# pcrelimits man page

Return to the PCRE index page.

This page is part of the PCRE HTML documentation. It was generated automatically from the original man page. If there is any nonsense in it, please consult the man page, in case the conversion went wrong.
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 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 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.

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. 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: 24 August 2011
Copyright © 1997-2011 University of Cambridge.

Return to the PCRE index page.