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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.
22
23A Unicode I<character> is an abstract entity. It is not bound to any
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24particular integer width, especially not to the C language C<char>.
25Unicode is language-neutral and display-neutral: it does not encode the
26language of the text and it does not define fonts or other graphical
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27layout details. Unicode operates on characters and on text built from
28those characters.
29
30Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK
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31SMALL LETTER ALPHA> and unique numbers for the characters, in this
32case 0x0041 and 0x03B1, respectively. These unique numbers are called
33I<code points>.
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34
35The Unicode standard prefers using hexadecimal notation for the code
1bfb14c4 36points. If numbers like C<0x0041> are unfamiliar to
376d9008 37you, take a peek at a later section, L</"Hexadecimal Notation">.
ba62762e 38The Unicode standard uses the notation C<U+0041 LATIN CAPITAL LETTER A>,
376d9008 39to give the hexadecimal code point and the normative name of
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40the character.
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,
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88Unicode is only represented as C<0x10000> (or 65536) characters from
89C<0x0000> to C<0xFFFF>. B<This is untrue.> Since Unicode 2.0, Unicode
90has been defined all the way up to 21 bits (C<0x10FFFF>), and since
91Unicode 3.1, characters have been defined beyond C<0xFFFF>. The first
92C<0x10000> characters are called the I<Plane 0>, or the I<Basic
93Multilingual Plane> (BMP). With Unicode 3.1, 17 planes in all are
94defined--but nowhere near full of defined characters, yet.
ba62762e 95
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96Another myth is that the 256-character blocks have something to
97do with languages--that each block would define the characters used
98by a language or a set of languages. B<This is also untrue.>
99The division into blocks exists, but it is almost completely
100accidental--an artifact of how the characters have been and
101still are allocated. Instead, there is a concept called I<scripts>,
102which is more useful: there is C<Latin> script, C<Greek> script, and
103so on. Scripts usually span varied parts of several blocks.
104For further information see L<Unicode::UCD>.
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105
106The Unicode code points are just abstract numbers. To input and
107output these abstract numbers, the numbers must be I<encoded> somehow.
108Unicode defines several I<character encoding forms>, of which I<UTF-8>
109is perhaps the most popular. UTF-8 is a variable length encoding that
110encodes Unicode characters as 1 to 6 bytes (only 4 with the currently
8baee566 111defined characters). Other encodings include UTF-16 and UTF-32 and their
1bfb14c4 112big- and little-endian variants (UTF-8 is byte-order independent)
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113The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms.
114
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115For more information about encodings--for instance, to learn what
116I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>.
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117
118=head2 Perl's Unicode Support
119
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120Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode
121natively. Perl 5.8.0, however, is the first recommended release for
122serious Unicode work. The maintenance release 5.6.1 fixed many of the
123problems of the initial Unicode implementation, but for example
1bfb14c4 124regular expressions still do not work with Unicode in 5.6.1.
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125
126B<Starting from Perl 5.8.0, the use of C<use utf8> is no longer
127necessary.> In earlier releases the C<utf8> pragma was used to declare
128that operations in the current block or file would be Unicode-aware.
376d9008 129This model was found to be wrong, or at least clumsy: the "Unicodeness"
1bfb14c4 130is now carried with the data, instead of being attached to the
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131operations. Only one case remains where an explicit C<use utf8> is
132needed: if your Perl script itself is encoded in UTF-8, you can use
133UTF-8 in your identifier names, and in string and regular expression
134literals, by saying C<use utf8>. This is not the default because
8f8cf39c 135scripts with legacy 8-bit data in them would break. See L<utf8>.
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136
137=head2 Perl's Unicode Model
138
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139Perl supports both pre-5.6 strings of eight-bit native bytes, and
140strings of Unicode characters. The principle is that Perl tries to
141keep its data as eight-bit bytes for as long as possible, but as soon
142as Unicodeness cannot be avoided, the data is transparently upgraded
143to Unicode.
ba62762e 144
4192de81 145Internally, Perl currently uses either whatever the native eight-bit
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146character set of the platform (for example Latin-1) is, defaulting to
147UTF-8, to encode Unicode strings. Specifically, if all code points in
148the string are C<0xFF> or less, Perl uses the native eight-bit
149character set. Otherwise, it uses UTF-8.
