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README file for PCRE (Perl-compatible regular expression library)
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-----------------------------------------------------------------
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The latest release of PCRE is always available from
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ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre-xxx.tar.gz
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Please read the NEWS file if you are upgrading from a previous release.
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PCRE has its own native API, but a set of "wrapper" functions that are based on
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the POSIX API are also supplied in the library libpcreposix. Note that this
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just provides a POSIX calling interface to PCRE: the regular expressions
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themselves still follow Perl syntax and semantics. The header file
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for the POSIX-style functions is called pcreposix.h. The official POSIX name is
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regex.h, but I didn't want to risk possible problems with existing files of
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that name by distributing it that way. To use it with an existing program that
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uses the POSIX API, it will have to be renamed or pointed at by a link.
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If you are using the POSIX interface to PCRE and there is already a POSIX regex
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library installed on your system, you must take care when linking programs to
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ensure that they link with PCRE's libpcreposix library. Otherwise they may pick
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up the "real" POSIX functions of the same name.
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Contributions by users of PCRE
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------------------------------
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You can find contributions from PCRE users in the directory
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ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/Contrib
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where there is also a README file giving brief descriptions of what they are.
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Several of them provide support for compiling PCRE on various flavours of
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Windows systems (I myself do not use Windows). Some are complete in themselves;
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others are pointers to URLs containing relevant files.
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Building PCRE on a Unix-like system
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-----------------------------------
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To build PCRE on a Unix-like system, first run the "configure" command from the
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PCRE distribution directory, with your current directory set to the directory
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where you want the files to be created. This command is a standard GNU
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"autoconf" configuration script, for which generic instructions are supplied in
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INSTALL.
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Most commonly, people build PCRE within its own distribution directory, and in
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this case, on many systems, just running "./configure" is sufficient, but the
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usual methods of changing standard defaults are available. For example,
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CFLAGS='-O2 -Wall' ./configure --prefix=/opt/local
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specifies that the C compiler should be run with the flags '-O2 -Wall' instead
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of the default, and that "make install" should install PCRE under /opt/local
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instead of the default /usr/local.
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If you want to build in a different directory, just run "configure" with that
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directory as current. For example, suppose you have unpacked the PCRE source
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into /source/pcre/pcre-xxx, but you want to build it in /build/pcre/pcre-xxx:
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cd /build/pcre/pcre-xxx
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/source/pcre/pcre-xxx/configure
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There are some optional features that can be included or omitted from the PCRE
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library. You can read more about them in the pcrebuild man page.
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. If you want to make use of the support for UTF-8 character strings in PCRE,
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you must add --enable-utf8 to the "configure" command. Without it, the code
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for handling UTF-8 is not included in the library. (Even when included, it
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still has to be enabled by an option at run time.)
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. You can build PCRE to recognized CR or NL as the newline character, instead
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of whatever your compiler uses for "\n", by adding --newline-is-cr or
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--newline-is-nl to the "configure" command, respectively. Only do this if you
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really understand what you are doing. On traditional Unix-like systems, the
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newline character is NL.
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. When called via the POSIX interface, PCRE uses malloc() to get additional
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storage for processing capturing parentheses if there are more than 10 of
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them. You can increase this threshold by setting, for example,
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--with-posix-malloc-threshold=20
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on the "configure" command.
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. PCRE has a counter which can be set to limit the amount of resources it uses.
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If the limit is exceeded during a match, the match fails. The default is ten
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million. You can change the default by setting, for example,
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--with-match-limit=500000
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on the "configure" command. This is just the default; individual calls to
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pcre_exec() can supply their own value. There is discussion on the pcreapi
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man page.
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. The default maximum compiled pattern size is around 64K. You can increase
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this by adding --with-link-size=3 to the "configure" command. You can
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increase it even more by setting --with-link-size=4, but this is unlikely
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ever to be necessary. If you build PCRE with an increased link size, test 2
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(and 5 if you are using UTF-8) will fail. Part of the output of these tests
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is a representation of the compiled pattern, and this changes with the link
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size.
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. You can build PCRE so that its match() function does not call itself
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recursively. Instead, it uses blocks of data from the heap via special
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functions pcre_stack_malloc() and pcre_stack_free() to save data that would
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otherwise be saved on the stack. To build PCRE like this, use
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--disable-stack-for-recursion
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on the "configure" command. PCRE runs more slowly in this mode, but it may be
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necessary in environments with limited stack sizes.
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The "configure" script builds five files:
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. libtool is a script that builds shared and/or static libraries
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. Makefile is built by copying Makefile.in and making substitutions.
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. config.h is built by copying config.in and making substitutions.
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. pcre-config is built by copying pcre-config.in and making substitutions.
