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revision 182 by ph10, Wed Jun 13 15:09:54 2007 UTC revision 583 by ph10, Tue Jan 11 16:49:55 2011 UTC
# Line 6  PCRE - Perl-compatible regular expressio Line 6  PCRE - Perl-compatible regular expressio
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. (Certain features that appeared in Python and PCRE before they  differences. Some features that appeared in Python and PCRE before they
10  appeared in Perl are also available using the Python syntax.)  appeared in Perl are also available using the Python syntax, there is some
11  .P  support for one or two .NET and Oniguruma syntax items, and there is an option
12  The current implementation of PCRE (release 7.x) corresponds approximately with  for requesting some minor changes that give better JavaScript compatibility.
13  Perl 5.10, including support for UTF-8 encoded strings and Unicode general  .P
14  category properties. However, UTF-8 and Unicode support has to be explicitly  The current implementation of PCRE corresponds approximately with Perl 5.12,
15  enabled; it is not the default. The Unicode tables correspond to Unicode  including support for UTF-8 encoded strings and Unicode general category
16  release 5.0.0.  properties. However, UTF-8 and Unicode support has to be explicitly enabled; it
17    is not the default. The Unicode tables correspond to Unicode release 5.2.0.
18  .P  .P
19  In addition to the Perl-compatible matching function, PCRE contains an  In addition to the Perl-compatible matching function, PCRE contains an
20  alternative matching function that matches the same compiled patterns in a  alternative function that matches the same compiled patterns in a different
21  different way. In certain circumstances, the alternative function has some  way. In certain circumstances, the alternative function has some advantages.
22  advantages. For a discussion of the two matching algorithms, see the  For a discussion of the two matching algorithms, see the
23  .\" HREF  .\" HREF
24  \fBpcrematching\fP  \fBpcrematching\fP
25  .\"  .\"
# Line 32  PCRE distribution. The Line 33  PCRE distribution. The
33  \fBpcrecpp\fP  \fBpcrecpp\fP
34  .\"  .\"
35  page has details of this interface. Other people's contributions can be found  page has details of this interface. Other people's contributions can be found
36  in the \fIContrib\fR directory at the primary FTP site, which is:  in the \fIContrib\fP directory at the primary FTP site, which is:
37  .sp  .sp
38  .\" 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">
39  .\" </a>  .\" </a>
# Line 41  ftp://ftp.csx.cam.ac.uk/pub/software/pro Line 42  ftp://ftp.csx.cam.ac.uk/pub/software/pro
42  Details of exactly which Perl regular expression features are and are not  Details of exactly which Perl regular expression features are and are not
43  supported by PCRE are given in separate documents. See the  supported by PCRE are given in separate documents. See the
44  .\" HREF  .\" HREF
45  \fBpcrepattern\fR  \fBpcrepattern\fP
46  .\"  .\"
47  and  and
48  .\" HREF  .\" HREF
49  \fBpcrecompat\fR  \fBpcrecompat\fP
50    .\"
51    pages. There is a syntax summary in the
52    .\" HREF
53    \fBpcresyntax\fP
54  .\"  .\"
55  pages.  page.
56  .P  .P
57  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
58  built. The  built. The
59  .\" HREF  .\" HREF
60  \fBpcre_config()\fR  \fBpcre_config()\fP
61  .\"  .\"
62  function makes it possible for a client to discover which features are  function makes it possible for a client to discover which features are
63  available. The features themselves are described in the  available. The features themselves are described in the
# Line 60  available. The features themselves are d Line 65  available. The features themselves are d
65  \fBpcrebuild\fP  \fBpcrebuild\fP
66  .\"  .\"
67  page. Documentation about building PCRE for various operating systems can be  page. Documentation about building PCRE for various operating systems can be
68  found in the \fBREADME\fP file in the source distribution.  found in the \fBREADME\fP and \fBNON-UNIX-USE\fP files in the source
69    distribution.
70  .P  .P
71  The library contains a number of undocumented internal functions and data  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  tables that are used by more than one of the exported external functions, but
# Line 77  not exported. Line 83  not exported.
83  The user documentation for PCRE comprises a number of different sections. In  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,  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,  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  all the sections, except the \fBpcredemo\fP section, are concatenated, for ease
87  follows:  of searching. The sections are as follows:
88  .sp  .sp
89    pcre              this document    pcre              this document
90    pcre-config       show PCRE installation configuration information    pcre-config       show PCRE installation configuration information
# Line 87  follows: Line 93  follows:
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    pcrecpp           details of the C++ wrapper    pcrecpp           details of the C++ wrapper
96      pcredemo          a demonstration C program that uses PCRE
97    pcregrep          description of the \fBpcregrep\fP command    pcregrep          description of the \fBpcregrep\fP command
98    pcrematching      discussion of the two matching algorithms    pcrematching      discussion of the two matching algorithms
99    pcrepartial       details of the partial matching facility    pcrepartial       details of the partial matching facility
# Line 96  follows: Line 103  follows:
103    pcreperform       discussion of performance issues    pcreperform       discussion of performance issues
104    pcreposix         the POSIX-compatible C API    pcreposix         the POSIX-compatible C API
105    pcreprecompile    details of saving and re-using precompiled patterns    pcreprecompile    details of saving and re-using precompiled patterns
106    pcresample        discussion of the sample program    pcresample        discussion of the pcredemo program
107    pcrestack         discussion of stack usage    pcrestack         discussion of stack usage
108      pcresyntax        quick syntax reference
109    pcretest          description of the \fBpcretest\fP testing command    pcretest          description of the \fBpcretest\fP testing command
110  .sp  .sp
111  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
# Line 121  distribution and the Line 129  distribution and the
129  documentation for details). In these cases the limit is substantially larger.  documentation for details). In these cases the limit is substantially larger.