4192de81 150
7ca610e8 151A user of Perl does not normally need to know nor care how Perl
20ba30f4 152happens to encode its internal strings, but it becomes relevant when
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153outputting Unicode strings to a stream without a discipline--one with
154the "default" encoding. In such a case, the raw bytes used internally
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155(the native character set or UTF-8, as appropriate for each string)
156will be used, and a "Wide character" warning will be issued if those
157strings contain a character beyond 0x00FF.
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158
159For example,
160
7ca610e8 161 perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
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162
163produces a fairly useless mixture of native bytes and UTF-8, as well
1bfb14c4 164as a warning:
4192de81 165
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166 Wide character in print at ...
167
168To output UTF-8, use the C<:utf8> output discipline. Prepending
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169
170 binmode(STDOUT, ":utf8");
171
376d9008 172to this sample program ensures that the output is completely UTF-8,
1bfb14c4 173and removes the program's warning.
ba62762e 174
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175If your locale environment variables (C<LANGUAGE>, C<LC_ALL>,
176C<LC_CTYPE>, C<LANG>) contain the strings 'UTF-8' or 'UTF8',
177regardless of case, then the default encoding of your STDIN, STDOUT,
178and STDERR and of B<any subsequent file open>, is UTF-8. Note that
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179this means that Perl expects other software to work, too: if Perl has
180been led to believe that STDIN should be UTF-8, but then STDIN coming
181in from another command is not UTF-8, Perl will complain about the
ac730995 182malformed UTF-8.
b310b053 183
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184All features that combine Unicode and I/O also require using the new
185PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though:
186you can see whether yours is by running "perl -V" and looking for
187C<useperlio=define>.
188
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189=head2 Unicode and EBCDIC
190
191Perl 5.8.0 also supports Unicode on EBCDIC platforms. There,
376d9008 192Unicode support is somewhat more complex to implement since
64c66fb6 193additional conversions are needed at every step. Some problems
dc4af4bb 194remain, see L<perlebcdic> for details.
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195
196In any case, the Unicode support on EBCDIC platforms is better than
197in the 5.6 series, which didn't work much at all for EBCDIC platform.
198On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
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199instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in
200that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is
201"EBCDIC-safe".
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202
203=head2 Creating Unicode
204
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205To create Unicode characters in literals for code points above C<0xFF>,
206use the C<\x{...}> notation in double-quoted strings:
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207
208 my $smiley = "\x{263a}";
209
376d9008 210Similarly, it can be used in regular expression literals
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211
212 $smiley =~ /\x{263a}/;
213
214At run-time you can use C<chr()>:
215
216 my $hebrew_alef = chr(0x05d0);
217
376d9008 218See L</"Further Resources"> for how to find all these numeric codes.
ba62762e 219
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220Naturally, C<ord()> will do the reverse: it turns a character into
221a code point.
ba62762e 222
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223Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>,
224and C<chr(...)> for arguments less than C<0x100> (decimal 256)
225generate an eight-bit character for backward compatibility with older
226Perls. For arguments of C<0x100> or more, Unicode characters are
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227always produced. If you want to force the production of Unicode
228characters regardless of the numeric value, use C<pack("U", ...)>
229instead of C<\x..>, C<\x{...}>, or C<chr()>.
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230
231You can also use the C<charnames> pragma to invoke characters
376d9008 232by name in double-quoted strings:
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233
234 use charnames ':full';
235 my $arabic_alef = "\N{ARABIC LETTER ALEF}";
236
237And, as mentioned above, you can also C<pack()> numbers into Unicode
238characters:
239
240 my $georgian_an = pack("U", 0x10a0);
241
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242Note that both C<\x{...}> and C<\N{...}> are compile-time string
243constants: you cannot use variables in them. if you want similar
244run-time functionality, use C<chr()> and C<charnames::vianame()>.
