PCRELIMITS(3)PCRELIMITS(3)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) if PCRE is compiled with the default internal linkage size of
2 bytes. 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 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. How‐
ever, 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 a limit to the number of forward references to subsequent sub‐
patterns 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
library.
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 indef‐
inite 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: 04 May 2012
Copyright (c) 1997-2012 University of Cambridge.
PCRE 8.30 04 May 2012 PCRELIMITS(3)
