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revision 208 by ph10, Mon Aug 6 15:23:29 2007 UTC revision 678 by ph10, Sun Aug 28 15:23:03 2011 UTC
# Line 15  man page, in case the conversion went wr Line 15  man page, in case the conversion went wr
15  <ul>  <ul>
16  <li><a name="TOC1" href="#SEC1">INTRODUCTION</a>  <li><a name="TOC1" href="#SEC1">INTRODUCTION</a>
17  <li><a name="TOC2" href="#SEC2">USER DOCUMENTATION</a>  <li><a name="TOC2" href="#SEC2">USER DOCUMENTATION</a>
18  <li><a name="TOC3" href="#SEC3">LIMITATIONS</a>  <li><a name="TOC3" href="#SEC3">AUTHOR</a>
19  <li><a name="TOC4" href="#SEC4">UTF-8 AND UNICODE PROPERTY SUPPORT</a>  <li><a name="TOC4" href="#SEC4">REVISION</a>
 <li><a name="TOC5" href="#SEC5">AUTHOR</a>  
 <li><a name="TOC6" href="#SEC6">REVISION</a>  
20  </ul>  </ul>
21  <br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>  <br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>
22  <P>  <P>
23  The PCRE library is a set of functions that implement regular expression  The PCRE library is a set of functions that implement regular expression
24  pattern matching using the same syntax and semantics as Perl, with just a few  pattern matching using the same syntax and semantics as Perl, with just a few
25  differences. (Certain features that appeared in Python and PCRE before they  differences. Some features that appeared in Python and PCRE before they
26  appeared in Perl are also available using the Python syntax.)  appeared in Perl are also available using the Python syntax, there is some
27    support for one or two .NET and Oniguruma syntax items, and there is an option
28    for requesting some minor changes that give better JavaScript compatibility.
29  </P>  </P>
30  <P>  <P>
31  The current implementation of PCRE (release 7.x) corresponds approximately with  The current implementation of PCRE corresponds approximately with Perl 5.12,
32  Perl 5.10, including support for UTF-8 encoded strings and Unicode general  including support for UTF-8 encoded strings and Unicode general category
33  category properties. However, UTF-8 and Unicode support has to be explicitly  properties. However, UTF-8 and Unicode support has to be explicitly enabled; it
34  enabled; it is not the default. The Unicode tables correspond to Unicode  is not the default. The Unicode tables correspond to Unicode release 6.0.0.
 release 5.0.0.  
35  </P>  </P>
36  <P>  <P>
37  In addition to the Perl-compatible matching function, PCRE contains an  In addition to the Perl-compatible matching function, PCRE contains an
38  alternative matching function that matches the same compiled patterns in a  alternative function that matches the same compiled patterns in a different
39  different way. In certain circumstances, the alternative function has some  way. In certain circumstances, the alternative function has some advantages.
40  advantages. For a discussion of the two matching algorithms, see the  For a discussion of the two matching algorithms, see the
41  <a href="pcrematching.html"><b>pcrematching</b></a>  <a href="pcrematching.html"><b>pcrematching</b></a>
42  page.  page.
43  </P>  </P>
# Line 70  function makes it possible for a client Line 69  function makes it possible for a client
69  available. The features themselves are described in the  available. The features themselves are described in the
70  <a href="pcrebuild.html"><b>pcrebuild</b></a>  <a href="pcrebuild.html"><b>pcrebuild</b></a>
71  page. Documentation about building PCRE for various operating systems can be  page. Documentation about building PCRE for various operating systems can be
72  found in the <b>README</b> file in the source distribution.  found in the <b>README</b> and <b>NON-UNIX-USE</b> files in the source
73    distribution.
74  </P>  </P>
75  <P>  <P>
76  The library contains a number of undocumented internal functions and data  The library contains a number of undocumented internal functions and data
