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1=head1 NAME
2
07fcf8ff 3perluniintro - Perl Unicode introduction
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4
5=head1 DESCRIPTION
6
7This document gives a general idea of Unicode and how to use Unicode
8in Perl.
9
10=head2 Unicode
11
376d9008 12Unicode is a character set standard which plans to codify all of the
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13writing systems of the world, plus many other symbols.
14
15Unicode and ISO/IEC 10646 are coordinated standards that provide code
376d9008 16points for characters in almost all modern character set standards,
ba62762e 17covering more than 30 writing systems and hundreds of languages,
376d9008 18including all commercially-important modern languages. All characters
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19in the largest Chinese, Japanese, and Korean dictionaries are also
20encoded. The standards will eventually cover almost all characters in
21more than 250 writing systems and thousands of languages.
4c496f0c 22Unicode 1.0 was released in October 1991, and 4.0 in April 2003.
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23
24A Unicode I<character> is an abstract entity. It is not bound to any
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25particular integer width, especially not to the C language C<char>.
26Unicode is language-neutral and display-neutral: it does not encode the
27language of the text and it does not define fonts or other graphical
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28layout details. Unicode operates on characters and on text built from
29those characters.
30
31Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK
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32SMALL LETTER ALPHA> and unique numbers for the characters, in this
33case 0x0041 and 0x03B1, respectively. These unique numbers are called
34I<code points>.
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35
36The Unicode standard prefers using hexadecimal notation for the code
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37points. If numbers like C<0x0041> are unfamiliar to you, take a peek
38at a later section, L</"Hexadecimal Notation">. The Unicode standard
39uses the notation C<U+0041 LATIN CAPITAL LETTER A>, to give the
40hexadecimal code point and the normative name of the character.
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41
42Unicode also defines various I<properties> for the characters, like
376d9008 43"uppercase" or "lowercase", "decimal digit", or "punctuation";
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44these properties are independent of the names of the characters.
45Furthermore, various operations on the characters like uppercasing,
376d9008 46lowercasing, and collating (sorting) are defined.
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47
48A Unicode character consists either of a single code point, or a
49I<base character> (like C<LATIN CAPITAL LETTER A>), followed by one or
50more I<modifiers> (like C<COMBINING ACUTE ACCENT>). This sequence of
376d9008 51base character and modifiers is called a I<combining character
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52sequence>.
53
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54Whether to call these combining character sequences "characters"
55depends on your point of view. If you are a programmer, you probably
56would tend towards seeing each element in the sequences as one unit,
57or "character". The whole sequence could be seen as one "character",
58however, from the user's point of view, since that's probably what it
59looks like in the context of the user's language.
60
61With this "whole sequence" view of characters, the total number of
62characters is open-ended. But in the programmer's "one unit is one
63character" point of view, the concept of "characters" is more
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64deterministic. In this document, we take that second point of view:
65one "character" is one Unicode code point, be it a base character or
66a combining character.
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67
68For some combinations, there are I<precomposed> characters.
69C<LATIN CAPITAL LETTER A WITH ACUTE>, for example, is defined as
ba62762e 70a single code point. These precomposed characters are, however,
376d9008 71only available for some combinations, and are mainly
ba62762e 72meant to support round-trip conversions between Unicode and legacy
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73standards (like the ISO 8859). In the general case, the composing
74method is more extensible. To support conversion between
ba62762e 75different compositions of the characters, various I<normalization
376d9008 76forms> to standardize representations are also defined.
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77
78Because of backward compatibility with legacy encodings, the "a unique
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79number for every character" idea breaks down a bit: instead, there is
80"at least one number for every character". The same character could
81be represented differently in several legacy encodings. The
82converse is also not true: some code points do not have an assigned
83character. Firstly, there are unallocated code points within
84otherwise used blocks. Secondly, there are special Unicode control
85characters that do not represent true characters.
