trunk/doc/pcreunicode.3

.TH PCREUNICODE 3 "27 February 2013" "PCRE 8.33"
.SH NAME
PCRE - Perl-compatible regular expressions
.SH "UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT"
.rs
.sp
As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30) and
UTF-32 (from release 8.32), by means of two additional libraries. They can be
built as well as, or instead of, the 8-bit library.
.
.
.SH "UTF-8 SUPPORT"
.rs
.sp
In order process UTF-8 strings, you must build PCRE's 8-bit library with UTF
support, and, in addition, you must call
.\" HREF
\fBpcre_compile()\fP
.\"
with the PCRE_UTF8 option flag, or the pattern must start with the sequence
(*UTF8) or (*UTF). When either of these is the case, both the pattern and any
subject strings that are matched against it are treated as UTF-8 strings
instead of strings of individual 1-byte characters.
.
.
.SH "UTF-16 AND UTF-32 SUPPORT"
.rs
.sp
In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit or
32-bit library with UTF support, and, in addition, you must call
.\" HREF
\fBpcre16_compile()\fP
.\"
or
.\" HREF
\fBpcre32_compile()\fP
.\"
with the PCRE_UTF16 or PCRE_UTF32 option flag, as appropriate. Alternatively,
the pattern must start with the sequence (*UTF16), (*UTF32), as appropriate, or
(*UTF), which can be used with either library. When UTF mode is set, both the
pattern and any subject strings that are matched against it are treated as
UTF-16 or UTF-32 strings instead of strings of individual 16-bit or 32-bit
characters.
.
.
.SH "UTF SUPPORT OVERHEAD"
.rs
.sp
If you compile PCRE with UTF 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_UTF[8|16|32] flag occasionally, so should not be very big.
.
.
.SH "UNICODE PROPERTY SUPPORT"
.rs
.sp
If PCRE is built with Unicode character property support (which implies UTF
support), the escape sequences \ep{..}, \eP{..}, and \eX can be used.
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&. Full lists is given in the
.\" HREF
\fBpcrepattern\fP
.\"
and
.\" HREF
\fBpcresyntax\fP
.\"
documentation. Only the short names for properties are supported. For example,
\ep{L} matches a letter. Its Perl synonym, \ep{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.
.
.
.\" HTML <a name="utf8strings"></a>
.SS "Validity of UTF-8 strings"
.rs
.sp
When you set the PCRE_UTF8 flag, the byte strings passed as patterns and
subjects are (by default) checked for validity on entry to the relevant
functions. The entire string is checked before any other processing takes
place. From release 7.3 of PCRE, the check is according the rules of RFC 3629,
which are themselves derived from the Unicode specification. Earlier releases
of PCRE followed the rules of RFC 2279, which allows the full range of 31-bit
values (0 to 0x7FFFFFFF). The current check allows only values in the range U+0
to U+10FFFF, excluding the surrogate area. (From release 8.33 the so-called 
"non-character" code points are no longer excluded because Unicode corrigendum 
#9 makes it clear that they should not be.)
.P
Characters in the "Surrogate Area" of Unicode are reserved for use by UTF-16,
where they are used in pairs to encode codepoints with values greater than
0xFFFF. The code points that are encoded by UTF-16 pairs are available
independently in the UTF-8 and UTF-32 encodings. (In other words, the whole
surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8 and
UTF-32.)
.P
If an invalid UTF-8 string is passed to PCRE, an error return is given. At
compile time, the only additional information is the offset to the first byte
of the failing character. The run-time functions \fBpcre_exec()\fP and
\fBpcre_dfa_exec()\fP also pass back this information, as well as a more
detailed reason code if the caller has provided memory in which to do this.
.P
In some situations, you may already know that your strings are valid, and
therefore want to skip these checks in order to improve performance, for
example in the case of a long subject string that is being scanned repeatedly.
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.
.P
Note that passing PCRE_NO_UTF8_CHECK to \fBpcre_compile()\fP just disables the
check for the pattern; it does not also apply to subject strings. If you want
to disable the check for a subject string you must pass this option to
\fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP.
.P
If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the result
is undefined and your program may crash.
.
.
.\" HTML <a name="utf16strings"></a>
.SS "Validity of UTF-16 strings"
.rs
.sp
When you set the PCRE_UTF16 flag, the strings of 16-bit data units that are
passed as patterns and subjects are (by default) checked for validity on entry
to the relevant functions. Values other than those in the surrogate range
U+D800 to U+DFFF are independent code points. Values in the surrogate range
must be used in pairs in the correct manner.
