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	.TH PCREUNICODE 3 "27 February 2013" "PCRE 8.33"
2	.SH NAME
3	PCRE - Perl-compatible regular expressions
4	.SH "UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT"
5	.rs
6	.sp
7	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	.
11	.
12	.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	.\" HREF
18	\fBpcre_compile()\fP
19	.\"
20	with the PCRE_UTF8 option flag, or the pattern must start with the sequence
21	(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	.
25	.
26	.SH "UTF-16 AND UTF-32 SUPPORT"
27	.rs
28	.sp
29	In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit or
30	32-bit library with UTF support, and, in addition, you must call
31	.\" HREF
32	\fBpcre16_compile()\fP
33	.\"
34	or
35	.\" HREF
36	\fBpcre32_compile()\fP
37	.\"
38	with the PCRE_UTF16 or PCRE_UTF32 option flag, as appropriate. Alternatively,
39	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	.
45	.
46	.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	library will be a bit bigger, but the additional run time overhead is limited
51	to testing the PCRE_UTF[8\|16\|32] flag occasionally, so should not be very big.
52	.
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	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	properties Any and L&. Full lists is given in the
63	.\" HREF
64	\fBpcrepattern\fP
65	.\"
66	and
67	.\" HREF
68	\fBpcresyntax\fP
69	.\"
70	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	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	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	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	.P
91	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	surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8 and
96	UTF-32.)
97	.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	of the failing character. The run-time functions \fBpcre_exec()\fP and
101	\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	therefore want to skip these checks in order to improve performance, for
106	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	.P
111	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	to disable the check for a subject string you must pass this option to
114	\fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP.
115	.P
116	If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the result
117	is undefined and your program may crash.
118	.
119	.
120	.\" HTML <a name="utf16strings"></a>
121	.SS "Validity of UTF-16 strings"
122	.rs
123	.sp
124	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	.P
130	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	unit of the failing character. The run-time functions \fBpcre16_exec()\fP and
133	\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	.P
136	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	However, if an invalid string is passed, the result is undefined.
142	.
143	.
144	.\" 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	to U+10FFFF, excluding the surrogate area U+D800 to U+DFFF.
152	.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	sequences. In this case, it does not diagnose an invalid UTF-32 string.
164	However, if an invalid string is passed, the result is undefined.
165	.
166	.
167	.SS "General comments about UTF modes"
168	.rs
169	.sp
170	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	.P
174	2. Octal numbers up to \e777 are recognized, and in UTF-8 mode they match
175	two-byte characters for values greater than \e177.
176	.P
177	3. Repeat quantifiers apply to complete UTF characters, not to individual
178	data units, for example: \ex{100}{3}.
179	.P
180	4. The dot metacharacter matches one UTF character instead of a single data
181	unit.
182	.P
183	5. The escape sequence \eC can be used to match a single byte in UTF-8 mode, or
184	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	.\" HREF
188	\fBpcrepattern\fP
189	.\"
190	documentation). The use of \eC is not supported in the alternative matching
191	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	.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	recognizes as digits, spaces, or word characters remain the same set as in
199	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	.\" 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	8. However, the horizontal and vertical white space matching escapes (\eh, \eH,
222	\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	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	.
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	Last updated: 27 February 2013
248	Copyright (c) 1997-2013 University of Cambridge.
249	.fi