NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | SEE ALSO | COLOPHON
REGEX(3) Linux Programmer's Manual REGEX(3)
regcomp, regexec, regerror, regfree - POSIX regex functions
#include <sys/types.h>
#include <regex.h>
int regcomp(regex_t *preg, const char *regex, int cflags);
int regexec(const regex_t *preg, const char *string, size_t nmatch,
regmatch_t pmatch[], int eflags);
size_t regerror(int errcode, const regex_t *preg, char *errbuf,
size_t errbuf_size);
void regfree(regex_t *preg);
regcomp() is used to compile a regular expression into a form that is suitable
for subsequent regexec() searches.
regcomp() is supplied with preg, a pointer to a pattern buffer storage area;
regex, a pointer to the null-terminated string and cflags, flags used to
determine the type of compilation.
All regular expression searching must be done via a compiled pattern buffer,
thus regexec() must always be supplied with the address of a regcomp()
initialized pattern buffer.
cflags may be the bitwise-or of one 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
Support for substring addressing of matches is not required. The
nmatch and pmatch arguments to regexec() are ignored if the pattern
buffer supplied was compiled with this flag set.
REG_NEWLINE
Match-any-character operators don't match a newline.
A non-matching 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.
regexec() is used to match a null-terminated string against the precompiled
pattern buffer, preg. nmatch and pmatch are used to provide information
regarding the location of any matches. eflags may be the bitwise-or of one or
both of REG_NOTBOL and REG_NOTEOL which cause changes in matching behavior
described below.
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)
Unless REG_NOSUB was set for the compilation of the pattern buffer, it is
possible to obtain substring match addressing information. pmatch must be
dimensioned to have at least nmatch elements. These are filled in by
regexec() with substring match addresses. Any unused structure elements will
contain the value -1.
The regmatch_t structure which is the type of pmatch is defined in <regex.h>.
typedef struct {
regoff_t rm_so;
regoff_t rm_eo;
} regmatch_t;
Each rm_so element that is not -1 indicates the start offset of the next
largest substring match within the string. The relative rm_eo element
indicates the end offset of the match, which is the offset of the first
character after the matching text.
regerror() is used to turn the error codes that can be returned by both
regcomp() and regexec() into error message strings.
regerror() is passed the error code, errcode, the pattern buffer, preg, a
pointer to a character string buffer, errbuf, and the size of the string
buffer, errbuf_size. It returns the size of the errbuf required to contain
the null-terminated error message string. If both errbuf and errbuf_size are
non-zero, errbuf is filled in with the first errbuf_size - 1 characters of the
error message and a terminating null.
Supplying regfree() with a precompiled pattern buffer, preg will free the
memory allocated to the pattern buffer by the compiling process, regcomp().
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.
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
Non specific error. This is not defined by POSIX.2.
REG_EESCAPE
Trailing backslash.
REG_EPAREN
Un-matched parenthesis group operators.
REG_ERANGE
Invalid use of the range operator, e.g., the ending point of the range
occurs prior to the starting point.
REG_ESIZE
Compiled regular expression requires a pattern buffer larger than 64Kb.
This is not defined by POSIX.2.
REG_ESPACE
The regex routines ran out of memory.
REG_ESUBREG
Invalid back reference to a subexpression.
POSIX.1-2001.
grep(1), regex(7), GNU regex manual
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
GNU 2008-05-29 REGEX(3)