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PCRELIMITS(3)                                                    PCRELIMITS(3)

       PCRE - Perl-compatible regular expressions


       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 65539 (sic) bytes if PCRE is compiled with the default internal
       linkage size of 2. If you want to process regular expressions that are truly enormous,  you  can  compile  PCRE
       with an internal linkage size of 3 or 4 (see the README file in the source distribution and the pcrebuild docu-
       mentation for details). In these cases the limit is substantially larger.  However, the speed of  execution  is

       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

       There is a limit to the number of forward references to subsequent subpatterns of around 200,000. Repeated for-
       ward 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 subject string is the largest positive number that an integer variable can hold. How-
       ever, 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 pro-
       cessed by certain patterns. For a discussion of stack issues, see the pcrestack documentation.


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


       Last updated: 30 November 2011
       Copyright (c) 1997-2011 University of Cambridge.