PCRE2 — Perl-compatible regular expressions (revised API) . .
PCRE2 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 PCRE2 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 PCRE2 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
if you are using CMake instead
of configure to build
PCRE2.
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 libpcre2-8 is built,
containing functions that take string arguments contained in
vectors of bytes, interpreted either as single-byte
characters, or UTF-8 strings. You can also build two other
libraries, called libpcre2-16 and libpcre2-32, which process
strings that are contained in vectors of 16-bit and 32-bit
code units, respectively. These can be interpreted either as
single-unit characters or UTF-16/UTF-32 strings. To build
these additional libraries, add one or both of the following
to the configure command:
--enable-pcre2-16 --enable-pcre2-32
If you do not want the 8-bit library, add
--disable-pcre2-8
as well. At least one of the three libraries must be
built. Note that the POSIX wrapper is for the 8-bit library
only, and that pcre2grep is an
8-bit program. Neither of these are built if you select only
the 16-bit or 32-bit libraries.
The Autotools PCRE2 building process uses libtool to build both shared and static
libraries by default. You can suppress an unwanted library by
adding one of
--disable-shared --disable-static
to the configure
command.
By default, PCRE2 is built with support for Unicode and UTF character strings. To build it without Unicode support, add
--disable-unicode
to the configure command.
This setting applies to all three libraries. It is not
possible to build one library with Unicode support, and
another without, in the same configuration.
Of itself, Unicode support does not make PCRE2 treat
strings as UTF-8, UTF-16 or UTF-32. To do that, applications
that use the library can set the PCRE2_UTF option when they
call pcre2_compile() to compile
a pattern. Alternatively, patterns may be started with (*UTF)
unless the application has locked this out by setting
PCRE2_NEVER_UTF.
UTF support allows the libraries to process character code
points up to 0x10ffff in the strings that they handle. It
also provides support for accessing the Unicode properties of
such characters, using pattern escapes such as \P, \p, and
\X. Only the general category properties such as Lu and Nd are
supported. Details are given in the pcre2pattern(3)
documentation.
Pattern escapes such as \d and \w do not by default make use of Unicode properties. The application can request that they do by setting the PCRE2_UCP option. Unless the application has set PCRE2_NEVER_UCP, a pattern may also request this by starting with (*UCP).
The \C escape sequence, which matches a single code unit,
even in a UTF mode, can cause unpredictable behaviour because
it may leave the current matching point in the middle of a
multi-code-unit character. The application can lock it out by
setting the PCRE2_NEVER_BACKSLASH_C option when calling
pcre2_compile(). There is also
a build-time option
--enable-never-backslash-C
(note the upper case C) which locks out the use of \C entirely.
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 building error occurs. See the pcre2jit(3) documentation for a discussion of JIT usage. When JIT support is enabled, pcre2grep automatically makes use of it, unless you add
--disable-pcre2grep-jit
to the "configure" command.
By default, PCRE2 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 PCRE2 to use carriage return (CR) instead, by adding
--enable-newline-is-cr
to the configure command.
There is also an --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 (CR immediately followed by LF). 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 PCRE2 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 PCRE2 to recognize any Unicode newline sequence. The Unicode newline sequences are the three just mentioned, plus the single characters VT (vertical tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029).
Whatever default line ending convention is selected when PCRE2 is built can be overridden by applications that use the library. 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, independently of what 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 PCRE2 is built can be overridden by applications that use the called.
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 code units. 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 PCRE2 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 PCRE2 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 pcre2_match() function, PCRE2 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 PCRE2'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 pcre2stack(3)
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 PCRE2 that works this way, add
--disable-stack-for-recursion
to the configure command. By
default, the system functions malloc() and free() are called to manage the heap memory
that is required, but custom memory management functions can
be called instead. PCRE2 runs noticeably more slowly when
built in this way. This option affects only the pcre2_match() function; it is not relevant
for pcre2_dfa_match().
Internally, PCRE2 has a function called match(), which it calls repeatedly
(sometimes recursively) when matching a pattern with the
pcre2_match() 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 pcre2_match(). The limit can be changed at
run time, as described in the pcre2api(3) 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 pcre2_dfa_match() 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.
PCRE2 uses fixed tables for processing characters whose
code points are less than 256. By default, PCRE2 is built
with a set of tables that are distributed in the file
src/pcre2_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".)
PCRE2 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. PCRE2 can, however, be compiled to run in an 8-bit EBCDIC environment by adding
--enable-ebcdic --disable-unicode
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).
It is not possible to support both EBCDIC and UTF-8 codes in the same version of the library. Consequently, --enable-unicode and --enable-ebcdic are mutually exclusive.
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, on non-Windows systems, pcre2grep supports the use of callouts with
string arguments within the patterns it is matching, in order
to run external scripts. For details, see the pcre2grep(3) documentation.
This support can be disabled by adding
--disable-pcre2grep-callout to the configure command.
By default, pcre2grep 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-pcre2grep-libz --enable-pcre2grep-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.
pcre2grep 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-pcre2grep-bufsize=50K
to the configure command.
The caller of pcre2grep can
override this value by using --buffer-size on the command
line.
If you add one of
--enable-pcre2test-libreadline --enable-pcre2test-libedit
to the configure command,
pcre2test is linked with the
libreadline orlibedit library, respectively, 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 pcre2test linked in this way, there may be
licensing issues. These can be avoided by linking instead
with libedit, which has a BSD
licence.
Setting --enable-pcre2test-libreadline causes the
−lreadline option to be
added to the pcre2test build.
In many operating environments with a sytem-installed
readline library 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.
If you add
--enable-debug
to the configure command,
additional debugging code is included in the build. This
feature is intended for use by the PCRE2 maintainers.
If you add
--enable-valgrind
to the configure command,
PCRE2 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 PCRE2
itself.
If your C compiler is gcc, you can build a version of
PCRE2 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 PCRE2 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
PCRE2, 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 PCRE2 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.
Last updated: 01 April 2016 Copyright (c) 1997-2016 University of Cambridge.
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This manual page is taken from the PCRE library, which is distributed under the BSD license. |