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86
87A common myth about Unicode is that it would be "16-bit", that is,
376d9008 88Unicode is only represented as C<0x10000> (or 65536) characters from
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89C<0x0000> to C<0xFFFF>. B<This is untrue.> Since Unicode 2.0 (July
901996), Unicode has been defined all the way up to 21 bits (C<0x10FFFF>),
91and since Unicode 3.1 (March 2001), characters have been defined
92beyond C<0xFFFF>. The first C<0x10000> characters are called the
93I<Plane 0>, or the I<Basic Multilingual Plane> (BMP). With Unicode
943.1, 17 (yes, seventeen) planes in all were defined--but they are
95nowhere near full of defined characters, yet.
ba62762e 96
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97Another myth is that the 256-character blocks have something to
98do with languages--that each block would define the characters used
99by a language or a set of languages. B<This is also untrue.>
100The division into blocks exists, but it is almost completely
101accidental--an artifact of how the characters have been and
102still are allocated. Instead, there is a concept called I<scripts>,
103which is more useful: there is C<Latin> script, C<Greek> script, and
104so on. Scripts usually span varied parts of several blocks.
105For further information see L<Unicode::UCD>.
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106
107The Unicode code points are just abstract numbers. To input and
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108output these abstract numbers, the numbers must be I<encoded> or
109I<serialised> somehow. Unicode defines several I<character encoding
110forms>, of which I<UTF-8> is perhaps the most popular. UTF-8 is a
111variable length encoding that encodes Unicode characters as 1 to 6
112bytes (only 4 with the currently defined characters). Other encodings
113include UTF-16 and UTF-32 and their big- and little-endian variants
114(UTF-8 is byte-order independent) The ISO/IEC 10646 defines the UCS-2
115and UCS-4 encoding forms.
ba62762e 116
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117For more information about encodings--for instance, to learn what
118I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>.
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119
120=head2 Perl's Unicode Support
121
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122Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode
123natively. Perl 5.8.0, however, is the first recommended release for
124serious Unicode work. The maintenance release 5.6.1 fixed many of the
125problems of the initial Unicode implementation, but for example
1bfb14c4 126regular expressions still do not work with Unicode in 5.6.1.
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127
128B<Starting from Perl 5.8.0, the use of C<use utf8> is no longer
129necessary.> In earlier releases the C<utf8> pragma was used to declare
130that operations in the current block or file would be Unicode-aware.
376d9008 131This model was found to be wrong, or at least clumsy: the "Unicodeness"
1bfb14c4 132is now carried with the data, instead of being attached to the
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133operations. Only one case remains where an explicit C<use utf8> is
134needed: if your Perl script itself is encoded in UTF-8, you can use
135UTF-8 in your identifier names, and in string and regular expression
136literals, by saying C<use utf8>. This is not the default because
8f8cf39c 137scripts with legacy 8-bit data in them would break. See L<utf8>.
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138
139=head2 Perl's Unicode Model
140
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141Perl supports both pre-5.6 strings of eight-bit native bytes, and
142strings of Unicode characters. The principle is that Perl tries to
143keep its data as eight-bit bytes for as long as possible, but as soon
144as Unicodeness cannot be avoided, the data is transparently upgraded
145to Unicode.
ba62762e 146
4192de81 147Internally, Perl currently uses either whatever the native eight-bit
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148character set of the platform (for example Latin-1) is, defaulting to
149UTF-8, to encode Unicode strings. Specifically, if all code points in
150the string are C<0xFF> or less, Perl uses the native eight-bit
151character set. Otherwise, it uses UTF-8.
4192de81 152
7ca610e8 153A user of Perl does not normally need to know nor care how Perl
20ba30f4 154happens to encode its internal strings, but it becomes relevant when
fae2c0fb 155outputting Unicode strings to a stream without a PerlIO layer -- one with
376d9008 156the "default" encoding. In such a case, the raw bytes used internally
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157(the native character set or UTF-8, as appropriate for each string)
158will be used, and a "Wide character" warning will be issued if those
159strings contain a character beyond 0x00FF.
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160
161For example,
162
7ca610e8 163 perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
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164
165produces a fairly useless mixture of native bytes and UTF-8, as well
1bfb14c4 166as a warning:
4192de81 167
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168 Wide character in print at ...
169
fae2c0fb 170To output UTF-8, use the C<:utf8> output layer. Prepending
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171
172 binmode(STDOUT, ":utf8");
173
376d9008 174to this sample program ensures that the output is completely UTF-8,
1bfb14c4 175and removes the program's warning.
ba62762e 176
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177You can enable automatic UTF-8-ification of your standard file
178handles, default C<open()> layer, and C<@ARGV> by using either
179the C<-C> command line switch or the C<PERL_UNICODE> environment
180variable, see L<perlrun> for the documentation of the C<-C> switch.
