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 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 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 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  sub-
       string 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 match-
       ing 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-termi-
       nated 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), GNU regex manual

COLOPHON
       This page is part of release 3.25 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)