Tristan Matthews | 0461646 | 2013-11-14 16:09:34 -0500 | [diff] [blame] | 1 | .TH PCRELIMITS 3 |
| 2 | .SH NAME |
| 3 | PCRE - Perl-compatible regular expressions |
| 4 | .SH "SIZE AND OTHER LIMITATIONS" |
| 5 | .rs |
| 6 | .sp |
| 7 | There are some size limitations in PCRE but it is hoped that they will never in |
| 8 | practice be relevant. |
| 9 | .P |
| 10 | The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is |
| 11 | compiled with the default internal linkage size of 2. If you want to process |
| 12 | regular expressions that are truly enormous, you can compile PCRE with an |
| 13 | internal linkage size of 3 or 4 (see the \fBREADME\fP file in the source |
| 14 | distribution and the |
| 15 | .\" HREF |
| 16 | \fBpcrebuild\fP |
| 17 | .\" |
| 18 | documentation for details). In these cases the limit is substantially larger. |
| 19 | However, the speed of execution is slower. |
| 20 | .P |
| 21 | All values in repeating quantifiers must be less than 65536. |
| 22 | .P |
| 23 | There is no limit to the number of parenthesized subpatterns, but there can be |
| 24 | no more than 65535 capturing subpatterns. |
| 25 | .P |
| 26 | There is a limit to the number of forward references to subsequent subpatterns |
| 27 | of around 200,000. Repeated forward references with fixed upper limits, for |
| 28 | example, (?2){0,100} when subpattern number 2 is to the right, are included in |
| 29 | the count. There is no limit to the number of backward references. |
| 30 | .P |
| 31 | The maximum length of name for a named subpattern is 32 characters, and the |
| 32 | maximum number of named subpatterns is 10000. |
| 33 | .P |
| 34 | The maximum length of a subject string is the largest positive number that an |
| 35 | integer variable can hold. However, when using the traditional matching |
| 36 | function, PCRE uses recursion to handle subpatterns and indefinite repetition. |
| 37 | This means that the available stack space may limit the size of a subject |
| 38 | string that can be processed by certain patterns. For a discussion of stack |
| 39 | issues, see the |
| 40 | .\" HREF |
| 41 | \fBpcrestack\fP |
| 42 | .\" |
| 43 | documentation. |
| 44 | . |
| 45 | . |
| 46 | .SH AUTHOR |
| 47 | .rs |
| 48 | .sp |
| 49 | .nf |
| 50 | Philip Hazel |
| 51 | University Computing Service |
| 52 | Cambridge CB2 3QH, England. |
| 53 | .fi |
| 54 | . |
| 55 | . |
| 56 | .SH REVISION |
| 57 | .rs |
| 58 | .sp |
| 59 | .nf |
| 60 | Last updated: 30 November 2011 |
| 61 | Copyright (c) 1997-2011 University of Cambridge. |
| 62 | .fi |