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1  .TH PCRE 3  .TH PCRE 3
2  .SH NAME  .SH NAME
3  PCRE - Perl-compatible regular expressions  PCRE - Perl-compatible regular expressions
4  .SH DESCRIPTION  .SH INTRODUCTION
5  .rs  .rs
6  .sp  .sp
7  The PCRE library is a set of functions that implement regular expression  The PCRE library is a set of functions that implement regular expression
8  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
9  differences. The current implementation of PCRE (release 4.x) corresponds  differences. Certain features that appeared in Python and PCRE before they
10  approximately with Perl 5.8, including support for UTF-8 encoded strings.  appeared in Perl are also available using the Python syntax. There is also some
11  However, this support has to be explicitly enabled; it is not the default.  support for certain .NET and Oniguruma syntax items, and there is an option for
12    requesting some minor changes that give better JavaScript compatibility.
13  PCRE is written in C and released as a C library. However, a number of people  .P
14  have written wrappers and interfaces of various kinds. A C++ class is included  The current implementation of PCRE (release 7.x) corresponds approximately with
15  in these contributions, which can be found in the \fIContrib\fR directory at  Perl 5.10, including support for UTF-8 encoded strings and Unicode general
16  the primary FTP site, which is:  category properties. However, UTF-8 and Unicode support has to be explicitly
17    enabled; it is not the default. The Unicode tables correspond to Unicode
18    release 5.0.0.
19    .P
20    In addition to the Perl-compatible matching function, PCRE contains an
21    alternative matching function that matches the same compiled patterns in a
22    different way. In certain circumstances, the alternative function has some
23    advantages. For a discussion of the two matching algorithms, see the
24    .\" HREF
25    \fBpcrematching\fP
26    .\"
27    page.
28    .P
29    PCRE is written in C and released as a C library. A number of people have
30    written wrappers and interfaces of various kinds. In particular, Google Inc.
31    have provided a comprehensive C++ wrapper. This is now included as part of the
32    PCRE distribution. The
33    .\" HREF
34    \fBpcrecpp\fP
35    .\"
36    page has details of this interface. Other people's contributions can be found
37    in the \fIContrib\fR directory at the primary FTP site, which is:
38    .sp
39  .\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">  .\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">
40  .\" </a>  .\" </a>
41  ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre  ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
42    .P
43  Details of exactly which Perl regular expression features are and are not  Details of exactly which Perl regular expression features are and are not
44  supported by PCRE are given in separate documents. See the  supported by PCRE are given in separate documents. See the
45  .\" HREF  .\" HREF
# Line 28  and Line 49  and
49  .\" HREF  .\" HREF
50  \fBpcrecompat\fR  \fBpcrecompat\fR
51  .\"  .\"
52  pages.  pages. There is a syntax summary in the
53    .\" HREF
54    \fBpcresyntax\fR
55    .\"
56    page.
57    .P
58  Some features of PCRE can be included, excluded, or changed when the library is  Some features of PCRE can be included, excluded, or changed when the library is
59  built. The  built. The
60  .\" HREF  .\" HREF
61  \fBpcre_config()\fR  \fBpcre_config()\fR
62  .\"  .\"
63  function makes it possible for a client to discover which features are  function makes it possible for a client to discover which features are
64  available. Documentation about building PCRE for various operating systems can  available. The features themselves are described in the
65  be found in the \fBREADME\fR file in the source distribution.  .\" HREF
66    \fBpcrebuild\fP
67  .SH USER DOCUMENTATION  .\"
68    page. Documentation about building PCRE for various operating systems can be
69    found in the \fBREADME\fP file in the source distribution.
70    .P
71    The library contains a number of undocumented internal functions and data
72    tables that are used by more than one of the exported external functions, but
73    which are not intended for use by external callers. Their names all begin with
74    "_pcre_", which hopefully will not provoke any name clashes. In some
75    environments, it is possible to control which external symbols are exported
76    when a shared library is built, and in these cases the undocumented symbols are
77    not exported.
78    .
79    .
