pcre2limits(3) — Linux manual page

NAME \| SIZE AND OTHER LIMITATIONS \| AUTHOR \| REVISION \| COLOPHON

PCRE2LIMITS(3)           Library Functions Manual          PCRE2LIMITS(3)

NAME top

       PCRE2 - Perl-compatible regular expressions (revised API)

SIZE AND OTHER LIMITATIONS top


       There are some size limitations in PCRE2 but it is hoped that they
       will never in practice be relevant.

       The maximum size of a compiled pattern is approximately 64
       thousand code units for the 8-bit and 16-bit libraries if PCRE2 is
       compiled with the default internal linkage size, which is 2 bytes
       for these libraries. If you want to process regular expressions
       that are truly enormous, you can compile PCRE2 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 pcre2build documentation for details. In these cases the
       limit is substantially larger.  However, the speed of execution is
       slower. In the 32-bit library, the internal linkage size is always
       4.

       The maximum length of a source pattern string is essentially
       unlimited; it is the largest number a PCRE2_SIZE variable can
       hold. However, the program that calls pcre2_compile() can specify
       a smaller limit.

       The maximum length (in code units) of a subject string is one less
       than the largest number a PCRE2_SIZE variable can hold. PCRE2_SIZE
       is an unsigned integer type, usually defined as size_t. Its
       maximum value (that is ~(PCRE2_SIZE)0) is reserved as a special
       indicator for zero-terminated strings and unset offsets.

       All values in repeating quantifiers must be less than 65536.

       There are two different limits that apply to branches of
       lookbehind assertions.  If every branch in such an assertion
       matches a fixed number of characters, the maximum length of any
       branch is 65535 characters. If any branch matches a variable
       number of characters, then the maximum matching length for every
       branch is limited. The default limit is set at compile time,
       defaulting to 255, but can be changed by the calling program.

       There is no limit to the number of parenthesized groups, but there
       can be no more than 65535 capture groups, and there is 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 default limit can be specified when PCRE2 is
       built; if not, the default is set to 250. An application can
       change this limit by calling pcre2_set_parens_nest_limit() to set
       the limit in a compile context.

       The maximum length of name for a named capture group is 32 code
       units, and the maximum number of such groups is 10000.

       The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or
       (*THEN) verb is 255 code units for the 8-bit library and 65535
       code units for the 16-bit and 32-bit libraries.

       The maximum length of a string argument to a callout is the
       largest number a 32-bit unsigned integer can hold.

       The maximum amount of heap memory used for matching is controlled
       by the heap limit, which can be set in a pattern or in a match
       context. The default is a very large number, effectively
       unlimited.

AUTHOR top


       Philip Hazel
       Retired from University Computing Service
       Cambridge, England.

REVISION top


       Last updated: 16 August 2023
       Copyright (c) 1997-2023 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 fetched from
       ⟨https://github.com/PhilipHazel/pcre2.git⟩ on 2025-08-11.  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-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 [email protected]

PCRE2 10.46-DEV               16 August 2023               PCRE2LIMITS(3)