REGEX(3)						     Linux Programmer's Manual							  REGEX(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);

DESCRIPTION

   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 arguments to regexec() are ignored if the pat-
	      tern buffer supplied was compiled with this flag set.

       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  execu-
	      tion 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 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 begin-
	      ning of the line.

       REG_NOTEOL
	      The match-end-of-line operator always fails to match (but see the compilation 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, which is the offset of the first character after the matching text.

   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 nonzero, 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_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.

CONFORMING TO

       POSIX.1-2001.

SEE ALSO

       grep(1), regex(7)

COLOPHON

       This  page is part of release 3.27 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)