Provided by: libpcre2-dev_10.21-1_amd64 bug


       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-

       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


       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:


       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.


       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.


       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 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

       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


       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


       (note the upper case C) which locks out the use of \C entirely.


       Just-in-time 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.  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 adding


       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


       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. Finally, 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).

       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.


       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 called.


       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


       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.


       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


       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().


       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


       to  the  configure  command.  This setting has no effect on the pcre2_dfa_match() matching

       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,


       to the configure command. This value can also be overridden at run 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  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".)


       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


       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 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 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  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,


       to the configure command. The caller  of  pcre2grep  can  override  this  value  by  using
       --buffer-size on the command line..


       If you add one of


       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

       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.


       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.


       If you add


       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


       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:

         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-

         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.


       pcre2api(3), pcre2-config(3).


       Philip Hazel
       University Computing Service
       Cambridge, England.


       Last updated: 16 October 2015
       Copyright (c) 1997-2015 University of Cambridge.