pcreposix(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | COMPILING A PATTERN | MATCHING NEWLINE CHARACTERS | MATCHING A PATTERN | ERROR MESSAGES | MEMORY USAGE | AUTHOR | REVISION | COLOPHON

PCREPOSIX(3)            Library Functions Manual            PCREPOSIX(3)

NAME         top

       PCRE - Perl-compatible regular expressions.

SYNOPSIS         top


       #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         top


       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         top


       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         top


       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         top


       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         top


       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         top


       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         top


       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.

REVISION         top


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

COLOPHON         top

       This page is part of the PCRE (Perl Compatible Regular
       Expressions) project.  Information about the project can be found
       at ⟨http://www.pcre.org/⟩.  If you have a bug report for this
       manual page, see
       ⟨http://bugs.exim.org/enter_bug.cgi?product=PCRE⟩.  This page was
       obtained from the tarball pcre-8.45.tar.gz fetched from
       ⟨ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/⟩ on
       2021-06-20.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-
       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to
       man-pages@man7.org

PCRE 8.30                    09 January 2012                PCREPOSIX(3)

Pages that refer to this page: pcreapi(3)