68 lines
2.3 KiB
Groff
68 lines
2.3 KiB
Groff
.TH PCRELIMITS 3 "24 June 2012" "PCRE 8.30"
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.SH NAME
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PCRE - Perl-compatible regular expressions
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.SH "SIZE AND OTHER LIMITATIONS"
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.rs
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.sp
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There are some size limitations in PCRE but it is hoped that they will never in
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practice be relevant.
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.P
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The maximum length of a compiled pattern is approximately 64K data units (bytes
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for the 8-bit library, 32-bit units for the 32-bit library, and 32-bit units for
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the 32-bit library) if PCRE is compiled with the default internal linkage size
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of 2 bytes. If you want to process regular expressions that are truly enormous,
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you can compile PCRE with an internal linkage size of 3 or 4 (when building the
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16-bit or 32-bit library, 3 is rounded up to 4). See the \fBREADME\fP file in
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the source distribution and the
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.\" HREF
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\fBpcrebuild\fP
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.\"
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documentation for details. In these cases the limit is substantially larger.
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However, the speed of execution is slower.
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.P
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All values in repeating quantifiers must be less than 65536.
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.P
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There is no limit to the number of parenthesized subpatterns, but there can be
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no more than 65535 capturing subpatterns.
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.P
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There is a limit to the number of forward references to subsequent subpatterns
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of around 200,000. Repeated forward references with fixed upper limits, for
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example, (?2){0,100} when subpattern number 2 is to the right, are included in
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the count. There is no limit to the number of backward references.
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.P
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The maximum length of name for a named subpattern is 32 characters, and the
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maximum number of named subpatterns is 10000.
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.P
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The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb
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is 255 for the 8-bit library and 65535 for the 16-bit and 32-bit library.
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.P
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The maximum length of a subject string is the largest positive number that an
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integer variable can hold. However, when using the traditional matching
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function, PCRE uses recursion to handle subpatterns and indefinite repetition.
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This means that the available stack space may limit the size of a subject
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string that can be processed by certain patterns. For a discussion of stack
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issues, see the
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.\" HREF
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\fBpcrestack\fP
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.\"
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documentation.
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.
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.
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.SH AUTHOR
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.rs
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.sp
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.nf
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Philip Hazel
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University Computing Service
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Cambridge CB2 3QH, England.
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.fi
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.
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.
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.SH REVISION
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.rs
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.sp
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.nf
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Last updated: 04 May 2012
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Copyright (c) 1997-2012 University of Cambridge.
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.fi
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