diff -r 000000000000 -r 7f656887cf89 libraries/spcre/libpcre/pcre/doc/pcre.3 --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/libraries/spcre/libpcre/pcre/doc/pcre.3 Wed Jun 23 15:52:26 2010 +0100 @@ -0,0 +1,294 @@ +.TH PCRE 3 +.SH NAME +PCRE - Perl-compatible regular expressions +.SH INTRODUCTION +.rs +.sp +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. Certain features that appeared in Python and PCRE before they +appeared in Perl are also available using the Python syntax. There is also some +support for certain .NET and Oniguruma syntax items, and there is an option for +requesting some minor changes that give better JavaScript compatibility. +.P +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. +.P +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 +.\" HREF +\fBpcrematching\fP +.\" +page. +.P +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 +.\" HREF +\fBpcrecpp\fP +.\" +page has details of this interface. Other people's contributions can be found +in the \fIContrib\fR directory at the primary FTP site, which is: +.sp +.\" HTML +.\" +ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre +.P +Details of exactly which Perl regular expression features are and are not +supported by PCRE are given in separate documents. See the +.\" HREF +\fBpcrepattern\fR +.\" +and +.\" HREF +\fBpcrecompat\fR +.\" +pages. There is a syntax summary in the +.\" HREF +\fBpcresyntax\fR +.\" +page. +.P +Some features of PCRE can be included, excluded, or changed when the library is +built. The +.\" HREF +\fBpcre_config()\fR +.\" +function makes it possible for a client to discover which features are +available. The features themselves are described in the +.\" HREF +\fBpcrebuild\fP +.\" +page. Documentation about building PCRE for various operating systems can be +found in the \fBREADME\fP file in the source distribution. +.P +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. +. +. +.SH "USER DOCUMENTATION" +.rs +.sp +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: +.sp + pcre this document + pcre-config show PCRE installation configuration information + 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 \fBpcregrep\fP command + pcrematching discussion of the two matching algorithms + pcrepartial details of the partial matching facility +.\" JOIN + pcrepattern syntax and semantics of supported + regular expressions + pcresyntax quick syntax reference + pcreperform discussion of performance issues + 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 \fBpcretest\fP testing command +.sp +In addition, in the "man" and HTML formats, there is a short page for each +C library function, listing its arguments and results. +. +. +.SH LIMITATIONS +.rs +.sp +There are some size limitations in PCRE but it is hoped that they will never in +practice be relevant. +.P +The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is +compiled with the default internal linkage size of 2. If you want to process +regular expressions that are truly enormous, you can compile PCRE with an +internal linkage size of 3 or 4 (see the \fBREADME\fP file in the source +distribution and the +.\" HREF +\fBpcrebuild\fP +.\" +documentation for details). In these cases the limit is substantially larger. +However, the speed of execution is slower. +.P +All values in repeating quantifiers must be less than 65536. +.P +There is no limit to the number of parenthesized subpatterns, but there can be +no more than 65535 capturing subpatterns. +.P +The maximum length of name for a named subpattern is 32 characters, and the +maximum number of named subpatterns is 10000. +.P +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. For a discussion of stack +issues, see the +.\" HREF +\fBpcrestack\fP +.\" +documentation. +. +.\" HTML +. +. +.SH "UTF-8 AND UNICODE PROPERTY SUPPORT" +.rs +.sp +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. +.P +In order process UTF-8 strings, you must build PCRE to include UTF-8 support in +the code, and, in addition, you must call +.\" HREF +\fBpcre_compile()\fP +.\" +with the PCRE_UTF8 option flag. When you do this, both the pattern and any +subject strings that are matched against it are treated as UTF-8 strings +instead of just strings of bytes. +.P +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 occasionally, so should not be very big. +.P +If PCRE is built with Unicode character property support (which implies UTF-8 +support), the escape sequences \ep{..}, \eP{..}, and \eX 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 +.\" HREF +\fBpcrepattern\fP +.\" +documentation. Only the short names for properties are supported. For example, +\ep{L} matches a letter. Its Perl synonym, \ep{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. +. +.\" HTML +. +.SS "Validity of UTF-8 strings" +.rs +.sp +When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects +are (by default) checked for validity on entry to the relevant functions. From +release 7.3 of PCRE, the check is according the rules of RFC 3629, which are +themselves derived from the Unicode specification. Earlier releases of PCRE +followed the rules of RFC 2279, which allows the full range of 31-bit values (0 +to 0x7FFFFFFF). The current check allows only values in the range U+0 to +U+10FFFF, excluding U+D800 to U+DFFF. +.P +The excluded code points are the "Low Surrogate Area" of Unicode, of which the +Unicode Standard says this: "The Low Surrogate Area does not contain any +character assignments, consequently no character code charts or namelists are +provided for this area. Surrogates are reserved for use with UTF-16 and then +must be used in pairs." The code points that are encoded by UTF-16 pairs are +available as independent code points in the UTF-8 encoding. (In other words, +the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up +UTF-8.) +.P +If an invalid UTF-8 string is passed to PCRE, an error return +(PCRE_ERROR_BADUTF8) is given. In some situations, you may already know that +your strings are valid, and therefore want to skip these checks in order to +improve performance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or +at run time, PCRE assumes that the pattern or subject it is given +(respectively) contains only valid UTF-8 codes. In this case, it does not +diagnose an invalid UTF-8 string. +.P +If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what +happens depends on why the string is invalid. If the string conforms to the +"old" definition of UTF-8 (RFC 2279), it is processed as a string of characters +in the range 0 to 0x7FFFFFFF. In other words, apart from the initial validity +test, PCRE (when in UTF-8 mode) handles strings according to the more liberal +rules of RFC 2279. However, if the string does not even conform to RFC 2279, +the result is undefined. Your program may crash. +.P +If you want to process strings of values in the full range 0 to 0x7FFFFFFF, +encoded in a UTF-8-like manner as per the old RFC, you can set +PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this +situation, you will have to apply your own validity check. +. +.SS "General comments about UTF-8 mode" +.rs +.sp +1. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte +UTF-8 character if the value is greater than 127. +.P +2. Octal numbers up to \e777 are recognized, and match two-byte UTF-8 +characters for values greater than \e177. +.P +3. Repeat quantifiers apply to complete UTF-8 characters, not to individual +bytes, for example: \ex{100}{3}. +.P +4. The dot metacharacter matches one UTF-8 character instead of a single byte. +.P +5. The escape sequence \eC can be used to match a single byte in UTF-8 mode, +but its use can lead to some strange effects. This facility is not available in +the alternative matching function, \fBpcre_dfa_exec()\fP. +.P +6. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW 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. 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 \ep{Nd}. +.P +7. Similarly, characters that match the POSIX named character classes are all +low-valued characters. +.P +8. However, the Perl 5.10 horizontal and vertical whitespace matching escapes +(\eh, \eH, \ev, and \eV) do match all the appropriate Unicode characters. +.P +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. +. +. +.SH AUTHOR +.rs +.sp +.nf +Philip Hazel +University Computing Service +Cambridge CB2 3QH, England. +.fi +.P +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 two initials, followed by the +two digits 10, at the domain cam.ac.uk. +. +. +.SH REVISION +.rs +.sp +.nf +Last updated: 12 April 2008 +Copyright (c) 1997-2008 University of Cambridge. +.fi