NAME

       PCRE - Perl-compatible regular expressions

SIZE AND OTHER LIMITATIONS

       There  are  some size limitations in PCRE but it is hoped that they will never in practice
       be relevant.

       The maximum length of a compiled pattern is approximately 64K data units  (bytes  for  the
       8-bit  library,  16-bit units for the 16-bit library) if PCRE is compiled with the default
       internal linkage size of 2 bytes. If you want to  process  regular  expressions  that  are
       truly  enormous,  you  can  compile  PCRE  with  an  internal linkage size of 3 or 4 (when
       building the 16-bit library, 3 is rounded up to 4). See the  README  file  in  the  source
       distribution  and  the  pcrebuild  documentation  for details. In these cases the limit is
       substantially larger.  However, the speed of execution is slower.

       All values in repeating quantifiers must be less than 65536.

       There is no limit to the number of parenthesized subpatterns, but there  can  be  no  more
       than 65535 capturing subpatterns.

       There  is  a limit to the number of forward references to subsequent subpatterns of around
       200,000. Repeated forward references with fixed upper  limits,  for  example,  (?2){0,100}
       when  subpattern number 2 is to the right, are included in the count. There is no limit to
       the number of backward references.

       The maximum length of name for a named subpattern is 32 characters, and the maximum number
       of named subpatterns is 10000.

       The  maximum  length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb is 255 for
       the 8-bit library and 65535 for the 16-bit library.

       The maximum length of a subject string is the largest  positive  number  that  an  integer
       variable  can  hold.  However,  when  using  the  traditional matching function, PCRE uses
       recursion to handle subpatterns and indefinite repetition.  This means that the  available
       stack  space  may  limit  the  size  of  a subject string that can be processed by certain
       patterns. For a discussion of stack issues, see the pcrestack documentation.

AUTHOR

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

REVISION

       Last updated: 04 May 2012
       Copyright (c) 1997-2012 University of Cambridge.