1PCRE2POSIX(3) Library Functions Manual PCRE2POSIX(3)
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6 PCRE2 - Perl-compatible regular expressions (revised API)
7
9 #include <pcre2posix.h>
11 int regcomp(regex_t *preg, const char *pattern,
13 int cflags);
14 int regexec(const 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 PCRE2 regular
26 expression 8-bit library. See the pcre2api documentation for a descrip‐
27 tion of PCRE2's native API, which contains much additional functional‐
28 ity. There are no POSIX-style wrappers for PCRE2's 16-bit and 32-bit
29 libraries.
30 The functions described here are just wrapper functions that ultimately
32 call the PCRE2 native API. Their prototypes are defined in the
33 pcre2posix.h header file, and on Unix systems the library itself is
34 called libpcre2-posix.a, so can be accessed by adding -lpcre2-posix to
35 the command for linking an application that uses them. Because the
36 POSIX functions call the native ones, it is also necessary to add
37 -lpcre2-8.
38 Those POSIX option bits that can reasonably be mapped to PCRE2 native
40 options have been implemented. In addition, the option REG_EXTENDED is
41 defined with the value zero. This has no effect, but since programs
42 that are written to the POSIX interface often use it, this makes it
43 easier to slot in PCRE2 as a replacement library. Other POSIX options
44 are not even defined.
45 There are also some options that are not defined by POSIX. These have
47 been added at the request of users who want to make use of certain
48 PCRE2-specific features via the POSIX calling interface or to add BSD
49 or GNU functionality.
50 When PCRE2 is called via these functions, it is only the API that is
52 POSIX-like in style. The syntax and semantics of the regular expres‐
53 sions themselves are still those of Perl, subject to the setting of
54 various PCRE2 options, as described below. "POSIX-like in style" means
55 that the API approximates to the POSIX definition; it is not fully
56 POSIX-compatible, and in multi-unit encoding domains it is probably
57 even less compatible.
58 The header for these functions is supplied as pcre2posix.h to avoid any
60 potential clash with other POSIX libraries. It can, of course, be
61 renamed or aliased as regex.h, which is the "correct" name. It provides
62 two structure types, regex_t for compiled internal forms, and reg‐
63 match_t for returning captured substrings. It also defines some con‐
64 stants whose names start with "REG_"; these are used for setting
65 options and identifying error codes.
66
68 The function regcomp() is called to compile a pattern into an internal
70 form. By default, the pattern is a C string terminated by a binary zero
71 (but see REG_PEND below). The preg argument is a pointer to a regex_t
72 structure that is used as a base for storing information about the com‐
73 piled regular expression. (It is also used for input when REG_PEND is
74 set.)
75 The argument cflags is either zero, or contains one or more of the bits
77 defined by the following macros:
78 REG_DOTALL
80 The PCRE2_DOTALL option is set when the regular expression is passed
82 for compilation to the native function. Note that REG_DOTALL is not
83 part of the POSIX standard.
84 REG_ICASE
86 The PCRE2_CASELESS option is set when the regular expression is passed
88 for compilation to the native function.
89 REG_NEWLINE
91 The PCRE2_MULTILINE option is set when the regular expression is passed
93 for compilation to the native function. Note that this does not mimic
94 the defined POSIX behaviour for REG_NEWLINE (see the following sec‐
95 tion).
96 REG_NOSPEC
98 The PCRE2_LITERAL option is set when the regular expression is passed
100 for compilation to the native function. This disables all meta charac‐
101 ters in the pattern, causing it to be treated as a literal string. The
102 only other options that are allowed with REG_NOSPEC are REG_ICASE,
103 REG_NOSUB, REG_PEND, and REG_UTF. Note that REG_NOSPEC is not part of
104 the POSIX standard.
