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README file for PCRE (Perl-compatible regular expression library)
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The latest release of PCRE is always available from

  ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre-xxx.tar.gz

Please read the NEWS file if you are upgrading from a previous release.


The PCRE APIs
-------------

PCRE is written in C, and it has its own API. The distribution now includes a
set of C++ wrapper functions, courtesy of Google Inc. (see the pcrecpp man page
for details).

Also included are a set of C wrapper functions that are based on the POSIX
API. These end up in the library called libpcreposix. Note that this just
provides a POSIX calling interface to PCRE: the regular expressions themselves
still follow Perl syntax and semantics. The header file for the POSIX-style
functions is called pcreposix.h. The official POSIX name is regex.h, but I
didn't want to risk possible problems with existing files of that name by
distributing it that way. To use it with an existing program that uses the
POSIX API, it will have to be renamed or pointed at by a link.

If you are using the POSIX interface to PCRE and there is already a POSIX regex
library installed on your system, you must take care when linking programs to
ensure that they link with PCRE's libpcreposix library. Otherwise they may pick
up the "real" POSIX functions of the same name.


Documentation for PCRE
----------------------

If you install PCRE in the normal way, you will end up with an installed set of
man pages whose names all start with "pcre". The one that is called "pcre"
lists all the others. In addition to these man pages, the PCRE documentation is
supplied in two other forms; however, as there is no standard place to install
them, they are left in the doc directory of the unpacked source distribution.
These forms are:

  1. Files called doc/pcre.txt, doc/pcregrep.txt, and doc/pcretest.txt. The
     first of these is a concatenation of the text forms of all the section 3
     man pages except those that summarize individual functions. The other two
     are the text forms of the section 1 man pages for the pcregrep and
     pcretest commands. Text forms are provided for ease of scanning with text
     editors or similar tools.

  2. A subdirectory called doc/html contains all the documentation in HTML
     form, hyperlinked in various ways, and rooted in a file called
     doc/index.html.


Contributions by users of PCRE
------------------------------

You can find contributions from PCRE users in the directory

  ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/Contrib

where there is also a README file giving brief descriptions of what they are.
Several of them provide support for compiling PCRE on various flavours of
Windows systems (I myself do not use Windows). Some are complete in themselves;
others are pointers to URLs containing relevant files.


Building PCRE on a Unix-like system
-----------------------------------

If you are using HP's ANSI C++ compiler (aCC), please see the special note
in the section entitled "Using HP's ANSI C++ compiler (aCC)" below.

To build PCRE on a Unix-like system, first run the "configure" command from the
PCRE distribution directory, with your current directory set to the directory
where you want the files to be created. This command is a standard GNU
"autoconf" configuration script, for which generic instructions are supplied in
INSTALL.

Most commonly, people build PCRE within its own distribution directory, and in
this case, on many systems, just running "./configure" is sufficient, but the
usual methods of changing standard defaults are available. For example:

CFLAGS='-O2 -Wall' ./configure --prefix=/opt/local

specifies that the C compiler should be run with the flags '-O2 -Wall' instead
of the default, and that "make install" should install PCRE under /opt/local
instead of the default /usr/local.

If you want to build in a different directory, just run "configure" with that
directory as current. For example, suppose you have unpacked the PCRE source
into /source/pcre/pcre-xxx, but you want to build it in /build/pcre/pcre-xxx:

cd /build/pcre/pcre-xxx
/source/pcre/pcre-xxx/configure

PCRE is written in C and is normally compiled as a C library. However, it is
possible to build it as a C++ library, though the provided building apparatus
does not have any features to support this.

There are some optional features that can be included or omitted from the PCRE
library. You can read more about them in the pcrebuild man page.

. If you want to suppress the building of the C++ wrapper library, you can add
  --disable-cpp to the "configure" command. Otherwise, when "configure" is run,
  will try to find a C++ compiler and C++ header files, and if it succeeds, it
  will try to build the C++ wrapper.

. If you want to make use of the support for UTF-8 character strings in PCRE,
  you must add --enable-utf8 to the "configure" command. Without it, the code
  for handling UTF-8 is not included in the library. (Even when included, it
  still has to be enabled by an option at run time.)

. If, in addition to support for UTF-8 character strings, you want to include
  support for the \P, \p, and \X sequences that recognize Unicode character
  properties, you must add --enable-unicode-properties to the "configure"
  command. This adds about 90K to the size of the library (in the form of a
  property table); only the basic two-letter properties such as Lu are
  supported.

. You can build PCRE to recognize either CR or LF as the newline character,
  instead of whatever your compiler uses for "\n", by adding --newline-is-cr or
  --newline-is-lf to the "configure" command, respectively. Only do this if you
  really understand what you are doing. On traditional Unix-like systems, the
  newline character is LF.

