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revision 208 by ph10, Mon Aug 6 15:23:29 2007 UTC revision 518 by ph10, Tue May 18 15:47:01 2010 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    support for one or two .NET and Oniguruma syntax items, and there is an option
12    for requesting some minor changes that give better JavaScript compatibility.
13  .P  .P
14  The current implementation of PCRE (release 7.x) corresponds approximately with  The current implementation of PCRE corresponds approximately with Perl
15  Perl 5.10, including support for UTF-8 encoded strings and Unicode general  5.10/5.11, including support for UTF-8 encoded strings and Unicode general
16  category properties. However, UTF-8 and Unicode support has to be explicitly  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  enabled; it is not the default. The Unicode tables correspond to Unicode
18  release 5.0.0.  release 5.2.0.
19  .P  .P
20  In addition to the Perl-compatible matching function, PCRE contains an  In addition to the Perl-compatible matching function, PCRE contains an
21  alternative matching function that matches the same compiled patterns in a  alternative function that matches the same compiled patterns in a different
22  different way. In certain circumstances, the alternative function has some  way. In certain circumstances, the alternative function has some advantages.
23  advantages. For a discussion of the two matching algorithms, see the  For a discussion of the two matching algorithms, see the
24  .\" HREF  .\" HREF
25  \fBpcrematching\fP  \fBpcrematching\fP
26  .\"  .\"
# Line 64  available. The features themselves are d Line 66  available. The features themselves are d
66  \fBpcrebuild\fP  \fBpcrebuild\fP
67  .\"  .\"
68  page. Documentation about building PCRE for various operating systems can be  page. Documentation about building PCRE for various operating systems can be
69  found in the \fBREADME\fP file in the source distribution.  found in the \fBREADME\fP and \fBNON-UNIX-USE\fP files in the source
70    distribution.
71  .P  .P
72  The library contains a number of undocumented internal functions and data  The library contains a number of undocumented internal functions and data
73  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 81  not exported. Line 84  not exported.
84  The user documentation for PCRE comprises a number of different sections. In  The user documentation for PCRE comprises a number of different sections. In
85  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,
86  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,
87  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
88  follows:  of searching. The sections are as follows:
89  .sp  .sp
90    pcre              this document    pcre              this document
91    pcre-config       show PCRE installation configuration information    pcre-config       show PCRE installation configuration information
# Line 91  follows: Line 94  follows:
94    pcrecallout       details of the callout feature    pcrecallout       details of the callout feature
95    pcrecompat        discussion of Perl compatibility    pcrecompat        discussion of Perl compatibility
96    pcrecpp           details of the C++ wrapper    pcrecpp           details of the C++ wrapper
97      pcredemo          a demonstration C program that uses PCRE
98    pcregrep          description of the \fBpcregrep\fP command    pcregrep          description of the \fBpcregrep\fP command
99    pcrematching      discussion of the two matching algorithms    pcrematching      discussion of the two matching algorithms
100    pcrepartial       details of the partial matching facility    pcrepartial       details of the partial matching facility
101  .\" JOIN  .\" JOIN
102    pcrepattern       syntax and semantics of supported    pcrepattern       syntax and semantics of supported
103                        regular expressions                        regular expressions
   pcresyntax        quick syntax reference  
104    pcreperform       discussion of performance issues    pcreperform       discussion of performance issues
105    pcreposix         the POSIX-compatible C API    pcreposix         the POSIX-compatible C API
106    pcreprecompile    details of saving and re-using precompiled patterns    pcreprecompile    details of saving and re-using precompiled patterns
107    pcresample        discussion of the sample program    pcresample        discussion of the pcredemo program
108    pcrestack         discussion of stack usage    pcrestack         discussion of stack usage
109      pcresyntax        quick syntax reference
110    pcretest          description of the \fBpcretest\fP testing command    pcretest          description of the \fBpcretest\fP testing command
111  .sp  .sp
112  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 144  issues, see the Line 148  issues, see the
148  \fBpcrestack\fP  \fBpcrestack\fP
149  .\"  .\"
150  documentation.  documentation.
 .sp  
 .\" HTML <a name="utf8support"></a>  
151  .  .
152  .  .
153    .\" HTML <a name="utf8support"></a>
154  .SH "UTF-8 AND UNICODE PROPERTY SUPPORT"  .SH "UTF-8 AND UNICODE PROPERTY SUPPORT"
155  .rs  .rs
156  .sp  .sp
# Line 161  the code, and, in addition, you must cal Line 164  the code, and, in addition, you must cal
164  .\" HREF  .\" HREF
165  \fBpcre_compile()\fP  \fBpcre_compile()\fP
166  .\"  .\"
167  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
168  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
169  instead of just strings of bytes.  strings that are matched against it are treated as UTF-8 strings instead of
170    strings of 1-byte characters.
171  .P  .P
172  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
173  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 182  documentation. Only the short names for Line 186  documentation. Only the short names for
186  \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.
187  Furthermore, in Perl, many properties may optionally be prefixed by "Is", for  Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
188  compatibility with Perl 5.6. PCRE does not support this.  compatibility with Perl 5.6. PCRE does not support this.
