pcrelimits(3) — Linux manual page


PCRELIMITS(3)           Library Functions Manual           PCRELIMITS(3)

NAME         top

       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 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         top

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

REVISION         top

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

COLOPHON         top

       This page is part of the PCRE (Perl Compatible Regular
       Expressions) project.  Information about the project can be found
       at ⟨http://www.pcre.org/⟩.  If you have a bug report for this
       manual page, see
       ⟨http://bugs.exim.org/enter_bug.cgi?product=PCRE⟩.  This page was
       obtained from the tarball pcre-8.45.tar.gz fetched from
       ⟨ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/⟩ on
       2021-08-27.  If you discover any rendering problems in this HTML
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       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to

PCRE 8.34                   05 November 2013               PCRELIMITS(3)