80    .SH "USER DOCUMENTATION"
81  .rs  .rs
82  .sp  .sp
83  The user documentation for PCRE has been split up into a number of different  The user documentation for PCRE comprises a number of different sections. In
84  sections. In the "man" format, each of these is a separate "man page". In the  the "man" format, each of these is a separate "man page". In the HTML format,
85  HTML format, each is a separate page, linked from the index page. In the plain  each is a separate page, linked from the index page. In the plain text format,
86  text format, all the sections are concatenated, for ease of searching. The  all the sections are concatenated, for ease of searching. The sections are as
87  sections are as follows:  follows:
88    .sp
89    pcre              this document    pcre              this document
90    pcreapi           details of PCRE's native API    pcre-config       show PCRE installation configuration information
91      pcreapi           details of PCRE's native C API
92    pcrebuild         options for building PCRE    pcrebuild         options for building PCRE
93    pcrecallout       details of the callout feature    pcrecallout       details of the callout feature
94    pcrecompat        discussion of Perl compatibility    pcrecompat        discussion of Perl compatibility
95    pcregrep          description of the \fBpcregrep\fR command    pcrecpp           details of the C++ wrapper
96      pcregrep          description of the \fBpcregrep\fP command
97      pcrematching      discussion of the two matching algorithms
98      pcrepartial       details of the partial matching facility
99    .\" JOIN
100    pcrepattern       syntax and semantics of supported    pcrepattern       syntax and semantics of supported
101                        regular expressions                        regular expressions
102      pcresyntax        quick syntax reference
103    pcreperform       discussion of performance issues    pcreperform       discussion of performance issues
104    pcreposix         the POSIX-compatible API    pcreposix         the POSIX-compatible C API
105      pcreprecompile    details of saving and re-using precompiled patterns
106    pcresample        discussion of the sample program    pcresample        discussion of the sample program
107    pcretest          the \fBpcretest\fR testing command    pcrestack         discussion of stack usage
108      pcretest          description of the \fBpcretest\fP testing command
109    .sp
110  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
111  library function, listing its arguments and results.  C library function, listing its arguments and results.
112    .
113    .
114  .SH LIMITATIONS  .SH LIMITATIONS
115  .rs  .rs
116  .sp  .sp
117  There are some size limitations in PCRE but it is hoped that they will never in  There are some size limitations in PCRE but it is hoped that they will never in
118  practice be relevant.  practice be relevant.
119    .P
120  The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is  The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is
121  compiled with the default internal linkage size of 2. If you want to process  compiled with the default internal linkage size of 2. If you want to process
122  regular expressions that are truly enormous, you can compile PCRE with an  regular expressions that are truly enormous, you can compile PCRE with an
123  internal linkage size of 3 or 4 (see the \fBREADME\fR file in the source  internal linkage size of 3 or 4 (see the \fBREADME\fP file in the source
124  distribution and the  distribution and the
125  .\" HREF  .\" HREF
126  \fBpcrebuild\fR  \fBpcrebuild\fP
127  .\"  .\"
128  documentation for details). If these cases the limit is substantially larger.  documentation for details). In these cases the limit is substantially larger.
129  However, the speed of execution will be slower.  However, the speed of execution is slower.
130    .P
131  All values in repeating quantifiers must be less than 65536.  All values in repeating quantifiers must be less than 65536.
132  The maximum number of capturing subpatterns is 65535.  .P
133    There is no limit to the number of parenthesized subpatterns, but there can be
134  There is no limit to the number of non-capturing subpatterns, but the maximum  no more than 65535 capturing subpatterns.
135  depth of nesting of all kinds of parenthesized subpattern, including capturing  .P
136  subpatterns, assertions, and other types of subpattern, is 200.  The maximum length of name for a named subpattern is 32 characters, and the
137    maximum number of named subpatterns is 10000.
138    .P
139  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
140  integer variable can hold. However, PCRE uses recursion to handle subpatterns  integer variable can hold. However, when using the traditional matching
141  and indefinite repetition. This means that the available stack space may limit  function, PCRE uses recursion to handle subpatterns and indefinite repetition.
142  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
143    string that can be processed by certain patterns. For a discussion of stack
144    issues, see the
145    .\" HREF
146    \fBpcrestack\fP
147    .\"
148    documentation.
149    .
150  .\" HTML <a name="utf8support"></a>  .\" HTML <a name="utf8support"></a>
151  .SH UTF-8 SUPPORT  .
