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, and 32-bit units for the 32-bit
       library) if PCRE is compiled with the default internal linkage size, which is 2 bytes  for
       the 8-bit and 16-bit libraries, and 4 bytes for the 32-bit library. 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 or 32-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, however, a limit to the depth  of  nesting  of
       parenthesized  subpatterns  of  all kinds. This is imposed in order to limit the amount of
       system stack used at compile time. The limit can be specified  when  PCRE  is  built;  the
       default is 250.

       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 and 32-bit libraries.

       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: 05 November 2013
       Copyright (c) 1997-2013 University of Cambridge.