181
182Note that this means that Perl expects other software to work, too:
183if Perl has been led to believe that STDIN should be UTF-8, but then
184STDIN coming in from another command is not UTF-8, Perl will complain
185about the malformed UTF-8.
b310b053 186
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187All features that combine Unicode and I/O also require using the new
188PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though:
189you can see whether yours is by running "perl -V" and looking for
190C<useperlio=define>.
191
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192=head2 Unicode and EBCDIC
193
194Perl 5.8.0 also supports Unicode on EBCDIC platforms. There,
376d9008 195Unicode support is somewhat more complex to implement since
64c66fb6 196additional conversions are needed at every step. Some problems
dc4af4bb 197remain, see L<perlebcdic> for details.
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198
199In any case, the Unicode support on EBCDIC platforms is better than
200in the 5.6 series, which didn't work much at all for EBCDIC platform.
201On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
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202instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in
203that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is
204"EBCDIC-safe".
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205
206=head2 Creating Unicode
207
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208To create Unicode characters in literals for code points above C<0xFF>,
209use the C<\x{...}> notation in double-quoted strings:
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210
211 my $smiley = "\x{263a}";
212
376d9008 213Similarly, it can be used in regular expression literals
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214
215 $smiley =~ /\x{263a}/;
216
217At run-time you can use C<chr()>:
218
219 my $hebrew_alef = chr(0x05d0);
220
376d9008 221See L</"Further Resources"> for how to find all these numeric codes.
ba62762e 222
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223Naturally, C<ord()> will do the reverse: it turns a character into
224a code point.
ba62762e 225
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226Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>,
227and C<chr(...)> for arguments less than C<0x100> (decimal 256)
228generate an eight-bit character for backward compatibility with older
229Perls. For arguments of C<0x100> or more, Unicode characters are
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230always produced. If you want to force the production of Unicode
231characters regardless of the numeric value, use C<pack("U", ...)>
232instead of C<\x..>, C<\x{...}>, or C<chr()>.
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233
234You can also use the C<charnames> pragma to invoke characters
376d9008 235by name in double-quoted strings:
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236
237 use charnames ':full';
238 my $arabic_alef = "\N{ARABIC LETTER ALEF}";
239
240And, as mentioned above, you can also C<pack()> numbers into Unicode
241characters:
242
243 my $georgian_an = pack("U", 0x10a0);
244
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245Note that both C<\x{...}> and C<\N{...}> are compile-time string
246constants: you cannot use variables in them. if you want similar
247run-time functionality, use C<chr()> and C<charnames::vianame()>.
248
1eda90df 249If you want to force the result to Unicode characters, use the special
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250C<"U0"> prefix. It consumes no arguments but causes the following bytes
251to be interpreted as the UTF-8 encoding of Unicode characters:
1eda90df 252
f337b084 253 my $chars = pack("U0W*", 0x80, 0x42);
771cd3b2 254
f337b084 255Likewise, you can stop such UTF-8 interpretation by using the special
771cd3b2 256C<"C0"> prefix.
1eda90df 257
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258=head2 Handling Unicode
259
260Handling Unicode is for the most part transparent: just use the
261strings as usual. Functions like C<index()>, C<length()>, and
262C<substr()> will work on the Unicode characters; regular expressions
263will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
264
1bfb14c4 265Note that Perl considers combining character sequences to be
c0c50798 266separate characters, so for example
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267
268 use charnames ':full';
269 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
270
271will print 2, not 1. The only exception is that regular expressions
272have C<\X> for matching a combining character sequence.
273
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274Life is not quite so transparent, however, when working with legacy
275encodings, I/O, and certain special cases:
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276
277=head2 Legacy Encodings
278
279When you combine legacy data and Unicode the legacy data needs
280to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
2575c402 281applicable) is assumed.
