README file for PCRE (Perl-compatible regular expression library)

-----------------------------------------------------------------

The latest release of PCRE is always available in three alternative formats

from:

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

  ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre-xxx.tar.bz2

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

There is a mailing list for discussion about the development of PCRE at

  pcre-dev@exim.org

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

The contents of this README file are:

  The PCRE APIs

  Documentation for PCRE

  Contributions by users of PCRE

  Building PCRE on non-Unix systems

  Building PCRE on Unix-like systems

  Retrieving configuration information on Unix-like systems

  Shared libraries on Unix-like systems

  Cross-compiling on Unix-like systems

  Using HP's ANSI C++ compiler (aCC)

  Making new tarballs

  Testing PCRE

  Character tables

  File manifest

The PCRE APIs

-------------

PCRE is written in C, and it has its own API. The distribution also includes a

set of C++ wrapper functions (see the pcrecpp man page for details), courtesy

of Google Inc.

In addition, there is a set of C wrapper functions that are based on the POSIX

regular expression API (see the pcreposix man page). 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 POSIX API is restricted, and does not give full access to

all of PCRE's facilities.

The header file for the POSIX-style functions is called pcreposix.h. The

official POSIX name is regex.h, but I did not want to risk possible problems

with existing files of that name by distributing it that way. To use PCRE with

an existing program that uses the POSIX API, pcreposix.h 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, as well as worrying about the regex.h header

file (as mentioned above), you must also take care when linking programs to

ensure that they link with PCRE's libpcreposix library. Otherwise they may pick

up the POSIX functions of the same name from the other library.

One way of avoiding this confusion is to compile PCRE with the addition of

-Dregcomp=PCREregcomp (and similarly for the other POSIX functions) to the

compiler flags (CFLAGS if you are using "configure" -- see below). This has the

effect of renaming the functions so that the names no longer clash. Of course,

you have to do the same thing for your applications, or write them using the

new names.

Documentation for PCRE

----------------------

If you install PCRE in the normal way on a Unix-like system, you will end up

with a set of man pages whose names all start with "pcre". The one that is just

called "pcre" lists all the others. In addition to these man pages, the PCRE

documentation is supplied in two other forms:

  1. There are files called doc/pcre.txt, doc/pcregrep.txt, and

     doc/pcretest.txt in the source distribution. 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.

     These text forms are provided for ease of scanning with text editors or

     similar tools. They are installed in <prefix>/share/doc/pcre, where

     <prefix> is the installation prefix (defaulting to /usr/local).

  2. A set of files containing all the documentation in HTML form, hyperlinked

     in various ways, and rooted in a file called index.html, is distributed in

     doc/html and installed in <prefix>/share/doc/pcre/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

There is a README file giving brief descriptions of what they are. Some are

complete in themselves; others are pointers to URLs containing relevant files.

Some of this material is likely to be well out-of-date. Several of the earlier

contributions provided support for compiling PCRE on various flavours of

Windows (I myself do not use Windows). Nowadays there is more Windows support

in the standard distribution, so these contibutions have been archived.

Building PCRE on non-Unix systems

---------------------------------

For a non-Unix system, please read the comments in the file NON-UNIX-USE,

though if your system supports the use of "configure" and "make" you may be

able to build PCRE in the same way as for Unix-like systems. PCRE can also be

configured in many platform environments using the GUI facility of CMake's

CMakeSetup. It creates Makefiles, solution files, etc.

PCRE has been compiled on many different operating systems. It should be

straightforward to build PCRE on any system that has a Standard C compiler and

library, because it uses only Standard C functions.

Building PCRE on Unix-like systems

----------------------------------

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.

The following instructions assume the use of the widely used "configure, make,

make install" process. There is also support for CMake in the PCRE

distribution; there are some comments about using CMake in the NON-UNIX-USE

file, though it can also be used in Unix-like systems.

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

the file INSTALL.

Most commonly, people build PCRE within its own distribution directory, and in

this case, on many systems, just running "./configure" is sufficient. However,

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,

  it 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 30K 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 or the sequence CRLF or any

  of the preceding, or any of the Unicode newline sequences as indicating the

  end of a line. Whatever you specify at build time is the default; the caller

  of PCRE can change the selection at run time. The default newline indicator

  is a single LF character (the Unix standard). You can specify the default

  newline indicator by adding --enable-newline-is-cr or --enable-newline-is-lf

  or --enable-newline-is-crlf or --enable-newline-is-anycrlf or

  --enable-newline-is-any to the "configure" command, respectively.

