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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);

   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 zero or more of the following:

	      Use POSIX Extended Regular Expression syntax  when  interpreting
	      regex.   If  not	set,  POSIX Basic Regular Expression syntax is

	      Do not differentiate case.  Subsequent regexec() searches	 using
	      this pattern buffer will be case insensitive.

	      Do  not report position of matches.  The nmatch and pmatch argu-
	      ments to regexec() are ignored if the  pattern  buffer  supplied
	      was compiled with this flag set.

	      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  immedi-
	      ately  before  a	newline, regardless of whether eflags contains

   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.

	      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.

	      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	subex-
       pression	 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  structure  elements
       will contain the value -1.

       The  regmatch_t	structure  which  is  the type of pmatch is defined in

	   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() returns zero for a successful compilation or  an  error  code
       for failure.

       regexec()  returns zero for a successful match or REG_NOMATCH for fail-

       The following errors can be returned by regcomp():

	      Invalid use of back reference operator.

	      Invalid use of pattern operators such as group or list.

	      Invalid use of repetition operators such as  using  '*'  as  the
	      first character.

	      Un-matched brace interval operators.

	      Un-matched bracket list operators.

	      Invalid collating element.

	      Unknown character class name.

	      Nonspecific error.  This is not defined by POSIX.2.

	      Trailing backslash.

	      Un-matched parenthesis group operators.

	      Invalid use of the range operator; for example, the ending point
	      of the range occurs prior to the starting point.

	      Compiled regular expression requires  a  pattern	buffer	larger
	      than 64Kb.  This is not defined by POSIX.2.

	      The regex routines ran out of memory.

	      Invalid back reference to a subexpression.

       For   an	  explanation	of   the  terms	 used  in  this	 section,  see

       |Interface	     | Attribute     | Value	      |
       |regcomp(), regexec() | Thread safety | MT-Safe locale |
       |regerror()	     | Thread safety | MT-Safe env    |
       |regfree()	     | Thread safety | MT-Safe	      |
       POSIX.1-2001, POSIX.1-2008.

       grep(1), regex(7)
       The glibc manual section, Regular Expressions

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GNU				  2015-08-08			      REGEX(3)