ba62762e 282
376d9008 283The C<Encode> module knows about many encodings and has interfaces
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284for doing conversions between those encodings:
285
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286 use Encode 'decode';
287 $data = decode("iso-8859-3", $data); # convert from legacy to utf-8
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288
289=head2 Unicode I/O
290
8baee566 291Normally, writing out Unicode data
ba62762e 292
8baee566 293 print FH $some_string_with_unicode, "\n";
ba62762e 294
8baee566 295produces raw bytes that Perl happens to use to internally encode the
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296Unicode string. Perl's internal encoding depends on the system as
297well as what characters happen to be in the string at the time. If
298any of the characters are at code points C<0x100> or above, you will get
299a warning. To ensure that the output is explicitly rendered in the
300encoding you desire--and to avoid the warning--open the stream with
301the desired encoding. Some examples:
ba62762e 302
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303 open FH, ">:utf8", "file";
304
305 open FH, ">:encoding(ucs2)", "file";
306 open FH, ">:encoding(UTF-8)", "file";
307 open FH, ">:encoding(shift_jis)", "file";
1d7919c5 308
376d9008 309and on already open streams, use C<binmode()>:
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310
311 binmode(STDOUT, ":utf8");
312
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313 binmode(STDOUT, ":encoding(ucs2)");
314 binmode(STDOUT, ":encoding(UTF-8)");
315 binmode(STDOUT, ":encoding(shift_jis)");
316
b5d8778e 317The matching of encoding names is loose: case does not matter, and
fae2c0fb 318many encodings have several aliases. Note that the C<:utf8> layer
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319must always be specified exactly like that; it is I<not> subject to
320the loose matching of encoding names.
b5d8778e 321
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322See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
323L<Encode::PerlIO> for the C<:encoding()> layer, and
324L<Encode::Supported> for many encodings supported by the C<Encode>
325module.
ba62762e 326
a5f0baef 327Reading in a file that you know happens to be encoded in one of the
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328Unicode or legacy encodings does not magically turn the data into
329Unicode in Perl's eyes. To do that, specify the appropriate
fae2c0fb 330layer when opening files
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331
332 open(my $fh,'<:utf8', 'anything');
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333 my $line_of_unicode = <$fh>;
334
ec90690f 335 open(my $fh,'<:encoding(Big5)', 'anything');
8baee566 336 my $line_of_unicode = <$fh>;
ba62762e 337
fae2c0fb 338The I/O layers can also be specified more flexibly with
376d9008 339the C<open> pragma. See L<open>, or look at the following example.
ba62762e 340
fae2c0fb 341 use open ':utf8'; # input and output default layer will be UTF-8
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342 open X, ">file";
343 print X chr(0x100), "\n";
ba62762e 344 close X;
1d7919c5 345 open Y, "<file";
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346 printf "%#x\n", ord(<Y>); # this should print 0x100
347 close Y;
348
fae2c0fb 349With the C<open> pragma you can use the C<:locale> layer
ba62762e 350
12f98225 351 BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
1ecefa54 352 # the :locale will probe the locale environment variables like LC_ALL
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353 use open OUT => ':locale'; # russki parusski
354 open(O, ">koi8");
355 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
356 close O;
357 open(I, "<koi8");
358 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
359 close I;
360
fae2c0fb 361or you can also use the C<':encoding(...)'> layer
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362
363 open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
8baee566 364 my $line_of_unicode = <$epic>;
ba62762e 365
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366These methods install a transparent filter on the I/O stream that
367converts data from the specified encoding when it is read in from the
a5f0baef 368stream. The result is always Unicode.
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369
370The L<open> pragma affects all the C<open()> calls after the pragma by
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371setting default layers. If you want to affect only certain
372streams, use explicit layers directly in the C<open()> call.
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373
374You can switch encodings on an already opened stream by using
8baee566 375C<binmode()>; see L<perlfunc/binmode>.
ba62762e 376
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377The C<:locale> does not currently (as of Perl 5.8.0) work with
378C<open()> and C<binmode()>, only with the C<open> pragma. The
8baee566 379C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
1ecefa54 380C<binmode()>, and the C<open> pragma.
ba62762e 381
fae2c0fb 382Similarly, you may use these I/O layers on output streams to
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383automatically convert Unicode to the specified encoding when it is
384written to the stream. For example, the following snippet copies the
385contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
386the file "text.utf8", encoded as UTF-8:
ba62762e 387
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388 open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis');
389 open(my $unicode, '>:utf8', 'text.utf8');
0cf8a8d9 390 while (<$nihongo>) { print $unicode $_ }
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391
392The naming of encodings, both by the C<open()> and by the C<open>
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393pragma allows for flexible names: C<koi8-r> and C<KOI8R> will both be
394understood.
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395
396Common encodings recognized by ISO, MIME, IANA, and various other
8baee566 397standardisation organisations are recognised; for a more detailed
1bfb14c4 398list see L<Encode::Supported>.
