Provided by: libpcre3-dev_8.39-12build1_amd64 bug

NAME

       PCRE - Perl-compatible regular expressions

BUILDING PCRE


       PCRE 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 PCRE 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.

PCRE BUILD-TIME OPTIONS


       The  rest  of  this  document describes the optional features of PCRE 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  using  the GUI facility of cmake-gui if you are using CMake instead of
       configure to build PCRE.

       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 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
       described.

BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES


       By  default,  a  library  called  libpcre  is built, containing functions that take string
       arguments contained in vectors of bytes, either as single-byte characters, or  interpreted
       as  UTF-8  strings.  You  can  also  build  a separate library, called libpcre16, in which
       strings are contained in vectors of 16-bit data units and interpreted  either  as  single-
       unit characters or UTF-16 strings, by adding

         --enable-pcre16

       to  the  configure  command.  You  can  also  build  yet  another separate library, called
       libpcre32, in which strings are contained in vectors of 32-bit data units and  interpreted
       either as single-unit characters or UTF-32 strings, by adding

         --enable-pcre32

       to the configure command. If you do not want the 8-bit library, add

         --disable-pcre8

       as  well.  At  least one of the three libraries must be built. Note that the C++ and POSIX
       wrappers are for the 8-bit library only, and that pcregrep is an 8-bit  program.  None  of
       these are built if you select only the 16-bit or 32-bit libraries.

BUILDING SHARED AND STATIC LIBRARIES


       The Autotools PCRE building process uses libtool to build both shared and static libraries
       by default. You can suppress one of these by adding one of

         --disable-shared
         --disable-static

       to the configure command, as required.

C++ SUPPORT


       By default, if the 8-bit library is being built, the configure script will  search  for  a
       C++  compiler  and  C++  header  files.  If it finds them, it automatically builds the C++
       wrapper library (which supports only 8-bit strings). You can disable this by adding

         --disable-cpp

       to the configure command.

UTF-8, UTF-16 AND UTF-32 SUPPORT


       To build PCRE with support for UTF Unicode character strings, add

         --enable-utf

       to the configure command. This setting applies to all three libraries, adding support  for
       UTF-8  to  the  8-bit  library,  support for UTF-16 to the 16-bit library, and support for
       UTF-32 to the to the 32-bit library. There are no separate  options  for  enabling  UTF-8,
       UTF-16  and  UTF-32  independently  because  that  would allow ridiculous settings such as
       requesting UTF-16 support while building only the 8-bit library. It  is  not  possible  to
       build  one  library  with  UTF support and another without in the same configuration. (For
       backwards compatibility, --enable-utf8 is a synonym of --enable-utf.)

       Of itself, this setting does not make PCRE treat strings as UTF-8, UTF-16  or  UTF-32.  As
       well  as  compiling  PCRE  with  this  option,  you  also  have have to set the PCRE_UTF8,
       PCRE_UTF16 or PCRE_UTF32 option  (as  appropriate)  when  you  call  one  of  the  pattern
       compiling functions.

       If you set --enable-utf when compiling in an EBCDIC environment, PCRE expects its input to
       be either ASCII or UTF-8 (depending on the run-time option). It is not possible to support
       both EBCDIC and UTF-8 codes in the same version of the library. Consequently, --enable-utf
       and --enable-ebcdic are mutually exclusive.

UNICODE CHARACTER PROPERTY SUPPORT


       UTF support allows the libraries to process character codepoints up  to  0x10ffff  in  the
       strings  that  they  handle.  On  its own, however, it does not provide any facilities for
       accessing the properties of such characters. If you want to be able  to  use  the  pattern
       escapes \P, \p, and \X, which refer to Unicode character properties, you must add

         --enable-unicode-properties

       to  the  configure  command.  This  implies  UTF  support, even if you have not explicitly
       requested it.

       Including Unicode property support adds around 30K of tables to the PCRE library. Only the
       general  category  properties  such  as  Lu and Nd are supported. Details are given in the
       pcrepattern documentation.

JUST-IN-TIME COMPILER SUPPORT


       Just-in-time 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  compile  time  error  occurs.   See  the  pcrejit
       documentation for a discussion of  JIT  usage.  When  JIT  support  is  enabled,  pcregrep
       automatically makes use of it, unless you add

         --disable-pcregrep-jit

       to the "configure" command.