105 REG_NOSUB
107 When a pattern that is compiled with this flag is passed to regexec()
109 for matching, the nmatch and pmatch arguments are ignored, and no cap‐
110 tured strings are returned. Versions of the PCRE library prior to 10.22
111 used to set the PCRE2_NO_AUTO_CAPTURE compile option, but this no
112 longer happens because it disables the use of backreferences.
113 REG_PEND
115 If this option is set, the reg_endp field in the preg structure (which
117 has the type const char *) must be set to point to the character beyond
118 the end of the pattern before calling regcomp(). The pattern itself may
119 now contain binary zeros, which are treated as data characters. Without
120 REG_PEND, a binary zero terminates the pattern and the re_endp field is
121 ignored. This is a GNU extension to the POSIX standard and should be
122 used with caution in software intended to be portable to other systems.
123 REG_UCP
125 The PCRE2_UCP option is set when the regular expression is passed for
127 compilation to the native function. This causes PCRE2 to use Unicode
128 properties when matchine \d, \w, etc., instead of just recognizing
129 ASCII values. Note that REG_UCP is not part of the POSIX standard.
130 REG_UNGREEDY
132 The PCRE2_UNGREEDY option is set when the regular expression is passed
134 for compilation to the native function. Note that REG_UNGREEDY is not
135 part of the POSIX standard.
136 REG_UTF
138 The PCRE2_UTF option is set when the regular expression is passed for
140 compilation to the native function. This causes the pattern itself and
141 all data strings used for matching it to be treated as UTF-8 strings.
142 Note that REG_UTF is not part of the POSIX standard.
143 In the absence of these flags, no options are passed to the native
145 function. This means the the regex is compiled with PCRE2 default
146 semantics. In particular, the way it handles newline characters in the
147 subject string is the Perl way, not the POSIX way. Note that setting
148 PCRE2_MULTILINE has only some of the effects specified for REG_NEWLINE.
149 It does not affect the way newlines are matched by the dot metacharac‐
150 ter (they are not) or by a negative class such as [^a] (they are).
151 The yield of regcomp() is zero on success, and non-zero otherwise. The
153 preg structure is filled in on success, and one other member of the
154 structure (as well as re_endp) is public: re_nsub contains the number
155 of capturing subpatterns in the regular expression. Various error codes
156 are defined in the header file.
157 NOTE: If the yield of regcomp() is non-zero, you must not attempt to
159 use the contents of the preg structure. If, for example, you pass it to
160 regexec(), the result is undefined and your program is likely to crash.
161
163 This area is not simple, because POSIX and Perl take different views of
165 things. It is not possible to get PCRE2 to obey POSIX semantics, but
166 then PCRE2 was never intended to be a POSIX engine. The following table
167 lists the different possibilities for matching newline characters in
168 Perl and PCRE2:
169 Default Change with
171 . matches newline no PCRE2_DOTALL
173 newline matches [^a] yes not changeable
174 $ matches \n at end yes PCRE2_DOLLAR_ENDONLY
175 $ matches \n in middle no PCRE2_MULTILINE
176 ^ matches \n in middle no PCRE2_MULTILINE
177 This is the equivalent table for a POSIX-compatible pattern matcher:
179 Default Change with
181 . matches newline yes REG_NEWLINE
183 newline matches [^a] yes REG_NEWLINE
184 $ matches \n at end no REG_NEWLINE
185 $ matches \n in middle no REG_NEWLINE
186 ^ matches \n in middle no REG_NEWLINE
187 This behaviour is not what happens when PCRE2 is called via its POSIX
189 API. By default, PCRE2's behaviour is the same as Perl's, except that
190 there is no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2
191 and Perl, there is no way to stop newline from matching [^a].