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399
400C<read()> reads characters and returns the number of characters.
401C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
402and C<sysseek()>.
403
8baee566 404Notice that because of the default behaviour of not doing any
fae2c0fb 405conversion upon input if there is no default layer,
ba62762e 406it is easy to mistakenly write code that keeps on expanding a file
1bfb14c4 407by repeatedly encoding the data:
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408
409 # BAD CODE WARNING
410 open F, "file";
8baee566 411 local $/; ## read in the whole file of 8-bit characters
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412 $t = <F>;
413 close F;
414 open F, ">:utf8", "file";
8baee566 415 print F $t; ## convert to UTF-8 on output
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416 close F;
417
418If you run this code twice, the contents of the F<file> will be twice
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419UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or
420explicitly opening also the F<file> for input as UTF-8.
ba62762e 421
0c901d84 422B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
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423Perl has been built with the new PerlIO feature (which is the default
424on most systems).
0c901d84 425
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426=head2 Displaying Unicode As Text
427
428Sometimes you might want to display Perl scalars containing Unicode as
8baee566 429simple ASCII (or EBCDIC) text. The following subroutine converts
1ecefa54 430its argument so that Unicode characters with code points greater than
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431255 are displayed as C<\x{...}>, control characters (like C<\n>) are
432displayed as C<\x..>, and the rest of the characters as themselves:
1ecefa54 433
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434 sub nice_string {
435 join("",
436 map { $_ > 255 ? # if wide character...
8baee566 437 sprintf("\\x{%04X}", $_) : # \x{...}
58c274a1 438 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
8baee566 439 sprintf("\\x%02X", $_) : # \x..
d0551e73 440 quotemeta(chr($_)) # else quoted or as themselves
f337b084 441 } unpack("W*", $_[0])); # unpack Unicode characters
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442 }
443
444For example,
445
446 nice_string("foo\x{100}bar\n")
447
d0551e73 448returns the string
58c274a1 449
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450 'foo\x{0100}bar\x0A'
451
452which is ready to be printed.
1ecefa54 453
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454=head2 Special Cases
455
456=over 4
457
458=item *
459
460Bit Complement Operator ~ And vec()
461
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462The bit complement operator C<~> may produce surprising results if
463used on strings containing characters with ordinal values above
464255. In such a case, the results are consistent with the internal
465encoding of the characters, but not with much else. So don't do
466that. Similarly for C<vec()>: you will be operating on the
467internally-encoded bit patterns of the Unicode characters, not on
468the code point values, which is very probably not what you want.
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469
470=item *
471
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472Peeking At Perl's Internal Encoding
473
474Normal users of Perl should never care how Perl encodes any particular
a5f0baef 475Unicode string (because the normal ways to get at the contents of a
376d9008 476string with Unicode--via input and output--should always be via
fae2c0fb 477explicitly-defined I/O layers). But if you must, there are two
a5f0baef 478ways of looking behind the scenes.
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479
480One way of peeking inside the internal encoding of Unicode characters
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481is to use C<unpack("C*", ...> to get the bytes of whatever the string
482encoding happens to be, or C<unpack("U0..", ...)> to get the bytes of the
483UTF-8 encoding:
ba62762e 484
8baee566 485 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
f337b084 486 print join(" ", unpack("U0(H2)*", pack("U", 0x100))), "\n";
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487
488Yet another way would be to use the Devel::Peek module:
489
490 perl -MDevel::Peek -e 'Dump(chr(0x100))'
491
1e54db1a 492That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes
376d9008 493and Unicode characters in C<PV>. See also later in this document
8800c35a 494the discussion about the C<utf8::is_utf8()> function.
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495
496=back
497
498=head2 Advanced Topics
499
500=over 4
501
502=item *
503
504String Equivalence
505
506The question of string equivalence turns somewhat complicated
376d9008 507in Unicode: what do you mean by "equal"?
ba62762e 508
07698885
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509(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
510C<LATIN CAPITAL LETTER A>?)
ba62762e 511
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512The short answer is that by default Perl compares equivalence (C<eq>,
513C<ne>) based only on code points of the characters. In the above
376d9008
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514case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any
515CAPITAL LETTER As should be considered equal, or even As of any case.
