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PCRE(3) 										  PCRE(3)

       pcreposix - POSIX API for Perl-compatible regular expressions.

       #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);

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

       The  functions  described  here are just wrapper functions that ultimately call the 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 com-
       mand for linking an application which 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 options REG_EXTENDED and REG_NOSUB are defined  with  the  value
       zero.  They  have  no  effect,  but since programs that are written to the POSIX interface
       often use them, 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 expressions themselves are still  those	of  Perl,
       subject to the setting of various PCRE options, as described below.

       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 regmatch_t for returning captured substrings. It also  defines  some  constants  whose
       names start with "REG_"; these are used for setting options and identifying error codes.

       The  function  regcomp() is called to compile a pattern into an internal form. The pattern
       is a C string terminated by a binary zero, and is passed in the argument pattern. The preg
       argument  is a pointer to a regex_t structure which is used as a base for storing informa-
       tion about the compiled expression.

       The argument cflags is either zero, or contains one or more of the  bits  defined  by  the
       following macros:


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


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

       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 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 publicized: re_nsub contains the
       number of capturing subpatterns in the regular expression. Various error codes are defined
       in the header file.

       The  function  regexec()  is  called  to match a pre-compiled pattern preg against a given
       string, which is terminated by a zero byte, subject to the options in  eflags.  These  can


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


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

       The portion of the string that was matched, and also any captured substrings, are returned
       via the pmatch argument, which points to an array of nmatch structures of type regmatch_t,
       containing the members 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.

       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 function is the
       size of buffer needed to hold the whole message.

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

       Philip Hazel <ph10@cam.ac.uk>
       University Computing Service,
       New Museums Site,
       Cambridge CB2 3QG, England.
       Phone: +44 1223 334714

       Copyright (c) 1997-2000 University of Cambridge.

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