245
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246Also note that if all the code points for pack "U" are below 0x100,
247bytes will be generated, just like if you were using C<chr()>.
248
249 my $bytes = pack("U*", 0x80, 0xFF);
250
251If you want to force the result to Unicode characters, use the special
252C<"U0"> prefix. It consumes no arguments but forces the result to be
253in Unicode characters, instead of bytes.
254
255 my $chars = pack("U0U*", 0x80, 0xFF);
256
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257=head2 Handling Unicode
258
259Handling Unicode is for the most part transparent: just use the
260strings as usual. Functions like C<index()>, C<length()>, and
261C<substr()> will work on the Unicode characters; regular expressions
262will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
263
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264Note that Perl considers combining character sequences to be
265characters, so for example
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266
267 use charnames ':full';
268 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
269
270will print 2, not 1. The only exception is that regular expressions
271have C<\X> for matching a combining character sequence.
272
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273Life is not quite so transparent, however, when working with legacy
274encodings, I/O, and certain special cases:
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275
276=head2 Legacy Encodings
277
278When you combine legacy data and Unicode the legacy data needs
279to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
280applicable) is assumed. You can override this assumption by
281using the C<encoding> pragma, for example
282
283 use encoding 'latin2'; # ISO 8859-2
284
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285in which case literals (string or regular expressions), C<chr()>,
286and C<ord()> in your whole script are assumed to produce Unicode
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287characters from ISO 8859-2 code points. Note that the matching for
288encoding names is forgiving: instead of C<latin2> you could have
289said C<Latin 2>, or C<iso8859-2>, or other variations. With just
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290
291 use encoding;
292
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293the environment variable C<PERL_ENCODING> will be consulted.
294If that variable isn't set, the encoding pragma will fail.
ba62762e 295
376d9008 296The C<Encode> module knows about many encodings and has interfaces
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297for doing conversions between those encodings:
298
299 use Encode 'from_to';
300 from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8
301
302=head2 Unicode I/O
303
8baee566 304Normally, writing out Unicode data
ba62762e 305
8baee566 306 print FH $some_string_with_unicode, "\n";
ba62762e 307
8baee566 308produces raw bytes that Perl happens to use to internally encode the
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309Unicode string. Perl's internal encoding depends on the system as
310well as what characters happen to be in the string at the time. If
311any of the characters are at code points C<0x100> or above, you will get
312a warning. To ensure that the output is explicitly rendered in the
313encoding you desire--and to avoid the warning--open the stream with
314the desired encoding. Some examples:
ba62762e 315
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316 open FH, ">:utf8", "file";
317
318 open FH, ">:encoding(ucs2)", "file";
319 open FH, ">:encoding(UTF-8)", "file";
320 open FH, ">:encoding(shift_jis)", "file";
1d7919c5 321
376d9008 322and on already open streams, use C<binmode()>:
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323
324 binmode(STDOUT, ":utf8");
325
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326 binmode(STDOUT, ":encoding(ucs2)");
327 binmode(STDOUT, ":encoding(UTF-8)");
328 binmode(STDOUT, ":encoding(shift_jis)");
329
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330The matching of encoding names is loose: case does not matter, and
331many encodings have several aliases. Note that C<:utf8> discipline
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332must always be specified exactly like that; it is I<not> subject to
333the loose matching of encoding names.
b5d8778e 334
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335See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
336L<Encode::PerlIO> for the C<:encoding()> layer, and
337L<Encode::Supported> for many encodings supported by the C<Encode>
338module.
