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3  <title>pcre specification</title>  <title>pcre specification</title>
4  </head>  </head>
5  <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">  <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6  This HTML document has been generated automatically from the original man page.  <h1>pcre man page</h1>
7  If there is any nonsense in it, please consult the man page, in case the  <p>
8  conversion went wrong.<br>  Return to the <a href="index.html">PCRE index page</a>.
9    </p>
10    <p>
11    This page is part of the PCRE HTML documentation. It was generated automatically
12    from the original man page. If there is any nonsense in it, please consult the
13    man page, in case the conversion went wrong.
14    <br>
15  <ul>  <ul>
16  <li><a name="TOC1" href="#SEC1">DESCRIPTION</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">LIMITATIONS</a>
19  <li><a name="TOC4" href="#SEC4">UTF-8 SUPPORT</a>  <li><a name="TOC4" href="#SEC4">UTF-8 AND UNICODE PROPERTY SUPPORT</a>
20  <li><a name="TOC5" href="#SEC5">AUTHOR</a>  <li><a name="TOC5" href="#SEC5">AUTHOR</a>
21  </ul>  </ul>
22  <br><a name="SEC1" href="#TOC1">DESCRIPTION</a><br>  <br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>
23  <P>  <P>
24  The PCRE library is a set of functions that implement regular expression  The PCRE library is a set of functions that implement regular expression
25  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
26  differences. The current implementation of PCRE (release 4.x) corresponds  differences. (Certain features that appeared in Python and PCRE before they
27  approximately with Perl 5.8, including support for UTF-8 encoded strings.  appeared in Perl are also available using the Python syntax.)
 However, this support has to be explicitly enabled; it is not the default.  
28  </P>  </P>
29  <P>  <P>
30  PCRE is written in C and released as a C library. However, a number of people  The current implementation of PCRE (release 7.x) corresponds approximately with
31  have written wrappers and interfaces of various kinds. A C++ class is included  Perl 5.10, including support for UTF-8 encoded strings and Unicode general
32  in these contributions, which can be found in the <i>Contrib</i> directory at  category properties. However, UTF-8 and Unicode support has to be explicitly
33  the primary FTP site, which is:  enabled; it is not the default. The Unicode tables correspond to Unicode
34  </P>  release 5.0.0.
35    </P>
36    <P>
37    In addition to the Perl-compatible matching function, PCRE contains an
38    alternative matching function that matches the same compiled patterns in a
39    different way. In certain circumstances, the alternative function has some
40    advantages. For a discussion of the two matching algorithms, see the
41    <a href="pcrematching.html"><b>pcrematching</b></a>
42    page.
43    </P>
44    <P>
45    PCRE is written in C and released as a C library. A number of people have
46    written wrappers and interfaces of various kinds. In particular, Google Inc.
47    have provided a comprehensive C++ wrapper. This is now included as part of the
48    PCRE distribution. The
49    <a href="pcrecpp.html"><b>pcrecpp</b></a>
50    page has details of this interface. Other people's contributions can be found
51    in the <i>Contrib</i> directory at the primary FTP site, which is:
52  <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>  <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>
53    </P>
54  <P>  <P>
55  Details of exactly which Perl regular expression features are and are not  Details of exactly which Perl regular expression features are and are not
56  supported by PCRE are given in separate documents. See the  supported by PCRE are given in separate documents. See the
# Line 41  Some features of PCRE can be included, e Line 64  Some features of PCRE can be included, e
64  built. The  built. The
65  <a href="pcre_config.html"><b>pcre_config()</b></a>  <a href="pcre_config.html"><b>pcre_config()</b></a>
66  function makes it possible for a client to discover which features are  function makes it possible for a client to discover which features are
67  available. Documentation about building PCRE for various operating systems can  available. The features themselves are described in the
68  be found in the <b>README</b> file in the source distribution.  <a href="pcrebuild.html"><b>pcrebuild</b></a>
69    page. Documentation about building PCRE for various operating systems can be
70    found in the <b>README</b> file in the source distribution.
71  </P>  </P>
 <br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>  
72  <P>  <P>
73  The user documentation for PCRE has been split up into a number of different  The library contains a number of undocumented internal functions and data
74  sections. In the "man" format, each of these is a separate "man page". In the  tables that are used by more than one of the exported external functions, but
75  HTML format, each is a separate page, linked from the index page. In the plain  which are not intended for use by external callers. Their names all begin with
76  text format, all the sections are concatenated, for ease of searching. The  "_pcre_", which hopefully will not provoke any name clashes. In some
77  sections are as follows:  environments, it is possible to control which external symbols are exported
78    when a shared library is built, and in these cases the undocumented symbols are
79    not exported.