152    .
153    .SH "UTF-8 AND UNICODE PROPERTY SUPPORT"
154  .rs  .rs
155  .sp  .sp
156  Starting at release 3.3, PCRE has had some support for character strings  From release 3.3, PCRE has had some support for character strings encoded in
157  encoded in the UTF-8 format. For release 4.0 this has been greatly extended to  the UTF-8 format. For release 4.0 this was greatly extended to cover most
158  cover most common requirements.  common requirements, and in release 5.0 additional support for Unicode general
159    category properties was added.
160    .P
161  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
162  the code, and, in addition, you must call  the code, and, in addition, you must call
163  .\" HREF  .\" HREF
164  \fBpcre_compile()\fR  \fBpcre_compile()\fP
165  .\"  .\"
166  with the PCRE_UTF8 option flag. When you do this, both the pattern and any  with the PCRE_UTF8 option flag. When you do this, both the pattern and any
167  subject strings that are matched against it are treated as UTF-8 strings  subject strings that are matched against it are treated as UTF-8 strings
168  instead of just strings of bytes.  instead of just strings of bytes.
169    .P
170  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
171  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
172  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.
173    .P
174  The following comments apply when PCRE is running in UTF-8 mode:  If PCRE is built with Unicode character property support (which implies UTF-8
175    support), the escape sequences \ep{..}, \eP{..}, and \eX are supported.
176  1. When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects  The available properties that can be tested are limited to the general
177  are checked for validity on entry to the relevant functions. If an invalid  category properties such as Lu for an upper case letter or Nd for a decimal
178  UTF-8 string is passed, an error return is given. In some situations, you may  number, the Unicode script names such as Arabic or Han, and the derived
179  already know that your strings are valid, and therefore want to skip these  properties Any and L&. A full list is given in the
180  checks in order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag  .\" HREF
181  at compile time or at run time, PCRE assumes that the pattern or subject it  \fBpcrepattern\fP
182  is given (respectively) contains only valid UTF-8 codes. In this case, it does  .\"
183  not diagnose an invalid UTF-8 string. If you pass an invalid UTF-8 string to  documentation. Only the short names for properties are supported. For example,
184  PCRE when PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  \ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported.
185  may crash.  Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
186    compatibility with Perl 5.6. PCRE does not support this.
187  2. In a pattern, the escape sequence \\x{...}, where the contents of the braces  .
188  is a string of hexadecimal digits, is interpreted as a UTF-8 character whose  .\" HTML <a name="utf8strings"></a>
189  code number is the given hexadecimal number, for example: \\x{1234}. If a  .
190  non-hexadecimal digit appears between the braces, the item is not recognized.  .SS "Validity of UTF-8 strings"
191  This escape sequence can be used either as a literal, or within a character  .rs
192  class.  .sp
193    When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects
194  3. The original hexadecimal escape sequence, \\xhh, matches a two-byte UTF-8  are (by default) checked for validity on entry to the relevant functions. From
195  character if the value is greater than 127.  release 7.3 of PCRE, the check is according the rules of RFC 3629, which are
196    themselves derived from the Unicode specification. Earlier releases of PCRE
197  4. Repeat quantifiers apply to complete UTF-8 characters, not to individual  followed the rules of RFC 2279, which allows the full range of 31-bit values (0
198  bytes, for example: \\x{100}{3}.  to 0x7FFFFFFF). The current check allows only values in the range U+0 to
199    U+10FFFF, excluding U+D800 to U+DFFF.
200  5. The dot metacharacter matches one UTF-8 character instead of a single byte.  .P
201    The excluded code points are the "Low Surrogate Area" of Unicode, of which the
202  6. The escape sequence \\C can be used to match a single byte in UTF-8 mode,  Unicode Standard says this: "The Low Surrogate Area does not contain any
203  but its use can lead to some strange effects.  character assignments, consequently no character code charts or namelists are
204    provided for this area. Surrogates are reserved for use with UTF-16 and then
205  7. The character escapes \\b, \\B, \\d, \\D, \\s, \\S, \\w, and \\W correctly  must be used in pairs." The code points that are encoded by UTF-16 pairs are
206    available as independent code points in the UTF-8 encoding. (In other words,
207    the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up
208    UTF-8.)
209    .P
210    If an invalid UTF-8 string is passed to PCRE, an error return
211    (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know that
212    your strings are valid, and therefore want to skip these checks in order to
213    improve performance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or
214    at run time, PCRE assumes that the pattern or subject it is given
215    (respectively) contains only valid UTF-8 codes. In this case, it does not
216    diagnose an invalid UTF-8 string.