. When called via the POSIX interface, PCRE uses malloc() to get additional
  storage for processing capturing parentheses if there are more than 10 of
  them. You can increase this threshold by setting, for example,

  --with-posix-malloc-threshold=20

  on the "configure" command.

. PCRE has a counter that can be set to limit the amount of resources it uses.
  If the limit is exceeded during a match, the match fails. The default is ten
  million. You can change the default by setting, for example,

  --with-match-limit=500000

  on the "configure" command. This is just the default; individual calls to
  pcre_exec() can supply their own value. There is discussion on the pcreapi
  man page.

. The default maximum compiled pattern size is around 64K. You can increase
  this by adding --with-link-size=3 to the "configure" command. You can
  increase it even more by setting --with-link-size=4, but this is unlikely
  ever to be necessary. If you build PCRE with an increased link size, test 2
  (and 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.

. You can build PCRE so that its internal match() function that is called from
  pcre_exec() does not call itself recursively. Instead, it uses blocks of data
  from the heap via special functions pcre_stack_malloc() and pcre_stack_free()
  to save data that would otherwise be saved on the stack. To build PCRE like
  this, use

  --disable-stack-for-recursion

  on the "configure" command. PCRE runs more slowly in this mode, but it may be
  necessary in environments with limited stack sizes. This applies only to the
  pcre_exec() function; it does not apply to pcre_dfa_exec(), which does not
  use deeply nested recursion.

The "configure" script builds eight files for the basic C library:

. pcre.h is the header file for C programs that call PCRE
. Makefile is the makefile that builds the library
. config.h contains build-time configuration options for the library
. pcre-config is a script that shows the settings of "configure" options
. libpcre.pc is data for the pkg-config command
. libtool is a script that builds shared and/or static libraries
. RunTest is a script for running tests on the library
. RunGrepTest is a script for running tests on the pcregrep command

In addition, if a C++ compiler is found, the following are also built:

. pcrecpp.h is the header file for programs that call PCRE via the C++ wrapper
. pcre_stringpiece.h is the header for the C++ "stringpiece" functions

The "configure" script also creates config.status, which is an executable
script that can be run to recreate the configuration, and config.log, which
contains compiler output from tests that "configure" runs.

Once "configure" has run, you can run "make". It builds two libraries, called
libpcre and libpcreposix, a test program called pcretest, and the pcregrep
command. If a C++ compiler was found on your system, it also builds the C++
wrapper library, which is called libpcrecpp, and some test programs called
pcrecpp_unittest, pcre_scanner_unittest, and pcre_stringpiece_unittest.

The command "make test" runs all the appropriate tests. Details of the PCRE
tests are given in a separate section of this document, below.

You can use "make install" to copy the libraries, the public header files
pcre.h, pcreposix.h, pcrecpp.h, and pcre_stringpiece.h (the last two only if
the C++ wrapper was built), and the man pages to appropriate live directories
on your system, in the normal way.

If you want to remove PCRE from your system, you can run "make uninstall".
This removes all the files that "make install" installed. However, it does not
remove any directories, because these are often shared with other programs.


Retrieving configuration information on Unix-like systems
---------------------------------------------------------

Running "make install" also installs the command pcre-config, which can be used
to recall information about the PCRE configuration and installation. For
example:

  pcre-config --version

prints the version number, and

  pcre-config --libs

outputs information about where the library is installed. This command can be
included in makefiles for programs that use PCRE, saving the programmer from
having to remember too many details.

The pkg-config command is another system for saving and retrieving information
about installed libraries. Instead of separate commands for each library, a
single command is used. For example:

  pkg-config --cflags pcre

The data is held in *.pc files that are installed in a directory called
pkgconfig.


Shared libraries on Unix-like systems
-------------------------------------

The default distribution builds PCRE as shared libraries and static libraries,
as long as the operating system supports shared libraries. Shared library
support relies on the "libtool" script which is built as part of the
"configure" process.

The libtool script is used to compile and link both shared and static
libraries. They are placed in a subdirectory called .libs when they are newly
built. The programs pcretest and pcregrep are built to use these uninstalled
libraries (by means of wrapper scripts in the case of shared libraries). When
you use "make install" to install shared libraries, pcregrep and pcretest are
automatically re-built to use the newly installed shared libraries before being
installed themselves. However, the versions left in the source directory still
use the uninstalled libraries.

To build PCRE using static libraries only you must use --disable-shared when
configuring it. For example:

./configure --prefix=/usr/gnu --disable-shared

Then run "make" in the usual way. Similarly, you can use --disable-static to
build only shared libraries.


Cross-compiling on a Unix-like system
-------------------------------------