80  </P>  </P>
81    <br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>
82  <P>  <P>
83    The user documentation for PCRE comprises a number of different sections. In
84    the "man" format, each of these is a separate "man page". In the HTML format,
85    each is a separate page, linked from the index page. In the plain text format,
86    all the sections are concatenated, for ease of searching. The sections are as
87    follows:
88  <pre>  <pre>
89    pcre              this document    pcre              this document
90    pcreapi           details of PCRE's native API    pcreapi           details of PCRE's native C API
91    pcrebuild         options for building PCRE    pcrebuild         options for building PCRE
92    pcrecallout       details of the callout feature    pcrecallout       details of the callout feature
93    pcrecompat        discussion of Perl compatibility    pcrecompat        discussion of Perl compatibility
94      pcrecpp           details of the C++ wrapper
95    pcregrep          description of the <b>pcregrep</b> command    pcregrep          description of the <b>pcregrep</b> command
96    pcrepattern       syntax and semantics of supported    pcrematching      discussion of the two matching algorithms
97                        regular expressions    pcrepartial       details of the partial matching facility
98      pcrepattern       syntax and semantics of supported regular expressions
99    pcreperform       discussion of performance issues    pcreperform       discussion of performance issues
100    pcreposix         the POSIX-compatible API    pcreposix         the POSIX-compatible C API
101      pcreprecompile    details of saving and re-using precompiled patterns
102    pcresample        discussion of the sample program    pcresample        discussion of the sample program
103    pcretest          the <b>pcretest</b> testing command    pcrestack         discussion of stack usage
104  </PRE>    pcretest          description of the <b>pcretest</b> testing command
105  </P>  </pre>
 <P>  
106  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
107  library function, listing its arguments and results.  C library function, listing its arguments and results.
108  </P>  </P>
109  <br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>  <br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>
110  <P>  <P>
# Line 84  regular expressions that are truly enorm Line 118  regular expressions that are truly enorm
118  internal linkage size of 3 or 4 (see the <b>README</b> file in the source  internal linkage size of 3 or 4 (see the <b>README</b> file in the source
119  distribution and the  distribution and the
120  <a href="pcrebuild.html"><b>pcrebuild</b></a>  <a href="pcrebuild.html"><b>pcrebuild</b></a>
121  documentation for details). If these cases the limit is substantially larger.  documentation for details). In these cases the limit is substantially larger.
122  However, the speed of execution will be slower.  However, the speed of execution is slower.
123    </P>
124    <P>
125    All values in repeating quantifiers must be less than 65536. The maximum
126    compiled length of subpattern with an explicit repeat count is 30000 bytes. The
127    maximum number of capturing subpatterns is 65535.
128  </P>  </P>
129  <P>  <P>
130  All values in repeating quantifiers must be less than 65536.  There is no limit to the number of parenthesized subpatterns, but there can be
131  The maximum number of capturing subpatterns is 65535.  no more than 65535 capturing subpatterns.
132  </P>  </P>
133  <P>  <P>
134  There is no limit to the number of non-capturing subpatterns, but the maximum  The maximum length of name for a named subpattern is 32 characters, and the
135  depth of nesting of all kinds of parenthesized subpattern, including capturing  maximum number of named subpatterns is 10000.
 subpatterns, assertions, and other types of subpattern, is 200.  
136  </P>  </P>
137  <P>  <P>
138  The maximum length of a subject string is the largest positive number that an  The maximum length of a subject string is the largest positive number that an
139  integer variable can hold. However, PCRE uses recursion to handle subpatterns  integer variable can hold. However, when using the traditional matching
140  and indefinite repetition. This means that the available stack space may limit  function, PCRE uses recursion to handle subpatterns and indefinite repetition.
141  the size of a subject string that can be processed by certain patterns.  This means that the available stack space may limit the size of a subject
142  </P>  string that can be processed by certain patterns. For a discussion of stack
143  <a name="utf8support"></a><br><a name="SEC4" href="#TOC1">UTF-8 SUPPORT</a><br>  issues, see the
144  <P>  <a href="pcrestack.html"><b>pcrestack</b></a>
145  Starting at release 3.3, PCRE has had some support for character strings  documentation.
146  encoded in the UTF-8 format. For release 4.0 this has been greatly extended to  <a name="utf8support"></a></P>
147  cover most common requirements.  <br><a name="SEC4" href="#TOC1">UTF-8 AND UNICODE PROPERTY SUPPORT</a><br>
148    <P>
149    From release 3.3, PCRE has had some support for character strings encoded in
150    the UTF-8 format. For release 4.0 this was greatly extended to cover most
151    common requirements, and in release 5.0 additional support for Unicode general
152    category properties was added.
153  </P>  </P>
154  <P>  <P>
155  In order process UTF-8 strings, you must build PCRE to include UTF-8 support in  In order process UTF-8 strings, you must build PCRE to include UTF-8 support in
# Line 119  instead of just strings of bytes. Line 162  instead of just strings of bytes.
162  <P>  <P>
163  If you compile PCRE with UTF-8 support, but do not use it at run time, the  If you compile PCRE with UTF-8 support, but do not use it at run time, the
164  library will be a bit bigger, but the additional run time overhead is limited  library will be a bit bigger, but the additional run time overhead is limited
165  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.
166    </P>
167    <P>
168    If PCRE is built with Unicode character property support (which implies UTF-8
169    support), the escape sequences \p{..}, \P{..}, and \X are supported.
