PCREBUILD(3) Library Functions Manual PCREBUILD(3)
PCRE - Perl-compatible regular expressions
PCRE is distributed with a configure script that can be used to
build the library in Unix-like environments using the
applications known as Autotools. Also in the distribution are
files to support building using CMake instead of configure. The
text file README contains general information about building with
Autotools (some of which is repeated below), and also has some
comments about building on various operating systems. There is a
lot more information about building PCRE without using Autotools
(including information about using CMake and building "by hand")
in the text file called NON-AUTOTOOLS-BUILD. You should consult
this file as well as the README file if you are building in a
non-Unix-like environment.
The rest of 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.
If you are not using Autotools or CMake, option selection can be
done by editing the config.h file, or by passing parameter
settings to the compiler, as described in NON-AUTOTOOLS-BUILD.
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.
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. You can also build yet another separate
library, called libpcre32, in which strings are contained in
vectors of 32-bit data units and interpreted either as single-
unit characters or UTF-32 strings, by adding
--enable-pcre32
to the configure command. If you do not want the 8-bit library,
add
--disable-pcre8
as well. At least one of the three 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 or 32-bit libraries.
The Autotools PCRE building process uses libtool to build both
shared and static libraries by default. You can suppress one of
these by adding one of
--disable-shared
--disable-static
to the configure command, as required.
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.
To build PCRE with support for UTF Unicode character strings, add
--enable-utf
to the configure command. This setting applies to all three
libraries, adding support for UTF-8 to the 8-bit library, support
for UTF-16 to the 16-bit library, and support for UTF-32 to the
to the 32-bit library. There are no separate options for enabling
UTF-8, UTF-16 and UTF-32 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 another 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, UTF-16 or UTF-32. As well as compiling PCRE with this
option, you also have have to set the PCRE_UTF8, PCRE_UTF16 or
PCRE_UTF32 option (as appropriate) 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.
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 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.
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.
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.
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.
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, in the 8-bit and
16-bit libraries, 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. In these
libraries, using longer offsets slows down the operation of PCRE
because it has to load additional data when handling them. For
the 32-bit library the value is always 4 and cannot be
overridden; the value of --with-link-size is ignored.
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().
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.
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".)
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.
The EBCDIC character that corresponds to an ASCII LF is assumed
to have the value 0x15 by default. However, in some EBCDIC
environments, 0x25 is used. In such an environment you should use
--enable-ebcdic-nl25
as well as, or instead of, --enable-ebcdic. The EBCDIC character
for CR has the same value as in ASCII, namely, 0x0d. Whichever of
0x15 and 0x25 is not chosen as LF is made to correspond to the
Unicode NEL character (which, in Unicode, is 0x85).
The options that select newline behaviour, such as --enable-
newline-is-cr, and equivalent run-time options, refer to these
character values in an EBCDIC environment.
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 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.
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.
By adding the
--enable-valgrind
option to to the configure command, PCRE will use valgrind
annotations to mark certain memory regions as unaddressable. This
allows it to detect invalid memory accesses, and is mostly useful
for debugging PCRE itself.
If your C compiler is gcc, you can build a version of PCRE that
can generate a code coverage report for its test suite. To enable
this, you must install lcov version 1.6 or above. Then specify
--enable-coverage
to the configure command and build PCRE in the usual way.
Note that using ccache (a caching C compiler) is incompatible
with code coverage reporting. If you have configured ccache to
run automatically on your system, you must set the environment
variable
CCACHE_DISABLE=1
before running make to build PCRE, so that ccache is not used.
When --enable-coverage is used, the following addition targets
are added to the Makefile:
make coverage
This creates a fresh coverage report for the PCRE test suite. It
is equivalent to running "make coverage-reset", "make coverage-
baseline", "make check", and then "make coverage-report".
make coverage-reset
This zeroes the coverage counters, but does nothing else.
make coverage-baseline
This captures baseline coverage information.
make coverage-report
This creates the coverage report.
make coverage-clean-report
This removes the generated coverage report without cleaning the
coverage data itself.
make coverage-clean-data
This removes the captured coverage data without removing the
coverage files created at compile time (*.gcno).
make coverage-clean
This cleans all coverage data including the generated coverage
report. For more information about code coverage, see the gcov
and lcov documentation.
pcreapi(3), pcre16, pcre32, pcre_config(3).
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
Last updated: 12 May 2013
Copyright (c) 1997-2013 University of Cambridge.
This page is part of the PCRE (Perl Compatible Regular
Expressions) project. Information about the project can be found
at ⟨http://www.pcre.org/⟩. If you have a bug report for this
manual page, see
⟨http://bugs.exim.org/enter_bug.cgi?product=PCRE⟩. This page was
obtained from the tarball pcre-8.45.tar.gz fetched from
⟨ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/⟩ on
2021-08-27. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
PCRE 8.33 12 May 2013 PCREBUILD(3)
Pages that refer to this page: pcreapi(3)
|
HTML rendering created 2021-08-27 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|