PCRE(3)PCRE(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 which is run
before the make command. The complete list of options for configure
(which includes the standard ones such as the selection of the instal‐
lation 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.
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.
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 performing a matching operation. By
limiting the number of times this function may be called, 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.
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
PCRE implements backtracking while matching 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.) An alter‐
native 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.
USING EBCDIC CODE
PCRE assumes by default that it will run in an environment where the
character code is ASCII (or UTF-8, 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: 09 December 2003Copyright (c) 1997-2003 University of Cambridge.
PCRE(3)
