This  document  describes  the  optional  features  of PCRE that can be
       selected when the library is compiled. It assumes use of the  configure
       script,  where the optional features are selected or deselected by pro-
       viding options to configure before running the make  command.  However,
       the  same  options  can be selected in both Unix-like and non-Unix-like
       environments using the GUI facility of cmake-gui if you are using CMake
       instead of configure to build PCRE.

       There  is  a  lot more information about building PCRE in non-Unix-like
       environments in the file called NON_UNIX_USE, which is part of the PCRE
       distribution.  You  should consult this file as well as the README file
       if you are building in a non-Unix-like environment.

       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.


       By  default,  a  library  called libpcre is built, containing functions
       that take string arguments contained in vectors  of  bytes,  either  as
       single-byte  characters,  or interpreted as UTF-8 strings. You can also
       build a separate library, called libpcre16, in which strings  are  con-
       tained  in  vectors of 16-bit data units and interpreted either as sin-
       gle-unit characters or UTF-16 strings, by adding


       to the configure command. If you do not want the 8-bit library, add


       as well. At least one of the two libraries must be built. Note that the
       C++  and  POSIX wrappers are for the 8-bit library only, and that pcre-
       grep is an 8-bit program. None of these are built if  you  select  only
       the 16-bit library.


       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


       to the configure command.


       To build PCRE with support for UTF Unicode character strings, add


       to the configure command.  This  setting  applies  to  both  libraries,
       adding support for UTF-8 to the 8-bit library and support for UTF-16 to
       the 16-bit library. There are no separate options  for  enabling  UTF-8
       and  UTF-16  independently because that would allow ridiculous settings
       such as  requesting  UTF-16  support  while  building  only  the  8-bit
       library.  It  is not possible to build one library with UTF support and
       the other without in the same configuration. (For backwards compatibil-
       ity, --enable-utf8 is a synonym of --enable-utf.)

       Of  itself,  this  setting does not make PCRE treat strings as UTF-8 or
       UTF-16. As well as compiling PCRE with this option, you also have  have
       to set the PCRE_UTF8 or PCRE_UTF16 option when you call one of the pat-
       tern compiling functions.

       If you set --enable-utf when compiling in an EBCDIC  environment,  PCRE
       expects  its  input  to be either ASCII or UTF-8 (depending on the run-
       time option). It is not possible to support both EBCDIC and UTF-8 codes
       in  the  same  version  of  the library. Consequently, --enable-utf and
       --enable-ebcdic are mutually exclusive.


       UTF support allows the libraries to process character codepoints up  to
       0x10ffff  in the strings that they handle. On its own, however, it does
       not provide any facilities for accessing the properties of such charac-
       ters. If you want to be able to use the pattern escapes \P, \p, and \X,
       which refer to Unicode character properties, you must add


       to the configure command. This implies UTF 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.


       Just-in-time compiler support is included in the build by specifying


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


       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


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


       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


       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.


       By  default,  the  sequence \R in a pattern matches any Unicode newline
       sequence, whatever has been selected as the line  ending  sequence.  If
       you specify


       the  default  is changed so that \R matches only CR, LF, or CRLF. What-
       ever is selected when PCRE is built can be overridden when the  library
       functions are called.


       When  the  8-bit library is called through the POSIX interface (see the
       pcreposix documentation), 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 func-
       tion uses space on the stack, because this is faster  than  using  mal-
       loc()  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


       sets by adding a setting such as


       to  the  configure command. The value given must be 2, 3, or 4. For the
       16-bit library, a value of 3 is rounded up to 4. Using  longer  offsets
       slows down the operation of PCRE because it has to load additional data
       when handling them.


       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


       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 instead.

       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 pcre_dfa_exec().


       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


       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


       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


       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  run-time  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".)


       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).
       This is the case for most computer operating systems.  PCRE  can,  how-
       ever, be compiled to run in an EBCDIC environment by adding


       to the configure command. This setting implies --enable-rebuild-charta-
       bles. You should only use it if you know that  you  are  in  an  EBCDIC
       environment  (for  example,  an  IBM  mainframe  operating system). The
       --enable-ebcdic option is incompatible with --enable-utf.


       By default, pcregrep reads all files as plain text. You can build it so
       that it recognizes files whose names end in .gz or .bz2, and reads them
       with libz or libbz2, respectively, by adding one or both of


       to the configure command. These options naturally require that the rel-
       evant  libraries  are installed on your system. Configuration will fail
       if they are not.


       pcregrep uses an internal buffer to hold a "window" on the file  it  is
       scanning, in order to be able to output "before" and "after" lines when
       it finds a match. The size of the buffer is controlled by  a  parameter
       whose default value is 20K. The buffer itself is three times this size,
       but because of the way it is used for holding "before" lines, the long-
       est  line  that  is guaranteed to be processable is the parameter size.
       You can change the default parameter value by adding, for example,

       library, and when its input is from a terminal, it reads it  using  the
       readline() function. This provides line-editing and history facilities.
       Note that libreadline is GPL-licensed, so if you distribute a binary of
       pcretest linked in this way, there may be licensing issues.

       Setting  this  option  causes  the -lreadline option to be added to the
       pcretest build. In many operating environments with  a  sytem-installed
       libreadline this is sufficient. However, in some environments (e.g.  if
       an unmodified distribution version of readline is in use),  some  extra
       configuration  may  be necessary. The INSTALL file for libreadline says

         "Readline uses the termcap functions, but does not link with the
         termcap or curses library itself, allowing applications which link
         with readline the to choose an appropriate library."

       If your environment has not been set up so that an appropriate  library
       is automatically included, you may need to add something like


       immediately before the configure command.


       pcreapi(3), pcre16, pcre_config(3).


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


       Last updated: 07 January 2012
       Copyright (c) 1997-2012 University of Cambridge.

PCRE 8.30                       07 January 2012                   PCREBUILD(3)
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