• 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
  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 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
  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, 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 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 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 (aq*(aq 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 3.19 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/.

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