Provided by: libpcre3-dev_8.31-2ubuntu2.3_amd64 
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.
BUILDING 8-BIT and 16-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. If you do not want the 8-bit library, add
--disable-pcre8
as well. At least one of the two 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 library.
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.
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 and UTF-16 SUPPORT
To build PCRE with support for UTF Unicode character strings, add
--enable-utf
to the configure command. This setting applies to both libraries, adding support for UTF-8 to the 8-bit
library and support for UTF-16 to the 16-bit library. There are no separate options for enabling UTF-8
and UTF-16 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 the
other 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 or UTF-16. As well as compiling PCRE
with this option, you also have have to set the PCRE_UTF8 or PCRE_UTF16 option 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, 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. Using longer offsets slows down the operation of PCRE because it has to load additional
data 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 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.
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.
SEE ALSO
pcreapi(3), pcre16, pcre_config(3).
AUTHOR
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
REVISION
Last updated: 07 January 2012
Copyright (c) 1997-2012 University of Cambridge.