PCRE2BUILD(3) Library Functions Manual PCRE2BUILD(3)
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 in-
formation about building with Autotools (some of which is repeated be-
low), 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
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 dese-
lected by providing options to configure before running the make com-
mand. 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 ob-
tained by running
The following sections include descriptions of "on/off" options whose
names begin with --enable or --disable. Because of the way that config-
ure works, --enable and --disable always come in pairs, so the comple-
mentary 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 configura-
tion 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 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:
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
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
to the configure command. This setting applies to all three libraries.
It is not possible to build one library with Unicode support and an-
other 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 pat-
tern. 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).
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 cur-
rent matching point in the middle of a multi-code-unit character. The
application can lock it out by setting the PCRE2_NEVER_BACKSLASH_C op-
tion 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 speci-
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 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
to the configure command. There is also an --enable-newline-is-lf op-
tion, 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
to the configure command. 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 charac-
ters 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
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. What-
ever 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 alter-
nation 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 suffi-
cient 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 set-
ting such as
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.
LIMITING PCRE2 RESOURCE USAGE
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
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 starts out using a 20KiB vector on the sys-
tem 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 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_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,
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 re-
cursion 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 pat-
terns. The limit does not apply to JIT matching.
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
to the configure command, the distributed tables are no longer used.
Instead, a program called pcre2_dftables is compiled and run. This out-
puts 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
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_com-
pile() in the same way as tables created by calling pcre2_maketables().
The tables are just a string of bytes, independent of hardware charac-
teristics such as endianness. This means they can be bundled with an
application that runs in different environments, to ensure consistent
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
to the configure command. This setting implies --enable-rebuild-charta-
bles. You should only use it if you know that you are in an EBCDIC en-
vironment (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 char-
acter (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
By default pcre2grep supports the use of callouts with string arguments
within the patterns it is matching. There are two kinds: one that gen-
erates output using local code, and another that calls an external pro-
gram 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 ig-
nored. For more details of pcre2grep callouts, see the pcre2grep docu-
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
to the configure command. These options naturally require that the rel-
evant 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 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 encoun-
tered, 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
to the configure command. The caller of pcre2grep can override these
values by using --buffer-size and --max-buffer-size on the command
PCRE2TEST OPTION FOR LIBREADLINE SUPPORT
If you add one of
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
immediately before the configure command.
INCLUDING DEBUGGING CODE
If you add
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
to the configure command, PCRE2 will use valgrind annotations to mark
certain memory regions as unaddressable. This allows it to detect in-
valid 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
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
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:
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 cover-
age 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, see the gcov and lcov docu-
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 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.
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
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 in-
stalled. This contains a single function called LLVMFuzzerTestOneIn-
put() 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
Setting --enable-fuzz-support also causes a binary called pcre2fuz-
zcheck 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.
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Last updated: 08 December 2021
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