regex(3) - Linux manual page (original) (raw)
regex(3) Library Functions Manual regex(3)
NAME top
regcomp, regexec, regerror, regfree - POSIX regex functionsLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <regex.h>**
**int regcomp(regex_t *restrict** _preg_**, const char *restrict** _regex_**,**
**int** _cflags_**);**
**int regexec(const regex_t *restrict** _preg_**, const char *restrict** _string_**,**
**size_t** _nmatch_**, regmatch_t** _pmatch_**[_Nullable restrict .**_nmatch_**],**
**int** _eflags_**);**
**size_t regerror(int** _errcode_**, const regex_t *_Nullable restrict** _preg_**,**
**char** _errbuf_**[_Nullable restrict .**_errbufsize_**],**
**size_t** _errbufsize_**);**
**void regfree(regex_t ***_preg_**);**
**typedef struct {**
**size_t re_nsub;**
**} regex_t;**
**typedef struct {**
**regoff_t rm_so;**
**regoff_t rm_eo;**
**} regmatch_t;**
**typedef** /* ... */ **regoff_t;**DESCRIPTION top
Compilation regcomp() is used to compile a regular expression into a form that is suitable for subsequent regexec() searches.
On success, the pattern buffer at _*preg_ is initialized. _regex_ is
a null-terminated string. The locale must be the same when
running **regexec**().
After **regcomp**() succeeds, _preg->rensub_ holds the number of
subexpressions in _regex_. Thus, a value of _preg->rensub_ + 1
passed as _nmatch_ to **regexec**() is sufficient to capture all
matches.
_cflags_ is the bitwise OR of zero or more of the following:
**REG_EXTENDED**
Use POSIX Extended Regular Expression syntax when
interpreting _regex_. If not set, POSIX Basic Regular
Expression syntax is used.
**REG_ICASE**
Do not differentiate case. Subsequent **regexec**() searches
using this pattern buffer will be case insensitive.
**REG_NOSUB**
Report only overall success. **regexec**() will use only
_pmatch_ for **REG_STARTEND**, ignoring _nmatch_.
**REG_NEWLINE**
Match-any-character operators don't match a newline.
A nonmatching list (**[^...]**) not containing a newline does
not match a newline.
Match-beginning-of-line operator (**^**) matches the empty
string immediately after a newline, regardless of whether
_eflags_, the execution flags of **regexec**(), contains
**REG_NOTBOL**.
Match-end-of-line operator (**$**) matches the empty string
immediately before a newline, regardless of whether _eflags_
contains **REG_NOTEOL**.Matching regexec() is used to match a null-terminated string against the compiled pattern buffer in *preg, which must have been initialised with regcomp(). eflags is the bitwise OR of zero or more of the following flags:
**REG_NOTBOL**
The match-beginning-of-line operator always fails to match
(but see the compilation flag **REG_NEWLINE** above). This
flag may be used when different portions of a string are
passed to **regexec**() and the beginning of the string should
not be interpreted as the beginning of the line.
**REG_NOTEOL**
The match-end-of-line operator always fails to match (but
see the compilation flag **REG_NEWLINE** above).
**REG_STARTEND**
Match [_string + pmatch[0].rmso_, _string + pmatch[0].rmeo_)
instead of [_string_, _string + strlen(string)_). This allows
matching embedded NUL bytes and avoids a [strlen(3)](../man3/strlen.3.html) on
known-length strings. If any matches are returned
(**REG_NOSUB** wasn't passed to **regcomp**(), the match succeeded,
and _nmatch_ > 0), they overwrite _pmatch_ as usual, and the
match offsets remain relative to _string_ (not _string +_
_pmatch[0].rmso_). This flag is a BSD extension, not
present in POSIX.Match offsets Unless REG_NOSUB was passed to regcomp(), it is possible to obtain the locations of matches within string: regexec() fills nmatch elements of pmatch with results: pmatch[0] corresponds to the entire match, pmatch[1] to the first subexpression, etc. If there were more matches than nmatch, they are discarded; if fewer, unused elements of pmatch are filled with -1s.
Each returned valid (non-**-1**) match corresponds to the range
[_string + rmso_, _string + rmeo_).
