:: RootR ::  Hosting Order Map Login   Secure Inter-Network Operations  
 
pcreposix(3) - phpMan

Command: man perldoc info search(apropos)  


PCREPOSIX(3)                         Library Functions Manual                        PCREPOSIX(3)



NAME
       PCRE - Perl-compatible regular expressions.

SYNOPSIS

       #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 description of PCRE's native API, which  con‐
       tains much additional functionality. There is no POSIX-style wrapper for PCRE's 16-bit and
       32-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 sys‐
       tems 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 expressions 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  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.

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  informa‐
       tion 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 section).

         REG_NOSUB

       The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed for  compila‐
       tion  to  the native function. In addition, when a pattern that is compiled with this flag
       is passed to regexec() for matching, 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 num‐
       ber 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 equivalent  for  PCRE_DOL‐
       LAR_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_DOL‐
       LAR_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 matching  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 loca‐
       tion), 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 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.

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

MEMORY USAGE

       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.

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)


/man
rootr.net - man pages