  If you specify --enable-newline-is-cr or --enable-newline-is-crlf, some of

  the standard tests will fail, because the lines in the test files end with

  LF. Even if the files are edited to change the line endings, there are likely

  to be some failures. With --enable-newline-is-anycrlf or

  --enable-newline-is-any, many tests should succeed, but there may be some

  failures.

. By default, the sequence \R in a pattern matches any Unicode line ending

  sequence. This is independent of the option specifying what PCRE considers to

  be the end of a line (see above). However, the caller of PCRE can restrict \R

  to match only CR, LF, or CRLF. You can make this the default by adding

  --enable-bsr-anycrlf to the "configure" command (bsr = "backslash R").

. 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 in a pattern. 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 more discussion on the

  pcreapi man page.

. There is a separate counter that limits the depth of recursive function calls

  during a matching process. This also has a default of ten million, which is

  essentially "unlimited". You can change the default by setting, for example,

  --with-match-limit-recursion=500000

  Recursive function calls use up the runtime stack; running out of stack can

  cause programs to crash in strange ways. There is a discussion about stack

  sizes in the pcrestack 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. Increasing the internal link size will reduce

  performance.

. You can build PCRE so that its internal match() function that is called from

  pcre_exec() does not call itself recursively. Instead, it uses memory blocks

  obtained from the heap via the 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. There is a discussion about stack sizes in the

  pcrestack man page.

. For speed, PCRE uses four tables for manipulating and identifying characters

  whose code point values are less than 256. By default, it uses a set of

  tables for ASCII encoding that is part of the distribution. If you specify

  --enable-rebuild-chartables

  a program called dftables is compiled and run in the default C locale when

  you obey "make". It builds a source file called pcre_chartables.c. If you do

  not specify this option, pcre_chartables.c is created as a copy of

  pcre_chartables.c.dist. See "Character tables" below for further information.

. It is possible to compile PCRE for use on systems that use EBCDIC as their

  default character code (as opposed to ASCII) by specifying

  --enable-ebcdic

  This automatically implies --enable-rebuild-chartables (see above).

. It is possible to compile pcregrep to use libz and/or libbz2, in order to

  read .gz and .bz2 files (respectively), by specifying one or both of

  --enable-pcregrep-libz

  --enable-pcregrep-libbz2

  Of course, the relevant libraries must be installed on your system.

. It is possible to compile pcretest so that it links with the libreadline

  library, by specifying

  --enable-pcretest-libreadline

  If this is done, when pcretest's input is from a terminal, it reads it using

  the readline() function. This provides line-editing and history facilities.

  Note that libreadline is GPL-licenced, 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 readline

  library this is sufficient. However, in some environments (e.g. if an

  unmodified distribution version of readline is in use), it may be necessary

  to specify something like LIBS="-lncurses" as well. This is because, to quote

  the readline INSTALL, "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."

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

. Makefile is the makefile that builds the library

. config.h contains build-time configuration options for the library

. pcre.h is the public PCRE header file

. 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 basic C library

. RunGrepTest is a script for running tests on the pcregrep command

Versions of config.h and pcre.h are distributed in the PCRE tarballs under

the names config.h.generic and pcre.h.generic. These are provided for the

benefit of those who have to built PCRE without the benefit of "configure". If

you use "configure", the .generic versions are not used.

If a C++ compiler is found, the following files are also built:

. libpcrecpp.pc is data for the pkg-config command

. pcrecpparg.h is a 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, "make" also builds the C++

wrapper library, which is called libpcrecpp, and some test programs called

pcrecpp_unittest, pcre_scanner_unittest, and pcre_stringpiece_unittest.

Building the C++ wrapper can be disabled by adding --disable-cpp to the

"configure" command.

The command "make check" runs all the appropriate tests. Details of the PCRE

tests are given below in a separate section of this document.

You can use "make install" to install PCRE into live directories on your

system. The following are installed (file names are all relative to the

<prefix> that is set when "configure" is run):

  Commands (bin):

    pcretest

    pcregrep

    pcre-config

  Libraries (lib):

    libpcre

    libpcreposix

    libpcrecpp (if C++ support is enabled)

  Configuration information (lib/pkgconfig):

    libpcre.pc

    libpcrecpp.pc (if C++ support is enabled)

  Header files (include):

    pcre.h

    pcreposix.h

    pcre_scanner.h      )

    pcre_stringpiece.h  ) if C++ support is enabled

    pcrecpp.h           )

    pcrecpparg.h        )

  Man pages (share/man/man{1,3}):

    pcregrep.1

    pcretest.1

    pcre.3

    pcre*.3 (lots more pages, all starting "pcre")

