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 *preg, const char *regex, int cflags);
12 int regexec(const regex_t *preg, const char *string, size_t nmatch,
14 regmatch_t pmatch[], int eflags);
15 size_t regerror(int errcode, const regex_t *preg, char *errbuf,
17 size_t errbuf_size);
18 void regfree(regex_t *preg);
20
22 POSIX regex compiling
23 regcomp() is used to compile a regular expression into a form that is
24 suitable for subsequent regexec() searches.
25 regcomp() is supplied with preg, a pointer to a pattern buffer storage
27 area; regex, a pointer to the null-terminated string and cflags, flags
28 used to determine the type of compilation.
29 All regular expression searching must be done via a compiled pattern
31 buffer, thus regexec() must always be supplied with the address of a
32 regcomp() initialized pattern buffer.
33 cflags is the bitwise-or of zero or more of the following:
35 REG_EXTENDED
37 Use POSIX Extended Regular Expression syntax when interpreting
38 regex. If not set, POSIX Basic Regular Expression syntax is
39 used.
40 REG_ICASE
42 Do not differentiate case. Subsequent regexec() searches using
43 this pattern buffer will be case insensitive.
44 REG_NOSUB
46 Do not report position of matches. The nmatch and pmatch argu‐
47 ments to regexec() are ignored if the pattern buffer supplied
48 was compiled with this flag set.
49 REG_NEWLINE
51 Match-any-character operators don't match a newline.
52 A nonmatching list ([^...]) not containing a newline does not
54 match a newline.
55 Match-beginning-of-line operator (^) matches the empty string
57 immediately after a newline, regardless of whether eflags, the
58 execution flags of regexec(), contains REG_NOTBOL.
59 Match-end-of-line operator ($) matches the empty string immedi‐
61 ately before a newline, regardless of whether eflags contains
62 REG_NOTEOL.
63 POSIX regex matching
65 regexec() is used to match a null-terminated string against the precom‐
66 piled pattern buffer, preg. nmatch and pmatch are used to provide in‐
67 formation regarding the location of any matches. eflags is the bit‐
68 wise-or of zero or more of the following flags:
69 REG_NOTBOL
71 The match-beginning-of-line operator always fails to match (but
72 see the compilation flag REG_NEWLINE above). This flag may be
73 used when different portions of a string are passed to regexec()
74 and the beginning of the string should not be interpreted as the
75 beginning of the line.
76 REG_NOTEOL
78 The match-end-of-line operator always fails to match (but see
79 the compilation flag REG_NEWLINE above).
80 REG_STARTEND
82 Use pmatch[0] on the input string, starting at byte
83 pmatch[0].rm_so and ending before byte pmatch[0].rm_eo. This
84 allows matching embedded NUL bytes and avoids a strlen(3) on
85 large strings. It does not use nmatch on input, and does not
86 change REG_NOTBOL or REG_NEWLINE processing. This flag is a BSD
87 extension, not present in POSIX.
88 Byte offsets
90 Unless REG_NOSUB was set for the compilation of the pattern buffer, it
91 is possible to obtain match addressing information. pmatch must be di‐
92 mensioned to have at least nmatch elements. These are filled in by
93 regexec() with substring match addresses. The offsets of the subex‐
94 pression starting at the ith open parenthesis are stored in pmatch[i].
95 The entire regular expression's match addresses are stored in
96 pmatch[0]. (Note that to return the offsets of N subexpression
97 matches, nmatch must be at least N+1.) Any unused structure elements
98 will contain the value -1.
99 The regmatch_t structure which is the type of pmatch is defined in
101 <regex.h>.
102 typedef struct {
104 regoff_t rm_so;
105 regoff_t rm_eo;
106 } regmatch_t;
107 Each rm_so element that is not -1 indicates the start offset of the
109 next largest substring match within the string. The relative rm_eo el‐
110 ement indicates the end offset of the match, which is the offset of the
111 first character after the matching text.
112 POSIX error reporting
114 regerror() is used to turn the error codes that can be returned by both
115 regcomp() and regexec() into error message strings.
116 regerror() is passed the error code, errcode, the pattern buffer, preg,
118 a pointer to a character string buffer, errbuf, and the size of the
119 string buffer, errbuf_size. It returns the size of the errbuf required
120 to contain the null-terminated error message string. If both errbuf
121 and errbuf_size are nonzero, errbuf is filled in with the first er‐
122 rbuf_size - 1 characters of the error message and a terminating null
123 byte ('\0').
124 POSIX pattern buffer freeing
126 Supplying regfree() with a precompiled pattern buffer, preg will free
127 the memory allocated to the pattern buffer by the compiling process,
128 regcomp().
129
131 regcomp() returns zero for a successful compilation or an error code
132 for failure.
133 regexec() returns zero for a successful match or REG_NOMATCH for fail‐
135 ure.
136
138 The following errors can be returned by regcomp():
139 REG_BADBR
141 Invalid use of back reference operator.
142 REG_BADPAT
144 Invalid use of pattern operators such as group or list.
145 REG_BADRPT
147 Invalid use of repetition operators such as using '*' as the
148 first character.
149 REG_EBRACE
151 Un-matched brace interval operators.
152 REG_EBRACK
154 Un-matched bracket list operators.
155 REG_ECOLLATE
157 Invalid collating element.
158 REG_ECTYPE
160 Unknown character class name.
161 REG_EEND
163 Nonspecific error. This is not defined by POSIX.2.
164 REG_EESCAPE
166 Trailing backslash.
167 REG_EPAREN
169 Un-matched parenthesis group operators.
170 REG_ERANGE
172 Invalid use of the range operator; for example, the ending point
173 of the range occurs prior to the starting point.
174 REG_ESIZE
176 Compiled regular expression requires a pattern buffer larger
177 than 64 kB. This is not defined by POSIX.2.
178 REG_ESPACE
180 The regex routines ran out of memory.
181 REG_ESUBREG
183 Invalid back reference to a subexpression.
184
186 For an explanation of the terms used in this section, see at‐
187 tributes(7).
188 ┌─────────────────────┬───────────────┬────────────────┐
190 │Interface │ Attribute │ Value │
191 ├─────────────────────┼───────────────┼────────────────┤
192 │regcomp(), regexec() │ Thread safety │ MT-Safe locale │
193 ├─────────────────────┼───────────────┼────────────────┤
194 │regerror() │ Thread safety │ MT-Safe env │
195 ├─────────────────────┼───────────────┼────────────────┤
196 │regfree() │ Thread safety │ MT-Safe │
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 5.10 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 2020-08-13 REGEX(3)