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 for the PCRE regular
       expression 8-bit library. See the pcreapi documentation for a  descrip-
       tion  of  PCRE's native API, which contains much additional functional-
       ity. There is no POSIX-style wrapper for PCRE's 16-bit library.

       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 POSIX 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.

       There are also some other options that are not defined by POSIX.  These
       have been added at the request of users who want to make use of certain
       PCRE-specific features via the POSIX calling interface.

       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-
       defined by the following macros:

         REG_DOTALL

       The PCRE_DOTALL option is set when the regular expression is passed for
       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_UCP

       The  PCRE_UCP  option  is set when the regular expression is passed for
       compilation to the native function. This causes  PCRE  to  use  Unicode
       properties  when  matchine  \d,  \w,  etc., instead of just recognizing
       ASCII values. Note that REG_UTF8 is not part of the POSIX standard.

         REG_UNGREEDY

       The PCRE_UNGREEDY option is set when the regular expression  is  passed
       for  compilation  to the native function. Note that REG_UNGREEDY is not
       part of the POSIX standard.

         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 are not)  or

       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
         newline matches [^a]       yes    not changeable
         $ matches \n at end        yes    PCRE_DOLLARENDONLY
         $ matches \n in middle     no     PCRE_MULTILINE
         ^ matches \n in middle     no     PCRE_MULTILINE

       This is the equivalent table for POSIX:

                                 Default   Change with

         . matches newline          yes    REG_NEWLINE
         newline matches [^a]       yes    REG_NEWLINE
         $ matches \n at end        no     REG_NEWLINE
         $ 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_NOTEMPTY

       The PCRE_NOTEMPTY option is set when calling the underlying PCRE match-
       ing function. Note that REG_NOTEMPTY is not part of the POSIX standard.
       However, setting this option can give more POSIX-like behaviour in some
       situations.

         REG_NOTEOL

       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.

       If the value of nmatch is zero, or if the value pmatch is NULL, no data
       about any matched strings is returned.

       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
       defined  in  the  header  file,  of which REG_NOMATCH is the "expected"
       failure code.

ERROR MESSAGES

       The regerror() function maps a non-zero errorcode from either regcomp()
       or  regexec()  to  a  printable message. If preg is not NULL, the error
       should have arisen from the use of that structure. A message terminated
       by  a  binary  zero  is  placed  in  errbuf. The length of the message,
       including the zero, is limited to errbuf_size. The yield of  the  func-
       tion is the size of buffer needed to hold the whole message.

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: 09 January 2012
       Copyright (c) 1997-2012 University of Cambridge.



PCRE 8.30                       09 January 2012                   PCREPOSIX(3)
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