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.
49 When PCRE2 is called via these functions, it is only the API that is
51 POSIX-like in style. The syntax and semantics of the regular expres‐
52 sions themselves are still those of Perl, subject to the setting of
53 various PCRE2 options, as described below. "POSIX-like in style" means
54 that the API approximates to the POSIX definition; it is not fully
55 POSIX-compatible, and in multi-unit encoding domains it is probably
56 even less compatible.
57 The header for these functions is supplied as pcre2posix.h to avoid any
59 potential clash with other POSIX libraries. It can, of course, be
60 renamed or aliased as regex.h, which is the "correct" name. It provides
61 two structure types, regex_t for compiled internal forms, and reg‐
62 match_t for returning captured substrings. It also defines some con‐
63 stants whose names start with "REG_"; these are used for setting
64 options and identifying error codes.
65
67 The function regcomp() is called to compile a pattern into an internal
69 form. The pattern is a C string terminated by a binary zero, and is
70 passed in the argument pattern. The preg argument is a pointer to a
71 regex_t structure that is used as a base for storing information about
72 the compiled regular expression.
73 The argument cflags is either zero, or contains one or more of the bits
75 defined by the following macros:
76 REG_DOTALL
78 The PCRE2_DOTALL option is set when the regular expression is passed
80 for compilation to the native function. Note that REG_DOTALL is not
81 part of the POSIX standard.
82 REG_ICASE
84 The PCRE2_CASELESS option is set when the regular expression is passed
86 for compilation to the native function.
87 REG_NEWLINE
89 The PCRE2_MULTILINE option is set when the regular expression is passed
91 for compilation to the native function. Note that this does not mimic
92 the defined POSIX behaviour for REG_NEWLINE (see the following sec‐
93 tion).
94 REG_NOSUB
96 When a pattern that is compiled with this flag is passed to regexec()
98 for matching, the nmatch and pmatch arguments are ignored, and no cap‐
99 tured strings are returned. Versions of the PCRE library prior to 10.22
100 used to set the PCRE2_NO_AUTO_CAPTURE compile option, but this no
101 longer happens because it disables the use of back references.
102 REG_UCP
104 The PCRE2_UCP option is set when the regular expression is passed for
106 compilation to the native function. This causes PCRE2 to use Unicode
107 properties when matchine \d, \w, etc., instead of just recognizing
108 ASCII values. Note that REG_UCP is not part of the POSIX standard.
109 REG_UNGREEDY
111 The PCRE2_UNGREEDY option is set when the regular expression is passed
113 for compilation to the native function. Note that REG_UNGREEDY is not
114 part of the POSIX standard.
115 REG_UTF
117 The PCRE2_UTF option is set when the regular expression is passed for
119 compilation to the native function. This causes the pattern itself and
120 all data strings used for matching it to be treated as UTF-8 strings.
121 Note that REG_UTF is not part of the POSIX standard.
122 In the absence of these flags, no options are passed to the native
124 function. This means the the regex is compiled with PCRE2 default
125 semantics. In particular, the way it handles newline characters in the
126 subject string is the Perl way, not the POSIX way. Note that setting
127 PCRE2_MULTILINE has only some of the effects specified for REG_NEWLINE.
128 It does not affect the way newlines are matched by the dot metacharac‐
129 ter (they are not) or by a negative class such as [^a] (they are).
130 The yield of regcomp() is zero on success, and non-zero otherwise. The
132 preg structure is filled in on success, and one member of the structure
133 is public: re_nsub contains the number of capturing subpatterns in the
134 regular expression. Various error codes are defined in the header file.
135 NOTE: If the yield of regcomp() is non-zero, you must not attempt to
137 use the contents of the preg structure. If, for example, you pass it to
138 regexec(), the result is undefined and your program is likely to crash.