ba62762e 339
a5f0baef 340Reading in a file that you know happens to be encoded in one of the
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341Unicode or legacy encodings does not magically turn the data into
342Unicode in Perl's eyes. To do that, specify the appropriate
343discipline when opening files
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344
345 open(my $fh,'<:utf8', 'anything');
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346 my $line_of_unicode = <$fh>;
347
ec90690f 348 open(my $fh,'<:encoding(Big5)', 'anything');
8baee566 349 my $line_of_unicode = <$fh>;
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350
351The I/O disciplines can also be specified more flexibly with
376d9008 352the C<open> pragma. See L<open>, or look at the following example.
ba62762e 353
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354 use open ':utf8'; # input and output default discipline will be UTF-8
355 open X, ">file";
356 print X chr(0x100), "\n";
ba62762e 357 close X;
1d7919c5 358 open Y, "<file";
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359 printf "%#x\n", ord(<Y>); # this should print 0x100
360 close Y;
361
362With the C<open> pragma you can use the C<:locale> discipline
363
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364 $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R';
365 # the :locale will probe the locale environment variables like LC_ALL
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366 use open OUT => ':locale'; # russki parusski
367 open(O, ">koi8");
368 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
369 close O;
370 open(I, "<koi8");
371 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
372 close I;
373
374or you can also use the C<':encoding(...)'> discipline
375
376 open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
8baee566 377 my $line_of_unicode = <$epic>;
ba62762e 378
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379These methods install a transparent filter on the I/O stream that
380converts data from the specified encoding when it is read in from the
a5f0baef 381stream. The result is always Unicode.
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382
383The L<open> pragma affects all the C<open()> calls after the pragma by
384setting default disciplines. If you want to affect only certain
385streams, use explicit disciplines directly in the C<open()> call.
386
387You can switch encodings on an already opened stream by using
8baee566 388C<binmode()>; see L<perlfunc/binmode>.
ba62762e 389
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390The C<:locale> does not currently (as of Perl 5.8.0) work with
391C<open()> and C<binmode()>, only with the C<open> pragma. The
8baee566 392C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
1ecefa54 393C<binmode()>, and the C<open> pragma.
ba62762e 394
8baee566 395Similarly, you may use these I/O disciplines on output streams to
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396automatically convert Unicode to the specified encoding when it is
397written to the stream. For example, the following snippet copies the
398contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
399the file "text.utf8", encoded as UTF-8:
ba62762e 400
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401 open(my $nihongo, '<:encoding(iso2022-jp)', 'text.jis');
402 open(my $unicode, '>:utf8', 'text.utf8');
403 while (<$nihongo>) { print $unicode }
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404
405The naming of encodings, both by the C<open()> and by the C<open>
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406pragma, is similar to the C<encoding> pragma in that it allows for
407flexible names: C<koi8-r> and C<KOI8R> will both be understood.
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408
409Common encodings recognized by ISO, MIME, IANA, and various other
8baee566 410standardisation organisations are recognised; for a more detailed
1bfb14c4 411list see L<Encode::Supported>.
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412
413C<read()> reads characters and returns the number of characters.
414C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
415and C<sysseek()>.
416
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417Notice that because of the default behaviour of not doing any
418conversion upon input if there is no default discipline,
ba62762e 419it is easy to mistakenly write code that keeps on expanding a file
1bfb14c4 420by repeatedly encoding the data:
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421
422 # BAD CODE WARNING
423 open F, "file";
8baee566 424 local $/; ## read in the whole file of 8-bit characters
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425 $t = <F>;
426 close F;
427 open F, ">:utf8", "file";
8baee566 428 print F $t; ## convert to UTF-8 on output
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429 close F;
430
431If you run this code twice, the contents of the F<file> will be twice
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432UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or
433explicitly opening also the F<file> for input as UTF-8.
ba62762e 434
0c901d84 435B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
ec71e770 436Perl has been built with the new PerlIO feature.
0c901d84 437
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438=head2 Displaying Unicode As Text
439
440Sometimes you might want to display Perl scalars containing Unicode as
8baee566 441simple ASCII (or EBCDIC) text. The following subroutine converts
1ecefa54 442its argument so that Unicode characters with code points greater than
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443255 are displayed as C<\x{...}>, control characters (like C<\n>) are
444displayed as C<\x..>, and the rest of the characters as themselves:
1ecefa54 445
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446 sub nice_string {
447 join("",
448 map { $_ > 255 ? # if wide character...
