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,
18 char *errbuf, size_t errbuf_size);
19 void regfree(regex_t *preg);
21
23 This set of functions provides a POSIX-style API for the PCRE regular
25 expression 8-bit library. See the pcreapi documentation for a descrip‐
26 tion of PCRE's native API, which contains much additional functional‐
27 ity. There is no POSIX-style wrapper for PCRE's 16-bit and 32-bit
28 library.
29 The functions described here are just wrapper functions that ultimately
31 call the PCRE native API. Their prototypes are defined in the
32 pcreposix.h header file, and on Unix systems the library itself is
33 called pcreposix.a, so can be accessed by adding -lpcreposix to the
34 command for linking an application that uses them. Because the POSIX
35 functions call the native ones, it is also necessary to add -lpcre.
36 I have implemented only those POSIX option bits that can be reasonably
38 mapped to PCRE native options. In addition, the option REG_EXTENDED is
39 defined with the value zero. This has no effect, but since programs
40 that are written to the POSIX interface often use it, this makes it
41 easier to slot in PCRE as a replacement library. Other POSIX options
42 are not even defined.
43 There are also some other options that are not defined by POSIX. These
45 have been added at the request of users who want to make use of certain
46 PCRE-specific features via the POSIX calling interface.
47 When PCRE is called via these functions, it is only the API that is
49 POSIX-like in style. The syntax and semantics of the regular expres‐
50 sions themselves are still those of Perl, subject to the setting of
51 various PCRE options, as described below. "POSIX-like in style" means
52 that the API approximates to the POSIX definition; it is not fully
53 POSIX-compatible, and in multi-byte encoding domains it is probably
54 even less compatible.
55 The header for these functions is supplied as pcreposix.h to avoid any
57 potential clash with other POSIX libraries. It can, of course, be
58 renamed or aliased as regex.h, which is the "correct" name. It provides
59 two structure types, regex_t for compiled internal forms, and reg‐
60 match_t for returning captured substrings. It also defines some con‐
61 stants whose names start with "REG_"; these are used for setting
62 options and identifying error codes.
63
65 The function regcomp() is called to compile a pattern into an internal
67 form. The pattern is a C string terminated by a binary zero, and is
68 passed in the argument pattern. The preg argument is a pointer to a
69 regex_t structure that is used as a base for storing information about
70 the compiled regular expression.
71 The argument cflags is either zero, or contains one or more of the bits
73 defined by the following macros:
74 REG_DOTALL
76 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
79 the POSIX standard.
80 REG_ICASE
82 The PCRE_CASELESS option is set when the regular expression is passed
84 for compilation to the native function.
85 REG_NEWLINE
87 The PCRE_MULTILINE option is set when the regular expression is passed
89 for compilation to the native function. Note that this does not mimic
90 the defined POSIX behaviour for REG_NEWLINE (see the following sec‐
91 tion).
92 REG_NOSUB
94 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is
96 passed for compilation to the native function. In addition, when a pat‐
97 tern that is compiled with this flag is passed to regexec() for match‐
98 ing, the nmatch and pmatch arguments are ignored, and no captured
99 strings are returned.
100 REG_UCP
102 The PCRE_UCP option is set when the regular expression is passed for
104 compilation to the native function. This causes PCRE to use Unicode
105 properties when matchine \d, \w, etc., instead of just recognizing
106 ASCII values. Note that REG_UTF8 is not part of the POSIX standard.
107 REG_UNGREEDY
109 The PCRE_UNGREEDY option is set when the regular expression is passed
111 for compilation to the native function. Note that REG_UNGREEDY is not
112 part of the POSIX standard.
113 REG_UTF8
115 The PCRE_UTF8 option is set when the regular expression is passed for
117 compilation to the native function. This causes the pattern itself and
118 all data strings used for matching it to be treated as UTF-8 strings.
119 Note that REG_UTF8 is not part of the POSIX standard.
120 In the absence of these flags, no options are passed to the native
122 function. This means the the regex is compiled with PCRE default
123 semantics. In particular, the way it handles newline characters in the
124 subject string is the Perl way, not the POSIX way. Note that setting
125 PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE.
126 It does not affect the way newlines are matched by . (they are not) or
127 by a negative class such as [^a] (they are).