  HTML documentation (share/doc/pcre/html):

    index.html

    *.html (lots more pages, hyperlinked from index.html)

  Text file documentation (share/doc/pcre):

    AUTHORS

    COPYING

    ChangeLog

    LICENCE

    NEWS

    README

    pcre.txt       (a concatenation of the man(3) pages)

    pcretest.txt   the pcretest man page

    pcregrep.txt   the pcregrep man page

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" 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

<prefix>/lib/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 build 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 Unix-like systems

------------------------------------

You can specify CC and CFLAGS in the normal way to the "configure" command, in

order to cross-compile PCRE for some other host. However, you should NOT

specify --enable-rebuild-chartables, because if you do, the dftables.c source

file is compiled and run on the local host, in order to generate the inbuilt

character tables (the pcre_chartables.c file). This will probably not work,

because dftables.c needs to be compiled with the local compiler, not the cross

compiler.

When --enable-rebuild-chartables is not specified, pcre_chartables.c is created

by making a copy of pcre_chartables.c.dist, which is a default set of tables

that assumes ASCII code. Cross-compiling with the default tables should not be

a problem.

If you need to modify the character tables when cross-compiling, you should

move pcre_chartables.c.dist out of the way, then compile dftables.c by hand and

run it on the local host to make a new version of pcre_chartables.c.dist.

Then when you cross-compile PCRE this new version of the tables will be used.

Using HP's ANSI C++ compiler (aCC)

----------------------------------

Unless C++ support is disabled by specifying the "--disable-cpp" option of the

"configure" script, you must include the "-AA" option in the CXXFLAGS

environment variable in order for the C++ components to compile correctly.

Also, note that the aCC compiler on PA-RISC platforms may have a defect whereby

needed libraries fail to get included when specifying the "-AA" compiler

option. If you experience unresolved symbols when linking the C++ programs,

use the workaround of specifying the following environment variable prior to

running the "configure" script:

  CXXLDFLAGS="-lstd_v2 -lCsup_v2"

Making new tarballs

-------------------

The command "make dist" creates three PCRE tarballs, in tar.gz, tar.bz2, and

zip formats. The command "make distcheck" does the same, but then does a trial

build of the new distribution to ensure that it works.

If you have modified any of the man page sources in the doc directory, you

should first run the PrepareRelease script before making a distribution. This

script creates the .txt and HTML forms of the documentation from the man pages.

Testing PCRE

------------

To test the basic PCRE library on a Unix system, run the RunTest script that is

created by the configuring process. There is also a script called RunGrepTest

that tests the options of the pcregrep command. If the C++ wrapper library is

built, three test programs called pcrecpp_unittest, pcre_scanner_unittest, and

pcre_stringpiece_unittest are also built.

Both the scripts and all the program tests are run if you obey "make check" or

"make test". For other systems, see the instructions in NON-UNIX-USE.

The RunTest script runs the pcretest test program (which is documented in its

own man page) on each of the testinput files in the testdata directory in

turn, and compares the output with the contents of the corresponding testoutput

files. A file called testtry is used to hold the main output from pcretest

(testsavedregex is also used as a working file). To run pcretest on just one of

the test files, give its number as an argument to RunTest, for example:

  RunTest 2

The first test file can also be fed directly into the perltest.pl script to

check that Perl gives the same results. The only difference you should see is

in the first few lines, where the Perl version is given instead of the PCRE

version.

The second set of tests check pcre_fullinfo(), pcre_info(), pcre_study(),

pcre_copy_substring(), pcre_get_substring(), pcre_get_substring_list(), error

detection, and run-time flags that are specific to PCRE, as well as the POSIX

wrapper API. It also uses the debugging flags to check some of the internals of

pcre_compile().

If you build PCRE with a locale setting that is not the standard C locale, the

character tables may be different (see next paragraph). In some cases, this may

cause failures in the second set of tests. For example, in a locale where the

isprint() function yields TRUE for characters in the range 128-255, the use of

[:isascii:] inside a character class defines a different set of characters, and

this shows up in this test as a difference in the compiled code, which is being

listed for checking. Where the comparison test output contains [\x00-\x7f] the

test will contain [\x00-\xff], and similarly in some other cases. This is not a

bug in PCRE.

The third set of tests checks pcre_maketables(), the facility for building a

set of character tables for a specific locale and using them instead of the

default tables. The tests make use of the "fr_FR" (French) locale. Before

running the test, the script checks for the presence of this locale by running

the "locale" command. If that command fails, or if it doesn't include "fr_FR"