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 for the PCRE regular
26 expression 8-bit library. See the pcreapi documentation for a descrip‐
27 tion of PCRE's native API, which contains much additional functional‐
28 ity. There is no POSIX-style wrapper for PCRE's 16-bit and 32-bit
29 library.
30 The functions described here are just wrapper functions that ultimately
32 call the PCRE native API. Their prototypes are defined in the
33 pcreposix.h header file, and on Unix systems the library itself is
34 called pcreposix.a, so can be accessed by adding -lpcreposix to the
35 command for linking an application that uses them. Because the POSIX
36 functions call the native ones, it is also necessary to add -lpcre.
37 I have implemented only those POSIX option bits that can be reasonably
39 mapped to PCRE native options. In addition, the option REG_EXTENDED is
40 defined with the value zero. This has no effect, but since programs
41 that are written to the POSIX interface often use it, this makes it
42 easier to slot in PCRE as a replacement library. Other POSIX options
43 are not even defined.
44 There are also some other options that are not defined by POSIX. These
46 have been added at the request of users who want to make use of certain
47 PCRE-specific features via the POSIX calling interface.
48 When PCRE is called via these functions, it is only the API that is
50 POSIX-like in style. The syntax and semantics of the regular expres‐
51 sions themselves are still those of Perl, subject to the setting of
52 various PCRE options, as described below. "POSIX-like in style" means
53 that the API approximates to the POSIX definition; it is not fully
54 POSIX-compatible, and in multi-byte encoding domains it is probably
55 even less compatible.
56 The header for these functions is supplied as pcreposix.h to avoid any
58 potential clash with other POSIX libraries. It can, of course, be
59 renamed or aliased as regex.h, which is the "correct" name. It provides
60 two structure types, regex_t for compiled internal forms, and reg‐
61 match_t for returning captured substrings. It also defines some con‐
62 stants whose names start with "REG_"; these are used for setting
63 options and identifying error codes.
64
66 The function regcomp() is called to compile a pattern into an internal
68 form. The pattern is a C string terminated by a binary zero, and is
69 passed in the argument pattern. The preg argument is a pointer to a
70 regex_t structure that is used as a base for storing information about
71 the compiled regular expression.
72 The argument cflags is either zero, or contains one or more of the bits
74 defined by the following macros:
75 REG_DOTALL
77 The PCRE_DOTALL option is set when the regular expression is passed for
79 compilation to the native function. Note that REG_DOTALL is not part of
80 the POSIX standard.
81 REG_ICASE
83 The PCRE_CASELESS option is set when the regular expression is passed
85 for compilation to the native function.
86 REG_NEWLINE
88 The PCRE_MULTILINE option is set when the regular expression is passed
90 for compilation to the native function. Note that this does not mimic
91 the defined POSIX behaviour for REG_NEWLINE (see the following sec‐
92 tion).
93 REG_NOSUB
95 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is
97 passed for compilation to the native function. In addition, when a pat‐
98 tern that is compiled with this flag is passed to regexec() for match‐
99 ing, the nmatch and pmatch arguments are ignored, and no captured
100 strings are returned.
101 REG_UCP
103 The PCRE_UCP option is set when the regular expression is passed for
105 compilation to the native function. This causes PCRE to use Unicode
106 properties when matchine \d, \w, etc., instead of just recognizing
107 ASCII values. Note that REG_UTF8 is not part of the POSIX standard.
108 REG_UNGREEDY
110 The PCRE_UNGREEDY option is set when the regular expression is passed
112 for compilation to the native function. Note that REG_UNGREEDY is not
113 part of the POSIX standard.
114 REG_UTF8
116 The PCRE_UTF8 option is set when the regular expression is passed for
118 compilation to the native function. This causes the pattern itself and
119 all data strings used for matching it to be treated as UTF-8 strings.
120 Note that REG_UTF8 is not part of the POSIX standard.
121 In the absence of these flags, no options are passed to the native
123 function. This means the the regex is compiled with PCRE default
124 semantics. In particular, the way it handles newline characters in the
125 subject string is the Perl way, not the POSIX way. Note that setting
126 PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE.
127 It does not affect the way newlines are matched by . (they are not) or
128 by a negative class such as [^a] (they are).
