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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
	      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  immedi‐
	      ately  before  a	newline, regardless of whether eflags contains
	      REG_NOTEOL.

   POSIX Regex Matching
       regexec() is used to match a null-terminated string against the precom‐
       piled  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)

   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 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	 fail‐
       ure.

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), GNU regex manual

COLOPHON
       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)
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