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PCREPOSIX(3)							  PCREPOSIX(3)

NAME
       PCRE - Perl-compatible regular expressions.

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 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‐
       stants whose names start	 with  "REG_";	these  are  used  for  setting
       options and identifying error codes.

COMPILING A PATTERN

       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 that is used as a base for storing information	 about
       the compiled regular expression.

       The argument cflags is either zero, or contains one or more of the bits
       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
       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.

       NOTE:  If  the  yield of regcomp() is non-zero, you must not attempt to
       use the contents of the preg structure. If, for example, you pass it to
       regexec(), the result is undefined and your program is likely to crash.

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
	 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

       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.

       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: 16 May 2010
       Copyright (c) 1997-2010 University of Cambridge.

								  PCREPOSIX(3)
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