Section (3) pcre2build
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
configure. The text
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
and building by hand) in the text file called
should consult this file as well as the
README file if you are building in a
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
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
configure to build
If you are not using Autotools or
CMake, option selection can be done by
config.h file, or
by passing parameter settings to the compiler, as described
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
The following sections include descriptions of on/off
options whose names begin with --enable or --disable. Because
of the way that
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
configure run, a summary
of the configuration is output.
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
arrays of bytes, interpreted either as single-byte
characters, or UTF-8 strings. You can also build two other
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
If you do not want the 8-bit library, add
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
UNICODE AND UTF SUPPORT
By default, PCRE2 is built with support for Unicode and UTF character strings. To build it without Unicode support, add
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
pcre2_compile() to compile
a pattern. Alternatively, patterns may be started with (*UTF)
unless the application has locked this out by setting
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
supported. Details are given in the pcre2pattern(3)
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
(note the upper case C) which locks out the use of C entirely.
JUST-IN-TIME COMPILER SUPPORT
Just-in-time (JIT) compiler support is included in the build by specifying
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
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
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(3) documentation for a discussion of JIT usage. When JIT support is enabled, pcre2grep automatically makes use of it, unless you add
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
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
There is a fourth option, specified by
which causes PCRE2 to recognize any of the three sequences CR, LF, or CRLF as indicating a line ending. A fifth option, specified by
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
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.
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
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.
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 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
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.
LIMITING PCRE2 RESOURCE USAGE
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(3) documentation.
The default is 10 million, but this can be changed by adding
a setting such as
This setting also applies to the
pcre2_dfa_match() matching function, and to
JIT matching (though the counting is done differently).
starts out using a 20KiB vector on the system stack to record
backtracking points. The more nested backtracking points
there are (that is, the deeper the search tree), the more
memory is needed. If the initial vector is not large enough,
heap memory is used, up to a certain limit, which is
specified in kibibytes (units of 1024 bytes). The limit can
be changed at run time, as described in the pcre2api(3) documentation.
The default limit (in effect unlimited) is 20 million. You
can change this by a setting such as
which limits the amount of heap to 500 KiB. This limit
applies only to interpretive matching in
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,
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
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
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
These tables are for ASCII codes only. If you add
the distributed tables are no longer used. Instead, a program
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
run on the local host. If you need to create alternative
tables when cross compiling, you will have to do so by
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
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
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 SUPPORT FOR EXTERNAL SCRIPTS
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 OPTIONS FOR COMPRESSED FILE SUPPORT
all files as plain text. You can build it so that it
recognizes files whose names end in
.bz2, and reads them with
libbz2, respectively, by adding one or both
These options naturally require that the relevant libraries
are installed on your system. Configuration will fail if they
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 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
The caller of
override these values by using --buffer-size and
--max-buffer-size on the command line.
PCRE2TEST OPTION FOR LIBREADLINE SUPPORT
If you add one of
pcre2test is linked with the
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
libedit, which has a BSD
Setting --enable-pcre2test-libreadline causes the
−lreadline option to be
added to the
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
immediately before the
INCLUDING DEBUGGING CODE
If you add
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
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
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
configure command and
build PCRE2 in the usual way.
Note that using
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
make to build
PCRE2, so that
ccache is not
When --enable-coverage is used, the following addition
targets are added to the
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.
This zeroes the coverage counters, but does nothing else.
This captures baseline coverage information.
This creates the coverage report.
This removes the generated coverage report without cleaning the coverage data itself.
This removes the captured coverage data without removing the coverage files created at compile time (*.gcno).
This cleans all coverage data including the generated
coverage report. For more information about code coverage,
DISABLING THE Z AND T FORMATTING MODIFIERS
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 Microsoft Visual Studio when __STDC_VERSION__ is defined and has a value greater than or equal to 199901L (indicating C99). However, there is at least one environment that claims to be C99 but does not support these modifiers. If
is specified, no use is made of the z or t modifiers. Instead or %td or %zu, %lu is used, with a cast for size_t values.
SUPPORT FOR FUZZERS
There is a special option for use by people who want to run fuzzing tests on PCRE2:
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
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.
Last updated: 03 March 2019 Copyright (c) 1997-2019 University of Cambridge.
This manual page is taken from the PCRE library, which is distributed under the BSD license.