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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()

       regcomp() is supplied with preg, a pointer to a pattern buffer storage area; regex, a pointer to the  null-ter-
       minated 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 sup-
       plied with the address of a regcomp() initialized pattern buffer.

       cflags may be the bitwise-or of one or more of the following:

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

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

              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.

              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 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.

              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  begin-
              ning 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 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 mes-
       sage 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().

       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.

       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.

              Non specific error.  This is not defined by POSIX.2.

              Trailing backslash.

              Un-matched parenthesis group operators.

              Invalid use of the range operator, e.g., the ending point of the range  occurs  prior  to  the  starting

              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.


       grep(1), regex(7), GNU regex manual

       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

GNU                               2008-05-29                          REGEX(3)