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 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 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.

   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, eg. 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




GNU                               1998-05-08                          REGEX(3)