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516
517The long answer is that you need to consider character normalization
376d9008 518and casing issues: see L<Unicode::Normalize>, Unicode Technical
ba62762e 519Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
376d9008
JB
520Mappings>, http://www.unicode.org/unicode/reports/tr15/ and
521http://www.unicode.org/unicode/reports/tr21/
ba62762e 522
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523As of Perl 5.8.0, the "Full" case-folding of I<Case
524Mappings/SpecialCasing> is implemented.
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525
526=item *
527
528String Collation
529
376d9008 530People like to see their strings nicely sorted--or as Unicode
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531parlance goes, collated. But again, what do you mean by collate?
532
07698885
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533(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
534C<LATIN CAPITAL LETTER A WITH GRAVE>?)
ba62762e 535
58c274a1 536The short answer is that by default, Perl compares strings (C<lt>,
ba62762e 537C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
1bfb14c4 538characters. In the above case, the answer is "after", since
da76a1f4 539C<0x00C1> > C<0x00C0>.
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540
541The long answer is that "it depends", and a good answer cannot be
542given without knowing (at the very least) the language context.
543See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
544http://www.unicode.org/unicode/reports/tr10/
545
546=back
547
548=head2 Miscellaneous
549
550=over 4
551
552=item *
553
3ff56b75 554Character Ranges and Classes
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555
556Character ranges in regular expression character classes (C</[a-z]/>)
557and in the C<tr///> (also known as C<y///>) operator are not magically
58c274a1 558Unicode-aware. What this means that C<[A-Za-z]> will not magically start
376d9008
JB
559to mean "all alphabetic letters"; not that it does mean that even for
5608-bit characters, you should be using C</[[:alpha:]]/> in that case.
ba62762e 561
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562For specifying character classes like that in regular expressions,
563you can use the various Unicode properties--C<\pL>, or perhaps
564C<\p{Alphabetic}>, in this particular case. You can use Unicode
565code points as the end points of character ranges, but there is no
566magic associated with specifying a certain range. For further
567information--there are dozens of Unicode character classes--see
568L<perlunicode>.
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569
570=item *
571
572String-To-Number Conversions
573
376d9008
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574Unicode does define several other decimal--and numeric--characters
575besides the familiar 0 to 9, such as the Arabic and Indic digits.
ba62762e 576Perl does not support string-to-number conversion for digits other
58c274a1 577than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
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578
579=back
580
581=head2 Questions With Answers
582
583=over 4
584
818c4caa 585=item *
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586
587Will My Old Scripts Break?
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588
589Very probably not. Unless you are generating Unicode characters
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590somehow, old behaviour should be preserved. About the only behaviour
591that has changed and which could start generating Unicode is the old
592behaviour of C<chr()> where supplying an argument more than 255
593produced a character modulo 255. C<chr(300)>, for example, was equal
594to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
595BREVE.
ba62762e 596
818c4caa 597=item *
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598
599How Do I Make My Scripts Work With Unicode?
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600
601Very little work should be needed since nothing changes until you
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602generate Unicode data. The most important thing is getting input as
603Unicode; for that, see the earlier I/O discussion.
ba62762e 604
818c4caa 605=item *
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606
607How Do I Know Whether My String Is In Unicode?
ba62762e 608
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609You shouldn't care. No, you really shouldn't. No, really. If you
610have to care--beyond the cases described above--it means that we
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611didn't get the transparency of Unicode quite right.
612
613Okay, if you insist:
614
8800c35a 615 print utf8::is_utf8($string) ? 1 : 0, "\n";
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616
617But note that this doesn't mean that any of the characters in the
618string are necessary UTF-8 encoded, or that any of the characters have
619code points greater than 0xFF (255) or even 0x80 (128), or that the
620string has any characters at all. All the C<is_utf8()> does is to
621return the value of the internal "utf8ness" flag attached to the
376d9008 622C<$string>. If the flag is off, the bytes in the scalar are interpreted
3c1c8017 623as a single byte encoding. If the flag is on, the bytes in the scalar
376d9008 624are interpreted as the (multi-byte, variable-length) UTF-8 encoded code
3c1c8017 625points of the characters. Bytes added to an UTF-8 encoded string are
1e54db1a 626automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars
376d9008 627are merged (double-quoted interpolation, explicit concatenation, and
3c1c8017
AT
628printf/sprintf parameter substitution), the result will be UTF-8 encoded
629as if copies of the byte strings were upgraded to UTF-8: for example,
630
631 $a = "ab\x80c";
632 $b = "\x{100}";
633 print "$a = $b\n";
634
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635the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but
636C<$a> will stay byte-encoded.