CODE VALUE OF NEWLINE


       By  default,  PCRE 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  PCRE  to  use
       carriage return (CR) instead, by adding

         --enable-newline-is-cr

       to  the configure command. There is also a --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. 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 PCRE to recognize any of the three sequences CR, LF, or CRLF as indicating a
       line ending. Finally, a fifth option, specified by

         --enable-newline-is-any

       causes PCRE to recognize any Unicode newline sequence.

       Whatever line ending convention is selected when PCRE is built can be overridden when  the
       library  functions  are  called.  At build time it is conventional to use the standard for
       your operating system.

WHAT \R MATCHES


       By default, the sequence \R in a pattern matches any Unicode  newline  sequence,  whatever
       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
       PCRE is built can be overridden when the library functions are called.

POSIX MALLOC USAGE


       When the  8-bit  library  is  called  through  the  POSIX  interface  (see  the  pcreposix
       documentation),  additional  working  storage  is  required  for  holding  the pointers to
       capturing substrings, because PCRE requires three  integers  per  substring,  whereas  the
       POSIX  interface  provides  only  two.  If the number of expected substrings is small, the
       wrapper function uses space on the stack, because this is faster than using  malloc()  for
       each  call. The default threshold above which the stack is no longer used is 10; it can be
       changed by adding a setting such as

         --with-posix-malloc-threshold=20

       to the configure command.

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 64K. 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 PCRE 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 PCRE 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.

AVOIDING EXCESSIVE STACK USAGE


       When matching with the  pcre_exec()  function,  PCRE  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 PCRE'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 pcrestack 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 PCRE that works this way, add

         --disable-stack-for-recursion

       to the configure command. With this configuration, PCRE will use the pcre_stack_malloc and
       pcre_stack_free variables to call memory management functions. By default these  point  to
       malloc()  and free(), but you can replace the pointers so that your own functions are used
       instead.

       Separate functions are provided rather than using pcre_malloc and  pcre_free  because  the
       usage  is  very predictable: the block sizes requested are always the same, and the blocks
       are always freed in reverse order. A calling program might be able to implement  optimized
       functions  that  perform better than malloc() and free(). PCRE runs noticeably more slowly
       when built in this way. This option affects only  the  pcre_exec()  function;  it  is  not
       relevant for pcre_dfa_exec().

LIMITING PCRE RESOURCE USAGE


       Internally,  PCRE  has  a  function  called  match(), which it calls repeatedly (sometimes
       recursively) when matching a pattern with the pcre_exec()  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 pcre_exec(). The  limit  can
       be  changed  at  run  time,  as  described in the pcreapi 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 has  no  effect  on  the  pcre_dfa_exec()  matching
       function.

       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,

         --with-match-limit-recursion=10000

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

CREATING CHARACTER TABLES AT BUILD TIME


       PCRE  uses  fixed tables for processing characters whose code values are less than 256. By
       default,  PCRE  is  built  with  a  set  of  tables  that  are  distributed  in  the  file
       pcre_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 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".)

USING EBCDIC CODE


       PCRE 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. PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by
       adding

         --enable-ebcdic

       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). The --enable-ebcdic option is incompatible with --enable-utf.

       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.

PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT


       By default, pcregrep 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-pcregrep-libz
         --enable-pcregrep-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.

PCREGREP BUFFER SIZE


       pcregrep  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,

         --with-pcregrep-bufsize=50K

       to the configure command. The caller of pcregrep can,  however,  override  this  value  by
       specifying a run-time option.

PCRETEST OPTION FOR LIBREADLINE SUPPORT


       If you add

         --enable-pcretest-libreadline

       to  the  configure  command, pcretest is linked with the libreadline library, 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 pcretest linked in this way, there may be licensing issues.

       Setting this option causes the -lreadline option to be added to  the  pcretest  build.  In
       many  operating  environments  with  a  sytem-installed  libreadline  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.

DEBUGGING WITH VALGRIND SUPPORT


       By adding the

         --enable-valgrind

       option  to  to  the  configure command, PCRE 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 PCRE itself.

CODE COVERAGE REPORTING


       If  your  C  compiler  is  gcc,  you  can build a version of PCRE 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 PCRE 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 PCRE, 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 PCRE 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.

SEE ALSO


       pcreapi(3), pcre16, pcre32, pcre_config(3).

AUTHOR


       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.

REVISION


       Last updated: 12 May 2013
       Copyright (c) 1997-2013 University of Cambridge.