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. RunTest is a script for running tests
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Once "configure" has run, you can run "make". It builds two libraries called
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libpcre and libpcreposix, a test program called pcretest, and the pcregrep
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command. You can use "make install" to copy these, the public header files
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pcre.h and pcreposix.h, and the man pages to appropriate live directories on
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your system, in the normal way.
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Running "make install" also installs the command pcre-config, which can be used
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to recall information about the PCRE configuration and installation. For
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example,
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pcre-config --version
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prints the version number, and
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pcre-config --libs
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outputs information about where the library is installed. This command can be
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included in makefiles for programs that use PCRE, saving the programmer from
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having to remember too many details.
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Shared libraries on Unix-like systems
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-------------------------------------
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The default distribution builds PCRE as two shared libraries and two static
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libraries, as long as the operating system supports shared libraries. Shared
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library support relies on the "libtool" script which is built as part of the
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"configure" process.
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The libtool script is used to compile and link both shared and static
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libraries. They are placed in a subdirectory called .libs when they are newly
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built. The programs pcretest and pcregrep are built to use these uninstalled
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libraries (by means of wrapper scripts in the case of shared libraries). When
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you use "make install" to install shared libraries, pcregrep and pcretest are
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automatically re-built to use the newly installed shared libraries before being
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installed themselves. However, the versions left in the source directory still
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use the uninstalled libraries.
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To build PCRE using static libraries only you must use --disable-shared when
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configuring it. For example
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./configure --prefix=/usr/gnu --disable-shared
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Then run "make" in the usual way. Similarly, you can use --disable-static to
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build only shared libraries.
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Cross-compiling on a Unix-like system
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-------------------------------------
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You can specify CC and CFLAGS in the normal way to the "configure" command, in
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order to cross-compile PCRE for some other host. However, during the building
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process, the dftables.c source file is compiled *and run* on the local host, in
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order to generate the default character tables (the chartables.c file). It
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therefore needs to be compiled with the local compiler, not the cross compiler.
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You can do this by specifying CC_FOR_BUILD (and if necessary CFLAGS_FOR_BUILD)
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when calling the "configure" command. If they are not specified, they default
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to the values of CC and CFLAGS.
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Building on non-Unix systems
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----------------------------
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For a non-Unix system, read the comments in the file NON-UNIX-USE, though if
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the system supports the use of "configure" and "make" you may be able to build
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PCRE in the same way as for Unix systems.
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PCRE has been compiled on Windows systems and on Macintoshes, but I don't know
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the details because I don't use those systems. It should be straightforward to
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build PCRE on any system that has a Standard C compiler, because it uses only
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Standard C functions.
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Testing PCRE
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------------
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To test PCRE on a Unix system, run the RunTest script that is created by the
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configuring process. (This can also be run by "make runtest", "make check", or
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"make test".) For other systems, see the instructions in NON-UNIX-USE.
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The script runs the pcretest test program (which is documented in its own man
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page) on each of the testinput files (in the testdata directory) in turn,
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and compares the output with the contents of the corresponding testoutput file.
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A file called testtry is used to hold the output from pcretest. To run pcretest
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on just one of the test files, give its number as an argument to RunTest, for
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example:
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RunTest 2
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The first file can also be fed directly into the perltest script to check that
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Perl gives the same results. The only difference you should see is in the first
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few lines, where the Perl version is given instead of the PCRE version.
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The second set of tests check pcre_fullinfo(), pcre_info(), pcre_study(),
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pcre_copy_substring(), pcre_get_substring(), pcre_get_substring_list(), error
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detection, and run-time flags that are specific to PCRE, as well as the POSIX
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wrapper API. It also uses the debugging flag to check some of the internals of
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pcre_compile().
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If you build PCRE with a locale setting that is not the standard C locale, the
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character tables may be different (see next paragraph). In some cases, this may
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cause failures in the second set of tests. For example, in a locale where the
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isprint() function yields TRUE for characters in the range 128-255, the use of
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[:isascii:] inside a character class defines a different set of characters, and
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this shows up in this test as a difference in the compiled code, which is being
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listed for checking. Where the comparison test output contains [\x00-\x7f] the
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test will contain [\x00-\xff], and similarly in some other cases. This is not a
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bug in PCRE.
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The third set of tests checks pcre_maketables(), the facility for building a
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set of character tables for a specific locale and using them instead of the
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default tables. The tests make use of the "fr_FR" (French) locale. Before
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running the test, the script checks for the presence of this locale by running
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the "locale" command. If that command fails, or if it doesn't include "fr_FR"
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in the list of available locales, the third test cannot be run, and a comment
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is output to say why. If running this test produces instances of the error
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** Failed to set locale "fr_FR"
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in the comparison output, it means that locale is not available on your system,
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despite being listed by "locale". This does not mean that PCRE is broken.