129 The yield of regcomp() is zero on success, and non-zero otherwise. The
131 preg structure is filled in on success, and one member of the structure
132 is public: re_nsub contains the number of capturing subpatterns in the
133 regular expression. Various error codes are defined in the header file.
134 NOTE: If the yield of regcomp() is non-zero, you must not attempt to
136 use the contents of the preg structure. If, for example, you pass it to
137 regexec(), the result is undefined and your program is likely to crash.
138
140 This area is not simple, because POSIX and Perl take different views of
142 things. It is not possible to get PCRE to obey POSIX semantics, but
143 then PCRE was never intended to be a POSIX engine. The following table
144 lists the different possibilities for matching newline characters in
145 PCRE:
146 Default Change with
148 . matches newline no PCRE_DOTALL
150 newline matches [^a] yes not changeable
151 $ matches \n at end yes PCRE_DOLLARENDONLY
152 $ matches \n in middle no PCRE_MULTILINE
153 ^ matches \n in middle no PCRE_MULTILINE
154 This is the equivalent table for POSIX:
156 Default Change with
158 . matches newline yes REG_NEWLINE
160 newline matches [^a] yes REG_NEWLINE
161 $ matches \n at end no REG_NEWLINE
162 $ matches \n in middle no REG_NEWLINE
163 ^ matches \n in middle no REG_NEWLINE
164 PCRE's behaviour is the same as Perl's, except that there is no equiva‐
166 lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is
167 no way to stop newline from matching [^a].
168 The default POSIX newline handling can be obtained by setting
170 PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE
171 behave exactly as for the REG_NEWLINE action.
172
174 The function regexec() is called to match a compiled pattern preg
176 against a given string, which is by default terminated by a zero byte
177 (but see REG_STARTEND below), subject to the options in eflags. These
178 can be:
179 REG_NOTBOL
181 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
183 function.
184 REG_NOTEMPTY
186 The PCRE_NOTEMPTY option is set when calling the underlying PCRE match‐
188 ing function. Note that REG_NOTEMPTY is not part of the POSIX standard.
189 However, setting this option can give more POSIX-like behaviour in some
190 situations.
191 REG_NOTEOL
193 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
195 function.
196 REG_STARTEND
198 The string is considered to start at string + pmatch[0].rm_so and to
200 have a terminating NUL located at string + pmatch[0].rm_eo (there need
201 not actually be a NUL at that location), regardless of the value of
202 nmatch. This is a BSD extension, compatible with but not specified by
203 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in
204 software intended to be portable to other systems. Note that a non-zero
205 rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location
206 of the string, not how it is matched.
207 If the pattern was compiled with the REG_NOSUB flag, no data about any
209 matched strings is returned. The nmatch and pmatch arguments of
210 regexec() are ignored.
211 If the value of nmatch is zero, or if the value pmatch is NULL, no data
213 about any matched strings is returned.
214 Otherwise,the portion of the string that was matched, and also any cap‐
216 tured substrings, are returned via the pmatch argument, which points to
217 an array of nmatch structures of type regmatch_t, containing the mem‐
218 bers rm_so and rm_eo. These contain the offset to the first character
219 of each substring and the offset to the first character after the end
220 of each substring, respectively. The 0th element of the vector relates
221 to the entire portion of string that was matched; subsequent elements
222 relate to the capturing subpatterns of the regular expression. Unused
223 entries in the array have both structure members set to -1.
224 A successful match yields a zero return; various error codes are
226 defined in the header file, of which REG_NOMATCH is the "expected"
227 failure code.
228
230 The regerror() function maps a non-zero errorcode from either regcomp()
232 or regexec() to a printable message. If preg is not NULL, the error
233 should have arisen from the use of that structure. A message terminated
234 by a binary zero is placed in errbuf. The length of the message,
235 including the zero, is limited to errbuf_size. The yield of the func‐
236 tion is the size of buffer needed to hold the whole message.
237
239 Compiling a regular expression causes memory to be allocated and asso‐
241 ciated with the preg structure. The function regfree() frees all such
242 memory, after which preg may no longer be used as a compiled expres‐
243 sion.
244
246 Philip Hazel
248 University Computing Service
249 Cambridge CB2 3QH, England.
250
252 Last updated: 09 January 2012
254 Copyright (c) 1997-2012 University of Cambridge.
255PCRE 8.30 09 January 2012 PCREPOSIX(3)