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Updated: Thursday, June 13, 2019
 
 

pcre2posix (3)

Name

pcre2posix - compatible regular expressions (revised API)

Synopsis

#include <pcre2posix.h>

int regcomp(regex_t *preg, const char *pattern,
int cflags);

int regexec(const 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

PCRE2POSIX(3)              Library Functions Manual              PCRE2POSIX(3)



NAME
       PCRE2 - Perl-compatible regular expressions (revised API)

SYNOPSIS

       #include <pcre2posix.h>

       int regcomp(regex_t *preg, const char *pattern,
            int cflags);

       int regexec(const 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 PCRE2 regular
       expression 8-bit library. See the pcre2api documentation for a descrip-
       tion  of PCRE2's native API, which contains much additional functional-
       ity. There are no POSIX-style wrappers for PCRE2's  16-bit  and  32-bit
       libraries.

       The functions described here are just wrapper functions that ultimately
       call the  PCRE2  native  API.  Their  prototypes  are  defined  in  the
       pcre2posix.h  header  file,  and  on Unix systems the library itself is
       called libpcre2-posix.a, so can be accessed by adding -lpcre2-posix  to
       the  command  for  linking  an  application that uses them. Because the
       POSIX functions call the native ones,  it  is  also  necessary  to  add
       -lpcre2-8.

       Those  POSIX  option bits that can reasonably be mapped to PCRE2 native
       options have been implemented. 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 PCRE2 as a replacement library. Other POSIX options
       are not even defined.

       There are also some options that are not defined by POSIX.  These  have
       been  added  at  the  request  of users who want to make use of certain
       PCRE2-specific features via the POSIX calling interface or to  add  BSD
       or GNU functionality.

       When  PCRE2  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 PCRE2 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-unit encoding  domains  it  is  probably
       even less compatible.

       The header for these functions is supplied as pcre2posix.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. By default, the pattern is a C string terminated by a binary zero
       (but  see  REG_PEND below). The preg argument is a pointer to a regex_t
       structure that is used as a base for storing information about the com-
       piled  regular  expression. (It is also used for input when REG_PEND is
       set.)

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

         REG_DOTALL

       The  PCRE2_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  PCRE2_CASELESS option is set when the regular expression is passed
       for compilation to the native function.

         REG_NEWLINE

       The PCRE2_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_NOSPEC

       The  PCRE2_LITERAL  option is set when the regular expression is passed
       for compilation to the native function. This disables all meta  charac-
       ters  in the pattern, causing it to be treated as a literal string. The
       only other options that are  allowed  with  REG_NOSPEC  are  REG_ICASE,
       REG_NOSUB,  REG_PEND,  and REG_UTF. Note that REG_NOSPEC is not part of
       the POSIX standard.

         REG_NOSUB

       When a pattern that is compiled with this flag is passed  to  regexec()
       for  matching, the nmatch and pmatch arguments are ignored, and no cap-
       tured strings are returned. Versions of the PCRE library prior to 10.22
       used  to  set  the  PCRE2_NO_AUTO_CAPTURE  compile  option, but this no
       longer happens because it disables the use of backreferences.

         REG_PEND

       If this option is set, the reg_endp field in the preg structure  (which
       has the type const char *) must be set to point to the character beyond
       the end of the pattern before calling regcomp(). The pattern itself may
       now contain binary zeros, which are treated as data characters. Without
       REG_PEND, a binary zero terminates the pattern and the re_endp field is
       ignored.  This  is  a GNU extension to the POSIX standard and should be
       used with caution in software intended to be portable to other systems.

         REG_UCP

       The PCRE2_UCP option is set when the regular expression is  passed  for
       compilation  to  the  native function. This causes PCRE2 to use Unicode
       properties when matchine \d, \w,  etc.,  instead  of  just  recognizing
       ASCII values. Note that REG_UCP is not part of the POSIX standard.