217    .P
218    If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what
219    happens depends on why the string is invalid. If the string conforms to the
220    "old" definition of UTF-8 (RFC 2279), it is processed as a string of characters
221    in the range 0 to 0x7FFFFFFF. In other words, apart from the initial validity
222    test, PCRE (when in UTF-8 mode) handles strings according to the more liberal
223    rules of RFC 2279. However, if the string does not even conform to RFC 2279,
224    the result is undefined. Your program may crash.
225    .P
226    If you want to process strings of values in the full range 0 to 0x7FFFFFFF,
227    encoded in a UTF-8-like manner as per the old RFC, you can set
228    PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this
229    situation, you will have to apply your own validity check.
230    .
231    .SS "General comments about UTF-8 mode"
232    .rs
233    .sp
234    1. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte
235    UTF-8 character if the value is greater than 127.
236    .P
237    2. Octal numbers up to \e777 are recognized, and match two-byte UTF-8
238    characters for values greater than \e177.
239    .P
240    3. Repeat quantifiers apply to complete UTF-8 characters, not to individual
241    bytes, for example: \ex{100}{3}.
242    .P
243    4. The dot metacharacter matches one UTF-8 character instead of a single byte.
244    .P
245    5. The escape sequence \eC can be used to match a single byte in UTF-8 mode,
246    but its use can lead to some strange effects. This facility is not available in
247    the alternative matching function, \fBpcre_dfa_exec()\fP.
248    .P
249    6. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly
250  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
251  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
252  values less than 256.  values less than 256. This remains true even when PCRE includes Unicode
253    property support, because to do otherwise would slow down PCRE in many common
254  8. Case-insensitive matching applies only to characters whose values are less  cases. If you really want to test for a wider sense of, say, "digit", you
255  than 256. PCRE does not support the notion of "case" for higher-valued  must use Unicode property tests such as \ep{Nd}.
256  characters.  .P
257    7. Similarly, characters that match the POSIX named character classes are all
258  9. PCRE does not support the use of Unicode tables and properties or the Perl  low-valued characters.
259  escapes \\p, \\P, and \\X.  .P
260    8. However, the Perl 5.10 horizontal and vertical whitespace matching escapes
261    (\eh, \eH, \ev, and \eV) do match all the appropriate Unicode characters.
262    .P
263    9. Case-insensitive matching applies only to characters whose values are less
264    than 128, unless PCRE is built with Unicode property support. Even when Unicode
265    property support is available, PCRE still uses its own character tables when
266    checking the case of low-valued characters, so as not to degrade performance.
267    The Unicode property information is used only for characters with higher
268    values. Even when Unicode property support is available, PCRE supports
269    case-insensitive matching only when there is a one-to-one mapping between a
270    letter's cases. There are a small number of many-to-one mappings in Unicode;
271    these are not supported by PCRE.
272    .
273    .
274  .SH AUTHOR  .SH AUTHOR
275  .rs  .rs
276  .sp  .sp
277  Philip Hazel <ph10@cam.ac.uk>  .nf
278  .br  Philip Hazel
279  University Computing Service,  University Computing Service
280  .br  Cambridge CB2 3QH, England.
281  Cambridge CB2 3QG, England.  .fi
282  .br  .P
283  Phone: +44 1223 334714  Putting an actual email address here seems to have been a spam magnet, so I've
284    taken it away. If you want to email me, use my two initials, followed by the
285  .in 0  two digits 10, at the domain cam.ac.uk.
286  Last updated: 20 August 2003  .
287  .br  .
288  Copyright (c) 1997-2003 University of Cambridge.  .SH REVISION
289    .rs
290    .sp
291    .nf
292    Last updated: 12 April 2008
293    Copyright (c) 1997-2008 University of Cambridge.
294    .fi

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