Provided by: libpcre2-dev_10.21-1_amd64 
NAME
PCRE2 - Perl-compatible regular expressions (revised API)
BUILDING PCRE2
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.
PCRE2 BUILD-TIME OPTIONS
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.
BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES
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.
BUILDING SHARED AND STATIC 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.
UNICODE AND UTF SUPPORT
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
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).
DISABLING THE USE OF \C
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
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 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.
NEWLINE RECOGNITION
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.
WHAT \R MATCHES
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.
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 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.
AVOIDING EXCESSIVE STACK USAGE
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 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().
LIMITING PCRE2 RESOURCE USAGE
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 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.
CREATING CHARACTER TABLES AT BUILD 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".)
USING EBCDIC CODE
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.
PCRE2GREP OPTIONS FOR COMPRESSED FILE SUPPORT
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 BUFFER SIZE
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..
PCRE2TEST OPTION FOR LIBREADLINE SUPPORT
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.
INCLUDING DEBUGGING CODE
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.
DEBUGGING WITH VALGRIND SUPPORT
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.
CODE COVERAGE REPORTING
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.
SEE ALSO
pcre2api(3), pcre2-config(3).
AUTHOR
Philip Hazel
University Computing Service
Cambridge, England.
REVISION
Last updated: 16 October 2015
Copyright (c) 1997-2015 University of Cambridge.