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 "on/off" options whose
names begin with --enable or --disable. 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. Options that specify values have names that start with
--with. At the end of a
configure run, a summary of the configuration
is output.
By default, a library called
libpcre2-8 is built, containing functions
that take string arguments contained in arrays 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 arrays 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. Unicode support also gives access to the
Unicode properties of characters, using pattern escapes such as \P, \p, and
\X. Only the general category properties such as
Lu and
Nd,
script names, and some bi-directional properties 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).
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 (JIT) 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. If in
doubt, use
--enable-jit=auto
which enables JIT only if the current hardware is supported. You can check if
JIT is enabled in the configuration summary that is output at the end of a
configure run. If you are enabling JIT under SELinux you may also want
to add
--enable-jit-sealloc
which enables the use of an execmem allocator in JIT that is compatible with
SELinux. This has no effect if JIT is not enabled. 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.
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. 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). The final
option is
--enable-newline-is-nul
which causes NUL (binary zero) to be set as the default line-ending character.
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
recommended 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
library.
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 64 thousand 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.
The
pcre2_match() function increments a counter each time it goes round
its main loop. Putting a limit on this counter controls the amount of
computing resource 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 also applies to the
pcre2_dfa_match() matching function, and to JIT matching (though the
counting is done differently).
The
pcre2_match() function uses heap memory to record backtracking
points. The more nested backtracking points there are (that is, the deeper the
search tree), the more memory is needed. There is an upper limit, specified in
kibibytes (units of 1024 bytes). This limit can be changed at run time, as
described in the
pcre2api documentation. The default limit (in effect
unlimited) is 20 million. You can change this by a setting such as
--with-heap-limit=500
which limits the amount of heap to 500 KiB. This limit applies only to
interpretive matching in
pcre2_match() and
pcre2_dfa_match(),
which may also use the heap for internal workspace when processing complicated
patterns. This limit does not apply when JIT (which has its own memory
arrangements) is used.
You can also explicitly limit the depth of nested backtracking in the
pcre2_match() interpreter. This limit defaults to the value that is set
for --with-match-limit. You can set a lower default limit by adding, for
example,
--with-match-limit-depth=10000
to the
configure command. This value can be overridden at run time. This
depth limit indirectly limits the amount of heap memory that is used, but
because the size of each backtracking "frame" depends on the number
of capturing parentheses in a pattern, the amount of heap that is used before
the limit is reached varies from pattern to pattern. This limit was more
useful in versions before 10.30, where function recursion was used for
backtracking.
As well as applying to
pcre2_match(), the depth limit also controls the
depth of recursive function calls in
pcre2_dfa_match(). These are used
for lookaround assertions, atomic groups, and recursion within patterns. The
limit does not apply to JIT matching.
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
pcre2_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
pcre2_dftables needs to be run on the
local host and therefore not compiled with the cross compiler.
If you need to create alternative tables when cross compiling, you will have to
do so "by hand". There may also be other reasons for creating tables
manually. To cause
pcre2_dftables to be built on the local host, run a
normal compiling command, and then run the program with the output file as its
argument, for example:
cc src/pcre2_dftables.c -o pcre2_dftables
./pcre2_dftables src/pcre2_chartables.c
This builds the tables in the default locale of the local host. If you want to
specify a locale, you must use the -L option:
LC_ALL=fr_FR ./pcre2_dftables -L src/pcre2_chartables.c
You can also specify -b (with or without -L). This causes the tables to be
written in binary instead of as source code. A set of binary tables can be
loaded into memory by an application and passed to
pcre2_compile() in
the same way as tables created by calling
pcre2_maketables(). The
tables are just a string of bytes, independent of hardware characteristics
such as endianness. This means they can be bundled with an application that
runs in different environments, to ensure consistent behaviour.
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
pcre2grep supports the use of callouts with string arguments
within the patterns it is matching. There are two kinds: one that generates
output using local code, and another that calls an external program or script.
If --disable-pcre2grep-callout-fork is added to the
configure command,
only the first kind of callout is supported; if --disable-pcre2grep-callout is
used, all callouts are completely ignored. For more details of
pcre2grep callouts, see the
pcre2grep documentation.
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 default starting size of
the buffer is 20KiB. 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 notional buffer size. If a longer
line is encountered,
pcre2grep automatically expands the buffer, up to
a specified maximum size, whose default is 1MiB or the starting size,
whichever is the larger. You can change the default parameter values by
adding, for example,
--with-pcre2grep-bufsize=51200
--with-pcre2grep-max-bufsize=2097152
to the
configure command. The caller of
pcre2grep can override
these values by using --buffer-size and --max-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 or
libedit 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.
The C99 standard defines formatting modifiers z and t for size_t and ptrdiff_t
values, respectively. By default, PCRE2 uses these modifiers in environments
other than old versions of Microsoft Visual Studio when __STDC_VERSION__ is
defined and has a value greater than or equal to 199901L (indicating support
for C99). However, there is at least one environment that claims to be C99 but
does not support these modifiers. If
--disable-percent-zt
is specified, no use is made of the z or t modifiers. Instead of %td or %zu, a
suitable format is used depending in the size of long for the platform.
There is a special option for use by people who want to run fuzzing tests on
PCRE2:
--enable-fuzz-support
At present this applies only to the 8-bit library. If set, it causes an extra
library called libpcre2-fuzzsupport.a to be built, but not installed. This
contains a single function called LLVMFuzzerTestOneInput() whose arguments are
a pointer to a string and the length of the string. When called, this function
tries to compile the string as a pattern, and if that succeeds, to match it.
This is done both with no options and with some random options bits that are
generated from the string.
Setting --enable-fuzz-support also causes a binary called
pcre2fuzzcheck
to be created. This is normally run under valgrind or used when PCRE2 is
compiled with address sanitizing enabled. It calls the fuzzing function and
outputs information about what it is doing. The input strings are specified by
arguments: if an argument starts with "=" the rest of it is a
literal input string. Otherwise, it is assumed to be a file name, and the
contents of the file are the test string.
In versions of PCRE2 prior to 10.30, there were two ways of handling
backtracking in the
pcre2_match() function. The default was to use the
system stack, but if
--disable-stack-for-recursion
was set, memory on the heap was used. From release 10.30 onwards this has
changed (the stack is no longer used) and this option now does nothing except
give a warning.
pcre2api(3),
pcre2-config(3).
Philip Hazel
Retired from University Computing Service
Cambridge, England.
Last updated: 27 July 2022
Copyright (c) 1997-2022 University of Cambridge.