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637
638Sometimes you might really need to know the byte length of a string
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639instead of the character length. For that use either the
640C<Encode::encode_utf8()> function or the C<bytes> pragma and its only
641defined function C<length()>:
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642
643 my $unicode = chr(0x100);
644 print length($unicode), "\n"; # will print 1
ce7675db
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645 require Encode;
646 print length(Encode::encode_utf8($unicode)), "\n"; # will print 2
ba62762e 647 use bytes;
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648 print length($unicode), "\n"; # will also print 2
649 # (the 0xC4 0x80 of the UTF-8)
ba62762e 650
818c4caa 651=item *
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652
653How Do I Detect Data That's Not Valid In a Particular Encoding?
ba62762e 654
8baee566
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655Use the C<Encode> package to try converting it.
656For example,
ba62762e 657
bb2f379c 658 use Encode 'decode_utf8';
a365f2ce
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659 eval { decode_utf8($string, Encode::FB_CROAK) };
660 if ($@) {
661 # $string is valid utf8
ba62762e 662 } else {
a365f2ce 663 # $string is not valid utf8
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664 }
665
f337b084 666Or use C<unpack> to try decoding it:
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667
668 use warnings;
f337b084 669 @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
ba62762e 670
a365f2ce
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671If invalid, a C<Malformed UTF-8 character> warning is produced. The "C0" means
672"process the string character per character". Without that, the
f337b084
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673C<unpack("U*", ...)> would work in C<U0> mode (the default if the format
674string starts with C<U>) and it would return the bytes making up the UTF-8
675encoding of the target string, something that will always work.
ba62762e 676
818c4caa 677=item *
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678
679How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
ba62762e 680
8baee566
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681This probably isn't as useful as you might think.
682Normally, you shouldn't need to.
ba62762e 683
1bfb14c4 684In one sense, what you are asking doesn't make much sense: encodings
376d9008 685are for characters, and binary data are not "characters", so converting
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686"data" into some encoding isn't meaningful unless you know in what
687character set and encoding the binary data is in, in which case it's
376d9008 688not just binary data, now is it?
8baee566 689
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690If you have a raw sequence of bytes that you know should be
691interpreted via a particular encoding, you can use C<Encode>:
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692
693 use Encode 'from_to';
694 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
695
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696The call to C<from_to()> changes the bytes in C<$data>, but nothing
697material about the nature of the string has changed as far as Perl is
698concerned. Both before and after the call, the string C<$data>
699contains just a bunch of 8-bit bytes. As far as Perl is concerned,
700the encoding of the string remains as "system-native 8-bit bytes".
8baee566
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701
702You might relate this to a fictional 'Translate' module:
703
704 use Translate;
705 my $phrase = "Yes";
706 Translate::from_to($phrase, 'english', 'deutsch');
707 ## phrase now contains "Ja"
ba62762e 708
8baee566 709The contents of the string changes, but not the nature of the string.
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710Perl doesn't know any more after the call than before that the
711contents of the string indicates the affirmative.
ba62762e 712
376d9008 713Back to converting data. If you have (or want) data in your system's
a5f0baef
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714native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
715pack/unpack to convert to/from Unicode.
ba62762e 716
f337b084
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717 $native_string = pack("W*", unpack("U*", $Unicode_string));
718 $Unicode_string = pack("U*", unpack("W*", $native_string));
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719
720If you have a sequence of bytes you B<know> is valid UTF-8,
721but Perl doesn't know it yet, you can make Perl a believer, too:
722
723 use Encode 'decode_utf8';
8baee566 724 $Unicode = decode_utf8($bytes);
ba62762e 725
f337b084
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726or:
727
728 $Unicode = pack("U0a*", $bytes);
729
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730You can convert well-formed UTF-8 to a sequence of bytes, but if
731you just want to convert random binary data into UTF-8, you can't.
1bfb14c4 732B<Any random collection of bytes isn't well-formed UTF-8>. You can
ba62762e 733use C<unpack("C*", $string)> for the former, and you can create
8baee566 734well-formed Unicode data by C<pack("U*", 0xff, ...)>.
ba62762e 735
818c4caa 736=item *
5cb3728c
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737
738How Do I Display Unicode? How Do I Input Unicode?
ba62762e 739
076d825e 740See http://www.alanwood.net/unicode/ and
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741http://www.cl.cam.ac.uk/~mgk25/unicode.html
742
818c4caa 743=item *
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744
745How Does Unicode Work With Traditional Locales?
