bionic (3) pcrelimits.3.gz

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.