139
141 This area is not simple, because POSIX and Perl take different views of
143 things. It is not possible to get PCRE2 to obey POSIX semantics, but
144 then PCRE2 was never intended to be a POSIX engine. The following table
145 lists the different possibilities for matching newline characters in
146 Perl and PCRE2:
147 Default Change with
149 . matches newline no PCRE2_DOTALL
151 newline matches [^a] yes not changeable
152 $ matches \n at end yes PCRE2_DOLLAR_ENDONLY
153 $ matches \n in middle no PCRE2_MULTILINE
154 ^ matches \n in middle no PCRE2_MULTILINE
155 This is the equivalent table for a POSIX-compatible pattern matcher:
157 Default Change with
159 . matches newline yes REG_NEWLINE
161 newline matches [^a] yes REG_NEWLINE
162 $ matches \n at end no REG_NEWLINE
163 $ matches \n in middle no REG_NEWLINE
164 ^ matches \n in middle no REG_NEWLINE
165 This behaviour is not what happens when PCRE2 is called via its POSIX
167 API. By default, PCRE2's behaviour is the same as Perl's, except that
168 there is no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2
169 and Perl, there is no way to stop newline from matching [^a].
170 Default POSIX newline handling can be obtained by setting PCRE2_DOTALL
172 and PCRE2_DOLLAR_ENDONLY when calling pcre2_compile() directly, but
173 there is no way to make PCRE2 behave exactly as for the REG_NEWLINE
174 action. When using the POSIX API, passing REG_NEWLINE to PCRE2's reg‐
175 comp() function causes PCRE2_MULTILINE to be passed to pcre2_compile(),
176 and REG_DOTALL passes PCRE2_DOTALL. There is no way to pass PCRE2_DOL‐
177 LAR_ENDONLY.
178
180 The function regexec() is called to match a compiled pattern preg
182 against a given string, which is by default terminated by a zero byte
183 (but see REG_STARTEND below), subject to the options in eflags. These
184 can be:
185 REG_NOTBOL
187 The PCRE2_NOTBOL option is set when calling the underlying PCRE2 match‐
189 ing function.
190 REG_NOTEMPTY
192 The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2
194 matching function. Note that REG_NOTEMPTY is not part of the POSIX
195 standard. However, setting this option can give more POSIX-like behav‐
196 iour in some situations.
197 REG_NOTEOL
199 The PCRE2_NOTEOL option is set when calling the underlying PCRE2 match‐
201 ing function.
202 REG_STARTEND
204 The string is considered to start at string + pmatch[0].rm_so and to
206 have a terminating NUL located at string + pmatch[0].rm_eo (there need
207 not actually be a NUL at that location), regardless of the value of
208 nmatch. This is a BSD extension, compatible with but not specified by
209 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in
210 software intended to be portable to other systems. Note that a non-zero
211 rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location
212 of the string, not how it is matched. Setting REG_STARTEND and passing
213 pmatch as NULL are mutually exclusive; the error REG_INVARG is
214 returned.
215 If the pattern was compiled with the REG_NOSUB flag, no data about any
217 matched strings is returned. The nmatch and pmatch arguments of
218 regexec() are ignored (except possibly as input for REG_STARTEND).
219 The value of nmatch may be zero, and the value pmatch may be NULL
221 (unless REG_STARTEND is set); in both these cases no data about any
222 matched strings is returned.
223 Otherwise, the portion of the string that was matched, and also any
225 captured substrings, are returned via the pmatch argument, which points
226 to an array of nmatch structures of type regmatch_t, containing the
227 members rm_so and rm_eo. These contain the byte offset to the first
228 character of each substring and the offset to the first character after
229 the end of each substring, respectively. The 0th element of the vector
230 relates to the entire portion of string that was matched; subsequent
231 elements relate to the capturing subpatterns of the regular expression.
232 Unused entries in the array have both structure members set to -1.
233 A successful match yields a zero return; various error codes are
235 defined in the header file, of which REG_NOMATCH is the "expected"
236 failure code.
237
239 The regerror() function maps a non-zero errorcode from either regcomp()
241 or regexec() to a printable message. If preg is not NULL, the error
242 should have arisen from the use of that structure. A message terminated
243 by a binary zero is placed in errbuf. If the buffer is too short, only
244 the first errbuf_size - 1 characters of the error message are used. The
245 yield of the function is the size of buffer needed to hold the whole
246 message, including the terminating zero. This value is greater than
247 errbuf_size if the message was truncated.
248
250 Compiling a regular expression causes memory to be allocated and asso‐
252 ciated with the preg structure. The function regfree() frees all such
253 memory, after which preg may no longer be used as a compiled expres‐
254 sion.
255
257 Philip Hazel
259 University Computing Service
260 Cambridge, England.
261
263 Last updated: 31 January 2016
265 Copyright (c) 1997-2016 University of Cambridge.
266PCRE2 10.22 31 January 2016 PCRE2POSIX(3)