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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 subse-
       quent 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 com-
       pilation.

       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 buf-
       fer.

       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
	      Do not report position of matches.  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 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 new-
	      line, regardless of whether eflags contains REG_NOTEOL.

   POSIX regex matching
       regexec() is used to match a null-terminated string against the precompiled  pattern  buf-
       fer,  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 match addressing information.  pmatch must be dimensioned to have at  least  nmatch
       elements.   These  are filled in by regexec() with substring match addresses.  The offsets
       of the subexpression starting at the ith open parenthesis are stored  in  pmatch[i].   The
       entire regular expression's match addresses are stored in pmatch[0].  (Note that to return
       the offsets of N subexpression matches, nmatch must be at least N+1.)  Any  unused  struc-
       ture 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 byte ('\0').

   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
	      Nonspecific 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)
       The glibc manual section, Regular Expression Matching

COLOPHON
       This  page  is  part of release 3.55 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					    2013-02-11					 REGEX(3)
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