.P
If an invalid UTF-16 string is passed to PCRE, an error return is given. At
compile time, the only additional information is the offset to the first data
unit of the failing character. The run-time functions \fBpcre16_exec()\fP and
\fBpcre16_dfa_exec()\fP also pass back this information, as well as a more
detailed reason code if the caller has provided memory in which to do this.
.P
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_UTF16_CHECK flag at compile time or at run time, PCRE assumes that
the pattern or subject it is given (respectively) contains only valid UTF-16
sequences. In this case, it does not diagnose an invalid UTF-16 string.
However, if an invalid string is passed, the result is undefined.
.
.
.\" HTML <a name="utf32strings"></a>
.SS "Validity of UTF-32 strings"
.rs
.sp
When you set the PCRE_UTF32 flag, the strings of 32-bit data units that are
passed as patterns and subjects are (by default) checked for validity on entry
to the relevant functions.  This check allows only values in the range U+0
to U+10FFFF, excluding the surrogate area U+D800 to U+DFFF.
.P
If an invalid UTF-32 string is passed to PCRE, an error return is given. At
compile time, the only additional information is the offset to the first data
unit of the failing character. The run-time functions \fBpcre32_exec()\fP and
\fBpcre32_dfa_exec()\fP also pass back this information, as well as a more
detailed reason code if the caller has provided memory in which to do this.
.P
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_UTF32_CHECK flag at compile time or at run time, PCRE assumes that
the pattern or subject it is given (respectively) contains only valid UTF-32
sequences. In this case, it does not diagnose an invalid UTF-32 string.
However, if an invalid string is passed, the result is undefined.
.
.
.SS "General comments about UTF modes"
.rs
.sp
1. Codepoints less than 256 can be specified in patterns by either braced or
unbraced hexadecimal escape sequences (for example, \ex{b3} or \exb3). Larger
values have to use braced sequences.
.P
2. Octal numbers up to \e777 are recognized, and in UTF-8 mode they match
two-byte characters for values greater than \e177.
.P
3. Repeat quantifiers apply to complete UTF characters, not to individual
data units, for example: \ex{100}{3}.
.P
4. The dot metacharacter matches one UTF character instead of a single data
unit.
.P
5. The escape sequence \eC can be used to match a single byte in UTF-8 mode, or
a single 16-bit data unit in UTF-16 mode, or a single 32-bit data unit in
UTF-32 mode, but its use can lead to some strange effects because it breaks up
multi-unit characters (see the description of \eC in the
.\" HREF
\fBpcrepattern\fP
.\"
documentation). The use of \eC is not supported in the alternative matching
function \fBpcre[16|32]_dfa_exec()\fP, nor is it supported in UTF mode by the
JIT optimization of \fBpcre[16|32]_exec()\fP. If JIT optimization is requested
for a UTF pattern that contains \eC, it will not succeed, and so the matching
will be carried out by the normal interpretive function.
.P
6. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly
test characters of any code value, but, by default, the characters that PCRE
recognizes as digits, spaces, or word characters remain the same set as in
non-UTF mode, all with values less than 256. This remains true even when PCRE
is built to include Unicode property support, because to do otherwise would
slow down PCRE in many common cases. Note in particular that this applies to
\eb and \eB, because they are defined in terms of \ew and \eW. If you really
want to test for a wider sense of, say, "digit", you can use explicit Unicode
property tests such as \ep{Nd}. Alternatively, if you set the PCRE_UCP option,
the way that the character escapes work is changed so that Unicode properties
are used to determine which characters match. There are more details in the
section on
.\" HTML <a href="pcrepattern.html#genericchartypes">
.\" </a>
generic character types
.\"
in the
.\" HREF
\fBpcrepattern\fP
.\"
documentation.
.P
7. Similarly, characters that match the POSIX named character classes are all
low-valued characters, unless the PCRE_UCP option is set.
.P
8. However, the horizontal and vertical white space matching escapes (\eh, \eH,
\ev, and \eV) do match all the appropriate Unicode characters, whether or not
PCRE_UCP is set.
