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NAME

       PCRE - Perl-compatible regular expressions


PCRE BUILD-TIME OPTIONS


       This  document  describes  the  optional  features  of PCRE that can be
       selected when the library is compiled. They are all selected, or  dese-
       lected, by providing options to the configure script that is run before
       the make command. The complete list of  options  for  configure  (which
       includes  the  standard  ones such as the selection of the installation
       directory) can be obtained by running

         ./configure --help

       The following sections include  descriptions  of  options  whose  names
       begin with --enable or --disable. These settings specify changes to the
       defaults for the configure command. Because of the way  that  configure
       works,  --enable  and --disable always come in pairs, so the complemen-
       tary option always exists as well, but as it specifies the default,  it
       is not described.


C++ SUPPORT


       By default, the configure script will search for a C++ compiler and C++
       header files. If it finds them, it automatically builds the C++ wrapper
       library for PCRE. You can disable this by adding

         --disable-cpp

       to the configure command.


UTF-8 SUPPORT


       To build PCRE with support for UTF-8 character strings, add

         --enable-utf8

       to  the  configure  command.  Of  itself, this does not make PCRE treat
       strings as UTF-8. As well as compiling PCRE with this option, you  also
       have  have to set the PCRE_UTF8 option when you call the pcre_compile()
       function.


UNICODE CHARACTER PROPERTY SUPPORT


       UTF-8 support allows PCRE to process character values greater than  255
       in  the  strings that it handles. On its own, however, it does not pro-
       vide any facilities for accessing the properties of such characters. If
       you  want  to  be able to use the pattern escapes \P, \p, and \X, which
       refer to Unicode character properties, you must add

         --enable-unicode-properties

       to the configure command. This implies UTF-8 support, even if you  have
       not explicitly requested it.

       Including  Unicode  property  support  adds around 30K of tables to the
       PCRE library. Only the general category properties such as  Lu  and  Nd
       are supported. Details are given in the pcrepattern documentation.


CODE VALUE OF NEWLINE


       By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
       the end of a line. This is the normal newline  character  on  Unix-like
       systems. You can compile PCRE to use character 13 (carriage return, CR)
       instead, by adding

         --enable-newline-is-cr

       to the  configure  command.  There  is  also  a  --enable-newline-is-lf
       option, which explicitly specifies linefeed as the newline character.

       Alternatively, you can specify that line endings are to be indicated by
       the two character sequence CRLF. If you want this, add

         --enable-newline-is-crlf

       to the configure command. There is a fourth option, specified by

         --enable-newline-is-anycrlf

       which causes PCRE to recognize any of the three sequences  CR,  LF,  or
       CRLF as indicating a line ending. Finally, a fifth option, specified by

         --enable-newline-is-any

       causes PCRE to recognize any Unicode newline sequence.

       Whatever line ending convention is selected when PCRE is built  can  be
       overridden  when  the library functions are called. At build time it is
       conventional to use the standard for your operating system.


BUILDING SHARED AND STATIC LIBRARIES


       The PCRE building process uses libtool to build both shared and  static
       Unix  libraries by default. You can suppress one of these by adding one
       of

         --disable-shared
         --disable-static

       to the configure command, as required.


POSIX MALLOC USAGE


       When PCRE is called through the POSIX interface (see the pcreposix doc-
       umentation),  additional  working  storage  is required for holding the
       pointers to capturing substrings, because PCRE requires three  integers
       per  substring,  whereas  the POSIX interface provides only two. If the
       number of expected substrings is small, the wrapper function uses space
       on the stack, because this is faster than using malloc() for each call.
       The default threshold above which the stack is no longer used is 10; it
       can be changed by adding a setting such as

         --with-posix-malloc-threshold=20

       to the configure command.