8baee566 449 sprintf("\\x{%04X}", $_) : # \x{...}
58c274a1 450 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
8baee566 451 sprintf("\\x%02X", $_) : # \x..
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452 chr($_) # else as themselves
453 } unpack("U*", $_[0])); # unpack Unicode characters
454 }
455
456For example,
457
458 nice_string("foo\x{100}bar\n")
459
8baee566 460returns:
58c274a1 461
8baee566 462 "foo\x{0100}bar\x0A"
1ecefa54 463
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464=head2 Special Cases
465
466=over 4
467
468=item *
469
470Bit Complement Operator ~ And vec()
471
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472The bit complement operator C<~> may produce surprising results if
473used on strings containing characters with ordinal values above
474255. In such a case, the results are consistent with the internal
475encoding of the characters, but not with much else. So don't do
476that. Similarly for C<vec()>: you will be operating on the
477internally-encoded bit patterns of the Unicode characters, not on
478the code point values, which is very probably not what you want.
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479
480=item *
481
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482Peeking At Perl's Internal Encoding
483
484Normal users of Perl should never care how Perl encodes any particular
a5f0baef 485Unicode string (because the normal ways to get at the contents of a
376d9008 486string with Unicode--via input and output--should always be via
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487explicitly-defined I/O disciplines). But if you must, there are two
488ways of looking behind the scenes.
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489
490One way of peeking inside the internal encoding of Unicode characters
376d9008 491is to use C<unpack("C*", ...> to get the bytes or C<unpack("H*", ...)>
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492to display the bytes:
493
8baee566 494 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
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495 print join(" ", unpack("H*", pack("U", 0x100))), "\n";
496
497Yet another way would be to use the Devel::Peek module:
498
499 perl -MDevel::Peek -e 'Dump(chr(0x100))'
500
8baee566 501That shows the UTF8 flag in FLAGS and both the UTF-8 bytes
376d9008 502and Unicode characters in C<PV>. See also later in this document
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503the discussion about the C<is_utf8> function of the C<Encode> module.
504
505=back
506
507=head2 Advanced Topics
508
509=over 4
510
511=item *
512
513String Equivalence
514
515The question of string equivalence turns somewhat complicated
376d9008 516in Unicode: what do you mean by "equal"?
ba62762e 517
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518(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
519C<LATIN CAPITAL LETTER A>?)
ba62762e 520
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521The short answer is that by default Perl compares equivalence (C<eq>,
522C<ne>) based only on code points of the characters. In the above
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523case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any
524CAPITAL LETTER As should be considered equal, or even As of any case.
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525
526The long answer is that you need to consider character normalization
376d9008 527and casing issues: see L<Unicode::Normalize>, Unicode Technical
ba62762e 528Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
376d9008
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529Mappings>, http://www.unicode.org/unicode/reports/tr15/ and
530http://www.unicode.org/unicode/reports/tr21/
ba62762e 531
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532As of Perl 5.8.0, the "Full" case-folding of I<Case
533Mappings/SpecialCasing> is implemented.
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534
535=item *
536
537String Collation
538
376d9008 539People like to see their strings nicely sorted--or as Unicode
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540parlance goes, collated. But again, what do you mean by collate?
541
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542(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
543C<LATIN CAPITAL LETTER A WITH GRAVE>?)
ba62762e 544
58c274a1 545The short answer is that by default, Perl compares strings (C<lt>,
ba62762e 546C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
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547characters. In the above case, the answer is "after", since
548C<0x00C1> > C<0x00C0>.
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549
550The long answer is that "it depends", and a good answer cannot be
551given without knowing (at the very least) the language context.
