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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 pat-
       tern 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 new-
              line.

              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 com-
              pilation flag REG_NEWLINE above) This flag may be used when  different  por-
              tions  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  compila-
              tion 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-termi-
       nated 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 ter-
       minating 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  charac-
              ter.

       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 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-
       nel.org/doc/man-pages/.



GNU                               2008-05-29                          REGEX(3)

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