--- code/trunk/doc/html/pcre.html 2007/02/24 21:41:06 83 +++ code/trunk/doc/html/pcre.html 2007/03/02 13:10:43 96 @@ -23,13 +23,18 @@

The PCRE library is a set of functions that implement regular expression pattern matching using the same syntax and semantics as Perl, with just a few -differences. The current implementation of PCRE (release 6.x) corresponds -approximately with Perl 5.8, including support for UTF-8 encoded strings and -Unicode general category properties. However, this support has to be explicitly -enabled; it is not the default. +differences. (Certain features that appeared in Python and PCRE before they +appeared in Perl are also available using the Python syntax.)

-In addition to the Perl-compatible matching function, PCRE also contains an +The current implementation of PCRE (release 7.x) corresponds approximately with +Perl 5.10, including support for UTF-8 encoded strings and Unicode general +category properties. However, UTF-8 and Unicode support has to be explicitly +enabled; it is not the default. The Unicode tables correspond to Unicode +release 5.0.0. +

+

+In addition to the Perl-compatible matching function, PCRE contains an alternative matching function that matches the same compiled patterns in a different way. In certain circumstances, the alternative function has some advantages. For a discussion of the two matching algorithms, see the @@ -95,6 +100,7 @@ pcreposix the POSIX-compatible C API pcreprecompile details of saving and re-using precompiled patterns pcresample discussion of the sample program + pcrestack discussion of stack usage pcretest description of the pcretest testing command In addition, in the "man" and HTML formats, there is a short page for each @@ -113,23 +119,30 @@ distribution and the pcrebuild documentation for details). In these cases the limit is substantially larger. -However, the speed of execution will be slower. +However, the speed of execution is slower. +

+

+All values in repeating quantifiers must be less than 65536. The maximum +compiled length of subpattern with an explicit repeat count is 30000 bytes. The +maximum number of capturing subpatterns is 65535.

-All values in repeating quantifiers must be less than 65536. -The maximum number of capturing subpatterns is 65535. +There is no limit to the number of parenthesized subpatterns, but there can be +no more than 65535 capturing subpatterns.

-There is no limit to the number of non-capturing subpatterns, but the maximum -depth of nesting of all kinds of parenthesized subpattern, including capturing -subpatterns, assertions, and other types of subpattern, is 200. +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. +string that can be processed by certain patterns. For a discussion of stack +issues, see the +pcrestack +documentation.


UTF-8 AND UNICODE PROPERTY SUPPORT

@@ -149,17 +162,20 @@

If you compile PCRE with UTF-8 support, but do not use it at run time, the library will be a bit bigger, but the additional run time overhead is limited -to testing the PCRE_UTF8 flag in several places, so should not be very large. +to testing the PCRE_UTF8 flag occasionally, so should not be very big.

If PCRE is built with Unicode character property support (which implies UTF-8 support), the escape sequences \p{..}, \P{..}, and \X are supported. The available properties that can be tested are limited to the general category properties such as Lu for an upper case letter or Nd for a decimal -number. A full list is given in the +number, the Unicode script names such as Arabic or Han, and the derived +properties Any and L&. A full list is given in the pcrepattern -documentation. The PCRE library is increased in size by about 90K when Unicode -property support is included. +documentation. Only the short names for properties are supported. For example, +\p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported. +Furthermore, in Perl, many properties may optionally be prefixed by "Is", for +compatibility with Perl 5.6. PCRE does not support this.

The following comments apply when PCRE is running in UTF-8 mode: @@ -177,16 +193,12 @@ may crash.

-2. In a pattern, the escape sequence \x{...}, where the contents of the braces -is a string of hexadecimal digits, is interpreted as a UTF-8 character whose -code number is the given hexadecimal number, for example: \x{1234}. If a -non-hexadecimal digit appears between the braces, the item is not recognized. -This escape sequence can be used either as a literal, or within a character -class. +2. An unbraced hexadecimal escape sequence (such as \xb3) matches a two-byte +UTF-8 character if the value is greater than 127.

-3. The original hexadecimal escape sequence, \xhh, matches a two-byte UTF-8 -character if the value is greater than 127. +3. Octal numbers up to \777 are recognized, and match two-byte UTF-8 +characters for values greater than \177.

4. Repeat quantifiers apply to complete UTF-8 characters, not to individual @@ -219,7 +231,10 @@ property support is available, PCRE still uses its own character tables when checking the case of low-valued characters, so as not to degrade performance. The Unicode property information is used only for characters with higher -values. +values. Even when Unicode property support is available, PCRE supports +case-insensitive matching only when there is a one-to-one mapping between a +letter's cases. There are a small number of many-to-one mappings in Unicode; +these are not supported by PCRE.


AUTHOR

@@ -227,15 +242,15 @@
University Computing Service,
-Cambridge CB2 3QG, England. +Cambridge CB2 3QH, England.

Putting an actual email address here seems to have been a spam magnet, so I've taken it away. If you want to email me, use my initial and surname, separated by a dot, at the domain ucs.cam.ac.uk. -Last updated: 07 March 2005 +Last updated: 23 November 2006
-Copyright © 1997-2005 University of Cambridge. +Copyright © 1997-2006 University of Cambridge.

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