552See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
553http://www.unicode.org/unicode/reports/tr10/
554
555=back
556
557=head2 Miscellaneous
558
559=over 4
560
561=item *
562
3ff56b75 563Character Ranges and Classes
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564
565Character ranges in regular expression character classes (C</[a-z]/>)
566and in the C<tr///> (also known as C<y///>) operator are not magically
58c274a1 567Unicode-aware. What this means that C<[A-Za-z]> will not magically start
376d9008
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568to mean "all alphabetic letters"; not that it does mean that even for
5698-bit characters, you should be using C</[[:alpha:]]/> in that case.
ba62762e 570
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571For specifying character classes like that in regular expressions,
572you can use the various Unicode properties--C<\pL>, or perhaps
573C<\p{Alphabetic}>, in this particular case. You can use Unicode
574code points as the end points of character ranges, but there is no
575magic associated with specifying a certain range. For further
576information--there are dozens of Unicode character classes--see
577L<perlunicode>.
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578
579=item *
580
581String-To-Number Conversions
582
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583Unicode does define several other decimal--and numeric--characters
584besides the familiar 0 to 9, such as the Arabic and Indic digits.
ba62762e 585Perl does not support string-to-number conversion for digits other
58c274a1 586than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
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587
588=back
589
590=head2 Questions With Answers
591
592=over 4
593
818c4caa 594=item *
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595
596Will My Old Scripts Break?
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597
598Very probably not. Unless you are generating Unicode characters
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599somehow, old behaviour should be preserved. About the only behaviour
600that has changed and which could start generating Unicode is the old
601behaviour of C<chr()> where supplying an argument more than 255
602produced a character modulo 255. C<chr(300)>, for example, was equal
603to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
604BREVE.
ba62762e 605
818c4caa 606=item *
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607
608How Do I Make My Scripts Work With Unicode?
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609
610Very little work should be needed since nothing changes until you
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611generate Unicode data. The most important thing is getting input as
612Unicode; for that, see the earlier I/O discussion.
ba62762e 613
818c4caa 614=item *
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615
616How Do I Know Whether My String Is In Unicode?
ba62762e 617
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618You shouldn't care. No, you really shouldn't. No, really. If you
619have to care--beyond the cases described above--it means that we
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620didn't get the transparency of Unicode quite right.
621
622Okay, if you insist:
623
624 use Encode 'is_utf8';
625 print is_utf8($string) ? 1 : 0, "\n";
626
627But note that this doesn't mean that any of the characters in the
628string are necessary UTF-8 encoded, or that any of the characters have
629code points greater than 0xFF (255) or even 0x80 (128), or that the
630string has any characters at all. All the C<is_utf8()> does is to
631return the value of the internal "utf8ness" flag attached to the
376d9008 632C<$string>. If the flag is off, the bytes in the scalar are interpreted
3c1c8017 633as a single byte encoding. If the flag is on, the bytes in the scalar
376d9008 634are interpreted as the (multi-byte, variable-length) UTF-8 encoded code
3c1c8017
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635points of the characters. Bytes added to an UTF-8 encoded string are
636automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars
376d9008 637are merged (double-quoted interpolation, explicit concatenation, and
3c1c8017
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638printf/sprintf parameter substitution), the result will be UTF-8 encoded
639as if copies of the byte strings were upgraded to UTF-8: for example,
640
641 $a = "ab\x80c";
642 $b = "\x{100}";
643 print "$a = $b\n";
644
1bfb14c4 645the output string will be UTF-8-encoded C<ab\x80c\x{100}\n>, but note
376d9008 646that C<$a> will stay byte-encoded.
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647
648Sometimes you might really need to know the byte length of a string
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649instead of the character length. For that use either the
650C<Encode::encode_utf8()> function or the C<bytes> pragma and its only
651defined function C<length()>:
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652
653 my $unicode = chr(0x100);
654 print length($unicode), "\n"; # will print 1
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655 require Encode;
656 print length(Encode::encode_utf8($unicode)), "\n"; # will print 2
ba62762e 657 use bytes;
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658 print length($unicode), "\n"; # will also print 2
659 # (the 0xC4 0x80 of the UTF-8)
ba62762e 660
818c4caa 661=item *
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662
663How Do I Detect Data That's Not Valid In a Particular Encoding?
ba62762e 664
8baee566
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665Use the C<Encode> package to try converting it.
