Introduction to Library Functions 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 providing options to configure
before running the make command. However, the same options
can be selected in both Unix-like and non-Unix-like environ-
ments 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 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.
C] SUPORT
By default, the configure script will search for a C] com-
piler and C] header files. If it finds them, it automati-
cally builds the C] wrapper library for PCRE. You can dis-
able this by adding
--disable-cpp
to the configure command.
UTF-8 SUPORT
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 PCREUTF8 option when
you call the pcrecompile() function.
UNICODE CHARACTER PROPERTY SUPORT
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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 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-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, speci-
fied 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
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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 over-
ridden 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 MALOC 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 mal-
loc() 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 PATERNS
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 enormous pat-
terns, so it is possible to compile PCRE to use three-byte
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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 EXCESIVE STACK USAGE
When matching with the pcreexec() function, PCRE implements
backtracking by making recursive calls to an internal func-
tion 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 pcrestackmalloc and pcrestackfree 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.
Separate functions are provided rather than using
pcremalloc and pcrefree because the usage is very predict-
able: 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
pcreexec() function; it is not relevant for the the
pcredfaexec() function.
LIMITING PCRE RESOURCE USAGE
Internally, PCRE has a function called match(), which it
calls repeatedly (sometimes recursively) when matching a
pattern with the pcreexec() 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 pcreexec(). 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
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--with-match-limit=500000
to the configure command. This setting has no effect on the
pcredfaexec() 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 speci-
fied) 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
pcrechartables.c.dist. These tables are for ASCI 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 ASCI (or Unicode, which is a
superset of ASCI). 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 main-
frame operating system).
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PCREGREP OPTIONS FOR COMPRESED FILE SUPORT
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.
PCRETEST OPTION FOR LIBREADLINE SUPORT
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-licenced, 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 ver-
sion of readline is in use), some extra configuration may be
necessary. The INSTAL 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 appropri-
ate library is automatically included, you may need to add
something like
LIBS="-ncurses"
immediately before the configure command.
SEE ALSO
pcreapi(3), pcreconfig(3).
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AUTHOR
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
REVISION
Last updated: 13 April 2008
Copyright (c) 1997-2008 University of Cambridge.
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWpcre
Interface Stability Uncommitted
NOTES
Source for PCRE is available on http:/opensolaris.org.
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