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746
747In Perl, not very well. Avoid using locales through the C<locale>
4c496f0c
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748pragma. Use only one or the other. But see L<perlrun> for the
749description of the C<-C> switch and its environment counterpart,
750C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features,
751for example by using locale settings.
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752
753=back
754
755=head2 Hexadecimal Notation
756
376d9008
JB
757The Unicode standard prefers using hexadecimal notation because
758that more clearly shows the division of Unicode into blocks of 256 characters.
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759Hexadecimal is also simply shorter than decimal. You can use decimal
760notation, too, but learning to use hexadecimal just makes life easier
1bfb14c4 761with the Unicode standard. The C<U+HHHH> notation uses hexadecimal,
076d825e 762for example.
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763
764The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
765a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
766four bits, or half a byte. C<print 0x..., "\n"> will show a
767hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
768show a decimal number in hexadecimal. If you have just the
376d9008 769"hex digits" of a hexadecimal number, you can use the C<hex()> function.
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770
771 print 0x0009, "\n"; # 9
772 print 0x000a, "\n"; # 10
773 print 0x000f, "\n"; # 15
774 print 0x0010, "\n"; # 16
775 print 0x0011, "\n"; # 17
776 print 0x0100, "\n"; # 256
777
778 print 0x0041, "\n"; # 65
779
780 printf "%x\n", 65; # 41
781 printf "%#x\n", 65; # 0x41
782
783 print hex("41"), "\n"; # 65
784
785=head2 Further Resources
786
787=over 4
788
789=item *
790
791Unicode Consortium
792
793 http://www.unicode.org/
794
795=item *
796
797Unicode FAQ
798
799 http://www.unicode.org/unicode/faq/
800
801=item *
802
803Unicode Glossary
804
805 http://www.unicode.org/glossary/
806
807=item *
808
809Unicode Useful Resources
810
811 http://www.unicode.org/unicode/onlinedat/resources.html
812
813=item *
814
815Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
816
076d825e 817 http://www.alanwood.net/unicode/
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818
819=item *
820
821UTF-8 and Unicode FAQ for Unix/Linux
822
823 http://www.cl.cam.ac.uk/~mgk25/unicode.html
824
825=item *
826
827Legacy Character Sets
828
829 http://www.czyborra.com/
830 http://www.eki.ee/letter/
831
832=item *
833
834The Unicode support files live within the Perl installation in the
835directory
836
837 $Config{installprivlib}/unicore
838
839in Perl 5.8.0 or newer, and
840
841 $Config{installprivlib}/unicode
842
843in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
844avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
551b6b6f 845The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
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846Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
847
848 perl "-V:installprivlib"
849
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850You can explore various information from the Unicode data files using
851the C<Unicode::UCD> module.
852
853=back
854
f6edf83b
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855=head1 UNICODE IN OLDER PERLS
856
857If you cannot upgrade your Perl to 5.8.0 or later, you can still
858do some Unicode processing by using the modules C<Unicode::String>,
859C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
860If you have the GNU recode installed, you can also use the
376d9008 861Perl front-end C<Convert::Recode> for character conversions.
f6edf83b 862
aaef10c5 863The following are fast conversions from ISO 8859-1 (Latin-1) bytes
63de3cb2 864to UTF-8 bytes and back, the code works even with older Perl 5 versions.
aaef10c5
JH
865
866 # ISO 8859-1 to UTF-8
867 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
868
869 # UTF-8 to ISO 8859-1
870 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
871
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872=head1 SEE ALSO
873
2575c402 874L<perlunitut>, L<perlunicode>, L<Encode>, L<open>, L<utf8>, L<bytes>,
4c496f0c
JH
875L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>,
876L<Unicode::UCD>
ba62762e 877
376d9008 878=head1 ACKNOWLEDGMENTS
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879
880Thanks to the kind readers of the perl5-porters@perl.org,
881perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
882mailing lists for their valuable feedback.
883
884=head1 AUTHOR, COPYRIGHT, AND LICENSE
885
0f2f9b7d 886Copyright 2001-2002 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>
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887
888This document may be distributed under the same terms as Perl itself.