PCREBUILD(3)                                                      PCREBUILD(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. It assumes use of the configure
       script, where the optional features are selected or deselected by
       providing 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
       complementary 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 Unicode 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()
       or pcre_compile2() functions.

       If you set --enable-utf8 when compiling in an EBCDIC environment, PCRE
       expects its input to be either ASCII or UTF-8 (depending on the runtime
       option). It is not possible to support both EBCDIC and UTF-8 codes in
       the same version of the library. Consequently, --enable-utf8 and
       --enable-ebcdic are mutually exclusive.

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
       provide 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 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
       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.

WHAT \R MATCHES

       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

         --enable-bsr-anycrlf

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

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.

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 truyl 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
       backtracking 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, but it may sometimes be necessary to
       increase the maximum stack size.  There is a discussion in the
       pcrestack documentation.) 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
       management 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().

LIMITING PCRE RESOURCE USAGE

       Internally, PCRE has a function called match(), which it calls
       repeatedly (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
       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. 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).
       This is the case for most computer operating systems. PCRE can,
       however, be compiled to run in an EBCDIC environment by adding

         --enable-ebcdic

       to the configure command. This setting implies --enable-rebuild-
       chartables. 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-utf8.

PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT

       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

         --enable-pcregrep-libz
         --enable-pcregrep-libbz2

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

PCRETEST OPTION FOR LIBREADLINE SUPPORT

       If you add

         --enable-pcretest-libreadline

       to the configure command, pcretest is linked with the libreadline
       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
       this:

         "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

         LIBS="-ncurses"

       immediately before the configure command.

SEE ALSO

       pcreapi(3), pcre_config(3).

AUTHOR

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

REVISION

       Last updated: 29 September 2009
       Copyright (c) 1997-2009 University of Cambridge.



                                                                  PCREBUILD(3)
