1REGEX(3) Linux Programmer's Manual REGEX(3)
2
6 regcomp, regexec, regerror, regfree - POSIX regex functions
7
9 #include <regex.h>
10 int regcomp(regex_t *restrict preg, const char *restrict regex,
12 int cflags);
13 int regexec(const regex_t *restrict preg, const char *restrict string,
14 size_t nmatch, regmatch_t pmatch[restrict], int eflags);
15 size_t regerror(int errcode, const regex_t *restrict preg,
17 char *restrict errbuf, size_t errbuf_size);
18 void regfree(regex_t *preg);
19
21 POSIX regex compiling
22 regcomp() is used to compile a regular expression into a form that is
23 suitable for subsequent regexec() searches.
24 regcomp() is supplied with preg, a pointer to a pattern buffer storage
26 area; regex, a pointer to the null-terminated string and cflags, flags
27 used to determine the type of compilation.
28 All regular expression searching must be done via a compiled pattern
30 buffer, thus regexec() must always be supplied with the address of a
31 regcomp() initialized pattern buffer.
32 cflags is the bitwise-or of zero or more of the following:
34 REG_EXTENDED
36 Use POSIX Extended Regular Expression syntax when interpreting
37 regex. If not set, POSIX Basic Regular Expression syntax is
38 used.
39 REG_ICASE
41 Do not differentiate case. Subsequent regexec() searches using
42 this pattern buffer will be case insensitive.
43 REG_NOSUB
45 Do not report position of matches. The nmatch and pmatch argu‐
46 ments to regexec() are ignored if the pattern buffer supplied
47 was compiled with this flag set.
48 REG_NEWLINE
50 Match-any-character operators don't match a newline.
51 A nonmatching list ([^...]) not containing a newline does not
53 match a newline.
54 Match-beginning-of-line operator (^) matches the empty string
56 immediately after a newline, regardless of whether eflags, the
57 execution flags of regexec(), contains REG_NOTBOL.
58 Match-end-of-line operator ($) matches the empty string immedi‐
60 ately before a newline, regardless of whether eflags contains
61 REG_NOTEOL.
62 POSIX regex matching
64 regexec() is used to match a null-terminated string against the precom‐
65 piled pattern buffer, preg. nmatch and pmatch are used to provide in‐
66 formation regarding the location of any matches. eflags is the bit‐
67 wise-or of zero or more of the following flags:
68 REG_NOTBOL
70 The match-beginning-of-line operator always fails to match (but
71 see the compilation flag REG_NEWLINE above). This flag may be
72 used when different portions of a string are passed to regexec()
73 and the beginning of the string should not be interpreted as the
74 beginning of the line.
75 REG_NOTEOL
77 The match-end-of-line operator always fails to match (but see
78 the compilation flag REG_NEWLINE above).
79 REG_STARTEND
81 Use pmatch[0] on the input string, starting at byte
82 pmatch[0].rm_so and ending before byte pmatch[0].rm_eo. This
83 allows matching embedded NUL bytes and avoids a strlen(3) on
84 large strings. It does not use nmatch on input, and does not
85 change REG_NOTBOL or REG_NEWLINE processing. This flag is a BSD
86 extension, not present in POSIX.
87 Byte offsets
89 Unless REG_NOSUB was set for the compilation of the pattern buffer, it
90 is possible to obtain match addressing information. pmatch must be di‐
91 mensioned to have at least nmatch elements. These are filled in by
92 regexec() with substring match addresses. The offsets of the subex‐
93 pression starting at the ith open parenthesis are stored in pmatch[i].
94 The entire regular expression's match addresses are stored in
95 pmatch[0]. (Note that to return the offsets of N subexpression
96 matches, nmatch must be at least N+1.) Any unused structure elements
97 will contain the value -1.
98 The regmatch_t structure which is the type of pmatch is defined in
100 <regex.h>.
101 typedef struct {
103 regoff_t rm_so;
104 regoff_t rm_eo;
105 } regmatch_t;
106 Each rm_so element that is not -1 indicates the start offset of the
108 next largest substring match within the string. The relative rm_eo el‐
109 ement indicates the end offset of the match, which is the offset of the
110 first character after the matching text.
111 POSIX error reporting
113 regerror() is used to turn the error codes that can be returned by both
114 regcomp() and regexec() into error message strings.
