# pcre2build

## 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 Autotools
           applications. 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. The files in the **vms**
           directory support building under OpenVMS.  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 "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.
    


## 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:
    
             --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. Setting --disable-shared ensures that
           PCRE2 libraries are built as static libraries. The binaries that
           are then created as part of the build process (for example,
           **pcre2test** and **pcre2grep**) are linked statically with one or more
           PCRE2 libraries, but may also be dynamically linked with other
           libraries such as **libc**. If you want these binaries to be fully
           statically linked, you can set LDFLAGS like this:
    
           LDFLAGS=--static ./configure --disable-shared
    
           Note the two hyphens in --static. Of course, this works only if
           static versions of all the relevant libraries are available for
           linking.
    


## 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. 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 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 (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.
    


## 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. 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.
    


## 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 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
    
             --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.
    


## 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 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.
    


## LIMITING VARIABLE-LENGTH LOOKBEHIND ASSERTIONS



    
           Lookbehind assertions in which one or more branches can match a
           variable number of characters are supported only if there is a
           maximum matching length for each top-level branch. There is a
           limit to this maximum that defaults to 255 characters. You can
           alter this default by a setting such as
    
             --with-max-varlookbehind=100
    
           The limit can be changed at runtime by calling
           **pcre2_set_max_varlookbehind()**. Lookbehind assertions in which
           every branch matches a fixed number of characters (not necessarily
           all the same) are not constrained by this limit.
    


## 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 **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.
    


## 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. You should only use it if you know that
           you are in an EBCDIC environment (for example, an IBM mainframe
           operating system).
    
           This setting implies --enable-rebuild-chartables, in order to
           ensure that you have the correct default character tables for your
           system's codepage. There is an exception when you set --enable-
           ebcdic-ignoring-compiler (see below), which allows using a default
           set of EBCDIC 1047 character tables rather than forcing use of
           --enable-rebuild-chartables.
    
           It is not supported to enable both EBCDIC input and either ASCII
           or UTF-8/16/32 in the same build of the library. When PCRE2 is
           built with EBCDIC support, it always operates in EBCDIC, and
           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
    
           (which implies --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.
    
           On systems requiring an EBCDIC build of PCRE2, the compiler should
           be set to use the correct codepage, so that C character literals
           such as 'z' use the correct numeric value for whichever EBCDIC
           codpage is in use. (PCRE2 cannot support multiple EBCDIC codepages
           dynamically.) However, if this not possible, then you can use
    
             --enable-ebcdic-ignoring-compiler
    
           in order to disregard the compiler's codepage, and instead force
           PCRE2 to use numeric constants corresponding to the EBCDIC 1047
           codepage instead. This can be used to build (or test) EBCDIC
           support on an ASCII/UTF-8 system such as Linux.
    


## 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 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.
    


## 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 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.
    


## 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**
           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 system-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.
    


## 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. 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.
    


## SUPPORT FOR FUZZERS



    
           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.
    


## OBSOLETE OPTION



    
           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.
    


## REVISION



    
           Last updated: 16 April 2024
           Copyright (c) 1997-2024 University of Cambridge.
    


* * *