NAME

PCRE - Perl-compatible regular expressions

BUILDING PCRE

PCRE is distributed with a configure script that can be used to build the library in Unix-like environments using the applications known as Autotools. Also in the distribution are files to support building using CMake instead of configure. The text file README contains general information about building with Autotools (some of which is repeated below), and also has some comments about building on various operating systems. There is a lot more information about building PCRE without using Autotools (including information about using CMake and building "by hand") in the text file called NON-AUTOTOOLS-BUILD. You should consult this file as well as the README file if you are building in a non-Unix-like environment.

PCRE BUILD-TIME OPTIONS

The rest of 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.

If you are not using Autotools or CMake, option selection can be done by editing the config.h file, or by passing parameter settings to the compiler, as described in NON-AUTOTOOLS-BUILD.

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.

BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES

By default, a library called libpcre is built, containing functions that take string arguments contained in vectors of bytes, either as single-byte characters, or interpreted as UTF-8 strings. You can also build a separate library, called libpcre16, in which strings are contained in vectors of 16-bit data units and interpreted either as single-unit characters or UTF-16 strings, by adding

--enable-pcre16

to the configure command. You can also build yet another separate library, called libpcre32, in which strings are contained in vectors of 32-bit data units and interpreted either as single-unit characters or UTF-32 strings, by adding

--enable-pcre32

to the configure command. If you do not want the 8-bit library, add

--disable-pcre8

as well. At least one of the three libraries must be built. Note that the C++ and POSIX wrappers are for the 8-bit library only, and that pcregrep is an 8-bit program. None of these are built if you select only the 16-bit or 32-bit libraries.

BUILDING SHARED AND STATIC LIBRARIES

The Autotools PCRE building process uses libtool to build both shared and static libraries by default. You can suppress one of these by adding one of

--disable-shared --disable-static

to the configure command, as required.

C++ SUPPORT

By default, if the 8-bit library is being built, the configure script will search for a C++ compiler and C++ header files. If it finds them, it automatically builds the C++ wrapper library (which supports only 8-bit strings). You can disable this by adding

--disable-cpp

to the configure command.

UTF-8, UTF-16 AND UTF-32 SUPPORT

To build PCRE with support for UTF Unicode character strings, add

--enable-utf

to the configure command. This setting applies to all three libraries, adding support for UTF-8 to the 8-bit library, support for UTF-16 to the 16-bit library, and support for UTF-32 to the to the 32-bit library. There are no separate options for enabling UTF-8, UTF-16 and UTF-32 independently because that would allow ridiculous settings such as requesting UTF-16 support while building only the 8-bit library. It is not possible to build one library with UTF support and another without in the same configuration. (For backwards compatibility, --enable-utf8 is a synonym of --enable-utf.)

Of itself, this setting does not make PCRE treat strings as UTF-8, UTF-16 or UTF-32. As well as compiling PCRE with this option, you also have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as appropriate) when you call one of the pattern compiling functions.

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

UNICODE CHARACTER PROPERTY SUPPORT

UTF support allows the libraries to process character codepoints up to 0x10ffff in the strings that they handle. 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 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.

JUST-IN-TIME COMPILER SUPPORT

Just-in-time compiler support is included in the build by specifying

--enable-jit

This support is available only for certain hardware architectures. If this option is set for an unsupported architecture, a compile time error occurs. See the pcrejit documentation for a discussion of JIT usage. When JIT support is enabled, pcregrep automatically makes use of it, unless you add

--disable-pcregrep-jit

to the "configure" command.

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.

POSIX MALLOC USAGE

When the 8-bit library 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, in the 8-bit and 16-bit libraries, 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 truly 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. For the 16-bit library, a value of 3 is rounded up to 4. In these libraries, using longer offsets slows down the operation of PCRE because it has to load additional data when handling them. For the 32-bit library the value is always 4 and cannot be overridden; the value of --with-link-size is ignored.

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 run-time 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-utf.

The EBCDIC character that corresponds to an ASCII LF is assumed to have the value 0x15 by default. However, in some EBCDIC environments, 0x25 is used. In such an environment you should use

--enable-ebcdic-nl25

as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR has the same value as in ASCII, namely, 0x0d. Whichever of 0x15 and 0x25 is not chosen as LF is made to correspond to the Unicode NEL character (which, in Unicode, is 0x85).

The options that select newline behaviour, such as --enable-newline-is-cr, and equivalent run-time options, refer to these character values in an EBCDIC environment.

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.

PCREGREP BUFFER SIZE

pcregrep uses an internal buffer to hold a "window" on the file it is scanning, in order to be able to output "before" and "after" lines when it finds a match. The size of the buffer is controlled by a parameter whose default value is 20K. The buffer itself is three times this size, but because of the way it is used for holding "before" lines, the longest line that is guaranteed to be processable is the parameter size. You can change the default parameter value by adding, for example,

--with-pcregrep-bufsize=50K

to the configure command. The caller of pcregrep can, however, override this value by specifying a run-time option.

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.

DEBUGGING WITH VALGRIND SUPPORT

By adding the

--enable-valgrind

option to to the configure command, PCRE will use valgrind annotations to mark certain memory regions as unaddressable. This allows it to detect invalid memory accesses, and is mostly useful for debugging PCRE itself.

CODE COVERAGE REPORTING

If your C compiler is gcc, you can build a version of PCRE that can generate a code coverage report for its test suite. To enable this, you must install lcov version 1.6 or above. Then specify

--enable-coverage

to the configure command and build PCRE in the usual way.

Note that using ccache (a caching C compiler) is incompatible with code coverage reporting. If you have configured ccache to run automatically on your system, you must set the environment variable

CCACHE_DISABLE=1

before running make to build PCRE, so that ccache is not used.

When --enable-coverage is used, the following addition targets are added to the Makefile:

make coverage

This creates a fresh coverage report for the PCRE test suite. It is equivalent to running "make coverage-reset", "make coverage-baseline", "make check", and then "make coverage-report".

make coverage-reset

This zeroes the coverage counters, but does nothing else.

make coverage-baseline

This captures baseline coverage information.

make coverage-report

This creates the coverage report.

make coverage-clean-report

This removes the generated coverage report without cleaning the coverage data itself.

make coverage-clean-data

This removes the captured coverage data without removing the coverage files created at compile time (*.gcno).

make coverage-clean

This cleans all coverage data including the generated coverage report. For more information about code coverage, see the gcov and lcov documentation.

AUTHOR

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

REVISION

Last updated: 12 May 2013
Copyright (c) 1997-2013 University of Cambridge.