128 The yield of regcomp() is zero on success, and non-zero otherwise. The
130 preg structure is filled in on success, and one member of the structure
131 is public: re_nsub contains the number of capturing subpatterns in the
132 regular expression. Various error codes are defined in the header file.
133 NOTE: If the yield of regcomp() is non-zero, you must not attempt to
135 use the contents of the preg structure. If, for example, you pass it to
136 regexec(), the result is undefined and your program is likely to crash.
137
139 This area is not simple, because POSIX and Perl take different views of
141 things. It is not possible to get PCRE to obey POSIX semantics, but
142 then PCRE was never intended to be a POSIX engine. The following table
143 lists the different possibilities for matching newline characters in
144 PCRE:
145 Default Change with
147 . matches newline no PCRE_DOTALL
149 newline matches [^a] yes not changeable
150 $ matches \n at end yes PCRE_DOLLARENDONLY
151 $ matches \n in middle no PCRE_MULTILINE
152 ^ matches \n in middle no PCRE_MULTILINE
153 This is the equivalent table for POSIX:
155 Default Change with
157 . matches newline yes REG_NEWLINE
159 newline matches [^a] yes REG_NEWLINE
160 $ matches \n at end no REG_NEWLINE
161 $ matches \n in middle no REG_NEWLINE
162 ^ matches \n in middle no REG_NEWLINE
163 PCRE's behaviour is the same as Perl's, except that there is no equiva‐
165 lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is
166 no way to stop newline from matching [^a].
167 The default POSIX newline handling can be obtained by setting
169 PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE
170 behave exactly as for the REG_NEWLINE action.
171
173 The function regexec() is called to match a compiled pattern preg
175 against a given string, which is by default terminated by a zero byte
176 (but see REG_STARTEND below), subject to the options in eflags. These
177 can be:
178 REG_NOTBOL
180 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
182 function.
183 REG_NOTEMPTY
185 The PCRE_NOTEMPTY option is set when calling the underlying PCRE match‐
187 ing function. Note that REG_NOTEMPTY is not part of the POSIX standard.
188 However, setting this option can give more POSIX-like behaviour in some
189 situations.
190 REG_NOTEOL
192 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
194 function.
195 REG_STARTEND
197 The string is considered to start at string + pmatch[0].rm_so and to
199 have a terminating NUL located at string + pmatch[0].rm_eo (there need
200 not actually be a NUL at that location), regardless of the value of
201 nmatch. This is a BSD extension, compatible with but not specified by
202 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in
203 software intended to be portable to other systems. Note that a non-zero
204 rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location
205 of the string, not how it is matched.
206 If the pattern was compiled with the REG_NOSUB flag, no data about any
208 matched strings is returned. The nmatch and pmatch arguments of
209 regexec() are ignored.
210 If the value of nmatch is zero, or if the value pmatch is NULL, no data
212 about any matched strings is returned.
213 Otherwise,the portion of the string that was matched, and also any cap‐
215 tured substrings, are returned via the pmatch argument, which points to
216 an array of nmatch structures of type regmatch_t, containing the mem‐
217 bers rm_so and rm_eo. These contain the offset to the first character
218 of each substring and the offset to the first character after the end
219 of each substring, respectively. The 0th element of the vector relates
220 to the entire portion of string that was matched; subsequent elements
221 relate to the capturing subpatterns of the regular expression. Unused
222 entries in the array have both structure members set to -1.
223 A successful match yields a zero return; various error codes are
225 defined in the header file, of which REG_NOMATCH is the "expected"
226 failure code.
227
229 The regerror() function maps a non-zero errorcode from either regcomp()
231 or regexec() to a printable message. If preg is not NULL, the error
232 should have arisen from the use of that structure. A message terminated
233 by a binary zero is placed in errbuf. The length of the message,
234 including the zero, is limited to errbuf_size. The yield of the func‐
235 tion is the size of buffer needed to hold the whole message.
236
238 Compiling a regular expression causes memory to be allocated and asso‐
240 ciated with the preg structure. The function regfree() frees all such
241 memory, after which preg may no longer be used as a compiled expres‐
242 sion.
243
245 Philip Hazel
247 University Computing Service
248 Cambridge CB2 3QH, England.
249
251 Last updated: 09 January 2012
253 Copyright (c) 1997-2012 University of Cambridge.
254PCRE 8.30 09 January 2012 PCREPOSIX(3)