HANDLING VERY LARGE PATTERNS


       Within  a  compiled  pattern,  offset values are used to point from one
       part to another (for example, from an opening parenthesis to an  alter-
       nation  metacharacter).  By default, two-byte values are used for these
       offsets, leading to a maximum size for a  compiled  pattern  of  around
       64K.  This  is sufficient to handle all but the most gigantic patterns.
       Nevertheless, some people do want to process enormous patterns,  so  it
       is  possible  to compile PCRE to use three-byte or four-byte offsets by
       adding a setting such as

         --with-link-size=3

       to the configure command. The value given must be 2,  3,  or  4.  Using
       longer  offsets slows down the operation of PCRE because it has to load
       additional bytes when handling them.


AVOIDING EXCESSIVE STACK USAGE


       When matching with the pcre_exec() function, PCRE implements backtrack-
       ing  by  making recursive calls to an internal function called match().
       In environments where the size of the stack is limited,  this  can  se-
       verely  limit  PCRE's operation. (The Unix environment does not usually
       suffer from this problem, but it may sometimes be necessary to increase
       the  maximum  stack size.  There is a discussion in the pcrestack docu-
       mentation.) An alternative approach to recursion that uses memory  from
       the  heap  to remember data, instead of using recursive function calls,
       has been implemented to work round the problem of limited  stack  size.
       If you want to build a version of PCRE that works this way, add

         --disable-stack-for-recursion

       to  the  configure  command. With this configuration, PCRE will use the
       pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
       ment  functions. By default these point to malloc() and free(), but you
       can replace the pointers so that your own functions are used.

       Separate functions are  provided  rather  than  using  pcre_malloc  and
       pcre_free  because  the  usage  is  very  predictable:  the block sizes
       requested are always the same, and  the  blocks  are  always  freed  in
       reverse  order.  A calling program might be able to implement optimized
       functions that perform better  than  malloc()  and  free().  PCRE  runs
       noticeably more slowly when built in this way. This option affects only
       the  pcre_exec()  function;  it   is   not   relevant   for   the   the
       pcre_dfa_exec() function.


LIMITING PCRE RESOURCE USAGE


       Internally,  PCRE has a function called match(), which it calls repeat-
       edly  (sometimes  recursively)  when  matching  a  pattern   with   the
       pcre_exec()  function.  By controlling the maximum number of times this
       function may be called during a single matching operation, a limit  can
       be  placed  on  the resources used by a single call to pcre_exec(). The
       limit can be changed at run time, as described in the pcreapi  documen-
       tation.  The default is 10 million, but this can be changed by adding a
       setting such as

         --with-match-limit=500000

       to  the  configure  command.  This  setting  has  no  effect   on   the
       pcre_dfa_exec() matching function.

       In  some  environments  it is desirable to limit the depth of recursive
       calls of match() more strictly than the total number of calls, in order
       to  restrict  the maximum amount of stack (or heap, if --disable-stack-
       for-recursion is specified) that is used. A second limit controls this;
       it  defaults  to  the  value  that is set for --with-match-limit, which
       imposes no additional constraints. However, you can set a  lower  limit
       by adding, for example,

         --with-match-limit-recursion=10000

       to  the  configure  command.  This  value can also be overridden at run
       time.


CREATING CHARACTER TABLES AT BUILD TIME


       PCRE uses fixed tables for processing characters whose code values  are
       less  than 256. By default, PCRE is built with a set of tables that are
       distributed in the file pcre_chartables.c.dist. These  tables  are  for
       ASCII codes only. If you add

         --enable-rebuild-chartables

       to  the  configure  command, the distributed tables are no longer used.
       Instead, a program called dftables is compiled and  run.  This  outputs
       the source for new set of tables, created in the default locale of your
       C runtime system. (This method of replacing the tables does not work if
       you  are cross compiling, because dftables is run on the local host. If
       you need to create alternative tables when cross  compiling,  you  will
       have to do so "by hand".)


USING EBCDIC CODE


       PCRE  assumes  by  default that it will run in an environment where the
       character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
       PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
       adding

         --enable-ebcdic

       to the configure command. This setting implies --enable-rebuild-charta-
       bles.


SEE ALSO


       pcreapi(3), pcre_config(3).


AUTHOR


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


REVISION


       Last updated: 05 June 2007
       Copyright (c) 1997-2007 University of Cambridge.

                                                                  PCREBUILD(3)

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