170    The available properties that can be tested are limited to the general
171    category properties such as Lu for an upper case letter or Nd for a decimal
172    number, the Unicode script names such as Arabic or Han, and the derived
173    properties Any and L&. A full list is given in the
174    <a href="pcrepattern.html"><b>pcrepattern</b></a>
175    documentation. Only the short names for properties are supported. For example,
176    \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
177    Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
178    compatibility with Perl 5.6. PCRE does not support this.
179  </P>  </P>
180  <P>  <P>
181  The following comments apply when PCRE is running in UTF-8 mode:  The following comments apply when PCRE is running in UTF-8 mode:
182  </P>  </P>
183  <P>  <P>
184  1. PCRE assumes that the strings it is given contain valid UTF-8 codes. It does  1. When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects
185  not diagnose invalid UTF-8 strings. If you pass invalid UTF-8 strings to PCRE,  are checked for validity on entry to the relevant functions. If an invalid
186  the results are undefined.  UTF-8 string is passed, an error return is given. In some situations, you may
187    already know that your strings are valid, and therefore want to skip these
188    checks in order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag
189    at compile time or at run time, PCRE assumes that the pattern or subject it
190    is given (respectively) contains only valid UTF-8 codes. In this case, it does
191    not diagnose an invalid UTF-8 string. If you pass an invalid UTF-8 string to
192    PCRE when PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program
193    may crash.
194  </P>  </P>
195  <P>  <P>
196  2. In a pattern, the escape sequence \x{...}, where the contents of the braces  2. An unbraced hexadecimal escape sequence (such as \xb3) matches a two-byte
197  is a string of hexadecimal digits, is interpreted as a UTF-8 character whose  UTF-8 character if the value is greater than 127.
 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.  
198  </P>  </P>
199  <P>  <P>
200  3. The original hexadecimal escape sequence, \xhh, matches a two-byte UTF-8  3. Octal numbers up to \777 are recognized, and match two-byte UTF-8
201  character if the value is greater than 127.  characters for values greater than \177.
202  </P>  </P>
203  <P>  <P>
204  4. Repeat quantifiers apply to complete UTF-8 characters, not to individual  4. Repeat quantifiers apply to complete UTF-8 characters, not to individual
# Line 150  bytes, for example: \x{100}{3}. Line 209  bytes, for example: \x{100}{3}.
209  </P>  </P>
210  <P>  <P>
211  6. The escape sequence \C can be used to match a single byte in UTF-8 mode,  6. The escape sequence \C can be used to match a single byte in UTF-8 mode,
212  but its use can lead to some strange effects.  but its use can lead to some strange effects. This facility is not available in
213    the alternative matching function, <b>pcre_dfa_exec()</b>.
214  </P>  </P>
215  <P>  <P>
216  7. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly  7. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
217  test characters of any code value, but the characters that PCRE recognizes as  test characters of any code value, but the characters that PCRE recognizes as
218  digits, spaces, or word characters remain the same set as before, all with  digits, spaces, or word characters remain the same set as before, all with
219  values less than 256.  values less than 256. This remains true even when PCRE includes Unicode
220  </P>  property support, because to do otherwise would slow down PCRE in many common
221  <P>  cases. If you really want to test for a wider sense of, say, "digit", you
222  8. Case-insensitive matching applies only to characters whose values are less  must use Unicode property tests such as \p{Nd}.
223  than 256. PCRE does not support the notion of "case" for higher-valued  </P>
224  characters.  <P>
225  </P>  8. Similarly, characters that match the POSIX named character classes are all
226  <P>  low-valued characters.
227  9. PCRE does not support the use of Unicode tables and properties or the Perl  </P>
228  escapes \p, \P, and \X.  <P>
229    9. Case-insensitive matching applies only to characters whose values are less
230    than 128, unless PCRE is built with Unicode property support. Even when Unicode
231    property support is available, PCRE still uses its own character tables when
232    checking the case of low-valued characters, so as not to degrade performance.
233    The Unicode property information is used only for characters with higher
234    values. Even when Unicode property support is available, PCRE supports
235    case-insensitive matching only when there is a one-to-one mapping between a
236    letter's cases. There are a small number of many-to-one mappings in Unicode;
237    these are not supported by PCRE.
238  </P>  </P>
239  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
240  <P>  <P>
241  Philip Hazel &#60;ph10@cam.ac.uk&#62;  Philip Hazel
242  <br>  <br>
243  University Computing Service,  University Computing Service,
244  <br>  <br>
245  Cambridge CB2 3QG, England.  Cambridge CB2 3QH, England.
 <br>  
 Phone: +44 1223 334714  
246  </P>  </P>
247  <P>  <P>
248  Last updated: 04 February 2003  Putting an actual email address here seems to have been a spam magnet, so I've
249    taken it away. If you want to email me, use my initial and surname, separated
250    by a dot, at the domain ucs.cam.ac.uk.
251    Last updated: 23 November 2006
252  <br>  <br>
253  Copyright &copy; 1997-2003 University of Cambridge.  Copyright &copy; 1997-2006 University of Cambridge.
254    <p>
255    Return to the <a href="index.html">PCRE index page</a>.
256    </p>

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