matched by . (they are not) or
126 by a negative class such as [^a] (they are).
127 The yield of regcomp() is zero on success, and non-zero otherwise. The
129 preg structure is filled in on success, and one member of the structure
130 is public: re_nsub contains the number of capturing subpatterns in the
131 regular expression. Various error codes are defined in the header file.
132 NOTE: If the yield of regcomp() is non-zero, you must not attempt to
134 use the contents of the preg structure. If, for example, you pass it to
135 regexec(), the result is undefined and your program is likely to crash.
136
138 This area is not simple, because POSIX and Perl take different views of
140 things. It is not possible to get PCRE to obey POSIX semantics, but
141 then PCRE was never intended to be a POSIX engine. The following table
142 lists the different possibilities for matching newline characters in
143 PCRE:
144 Default Change with
146 . matches newline no PCRE_DOTALL
148 newline matches [^a] yes not changeable
149 $ matches \n at end yes PCRE_DOLLARENDONLY
150 $ matches \n in middle no PCRE_MULTILINE
151 ^ matches \n in middle no PCRE_MULTILINE
152 This is the equivalent table for POSIX:
154 Default Change with
156 . matches newline yes REG_NEWLINE
158 newline matches [^a] yes REG_NEWLINE
159 $ matches \n at end no REG_NEWLINE
160 $ matches \n in middle no REG_NEWLINE
161 ^ matches \n in middle no REG_NEWLINE
162 PCRE's behaviour is the same as Perl's, except that there is no equiva‐
164 lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is
165 no way to stop newline from matching [^a].
166 The default POSIX newline handling can be obtained by setting
168 PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE
169 behave exactly as for the REG_NEWLINE action.
170
172 The function regexec() is called to match a compiled pattern preg
174 against a given string, which is by default terminated by a zero byte
175 (but see REG_STARTEND below), subject to the options in eflags. These
176 can be:
177 REG_NOTBOL
179 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
181 function.
182 REG_NOTEMPTY
184 The PCRE_NOTEMPTY option is set when calling the underlying PCRE match‐
186 ing function. Note that REG_NOTEMPTY is not part of the POSIX standard.
187 However, setting this option can give more POSIX-like behaviour in some
188 situations.
189 REG_NOTEOL
191 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
193 function.
194 REG_STARTEND
196 The string is considered to start at string + pmatch[0].rm_so and to
198 have a terminating NUL located at string + pmatch[0].rm_eo (there need
199 not actually be a NUL at that location), regardless of the value of
200 nmatch. This is a BSD extension, compatible with but not specified by
201 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in
202 software intended to be portable to other systems. Note that a non-zero
203 rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location
204 of the string, not how it is matched.
205 If the pattern was compiled with the REG_NOSUB flag, no data about any
207 matched strings is returned. The nmatch and pmatch arguments of
208 regexec() are ignored.
209 If the value of nmatch is zero, or if the value pmatch is NULL, no data
211 about any matched strings is returned.
212 Otherwise,the portion of the string that was matched, and also any cap‐
214 tured substrings, are returned via the pmatch argument, which points to
215 an array of nmatch structures of type regmatch_t, containing the mem‐
216 bers rm_so and rm_eo. These contain the offset to the first character
217 of each substring and the offset to the first character after the end
218 of each substring, respectively. The 0th element of the vector relates
219 to the entire portion of string that was matched; subsequent elements
220 relate to the capturing subpatterns of the regular expression. Unused
221 entries in the array have both structure members set to -1.
222 A successful match yields a zero return; various error codes are
224 defined in the header file, of which REG_NOMATCH is the "expected"
225 failure code.
226
228 The regerror() function maps a non-zero errorcode from either regcomp()
230 or regexec() to a printable message. If preg is not NULL, the error
231 should have arisen from the use of that structure. A message terminated
232 by a binary zero is placed in errbuf. The length of the message,
233 including the zero, is limited to errbuf_size. The yield of the func‐
234 tion is the size of buffer needed to hold the whole message.
235
237 Compiling a regular expression causes memory to be allocated and asso‐
239 ciated with the preg structure. The function regfree() frees all such
240 memory, after which preg may no longer be used as a compiled expres‐
241 sion.
242
244 Philip Hazel
246 University Computing Service
247 Cambridge CB2 3QH, England.
248
250 Last updated: 16 May 2010
252 Copyright (c) 1997-2010 University of Cambridge.
253 PCREPOSIX(3)