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-8.44.tar.gz fetched from
       ⟨ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/⟩ on
       2020-09-18.  If you discover any rendering problems in this HTML ver‐
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       source for the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original man‐
       ual page), send a mail to man-pages@man7.org

PCRE 8.34                     05 November 2013                 PCRELIMITS(3)