_regofft_ is a signed integer type capable of storing the largest
value that can be stored in either an _ptrdifft_ type or a _ssizet_
type.Error reporting regerror() is used to turn the error codes that can be returned by both regcomp() and regexec() into error message strings.
If _preg_ isn't a null pointer, _errcode_ must be the latest error
returned from an operation on _preg_.
If _errbufsize_ isn't 0, up to _errbufsize_ bytes are copied to
_errbuf_; the error string is always null-terminated, and truncated
to fit.Freeing regfree() deinitializes the pattern buffer at *preg, freeing any associated memory; *preg must have been initialized via regcomp().
RETURN VALUE top
**regcomp**() returns zero for a successful compilation or an error
code for failure.
**regexec**() returns zero for a successful match or **REG_NOMATCH** for
failure.
**regerror**() returns the size of the buffer required to hold the
string.ERRORS top
The following errors can be returned by **regcomp**():
**REG_BADBR**
Invalid use of back reference operator.
**REG_BADPAT**
Invalid use of pattern operators such as group or list.
**REG_BADRPT**
Invalid use of repetition operators such as using '*' as
the first character.
**REG_EBRACE**
Un-matched brace interval operators.
**REG_EBRACK**
Un-matched bracket list operators.
**REG_ECOLLATE**
Invalid collating element.
**REG_ECTYPE**
Unknown character class name.
**REG_EEND**
Nonspecific error. This is not defined by POSIX.
**REG_EESCAPE**
Trailing backslash.
**REG_EPAREN**
Un-matched parenthesis group operators.
**REG_ERANGE**
Invalid use of the range operator; for example, the ending
point of the range occurs prior to the starting point.
**REG_ESIZE**
Compiled regular expression requires a pattern buffer
larger than 64 kB. This is not defined by POSIX.
**REG_ESPACE**
The regex routines ran out of memory.
**REG_ESUBREG**
Invalid back reference to a subexpression.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌───────────────────────────────┬───────────────┬────────────────┐
│ **Interface** │ **Attribute** │ **Value** │
├───────────────────────────────┼───────────────┼────────────────┤
│ **regcomp**(), **regexec**() │ Thread safety │ MT-Safe locale │
├───────────────────────────────┼───────────────┼────────────────┤
│ **regerror**() │ Thread safety │ MT-Safe env │
├───────────────────────────────┼───────────────┼────────────────┤
│ **regfree**() │ Thread safety │ MT-Safe │
└───────────────────────────────┴───────────────┴────────────────┘STANDARDS top
POSIX.1-2008.HISTORY top
POSIX.1-2001.
Prior to POSIX.1-2008, _regofft_ was required to be capable of
storing the largest value that can be stored in either an _offt_
type or a _ssizet_ type.CAVEATS top
_rensub_ is only required to be initialized if **REG_NOSUB** wasn't
specified, but all known implementations initialize it regardless.
Both _regext_ and _regmatcht_ may (and do) have more members, in any
order. Always reference them by name.EXAMPLES top
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <regex.h>
#define ARRAY_SIZE(arr) (sizeof((arr)) / sizeof((arr)[0]))
static const char *const str =
"1) John Driverhacker;\n2) John Doe;\n3) John Foo;\n";
static const char *const re = "John.*o";
int main(void)
{
static const char *s = str;
regex_t regex;
regmatch_t pmatch[1];
regoff_t off, len;
if (regcomp(®ex, re, REG_NEWLINE))
exit(EXIT_FAILURE);
printf("String = \"%s\"\n", str);
printf("Matches:\n");
for (unsigned int i = 0; ; i++) {
if (regexec(®ex, s, ARRAY_SIZE(pmatch), pmatch, 0))
break;
off = pmatch[0].rm_so + (s - str);
len = pmatch[0].rm_eo - pmatch[0].rm_so;
printf("#%zu:\n", i);
printf("offset = %jd; length = %jd\n", (intmax_t) off,
(intmax_t) len);
printf("substring = \"%.*s\"\n", len, s + pmatch[0].rm_so);
s += pmatch[0].rm_eo;
}
exit(EXIT_SUCCESS);
}SEE ALSO top
[grep(1)](../man1/grep.1.html), [regex(7)](../man7/regex.7.html)
The glibc manual section, _Regular Expressions_COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-08-21 regex(3)
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