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REGCOMP(3) Linux Programmer’s Manual REGCOMP(3)
NAME
regcomp, regexec, regerror, regfree - POSIX regex functions
SYNOPSIS
#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);
POSIX REGEX COMPILING
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 parameters 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 new-
line.
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.
POSIX REGEX MATCHING
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 behaviour described below.
REG_NOTBOL
The match-beginning-of-line operator always fails to match (but see the com-
pilation 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 compila-
tion flag REG_NEWLINE above)
BYTE OFFSETS
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.
POSIX ERROR REPORTING
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.
POSIX PATTERN BUFFER FREEING
Supplying regfree with a precompiled pattern buffer, preg will free the memory
allocated to the pattern buffer by the compiling process, regcomp.
RETURN VALUE
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.
ERRORS
The following errors can be returned by regcomp:
REG_BADRPT
Invalid use of repetition operators such as using ‘*’ as the first charac-
ter.
REG_BADBR
Invalid use of back reference operator.
REG_EBRACE
Un-matched brace interval operators.
REG_EBRACK
Un-matched bracket list operators.
REG_ERANGE
Invalid use of the range operator, eg. the ending point of the range occurs
prior to the starting point.
REG_ECTYPE
Unknown character class name.
REG_ECOLLATE
Invalid collating element.
REG_EPAREN
Un-matched parenthesis group operators.
REG_ESUBREG
Invalid back reference to a subexpression.
REG_EEND
Non specific error. This is not defined by POSIX.2.
REG_EESCAPE
Trailing backslash.
REG_BADPAT
Invalid use of pattern operators such as group or list.
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.
CONFORMING TO
POSIX.2
SEE ALSO
regex(7), GNU regex manual
GNU 1998-05-08 REGCOMP(3)
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Under GNU General Public License
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