Provided by: libpcre3-dev_8.39-12_amd64 bug

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
       contains  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
       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 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
       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 section).

         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 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
       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  equivalent  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 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
       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  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.