# Line 86  not exported. Line 86  not exported.
86  The user documentation for PCRE comprises a number of different sections. In  The user documentation for PCRE comprises a number of different sections. In
87  the "man" format, each of these is a separate "man page". In the HTML format,  the "man" format, each of these is a separate "man page". In the HTML format,
88  each is a separate page, linked from the index page. In the plain text format,  each is a separate page, linked from the index page. In the plain text format,
89  all the sections are concatenated, for ease of searching. The sections are as  all the sections, except the <b>pcredemo</b> section, are concatenated, for ease
90  follows:  of searching. The sections are as follows:
91  <pre>  <pre>
92    pcre              this document    pcre              this document
93    pcre-config       show PCRE installation configuration information    pcre-config       show PCRE installation configuration information
# Line 96  follows: Line 96  follows:
96    pcrecallout       details of the callout feature    pcrecallout       details of the callout feature
97    pcrecompat        discussion of Perl compatibility    pcrecompat        discussion of Perl compatibility
98    pcrecpp           details of the C++ wrapper    pcrecpp           details of the C++ wrapper
99      pcredemo          a demonstration C program that uses PCRE
100    pcregrep          description of the <b>pcregrep</b> command    pcregrep          description of the <b>pcregrep</b> command
101      pcrejit           discussion of the just-in-time optimization support
102      pcrelimits        details of size and other limits
103    pcrematching      discussion of the two matching algorithms    pcrematching      discussion of the two matching algorithms
104    pcrepartial       details of the partial matching facility    pcrepartial       details of the partial matching facility
105    pcrepattern       syntax and semantics of supported regular expressions    pcrepattern       syntax and semantics of supported regular expressions
   pcresyntax        quick syntax reference  
106    pcreperform       discussion of performance issues    pcreperform       discussion of performance issues
107    pcreposix         the POSIX-compatible C API    pcreposix         the POSIX-compatible C API
108    pcreprecompile    details of saving and re-using precompiled patterns    pcreprecompile    details of saving and re-using precompiled patterns
109    pcresample        discussion of the sample program    pcresample        discussion of the pcredemo program
110    pcrestack         discussion of stack usage    pcrestack         discussion of stack usage
111      pcresyntax        quick syntax reference
112    pcretest          description of the <b>pcretest</b> testing command    pcretest          description of the <b>pcretest</b> testing command
113      pcreunicode       discussion of Unicode and UTF-8 support
114  </pre>  </pre>
115  In addition, in the "man" and HTML formats, there is a short page for each  In addition, in the "man" and HTML formats, there is a short page for each
116  C library function, listing its arguments and results.  C library function, listing its arguments and results.
117  </P>  </P>
118  <br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>  <br><a name="SEC3" href="#TOC1">AUTHOR</a><br>
 <P>  
 There are some size limitations in PCRE but it is hoped that they will never in  
 practice be relevant.  
 </P>  
 <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 <b>README</b> file in the source  
 distribution and the  
 <a href="pcrebuild.html"><b>pcrebuild</b></a>  
 documentation for details). In these cases the limit is substantially larger.  
 However, the speed of execution is slower.  
 </P>  
 <P>  
 All values in repeating quantifiers must be less than 65536.  
 </P>  
 <P>  
 There is no limit to the number of parenthesized subpatterns, but there can be  
 no more than 65535 capturing subpatterns.  
 </P>  
 <P>  
 The maximum length of name for a named subpattern is 32 characters, and the  
 maximum number of named subpatterns is 10000.  
 </P>  
 <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  
 <a href="pcrestack.html"><b>pcrestack</b></a>  
 documentation.  
 <a name="utf8support"></a></P>  
 <br><a name="SEC4" href="#TOC1">UTF-8 AND UNICODE PROPERTY SUPPORT</a><br>  
 <P>  
 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>  
 <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  
 <a href="pcre_compile.html"><b>pcre_compile()</b></a>  
 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>  
 <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>  
 <P>  
 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  
 <a href="pcrepattern.html"><b>pcrepattern</b></a>  
 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.  
 </P>  
 <P>  
 The following comments apply when PCRE is running in UTF-8 mode:  
 </P>  
 <P>  
 1. When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects  
 are checked for validity on entry to the relevant functions. If an invalid  
 UTF-8 string is passed, an error return 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. If you pass an invalid UTF-8 string to  
 PCRE when PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  
 may crash.  
 </P>  
 <P>  
 2. An unbraced hexadecimal escape sequence (such as \xb3) matches a two-byte  
 UTF-8 character if the value is greater than 127.  
 </P>  
 <P>  
 3. Octal numbers up to \777 are recognized, and match two-byte UTF-8  
 characters for values greater than \177.  
 </P>  
 <P>  
 4. Repeat quantifiers apply to complete UTF-8 characters, not to individual  
 bytes, for example: \x{100}{3}.  
 </P>  
 <P>  
 5. The dot metacharacter matches one UTF-8 character instead of a single byte.  
 </P>  
 <P>  
 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. This facility is not available in  
 the alternative matching function, <b>pcre_dfa_exec()</b>.  
 </P>  
 <P>  
 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. 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}.  
 </P>  
 <P>  
 8. Similarly, characters that match the POSIX named character classes are all  
 low-valued characters.  
 </P>  
 <P>  
 9. However, the Perl 5.10 horizontal and vertical whitespace matching escapes  
 (\h, \H, \v, and \V) do match all the appropriate Unicode characters.  
 </P>  
 <P>  
 10. 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.  
 </P>  
 <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>  
119  <P>  <P>
120  Philip Hazel  Philip Hazel
121  <br>  <br>
# Line 257  Putting an actual email address here see Line 129  Putting an actual email address here see
129  taken it away. If you want to email me, use my two initials, followed by the  taken it away. If you want to email me, use my two initials, followed by the
130  two digits 10, at the domain cam.ac.uk.  two digits 10, at the domain cam.ac.uk.
131  </P>  </P>
132  <br><a name="SEC6" href="#TOC1">REVISION</a><br>  <br><a name="SEC4" href="#TOC1">REVISION</a><br>
133  <P>  <P>
134  Last updated: 06 August 2007  Last updated: 24 August 2011
135  <br>  <br>
136  Copyright &copy; 1997-2007 University of Cambridge.  Copyright &copy; 1997-2011 University of Cambridge.
137  <br>  <br>
138  <p>  <p>
139  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.

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