130  However, the speed of execution is slower.  However, the speed of execution is slower.
131  .P  .P
132  All values in repeating quantifiers must be less than 65536. The maximum  All values in repeating quantifiers must be less than 65536.
 compiled length of subpattern with an explicit repeat count is 30000 bytes. The  
 maximum number of capturing subpatterns is 65535.  
133  .P  .P
134  There is no limit to the number of parenthesized subpatterns, but there can be  There is no limit to the number of parenthesized subpatterns, but there can be
135  no more than 65535 capturing subpatterns.  no more than 65535 capturing subpatterns.
# Line 141  issues, see the Line 147  issues, see the
147  \fBpcrestack\fP  \fBpcrestack\fP
148  .\"  .\"
149  documentation.  documentation.
 .sp  
 .\" HTML <a name="utf8support"></a>  
150  .  .
151  .  .
152    .\" HTML <a name="utf8support"></a>
153  .SH "UTF-8 AND UNICODE PROPERTY SUPPORT"  .SH "UTF-8 AND UNICODE PROPERTY SUPPORT"
154  .rs  .rs
155  .sp  .sp
# Line 158  the code, and, in addition, you must cal Line 163  the code, and, in addition, you must cal
163  .\" HREF  .\" HREF
164  \fBpcre_compile()\fP  \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, or the pattern must start with the sequence
167  subject strings that are matched against it are treated as UTF-8 strings  (*UTF8). When either of these is the case, both the pattern and any subject
168  instead of just strings of bytes.  strings that are matched against it are treated as UTF-8 strings instead of
169    strings of 1-byte characters.
170  .P  .P
171  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
172  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
# Line 179  documentation. Only the short names for Line 185  documentation. Only the short names for
185  \ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported.  \ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported.
186  Furthermore, in Perl, many properties may optionally be prefixed by "Is", for  Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
187  compatibility with Perl 5.6. PCRE does not support this.  compatibility with Perl 5.6. PCRE does not support this.
188  .P  .
189  The following comments apply when PCRE is running in UTF-8 mode:  .
190  .P  .\" HTML <a name="utf8strings"></a>
191  1. When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects  .SS "Validity of UTF-8 strings"
192  are checked for validity on entry to the relevant functions. If an invalid  .rs
193  UTF-8 string is passed, an error return is given. In some situations, you may  .sp
194  already know that your strings are valid, and therefore want to skip these  When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects
195  checks in order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag  are (by default) checked for validity on entry to the relevant functions. From
196  at compile time or at run time, PCRE assumes that the pattern or subject it  release 7.3 of PCRE, the check is according the rules of RFC 3629, which are
197  is given (respectively) contains only valid UTF-8 codes. In this case, it does  themselves derived from the Unicode specification. Earlier releases of PCRE
198  not diagnose an invalid UTF-8 string. If you pass an invalid UTF-8 string to  followed the rules of RFC 2279, which allows the full range of 31-bit values (0
199  PCRE when PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  to 0x7FFFFFFF). The current check allows only values in the range U+0 to
200  may crash.  U+10FFFF, excluding U+D800 to U+DFFF.
201  .P  .P
202  2. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte  The excluded code points are the "Low Surrogate Area" of Unicode, of which the
203    Unicode Standard says this: "The Low Surrogate Area does not contain any
204    character assignments, consequently no character code charts or namelists are
205    provided for this area. Surrogates are reserved for use with UTF-16 and then
206    must be used in pairs." The code points that are encoded by UTF-16 pairs are
207    available as independent code points in the UTF-8 encoding. (In other words,
208    the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up
209    UTF-8.)
210    .P
211    If an invalid UTF-8 string is passed to PCRE, an error return
212    (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know that
213    your strings are valid, and therefore want to skip these checks in order to
214    improve performance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or
215    at run time, PCRE assumes that the pattern or subject it is given
216    (respectively) contains only valid UTF-8 codes. In this case, it does not
217    diagnose an invalid UTF-8 string.
218    .P
219    If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what
220    happens depends on why the string is invalid. If the string conforms to the
221    "old" definition of UTF-8 (RFC 2279), it is processed as a string of characters
222    in the range 0 to 0x7FFFFFFF. In other words, apart from the initial validity
223    test, PCRE (when in UTF-8 mode) handles strings according to the more liberal
224    rules of RFC 2279. However, if the string does not even conform to RFC 2279,
225    the result is undefined. Your program may crash.
