pcreposix

SYNOPSIS OF POSIX API

       #include <pcreposix.h>

       int regcomp(regex_t *preg, const char *pattern,
            int cflags);

       int regexec(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

       This  set  of  functions provides a POSIX-style API to the PCRE regular
       expression package. See the pcreapi documentation for a description  of
       PCRE's native API, which contains much additional functionality.

       The functions described here are just wrapper functions that ultimately
       call  the  PCRE  native  API.  Their  prototypes  are  defined  in  the
       pcreposix.h  header  file,  and  on  Unix systems the library itself is
       called pcreposix.a, so can be accessed by  adding  -lpcreposix  to  the
       command  for  linking  an application that uses them. Because the POSIX
       functions call the native ones, it is also necessary to add -lpcre.

       I have implemented only those option bits that can be reasonably mapped
       to PCRE native options. In addition, the option REG_EXTENDED is defined
       with the value zero. This has no effect, but since  programs  that  are
       written  to  the  POSIX interface often use it, this makes it easier to
       slot in PCRE as a replacement library. Other POSIX options are not even
       defined.

       When  PCRE  is  called  via these functions, it is only the API that is
       POSIX-like in style. The syntax and semantics of  the  regular  expres-
       sions  themselves  are  still  those of Perl, subject to the setting of
       various PCRE options, as described below. "POSIX-like in  style"  means
       that  the  API  approximates  to  the POSIX definition; it is not fully
       POSIX-compatible, and in multi-byte encoding  domains  it  is  probably
       even less compatible.

       The  header for these functions is supplied as pcreposix.h to avoid any
       potential clash with other POSIX  libraries.  It  can,  of  course,  be
       renamed or aliased as regex.h, which is the "correct" name. It provides
       two structure types, regex_t for  compiled  internal  forms,  and  reg-
       match_t  for  returning  captured substrings. It also defines some con-
       stants whose names start  with  "REG_";  these  are  used  for  setting
       options and identifying error codes.

COMPILING A PATTERN

       compilation to the native function. Note that REG_DOTALL is not part of
       the POSIX standard.

         REG_ICASE

       The PCRE_CASELESS option is set when the regular expression  is  passed
       for compilation to the native function.

         REG_NEWLINE

       The  PCRE_MULTILINE option is set when the regular expression is passed
       for compilation to the native function. Note that this does  not  mimic
       the  defined  POSIX  behaviour  for REG_NEWLINE (see the following sec-
       tion).

         REG_NOSUB

       The PCRE_NO_AUTO_CAPTURE option is set when the regular  expression  is
       passed for compilation to the native function. In addition, when a pat-
       tern that is compiled with this flag is passed to regexec() for  match-
       ing,  the  nmatch  and  pmatch  arguments  are ignored, and no captured
       strings are returned.

         REG_UTF8

       The PCRE_UTF8 option is set when the regular expression is  passed  for
       compilation  to the native function. This causes the pattern itself and
       all data strings used for matching it to be treated as  UTF-8  strings.
       Note that REG_UTF8 is not part of the POSIX standard.

       In  the  absence  of  these  flags, no options are passed to the native
       function.  This means the the  regex  is  compiled  with  PCRE  default
       semantics.  In particular, the way it handles newline characters in the
       subject string is the Perl way, not the POSIX way.  Note  that  setting
       PCRE_MULTILINE  has only some of the effects specified for REG_NEWLINE.
       It does not affect the way newlines are matched by . (they  aren't)  or
       by a negative class such as [^a] (they are).

       The  yield of regcomp() is zero on success, and non-zero otherwise. The
       preg structure is filled in on success, and one member of the structure
       is  public: re_nsub contains the number of capturing subpatterns in the
       regular expression. Various error codes are defined in the header file.

MATCHING NEWLINE CHARACTERS

       This area is not simple, because POSIX and Perl take different views of
       things.   It  is  not possible to get PCRE to obey POSIX semantics, but
       then PCRE was never intended to be a POSIX engine. The following  table
       lists  the  different  possibilities for matching newline characters in
       PCRE:

                                 Default   Change with

         . matches newline          no     PCRE_DOTALL
         $ matches \n in middle     no     REG_NEWLINE
         ^ matches \n in middle     no     REG_NEWLINE

       PCRE's behaviour is the same as Perl's, except that there is no equiva-
       lent  for  PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is
       no way to stop newline from matching [^a].

       The  default  POSIX  newline  handling  can  be  obtained  by   setting
       PCRE_DOTALL  and  PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE
       behave exactly as for the REG_NEWLINE action.

MATCHING A PATTERN

       The function regexec() is called  to  match  a  compiled  pattern  preg
       against  a  given string, which is by default terminated by a zero byte
       (but see REG_STARTEND below), subject to the options in  eflags.  These
       can be:

         REG_NOTBOL

       The PCRE_NOTBOL option is set when calling the underlying PCRE matching
       function.

         REG_NOTEOL

       The PCRE_NOTEOL option is set when calling the underlying PCRE matching
       function.

         REG_STARTEND

       The  string  is  considered to start at string + pmatch[0].rm_so and to
       have a terminating NUL located at string + pmatch[0].rm_eo (there  need
       not  actually  be  a  NUL at that location), regardless of the value of
       nmatch. This is a BSD extension, compatible with but not  specified  by
       IEEE  Standard  1003.2  (POSIX.2),  and  should be used with caution in
       software intended to be portable to other systems. Note that a non-zero
       rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location
       of the string, not how it is matched.

       If the pattern was compiled with the REG_NOSUB flag, no data about  any
       matched  strings  is  returned.  The  nmatch  and  pmatch  arguments of
       regexec() are ignored.

       Otherwise,the portion of the string that was matched, and also any cap-
       tured substrings, are returned via the pmatch argument, which points to
       an array of nmatch structures of type regmatch_t, containing  the  mem-
       bers  rm_so  and rm_eo. These contain the offset to the first character
       of each substring and the offset to the first character after  the  end
       of  each substring, respectively. The 0th element of the vector relates
       to the entire portion of string that was matched;  subsequent  elements
       relate  to  the capturing subpatterns of the regular expression. Unused
       entries in the array have both structure members set to -1.

       A successful match yields  a  zero  return;  various  error  codes  are

MEMORY USAGE

       Compiling  a regular expression causes memory to be allocated and asso-
       ciated with the preg structure. The function regfree() frees  all  such
       memory,  after  which  preg may no longer be used as a compiled expres-
       sion.

AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.

REVISION

       Last updated: 05 April 2008
       Copyright (c) 1997-2008 University of Cambridge.



                                                                  PCREPOSIX(3)