--- code/trunk/doc/html/pcre.html 2007/02/24 21:40:24 71 +++ code/trunk/doc/html/pcre.html 2007/03/02 13:10:43 96 @@ -3,31 +3,54 @@ pcre specification -This HTML document has been generated automatically from the original man page. -If there is any nonsense in it, please consult the man page, in case the -conversion went wrong.
+

pcre man page

+

+Return to the PCRE index page. +

+

+This page is part of the PCRE HTML documentation. It was generated automatically +from the original man page. If there is any nonsense in it, please consult the +man page, in case the conversion went wrong. +

-
DESCRIPTION
+
INTRODUCTION

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 4.x) corresponds -approximately with Perl 5.8, including support for UTF-8 encoded strings. -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.)

-PCRE is written in C and released as a C library. However, a number of people -have written wrappers and interfaces of various kinds. A C++ class is included -in these contributions, which can be found in the Contrib directory at -the primary FTP site, which is: -

+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 +pcrematching +page. +

+

+PCRE is written in C and released as a C library. A number of people have +written wrappers and interfaces of various kinds. In particular, Google Inc. +have provided a comprehensive C++ wrapper. This is now included as part of the +PCRE distribution. The +pcrecpp +page has details of this interface. Other people's contributions can be found +in the Contrib directory at the primary FTP site, which is: ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre +

Details of exactly which Perl regular expression features are and are not supported by PCRE are given in separate documents. See the @@ -41,36 +64,47 @@ built. The pcre_config() function makes it possible for a client to discover which features are -available. Documentation about building PCRE for various operating systems can -be found in the README file in the source distribution. +available. The features themselves are described in the +pcrebuild +page. Documentation about building PCRE for various operating systems can be +found in the README file in the source distribution.

-
USER DOCUMENTATION

-The user documentation for PCRE has been split up into a number of different -sections. In the "man" format, each of these is a separate "man page". In the -HTML format, each is a separate page, linked from the index page. In the plain -text format, all the sections are concatenated, for ease of searching. The -sections are as follows: +The library contains a number of undocumented internal functions and data +tables that are used by more than one of the exported external functions, but +which are not intended for use by external callers. Their names all begin with +"_pcre_", which hopefully will not provoke any name clashes. In some +environments, it is possible to control which external symbols are exported +when a shared library is built, and in these cases the undocumented symbols are +not exported.

+
USER DOCUMENTATION

+The user documentation for PCRE comprises a number of different sections. In +the "man" format, each of these is a separate "man page". In the HTML format, +each is a separate page, linked from the index page. In the plain text format, +all the sections are concatenated, for ease of searching. The sections are as +follows:

   pcre              this document
-  pcreapi           details of PCRE's native API
+  pcreapi           details of PCRE's native C API
   pcrebuild         options for building PCRE
   pcrecallout       details of the callout feature
   pcrecompat        discussion of Perl compatibility
+  pcrecpp           details of the C++ wrapper
   pcregrep          description of the pcregrep command
-  pcrepattern       syntax and semantics of supported
-                      regular expressions
+  pcrematching      discussion of the two matching algorithms
+  pcrepartial       details of the partial matching facility
+  pcrepattern       syntax and semantics of supported regular expressions
   pcreperform       discussion of performance issues
-  pcreposix         the POSIX-compatible API
+  pcreposix         the POSIX-compatible C API
+  pcreprecompile    details of saving and re-using precompiled patterns
   pcresample        discussion of the sample program
-  pcretest          the pcretest testing command
-
-

-

+ 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 -library function, listing its arguments and results. +C library function, listing its arguments and results.


LIMITATIONS

@@ -84,29 +118,38 @@ internal linkage size of 3 or 4 (see the README file in the source distribution and the pcrebuild -documentation for details). If these cases the limit is substantially larger. -However, the speed of execution will be slower. +documentation for details). In these cases the limit is substantially larger. +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, 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. -

-
UTF-8 SUPPORT
-

-Starting at release 3.3, PCRE has had some support for character strings -encoded in the UTF-8 format. For release 4.0 this has been greatly extended to -cover most common requirements. +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. For a discussion of stack +issues, see the +pcrestack +documentation. +

+
UTF-8 AND UNICODE PROPERTY SUPPORT
+

+From release 3.3, PCRE has had some support for character strings encoded in +the UTF-8 format. For release 4.0 this was greatly extended to cover most +common requirements, and in release 5.0 additional support for Unicode general +category properties was added.

In order process UTF-8 strings, you must build PCRE to include UTF-8 support in @@ -119,7 +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, 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. 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: @@ -137,16 +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 @@ -157,34 +209,48 @@

6. The escape sequence \C can be used to match a single byte in UTF-8 mode, -but its use can lead to some strange effects. +but its use can lead to some strange effects. This facility is not available in +the alternative matching function, pcre_dfa_exec().

7. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly test characters of any code value, but the characters that PCRE recognizes as digits, spaces, or word characters remain the same set as before, all with -values less than 256. -

-

-8. Case-insensitive matching applies only to characters whose values are less -than 256. PCRE does not support the notion of "case" for higher-valued -characters. -

-

-9. PCRE does not support the use of Unicode tables and properties or the Perl -escapes \p, \P, and \X. +values less than 256. This remains true even when PCRE includes Unicode +property support, because to do otherwise would slow down PCRE in many common +cases. If you really want to test for a wider sense of, say, "digit", you +must use Unicode property tests such as \p{Nd}. +

+

+8. Similarly, characters that match the POSIX named character classes are all +low-valued characters. +

+

+9. Case-insensitive matching applies only to characters whose values are less +than 128, unless PCRE is built with Unicode property support. Even when Unicode +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. 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

-Philip Hazel <ph10@cam.ac.uk> +Philip Hazel
University Computing Service,
-Cambridge CB2 3QG, England. -
-Phone: +44 1223 334714 +Cambridge CB2 3QH, England.

-Last updated: 20 August 2003 +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: 23 November 2006
-Copyright © 1997-2003 University of Cambridge. +Copyright © 1997-2006 University of Cambridge. +

+Return to the PCRE index page. +