pcrebuild
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. It assumes use of the configure
script, where the optional features are selected or deselected by pro-
viding 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 CMakeSetup if you are using
CMake instead of configure to build PCRE.
The complete list of options for configure (which includes the stan-
dard 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 con-
figure works, --enable and --disable always come in pairs, so the com-
plementary 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 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.
CODE VALUE OF NEWLINE
By default, PCRE interprets character 10 (linefeed, LF) as indicating
the end of a line. This is the normal newline character on Unix-like
systems. You can compile PCRE to use character 13 (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. What-
ever is selected when PCRE is built can be overridden when the library
functions are called.
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
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 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.
AVOIDING EXCESSIVE STACK USAGE
When matching with the pcre_exec() function, PCRE implements back-
tracking 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 lim-
ited 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 manage-
ment functions. By default these point to malloc() and free(), but you
can replace the pointers so that your own functions are used.
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 the the
pcre_dfa_exec() function.
LIMITING PCRE RESOURCE USAGE
Internally, PCRE has a function called match(), which it calls repeat-
edly (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 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.
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 con-
trols 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 runtime 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, how-
ever, 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).
SEE ALSO
pcreapi(3), pcre_config(3).
AUTHOR
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
REVISION
Last updated: 21 September 2007
Copyright (c) 1997-2007 University of Cambridge.
PCREBUILD(3)