.P
9. Case-insensitive matching applies only to characters whose values are less
than 128, unless PCRE is built with Unicode property support. A few Unicode
characters such as Greek sigma have more than two codepoints that are
case-equivalent. Up to and including PCRE release 8.31, only one-to-one case
mappings were supported, but later releases (with Unicode property support) do
treat as case-equivalent all versions of characters such as Greek sigma.
.
.
.SH AUTHOR
.rs
.sp
.nf
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
.fi
.
.
.SH REVISION
.rs
.sp
.nf
Last updated: 27 February 2013
Copyright (c) 1997-2013 University of Cambridge.
.fi
1	ph10	1261	.TH PCREUNICODE 3 "27 February 2013" "PCRE 8.33"
2	ph10	678	.SH NAME
3			PCRE - Perl-compatible regular expressions
4	ph10	1214	.SH "UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT"
5	ph10	678	.rs
6			.sp
7	ph10	1214	As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30) and
8			UTF-32 (from release 8.32), by means of two additional libraries. They can be
9			built as well as, or instead of, the 8-bit library.
10	ph10	868	.
11	ph10	1214	.
12	ph10	868	.SH "UTF-8 SUPPORT"
13			.rs
14			.sp
15			In order process UTF-8 strings, you must build PCRE's 8-bit library with UTF
16			support, and, in addition, you must call
17	ph10	678	.\" HREF
18			\fBpcre_compile()\fP
19			.\"
20			with the PCRE_UTF8 option flag, or the pattern must start with the sequence
21	ph10	1219	(UTF8) or (UTF). When either of these is the case, both the pattern and any
22			subject strings that are matched against it are treated as UTF-8 strings
23			instead of strings of individual 1-byte characters.
24	ph10	868	.
25			.
26	ph10	1214	.SH "UTF-16 AND UTF-32 SUPPORT"
27	ph10	868	.rs
28			.sp
29	ph10	1221	In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit or
30	ph10	1214	32-bit library with UTF support, and, in addition, you must call
31			.\" HREF
32	ph10	868	\fBpcre16_compile()\fP
33			.\"
34	ph10	1214	or
35			.\" HREF
36	chpe	1055	\fBpcre32_compile()\fP
37			.\"
38	ph10	1214	with the PCRE_UTF16 or PCRE_UTF32 option flag, as appropriate. Alternatively,
39	ph10	1219	the pattern must start with the sequence (UTF16), (UTF32), as appropriate, or
40			(*UTF), which can be used with either library. When UTF mode is set, both the
41			pattern and any subject strings that are matched against it are treated as
42			UTF-16 or UTF-32 strings instead of strings of individual 16-bit or 32-bit
43			characters.
44	chpe	1055	.
45			.
46	ph10	868	.SH "UTF SUPPORT OVERHEAD"
47			.rs
48			.sp
49			If you compile PCRE with UTF support, but do not use it at run time, the
50	ph10	678	library will be a bit bigger, but the additional run time overhead is limited
51	chpe	1055	to testing the PCRE_UTF[8\|16\|32] flag occasionally, so should not be very big.
52	ph10	868	.
53			.
54			.SH "UNICODE PROPERTY SUPPORT"
55			.rs
56			.sp
57			If PCRE is built with Unicode character property support (which implies UTF
58			support), the escape sequences \ep{..}, \eP{..}, and \eX can be used.
59	ph10	678	The available properties that can be tested are limited to the general
60			category properties such as Lu for an upper case letter or Nd for a decimal
61			number, the Unicode script names such as Arabic or Han, and the derived
62	ph10	1214	properties Any and L&. Full lists is given in the
63	ph10	678	.\" HREF
64			\fBpcrepattern\fP
65			.\"
66	ph10	1214	and
67			.\" HREF
68			\fBpcresyntax\fP
69			.\"
70	ph10	678	documentation. Only the short names for properties are supported. For example,
71			\ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported.
72			Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
73			compatibility with Perl 5.6. PCRE does not support this.
74			.
75			.
76			.\" HTML <a name="utf8strings"></a>
77			.SS "Validity of UTF-8 strings"
78			.rs
79			.sp
80	ph10	868	When you set the PCRE_UTF8 flag, the byte strings passed as patterns and
81			subjects are (by default) checked for validity on entry to the relevant
82	ph10	959	functions. The entire string is checked before any other processing takes
83			place. From release 7.3 of PCRE, the check is according the rules of RFC 3629,
84			which are themselves derived from the Unicode specification. Earlier releases
85			of PCRE followed the rules of RFC 2279, which allows the full range of 31-bit
86			values (0 to 0x7FFFFFFF). The current check allows only values in the range U+0
87	ph10	1261	to U+10FFFF, excluding the surrogate area. (From release 8.33 the so-called
88			"non-character" code points are no longer excluded because Unicode corrigendum
89			#9 makes it clear that they should not be.)
