PCREBUILD(3)PCREBUILD(3)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. They are all selected, or dese‐
lected, by providing options to the configure script that is run before
the make command. 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 describe certain 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.
C++ SUPPORT
By default, the configure script will search for a C++ compiler and C++
header files. If it finds them, it automatically builds the C++ wrapper
library for PCRE. You can disable this by adding
--disable-cpp
to the configure command.
UTF-8 SUPPORT
To build PCRE with support for UTF-8 character strings, add
--enable-utf8
to the configure command. Of itself, this does not make PCRE treat
strings as UTF-8. As well as compiling PCRE with this option, you also
have have to set the PCRE_UTF8 option when you call the pcre_compile()
function.
UNICODE CHARACTER PROPERTY SUPPORT
UTF-8 support allows PCRE to process character values greater than 255
in the strings that it handles. On its own, however, it does not pro‐
vide 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-8 support, even if you have
not explicitly requested it.
Including Unicode property support adds around 90K of tables to the
PCRE library, approximately doubling its size. Only the general cate‐
gory properties such as Lu and Nd are supported. Details are given in
the pcrepattern documentation.
CODE VALUE OF NEWLINE
By default, PCRE treats character 10 (linefeed) as the newline charac‐
ter. This is the normal newline character on Unix-like systems. You can
compile PCRE to use character 13 (carriage return) instead by adding
--enable-newline-is-cr
to the configure command. For completeness there is also a --enable-
newline-is-lf option, which explicitly specifies linefeed as the new‐
line character.
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.
POSIX MALLOC USAGE
When PCRE is called through the POSIX interface (see the pcreposix doc‐
umentation), 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.
LIMITING PCRE RESOURCE USAGE
Internally, PCRE has a function called match(), which it calls repeat‐
edly (possibly 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 documen‐
tation. 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.
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 alter‐
nation 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 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. Using
longer offsets slows down the operation of PCRE because it has to load
additional bytes when handling them.
If you build PCRE with an increased link size, test 2 (and test 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.
AVOIDING EXCESSIVE STACK USAGE
When matching with the pcre_exec() function, PCRE implements backtrack‐
ing by making recursive calls to an internal function called match().
In environments where the size of the stack is limited, this can se‐
verely limit PCRE's operation. (The Unix environment does not usually
suffer from this problem.) An alternative approach that uses memory
from the heap to remember data, instead of using recursive function
calls, has been implemented to work round this problem. 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 manage‐
ment functions. Separate functions are provided 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 the
standard malloc() and free() functions. PCRE runs noticeably more
slowly when built in this way. This option affects only the pcre_exec()
function; it is not relevant for the the pcre_dfa_exec() function.
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).
PCRE can, however, be compiled to run in an EBCDIC environment by
adding
--enable-ebcdic
to the configure command.
Last updated: 15 August 2005Copyright (c) 1997-2005 University of Cambridge.
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