         REG_UNGREEDY

       The  PCRE2_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_UTF

       The  PCRE2_UTF  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_UTF 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 PCRE2 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
       PCRE2_MULTILINE has only some of the effects specified for REG_NEWLINE.
       It  does not affect the way newlines are matched by the dot metacharac-
       ter (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 other member of the
       structure (as well as re_endp) 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 PCRE2 to obey POSIX semantics, but
       then PCRE2 was never intended to be a POSIX engine. The following table
       lists  the  different  possibilities for matching newline characters in
       Perl and PCRE2:

                                 Default   Change with

         . matches newline          no     PCRE2_DOTALL
         newline matches [^a]       yes    not changeable
         $ matches \n at end        yes    PCRE2_DOLLAR_ENDONLY
         $ matches \n in middle     no     PCRE2_MULTILINE
         ^ matches \n in middle     no     PCRE2_MULTILINE

       This is the equivalent table for a POSIX-compatible pattern matcher:

                                 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

       This behaviour is not what happens when PCRE2 is called via  its  POSIX
       API.  By  default, PCRE2's behaviour is the same as Perl's, except that
       there is no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both  PCRE2
       and Perl, there is no way to stop newline from matching [^a].

       Default  POSIX newline handling can be obtained by setting PCRE2_DOTALL
       and PCRE2_DOLLAR_ENDONLY when  calling  pcre2_compile()  directly,  but
       there  is  no  way  to make PCRE2 behave exactly as for the REG_NEWLINE
       action. When using the POSIX API, passing REG_NEWLINE to  PCRE2's  reg-
       comp() function causes PCRE2_MULTILINE to be passed to pcre2_compile(),
       and REG_DOTALL passes PCRE2_DOTALL. There is no way to pass  PCRE2_DOL-
       LAR_ENDONLY.

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 PCRE2_NOTBOL option is set when calling the underlying PCRE2 match-
       ing function.

         REG_NOTEMPTY

       The  PCRE2_NOTEMPTY  option  is  set  when calling the underlying PCRE2
       matching function. Note that REG_NOTEMPTY is  not  part  of  the  POSIX
       standard.  However, setting this option can give more POSIX-like behav-
       iour in some situations.

         REG_NOTEOL

       The PCRE2_NOTEOL option is set when calling the underlying PCRE2 match-
       ing function.

         REG_STARTEND

       When  this  option  is  set,  the  subject  string  starts  at string +
       pmatch[0].rm_so and ends at  string  +  pmatch[0].rm_eo,  which  should
       point  to  the  first  character beyond the string. There may be binary
       zeros within the subject string, and indeed, using REG_STARTEND is  the
       only way to pass a subject string that contains a binary zero.

       Whatever  the  value  of  pmatch[0].rm_so,  the  offsets of the matched
       string and any captured substrings are  still  given  relative  to  the
       start  of  string  itself. (Before PCRE2 release 10.30 these were given
       relative to string +  pmatch[0].rm_so,  but  this  differs  from  other
       implementations.)

       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  and
       length  of  the string, not how it is matched. Setting REG_STARTEND and
       passing pmatch as NULL are mutually exclusive; the error REG_INVARG  is
       returned.

       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 (except possibly as input for REG_STARTEND).

       The  value  of  nmatch  may  be  zero, and the value pmatch may be NULL
       (unless REG_STARTEND is set); in both these cases  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 byte  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. If the buffer is too short,  only
       the first errbuf_size - 1 characters of the error message are used. The
       yield of the function is the size of buffer needed to  hold  the  whole
       message,  including  the  terminating  zero. This value is greater than
       errbuf_size if the message was truncated.

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, England.

REVISION

       Last updated: 15 June 2017
       Copyright (c) 1997-2017 University of Cambridge.



ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------+
       |ATTRIBUTE TYPE | ATTRIBUTE VALUE  |
       +---------------+------------------+
       |Availability   | library/pcre2    |
       +---------------+------------------+
       |Stability      | Uncommitted      |
       +---------------+------------------+
NOTES
       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source  was  downloaded from  ftp://ftp.csx.cam.ac.uk/pub/software/pro-
       gramming/pcre/pcre2-10.32.tar.gz

       Further information about this software can be found on the open source
       community website at http://pcre.org/.



PCRE2 10.30                      15 June 2017                    PCRE2POSIX(3)