90	ph10	678	.P
91	ph10	1214	Characters in the "Surrogate Area" of Unicode are reserved for use by UTF-16,
92			where they are used in pairs to encode codepoints with values greater than
93			0xFFFF. The code points that are encoded by UTF-16 pairs are available
94			independently in the UTF-8 and UTF-32 encodings. (In other words, the whole
95	ph10	1221	surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8 and
96	ph10	1214	UTF-32.)
97	ph10	678	.P
98			If an invalid UTF-8 string is passed to PCRE, an error return is given. At
99			compile time, the only additional information is the offset to the first byte
100	ph10	968	of the failing character. The run-time functions \fBpcre_exec()\fP and
101	ph10	678	\fBpcre_dfa_exec()\fP also pass back this information, as well as a more
102			detailed reason code if the caller has provided memory in which to do this.
103			.P
104			In some situations, you may already know that your strings are valid, and
105	ph10	959	therefore want to skip these checks in order to improve performance, for
106	ph10	1214	example in the case of a long subject string that is being scanned repeatedly.
107			If you set the PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE
108			assumes that the pattern or subject it is given (respectively) contains only
109			valid UTF-8 codes. In this case, it does not diagnose an invalid UTF-8 string.
110	ph10	678	.P
111	ph10	1221	Note that passing PCRE_NO_UTF8_CHECK to \fBpcre_compile()\fP just disables the
112			check for the pattern; it does not also apply to subject strings. If you want
113	ph10	1214	to disable the check for a subject string you must pass this option to
114			\fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP.
115	ph10	678	.P
116	ph10	1221	If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the result
117	ph10	1214	is undefined and your program may crash.
118	ph10	678	.
119			.
120	ph10	868	.\" HTML <a name="utf16strings"></a>
121			.SS "Validity of UTF-16 strings"
122	ph10	678	.rs
123			.sp
124	ph10	868	When you set the PCRE_UTF16 flag, the strings of 16-bit data units that are
125			passed as patterns and subjects are (by default) checked for validity on entry
126			to the relevant functions. Values other than those in the surrogate range
127			U+D800 to U+DFFF are independent code points. Values in the surrogate range
128			must be used in pairs in the correct manner.
129	ph10	678	.P
130	ph10	868	If an invalid UTF-16 string is passed to PCRE, an error return is given. At
131			compile time, the only additional information is the offset to the first data
132	ph10	968	unit of the failing character. The run-time functions \fBpcre16_exec()\fP and
133	ph10	868	\fBpcre16_dfa_exec()\fP also pass back this information, as well as a more
134			detailed reason code if the caller has provided memory in which to do this.
135	ph10	678	.P
136	ph10	868	In some situations, you may already know that your strings are valid, and
137			therefore want to skip these checks in order to improve performance. If you set
138			the PCRE_NO_UTF16_CHECK flag at compile time or at run time, PCRE assumes that
139			the pattern or subject it is given (respectively) contains only valid UTF-16
140			sequences. In this case, it does not diagnose an invalid UTF-16 string.
141	ph10	1214	However, if an invalid string is passed, the result is undefined.
142	ph10	868	.
143			.
144	chpe	1055	.\" HTML <a name="utf32strings"></a>
145			.SS "Validity of UTF-32 strings"
146			.rs
147			.sp
148			When you set the PCRE_UTF32 flag, the strings of 32-bit data units that are
149			passed as patterns and subjects are (by default) checked for validity on entry
150			to the relevant functions. This check allows only values in the range U+0
151	ph10	1261	to U+10FFFF, excluding the surrogate area U+D800 to U+DFFF.
152	chpe	1055	.P
153			If an invalid UTF-32 string is passed to PCRE, an error return is given. At
154			compile time, the only additional information is the offset to the first data
155			unit of the failing character. The run-time functions \fBpcre32_exec()\fP and
156			\fBpcre32_dfa_exec()\fP also pass back this information, as well as a more
157			detailed reason code if the caller has provided memory in which to do this.