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The fourth test checks the UTF-8 support. It is not run automatically unless
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PCRE is built with UTF-8 support. To do this you must set --enable-utf8 when
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running "configure". This file can be also fed directly to the perltest script,
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provided you are running Perl 5.8 or higher. (For Perl 5.6, a small patch,
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commented in the script, can be be used.)
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The fifth and final file tests error handling with UTF-8 encoding, and internal
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UTF-8 features of PCRE that are not relevant to Perl.
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Character tables
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----------------
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PCRE uses four tables for manipulating and identifying characters. The final
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argument of the pcre_compile() function is a pointer to a block of memory
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containing the concatenated tables. A call to pcre_maketables() can be used to
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generate a set of tables in the current locale. If the final argument for
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pcre_compile() is passed as NULL, a set of default tables that is built into
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the binary is used.
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The source file called chartables.c contains the default set of tables. This is
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not supplied in the distribution, but is built by the program dftables
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(compiled from dftables.c), which uses the ANSI C character handling functions
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such as isalnum(), isalpha(), isupper(), islower(), etc. to build the table
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sources. This means that the default C locale which is set for your system will
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control the contents of these default tables. You can change the default tables
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by editing chartables.c and then re-building PCRE. If you do this, you should
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probably also edit Makefile to ensure that the file doesn't ever get
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re-generated.
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The first two 256-byte tables provide lower casing and case flipping functions,
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respectively. The next table consists of three 32-byte bit maps which identify
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digits, "word" characters, and white space, respectively. These are used when
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building 32-byte bit maps that represent character classes.
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The final 256-byte table has bits indicating various character types, as
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follows:
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1 white space character
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2 letter
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4 decimal digit
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8 hexadecimal digit
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16 alphanumeric or '_'
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128 regular expression metacharacter or binary zero
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You should not alter the set of characters that contain the 128 bit, as that
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will cause PCRE to malfunction.
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Manifest
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--------
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The distribution should contain the following files:
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(A) The actual source files of the PCRE library functions and their
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headers:
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dftables.c auxiliary program for building chartables.c
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get.c )
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maketables.c )
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study.c ) source of
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pcre.c ) the functions
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pcreposix.c )
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printint.c )
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pcre.in "source" for the header for the external API; pcre.h
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is built from this by "configure"
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pcreposix.h header for the external POSIX wrapper API
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internal.h header for internal use
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config.in template for config.h, which is built by configure
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(B) Auxiliary files:
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AUTHORS information about the author of PCRE
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ChangeLog log of changes to the code
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INSTALL generic installation instructions
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LICENCE conditions for the use of PCRE
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COPYING the same, using GNU's standard name
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Makefile.in template for Unix Makefile, which is built by configure
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NEWS important changes in this release
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NON-UNIX-USE notes on building PCRE on non-Unix systems
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README this file
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RunTest.in template for a Unix shell script for running tests
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config.guess ) files used by libtool,
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config.sub ) used only when building a shared library
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configure a configuring shell script (built by autoconf)
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configure.in the autoconf input used to build configure
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doc/Tech.Notes notes on the encoding
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doc/*.3 man page sources for the PCRE functions
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doc/*.1 man page sources for pcregrep and pcretest
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doc/html/* HTML documentation
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doc/pcre.txt plain text version of the man pages
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doc/pcretest.txt plain text documentation of test program
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doc/perltest.txt plain text documentation of Perl test program
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install-sh a shell script for installing files
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ltmain.sh file used to build a libtool script
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pcretest.c comprehensive test program
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pcredemo.c simple demonstration of coding calls to PCRE
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perltest Perl test program
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pcregrep.c source of a grep utility that uses PCRE
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pcre-config.in source of script which retains PCRE information
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testdata/testinput1 test data, compatible with Perl
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testdata/testinput2 test data for error messages and non-Perl things
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testdata/testinput3 test data for locale-specific tests
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testdata/testinput4 test data for UTF-8 tests compatible with Perl
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testdata/testinput5 test data for other UTF-8 tests
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testdata/testoutput1 test results corresponding to testinput1
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testdata/testoutput2 test results corresponding to testinput2
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testdata/testoutput3 test results corresponding to testinput3
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testdata/testoutput4 test results corresponding to testinput4
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testdata/testoutput5 test results corresponding to testinput5
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(C) Auxiliary files for Win32 DLL
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dll.mk
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pcre.def
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(D) Auxiliary file for VPASCAL
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makevp.bat
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Philip Hazel <ph10@cam.ac.uk>
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December 2003
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