189  .P  .
190  The following comments apply when PCRE is running in UTF-8 mode:  .
191  .P  .\" HTML <a name="utf8strings"></a>
192  1. When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects  .SS "Validity of UTF-8 strings"
193  are checked for validity on entry to the relevant functions. If an invalid  .rs
194  UTF-8 string is passed, an error return is given. In some situations, you may  .sp
195  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
196  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
197  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
198  is given (respectively) contains only valid UTF-8 codes. In this case, it does  themselves derived from the Unicode specification. Earlier releases of PCRE
199  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
200  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
201  may crash.  U+10FFFF, excluding U+D800 to U+DFFF.
202  .P  .P
203  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
204    Unicode Standard says this: "The Low Surrogate Area does not contain any
205    character assignments, consequently no character code charts or namelists are
206    provided for this area. Surrogates are reserved for use with UTF-16 and then
207    must be used in pairs." The code points that are encoded by UTF-16 pairs are
208    available as independent code points in the UTF-8 encoding. (In other words,
209    the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up
210    UTF-8.)
211    .P
212    If an invalid UTF-8 string is passed to PCRE, an error return
213    (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know that
214    your strings are valid, and therefore want to skip these checks in order to
215    improve performance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or
216    at run time, PCRE assumes that the pattern or subject it is given
217    (respectively) contains only valid UTF-8 codes. In this case, it does not
218    diagnose an invalid UTF-8 string.
219    .P
220    If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what
221    happens depends on why the string is invalid. If the string conforms to the
222    "old" definition of UTF-8 (RFC 2279), it is processed as a string of characters
223    in the range 0 to 0x7FFFFFFF. In other words, apart from the initial validity
224    test, PCRE (when in UTF-8 mode) handles strings according to the more liberal
225    rules of RFC 2279. However, if the string does not even conform to RFC 2279,
226    the result is undefined. Your program may crash.
227    .P
228    If you want to process strings of values in the full range 0 to 0x7FFFFFFF,
229    encoded in a UTF-8-like manner as per the old RFC, you can set
230    PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this
231    situation, you will have to apply your own validity check.
232    .
233    .
234    .SS "General comments about UTF-8 mode"
235    .rs
236    .sp
237    1. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte
238  UTF-8 character if the value is greater than 127.  UTF-8 character if the value is greater than 127.
239  .P  .P
240  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
241  characters for values greater than \e177.  characters for values greater than \e177.
242  .P  .P
243  4. Repeat quantifiers apply to complete UTF-8 characters, not to individual  3. Repeat quantifiers apply to complete UTF-8 characters, not to individual
244  bytes, for example: \ex{100}{3}.  bytes, for example: \ex{100}{3}.
245  .P  .P
246  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.
247  .P  .P
248  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,
249  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
250  the alternative matching function, \fBpcre_dfa_exec()\fP.  the alternative matching function, \fBpcre_dfa_exec()\fP.
251  .P  .P
252  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
253  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
254  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,
255  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
256  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
257  cases. If you really want to test for a wider sense of, say, "digit", you  in many common cases. Note that this also applies to \eb, because it is defined
258  must use Unicode property tests such as \ep{Nd}.  in terms of \ew and \eW. If you really want to test for a wider sense of, say,
259    "digit", you can use explicit Unicode property tests such as \ep{Nd}.
260    Alternatively, if you set the PCRE_UCP option, the way that the character
261    escapes work is changed so that Unicode properties are used to determine which
262    characters match. There are more details in the section on
263    .\" HTML <a href="pcrepattern.html#genericchartypes">
264    .\" </a>
265    generic character types
266    .\"
267    in the
268    .\" HREF
269    \fBpcrepattern\fP
270    .\"
271    documentation.
272  .P  .P
273  8. Similarly, characters that match the POSIX named character classes are all  7. Similarly, characters that match the POSIX named character classes are all
274  low-valued characters.  low-valued characters, unless the PCRE_UCP option is set.
275  .P  .P
276  9. However, the Perl 5.10 horizontal and vertical whitespace matching escapes  8. However, the Perl 5.10 horizontal and vertical whitespace matching escapes
277  (\eh, \eH, \ev, and \eV) do match all the appropriate Unicode characters.  (\eh, \eH, \ev, and \eV) do match all the appropriate Unicode characters,
278    whether or not PCRE_UCP is set.
279  .P  .P
280  10. Case-insensitive matching applies only to characters whose values are less  9. Case-insensitive matching applies only to characters whose values are less
281  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
282  property support is available, PCRE still uses its own character tables when  property support is available, PCRE still uses its own character tables when
283  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.
# Line 254  two digits 10, at the domain cam.ac.uk. Line 306  two digits 10, at the domain cam.ac.uk.
306  .rs  .rs
307  .sp  .sp
308  .nf  .nf
309  Last updated: 06 August 2007  Last updated: 12 May 2010
310  Copyright (c) 1997-2007 University of Cambridge.  Copyright (c) 1997-2010 University of Cambridge.
311  .fi  .fi

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