Man Pages

pcrebuild(3) - phpMan pcrebuild(3) - phpMan

Command: man perldoc info search(apropos)  

PCREBUILD(3)                                                      PCREBUILD(3)

       PCRE - Perl-compatible regular expressions


       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  con-
       figure to build PCRE.

       There  is  a  lot  more  information  about  building  PCRE  in  non-Unix-like  environments in the file called
       NON_UNIX_USE, which is part of the PCRE distribution. You should consult this file as well as the  README  file
       if you are building in a non-Unix-like environment.

       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 set-
       tings  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 spec-
       ifies the default, it is not described.


       The  PCRE building process uses libtool to build both shared and static Unix libraries by default. You can sup-
       press one of these by adding one of


       to the configure command, as required.


       By default, the configure script will search for a C++ compiler and C++ header files.  If  it  finds  them,  it
       automatically builds the C++ wrapper library for PCRE. You can disable this by adding


       to the configure command.


       To build PCRE with support for UTF-8 Unicode character strings, add


       to  the configure command. Of itself, this does not make PCRE treat strings as UTF-8. As well as compiling PCRE
       with this option, you also have have to set the PCRE_UTF8 option when you call the pcre_compile() or  pcre_com-
       pile2() functions.

       If  you set --enable-utf8 when compiling in an EBCDIC environment, PCRE expects its input to be either ASCII or
       UTF-8 (depending on the runtime option). It is not possible to support both EBCDIC and UTF-8 codes in the  same
       version of the library. Consequently, --enable-utf8 and --enable-ebcdic are mutually exclusive.


       UTF-8  support  allows PCRE to process character values greater than 255 in the strings that it handles. 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


       to the configure command. This implies UTF-8 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 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 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


       to the "configure" command.


       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


       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


       to the configure command. There is a fourth option, specified by


       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


       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.


       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


       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.


       When PCRE 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


       to the configure command.


       Within a compiled pattern, offset values are used to point from one part to another (for example, from an open-
       ing parenthesis to an alternation metacharacter). By default, two-byte values are used for these offsets, lead-
       ing 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 truyl enormous patterns, so it is possible to
       compile PCRE 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. Using longer offsets slows down the operation  of
       PCRE because it has to load additional bytes when handling them.


       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


       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 pre-
       dictable: 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().


       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


       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-recur-
       sion 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  exam-


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


       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".)


       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


       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-utf8.


       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


       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  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 pcregrep can, however, override this value by specifying a run-time


       If you add


       to the configure command, pcretest is linked with the libreadline library, and when its input is from a  termi-
       nal,  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 licens-
       ing issues.

       Setting  this option causes the -lreadline option to be added to the pcretest build. In many operating environ-
       ments with a sytem-installed libreadline this is sufficient. However, in some environments (e.g.  if an unmodi-
       fied  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.


       pcreapi(3), pcre_config(3).


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


       Last updated: 06 September 2011
       Copyright (c) 1997-2011 University of Cambridge.