115 regerror() is passed the error code, errcode, the pattern buffer, preg,
117 a pointer to a character string buffer, errbuf, and the size of the
118 string buffer, errbuf_size. It returns the size of the errbuf required
119 to contain the null-terminated error message string. If both errbuf
120 and errbuf_size are nonzero, errbuf is filled in with the first er‐
121 rbuf_size - 1 characters of the error message and a terminating null
122 byte ('\0').
123 POSIX pattern buffer freeing
125 Supplying regfree() with a precompiled pattern buffer, preg will free
126 the memory allocated to the pattern buffer by the compiling process,
127 regcomp().
128
130 regcomp() returns zero for a successful compilation or an error code
131 for failure.
132 regexec() returns zero for a successful match or REG_NOMATCH for fail‐
134 ure.
135
137 The following errors can be returned by regcomp():
138 REG_BADBR
140 Invalid use of back reference operator.
141 REG_BADPAT
143 Invalid use of pattern operators such as group or list.
144 REG_BADRPT
146 Invalid use of repetition operators such as using '*' as the
147 first character.
148 REG_EBRACE
150 Un-matched brace interval operators.
151 REG_EBRACK
153 Un-matched bracket list operators.
154 REG_ECOLLATE
156 Invalid collating element.
157 REG_ECTYPE
159 Unknown character class name.
160 REG_EEND
162 Nonspecific error. This is not defined by POSIX.2.
163 REG_EESCAPE
165 Trailing backslash.
166 REG_EPAREN
168 Un-matched parenthesis group operators.
169 REG_ERANGE
171 Invalid use of the range operator; for example, the ending point
172 of the range occurs prior to the starting point.
173 REG_ESIZE
175 Compiled regular expression requires a pattern buffer larger
176 than 64 kB. This is not defined by POSIX.2.
177 REG_ESPACE
179 The regex routines ran out of memory.
180 REG_ESUBREG
182 Invalid back reference to a subexpression.
183
185 For an explanation of the terms used in this section, see at‐
186 tributes(7).
187 ┌─────────────────────────────────────┬───────────────┬────────────────┐
189 │Interface │ Attribute │ Value │
190 ├─────────────────────────────────────┼───────────────┼────────────────┤
191 │regcomp(), regexec() │ Thread safety │ MT-Safe locale │
192 ├─────────────────────────────────────┼───────────────┼────────────────┤
193 │regerror() │ Thread safety │ MT-Safe env │
194 ├─────────────────────────────────────┼───────────────┼────────────────┤
195 │regfree() │ Thread safety │ MT-Safe │
196 └─────────────────────────────────────┴───────────────┴────────────────┘
197
199 POSIX.1-2001, POSIX.1-2008.
200
202 #include <stdint.h>
203 #include <stdio.h>
204 #include <stdlib.h>
205 #include <regex.h>
206 #define ARRAY_SIZE(arr) (sizeof((arr)) / sizeof((arr)[0]))
208 static const char *const str =
210 "1) John Driverhacker;\n2) John Doe;\n3) John Foo;\n";
211 static const char *const re = "John.*o";
212 int main(void)
214 {
215 static const char *s = str;
216 regex_t regex;
217 regmatch_t pmatch[1];
218 regoff_t off, len;
219 if (regcomp(®ex, re, REG_NEWLINE))
221 exit(EXIT_FAILURE);
222 printf("String = \"%s\"\n", str);
224 printf("Matches:\n");
225 for (int i = 0; ; i++) {
227 if (regexec(®ex, s, ARRAY_SIZE(pmatch), pmatch, 0))
228 break;
229 off = pmatch[0].rm_so + (s - str);
231 len = pmatch[0].rm_eo - pmatch[0].rm_so;
232 printf("#%d:\n", i);
233 printf("offset = %jd; length = %jd\n", (intmax_t) off,
234 (intmax_t) len);
235 printf("substring = \"%.*s\"\n", len, s + pmatch[0].rm_so);
236 s += pmatch[0].rm_eo;
238 }
239 exit(EXIT_SUCCESS);
241 }
242
244 grep(1), regex(7)
245 The glibc manual section, Regular Expressions
247
249 This page is part of release 5.12 of the Linux man-pages project. A
250 description of the project, information about reporting bugs, and the
251 latest version of this page, can be found at
252 https://www.kernel.org/doc/man-pages/.
253GNU 2021-03-22 REGEX(3)