192 Default POSIX newline handling can be obtained by setting PCRE2_DOTALL
194 and PCRE2_DOLLAR_ENDONLY when calling pcre2_compile() directly, but
195 there is no way to make PCRE2 behave exactly as for the REG_NEWLINE
196 action. When using the POSIX API, passing REG_NEWLINE to PCRE2's reg‐
197 comp() function causes PCRE2_MULTILINE to be passed to pcre2_compile(),
198 and REG_DOTALL passes PCRE2_DOTALL. There is no way to pass PCRE2_DOL‐
199 LAR_ENDONLY.
200
202 The function regexec() is called to match a compiled pattern preg
204 against a given string, which is by default terminated by a zero byte
205 (but see REG_STARTEND below), subject to the options in eflags. These
206 can be:
207 REG_NOTBOL
209 The PCRE2_NOTBOL option is set when calling the underlying PCRE2 match‐
211 ing function.
212 REG_NOTEMPTY
214 The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2
216 matching function. Note that REG_NOTEMPTY is not part of the POSIX
217 standard. However, setting this option can give more POSIX-like behav‐
218 iour in some situations.
219 REG_NOTEOL
221 The PCRE2_NOTEOL option is set when calling the underlying PCRE2 match‐
223 ing function.
224 REG_STARTEND
226 When this option is set, the subject string starts at string +
228 pmatch[0].rm_so and ends at string + pmatch[0].rm_eo, which should
229 point to the first character beyond the string. There may be binary
230 zeros within the subject string, and indeed, using REG_STARTEND is the
231 only way to pass a subject string that contains a binary zero.
232 Whatever the value of pmatch[0].rm_so, the offsets of the matched
234 string and any captured substrings are still given relative to the
235 start of string itself. (Before PCRE2 release 10.30 these were given
236 relative to string + pmatch[0].rm_so, but this differs from other
237 implementations.)
238 This is a BSD extension, compatible with but not specified by IEEE
240 Standard 1003.2 (POSIX.2), and should be used with caution in software
241 intended to be portable to other systems. Note that a non-zero rm_so
242 does not imply REG_NOTBOL; REG_STARTEND affects only the location and
243 length of the string, not how it is matched. Setting REG_STARTEND and
244 passing pmatch as NULL are mutually exclusive; the error REG_INVARG is
245 returned.
246 If the pattern was compiled with the REG_NOSUB flag, no data about any
248 matched strings is returned. The nmatch and pmatch arguments of
249 regexec() are ignored (except possibly as input for REG_STARTEND).
250 The value of nmatch may be zero, and the value pmatch may be NULL
252 (unless REG_STARTEND is set); in both these cases no data about any
253 matched strings is returned.
254 Otherwise, the portion of the string that was matched, and also any
256 captured substrings, are returned via the pmatch argument, which points
257 to an array of nmatch structures of type regmatch_t, containing the
258 members rm_so and rm_eo. These contain the byte offset to the first
259 character of each substring and the offset to the first character after
260 the end of each substring, respectively. The 0th element of the vector
261 relates to the entire portion of string that was matched; subsequent
262 elements relate to the capturing subpatterns of the regular expression.
263 Unused entries in the array have both structure members set to -1.
264 A successful match yields a zero return; various error codes are
266 defined in the header file, of which REG_NOMATCH is the "expected"
267 failure code.
268
270 The regerror() function maps a non-zero errorcode from either regcomp()
272 or regexec() to a printable message. If preg is not NULL, the error
273 should have arisen from the use of that structure. A message terminated
274 by a binary zero is placed in errbuf. If the buffer is too short, only
275 the first errbuf_size - 1 characters of the error message are used. The
276 yield of the function is the size of buffer needed to hold the whole
277 message, including the terminating zero. This value is greater than
278 errbuf_size if the message was truncated.
279
281 Compiling a regular expression causes memory to be allocated and asso‐
283 ciated with the preg structure. The function regfree() frees all such
284 memory, after which preg may no longer be used as a compiled expres‐
285 sion.
286
288 Philip Hazel
290 University Computing Service
291 Cambridge, England.
292
294 Last updated: 15 June 2017
296 Copyright (c) 1997-2017 University of Cambridge.
297PCRE2 10.30 15 June 2017 PCRE2POSIX(3)