158			.P
159			In some situations, you may already know that your strings are valid, and
160			therefore want to skip these checks in order to improve performance. If you set
161			the PCRE_NO_UTF32_CHECK flag at compile time or at run time, PCRE assumes that
162			the pattern or subject it is given (respectively) contains only valid UTF-32
163	ph10	1221	sequences. In this case, it does not diagnose an invalid UTF-32 string.
164	ph10	1214	However, if an invalid string is passed, the result is undefined.
165	chpe	1055	.
166			.
167	ph10	868	.SS "General comments about UTF modes"
168			.rs
169			.sp
170	ph10	1214	1. Codepoints less than 256 can be specified in patterns by either braced or
171			unbraced hexadecimal escape sequences (for example, \ex{b3} or \exb3). Larger
172			values have to use braced sequences.
173	ph10	678	.P
174	ph10	1214	2. Octal numbers up to \e777 are recognized, and in UTF-8 mode they match
175	ph10	868	two-byte characters for values greater than \e177.
176	ph10	678	.P
177	ph10	868	3. Repeat quantifiers apply to complete UTF characters, not to individual
178			data units, for example: \ex{100}{3}.
179			.P
180	ph10	903	4. The dot metacharacter matches one UTF character instead of a single data
181	ph10	868	unit.
182			.P
183			5. The escape sequence \eC can be used to match a single byte in UTF-8 mode, or
184	chpe	1055	a single 16-bit data unit in UTF-16 mode, or a single 32-bit data unit in
185			UTF-32 mode, but its use can lead to some strange effects because it breaks up
186			multi-unit characters (see the description of \eC in the
187	ph10	737	.\" HREF
188			\fBpcrepattern\fP
189			.\"
190			documentation). The use of \eC is not supported in the alternative matching
191	ph10	1214	function \fBpcre[16\|32]_dfa_exec()\fP, nor is it supported in UTF mode by the
192			JIT optimization of \fBpcre[16\|32]_exec()\fP. If JIT optimization is requested
193			for a UTF pattern that contains \eC, it will not succeed, and so the matching
194			will be carried out by the normal interpretive function.
195	ph10	678	.P
196			6. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly
197			test characters of any code value, but, by default, the characters that PCRE
198	ph10	903	recognizes as digits, spaces, or word characters remain the same set as in
199	ph10	868	non-UTF mode, all with values less than 256. This remains true even when PCRE
200			is built to include Unicode property support, because to do otherwise would
201			slow down PCRE in many common cases. Note in particular that this applies to
202			\eb and \eB, because they are defined in terms of \ew and \eW. If you really
203			want to test for a wider sense of, say, "digit", you can use explicit Unicode
204			property tests such as \ep{Nd}. Alternatively, if you set the PCRE_UCP option,
205			the way that the character escapes work is changed so that Unicode properties
206			are used to determine which characters match. There are more details in the
207			section on
208	ph10	678	.\" HTML <a href="pcrepattern.html#genericchartypes">
209			.\" </a>
210			generic character types
211			.\"
212			in the
213			.\" HREF
214			\fBpcrepattern\fP
215			.\"
216			documentation.
217			.P
218			7. Similarly, characters that match the POSIX named character classes are all
219			low-valued characters, unless the PCRE_UCP option is set.
220			.P
221	ph10	968	8. However, the horizontal and vertical white space matching escapes (\eh, \eH,
222	ph10	678	\ev, and \eV) do match all the appropriate Unicode characters, whether or not
223			PCRE_UCP is set.
224			.P
225			9. Case-insensitive matching applies only to characters whose values are less
226	ph10	1046	than 128, unless PCRE is built with Unicode property support. A few Unicode
227			characters such as Greek sigma have more than two codepoints that are
228			case-equivalent. Up to and including PCRE release 8.31, only one-to-one case
229			mappings were supported, but later releases (with Unicode property support) do
230			treat as case-equivalent all versions of characters such as Greek sigma.
231	ph10	678	.
232			.
233			.SH AUTHOR
234			.rs
235			.sp
236			.nf
237			Philip Hazel
238			University Computing Service
239			Cambridge CB2 3QH, England.
240			.fi
241			.
242			.
243			.SH REVISION
244			.rs
245			.sp
246			.nf
247	ph10	1261	Last updated: 27 February 2013
248			Copyright (c) 1997-2013 University of Cambridge.
249	ph10	678	.fi