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PCRE(3)


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 deselected, by
  providing options to the configure script which 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 describe certain 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 complementary option always exists
  as well, but as it specifies the default, it is not described.


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.


CODE VALUE OF NEWLINE

  By default, PCRE treats character 10 (linefeed) as the newline character.
  This is the normal newline character on Unix-like systems. You can compile
  PCRE to use character 13 (carriage return) instead by adding

    --enable-newline-is-cr

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


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
  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 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.


LIMITING PCRE RESOURCE USAGE

  Internally, PCRE has a function called match() which it calls repeatedly
  (possibly recursively) when performing a matching operation. By limiting
  the number of times this function may be called, 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 documentation. The default
  is 10 million, but this can be changed by adding a setting such as

    --with-match-limit=500000

  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 alternation
  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.

  If you build PCRE with an increased link size, test 2 (and test 5 if you
  are using UTF-8) will fail. Part of the output of these tests is a
  representation of the compiled pattern, and this changes with the link
  size.


AVOIDING EXCESSIVE STACK USAGE

  PCRE implements backtracking while matching by making recursive calls to an
  internal function called match(). In environments where the size of the
  stack is limited, this can severely limit PCRE's operation. (The Unix
  environment does not usually suffer from this problem.) An alternative
  approach that uses memory from the heap to remember data, instead of using
  recursive function calls, has been implemented to work round this problem.
  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 management
  functions. Separate functions are provided 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 the standard
  malloc() and free() functions. PCRE runs noticeably more slowly when built
  in this way.


USING EBCDIC CODE

  PCRE assumes by default that it will run in an environment where the
  character code is ASCII (or UTF-8, 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.


Last updated: 09 December 2003

Copyright (c) 1997-2003 University of Cambridge.

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