226    .P
227    If you want to process strings of values in the full range 0 to 0x7FFFFFFF,
228    encoded in a UTF-8-like manner as per the old RFC, you can set
229    PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this
230    situation, you will have to apply your own validity check.
231    .
232    .
233    .SS "General comments about UTF-8 mode"
234    .rs
235    .sp
236    1. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte
237  UTF-8 character if the value is greater than 127.  UTF-8 character if the value is greater than 127.
238  .P  .P
239  3. Octal numbers up to \e777 are recognized, and match two-byte UTF-8  2. Octal numbers up to \e777 are recognized, and match two-byte UTF-8
240  characters for values greater than \e177.  characters for values greater than \e177.
241  .P  .P
242  4. Repeat quantifiers apply to complete UTF-8 characters, not to individual  3. Repeat quantifiers apply to complete UTF-8 characters, not to individual
243  bytes, for example: \ex{100}{3}.  bytes, for example: \ex{100}{3}.
244  .P  .P
245  5. The dot metacharacter matches one UTF-8 character instead of a single byte.  4. The dot metacharacter matches one UTF-8 character instead of a single byte.
246  .P  .P
247  6. The escape sequence \eC can be used to match a single byte in UTF-8 mode,  5. The escape sequence \eC can be used to match a single byte in UTF-8 mode,
248  but its use can lead to some strange effects. This facility is not available in  but its use can lead to some strange effects. This facility is not available in
249  the alternative matching function, \fBpcre_dfa_exec()\fP.  the alternative matching function, \fBpcre_dfa_exec()\fP.
250  .P  .P
251  7. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly  6. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly
252  test characters of any code value, but the characters that PCRE recognizes as  test characters of any code value, but, by default, the characters that PCRE
253  digits, spaces, or word characters remain the same set as before, all with  recognizes as digits, spaces, or word characters remain the same set as before,
254  values less than 256. This remains true even when PCRE includes Unicode  all with values less than 256. This remains true even when PCRE is built to
255  property support, because to do otherwise would slow down PCRE in many common  include Unicode property support, because to do otherwise would slow down PCRE
256  cases. If you really want to test for a wider sense of, say, "digit", you  in many common cases. Note in particular that this applies to \eb and \eB,
257  must use Unicode property tests such as \ep{Nd}.  because they are defined in terms of \ew and \eW. If you really want to test
258    for a wider sense of, say, "digit", you can use explicit Unicode property tests
259    such as \ep{Nd}. Alternatively, if you set the PCRE_UCP option, the way that
260    the character escapes work is changed so that Unicode properties are used to
261    determine which characters match. There are more details in the section on
262    .\" HTML <a href="pcrepattern.html#genericchartypes">
263    .\" </a>
264    generic character types
265    .\"
266    in the
267    .\" HREF
268    \fBpcrepattern\fP
269    .\"
270    documentation.
271  .P  .P
272  8. Similarly, characters that match the POSIX named character classes are all  7. Similarly, characters that match the POSIX named character classes are all
273  low-valued characters.  low-valued characters, unless the PCRE_UCP option is set.
274  .P  .P
275  9. However, the Perl 5.10 horizontal and vertical whitespace matching escapes  8. However, the horizontal and vertical whitespace matching escapes (\eh, \eH,
276  (\eh, \eH, \ev, and \eV) do match all the appropriate Unicode characters.  \ev, and \eV) do match all the appropriate Unicode characters, whether or not
277    PCRE_UCP is set.
278  .P  .P
279  10. Case-insensitive matching applies only to characters whose values are less  9. Case-insensitive matching applies only to characters whose values are less
280  than 128, unless PCRE is built with Unicode property support. Even when Unicode  than 128, unless PCRE is built with Unicode property support. Even when Unicode
281  property support is available, PCRE still uses its own character tables when  property support is available, PCRE still uses its own character tables when
282  checking the case of low-valued characters, so as not to degrade performance.  checking the case of low-valued characters, so as not to degrade performance.
283  The Unicode property information is used only for characters with higher  The Unicode property information is used only for characters with higher
284  values. Even when Unicode property support is available, PCRE supports  values. Furthermore, PCRE supports case-insensitive matching only when there is
285  case-insensitive matching only when there is a one-to-one mapping between a  a one-to-one mapping between a letter's cases. There are a small number of
286  letter's cases. There are a small number of many-to-one mappings in Unicode;  many-to-one mappings in Unicode; these are not supported by PCRE.
 these are not supported by PCRE.  
287  .  .
288  .  .
289  .SH AUTHOR  .SH AUTHOR
# Line 251  two digits 10, at the domain cam.ac.uk. Line 304  two digits 10, at the domain cam.ac.uk.
304  .rs  .rs
305  .sp  .sp
306  .nf  .nf
307  Last updated: 13 June 2007  Last updated: 13 November 2010
308  Copyright (c) 1997-2007 University of Cambridge.  Copyright (c) 1997-2010 University of Cambridge.
309  .fi  .fi

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