666For example,
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667
668 use Encode 'encode_utf8';
8baee566 669 if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) {
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670 # valid
671 } else {
672 # invalid
673 }
674
8baee566 675For UTF-8 only, you can use:
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676
677 use warnings;
8baee566 678 @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
ba62762e 679
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680If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack>
681warning is produced. The "U0" means "expect strictly UTF-8 encoded
682Unicode". Without that the C<unpack("U*", ...)> would accept also
683data like C<chr(0xFF>), similarly to the C<pack> as we saw earlier.
ba62762e 684
818c4caa 685=item *
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686
687How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
ba62762e 688
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689This probably isn't as useful as you might think.
690Normally, you shouldn't need to.
ba62762e 691
1bfb14c4 692In one sense, what you are asking doesn't make much sense: encodings
376d9008 693are for characters, and binary data are not "characters", so converting
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694"data" into some encoding isn't meaningful unless you know in what
695character set and encoding the binary data is in, in which case it's
376d9008 696not just binary data, now is it?
8baee566 697
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698If you have a raw sequence of bytes that you know should be
699interpreted via a particular encoding, you can use C<Encode>:
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700
701 use Encode 'from_to';
702 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
703
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704The call to C<from_to()> changes the bytes in C<$data>, but nothing
705material about the nature of the string has changed as far as Perl is
706concerned. Both before and after the call, the string C<$data>
707contains just a bunch of 8-bit bytes. As far as Perl is concerned,
708the encoding of the string remains as "system-native 8-bit bytes".
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709
710You might relate this to a fictional 'Translate' module:
711
712 use Translate;
713 my $phrase = "Yes";
714 Translate::from_to($phrase, 'english', 'deutsch');
715 ## phrase now contains "Ja"
ba62762e 716
8baee566 717The contents of the string changes, but not the nature of the string.
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718Perl doesn't know any more after the call than before that the
719contents of the string indicates the affirmative.
ba62762e 720
376d9008 721Back to converting data. If you have (or want) data in your system's
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722native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
723pack/unpack to convert to/from Unicode.
ba62762e 724
8baee566
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725 $native_string = pack("C*", unpack("U*", $Unicode_string));
726 $Unicode_string = pack("U*", unpack("C*", $native_string));
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727
728If you have a sequence of bytes you B<know> is valid UTF-8,
729but Perl doesn't know it yet, you can make Perl a believer, too:
730
731 use Encode 'decode_utf8';
8baee566 732 $Unicode = decode_utf8($bytes);
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733
734You can convert well-formed UTF-8 to a sequence of bytes, but if
735you just want to convert random binary data into UTF-8, you can't.
1bfb14c4 736B<Any random collection of bytes isn't well-formed UTF-8>. You can
ba62762e 737use C<unpack("C*", $string)> for the former, and you can create
8baee566 738well-formed Unicode data by C<pack("U*", 0xff, ...)>.
ba62762e 739
818c4caa 740=item *
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741
742How Do I Display Unicode? How Do I Input Unicode?
ba62762e 743
076d825e 744See http://www.alanwood.net/unicode/ and
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745http://www.cl.cam.ac.uk/~mgk25/unicode.html
746
818c4caa 747=item *
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748
749How Does Unicode Work With Traditional Locales?
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750
751In Perl, not very well. Avoid using locales through the C<locale>
752pragma. Use only one or the other.
753
754=back
755
756=head2 Hexadecimal Notation
757
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758The Unicode standard prefers using hexadecimal notation because
759that more clearly shows the division of Unicode into blocks of 256 characters.
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760Hexadecimal is also simply shorter than decimal. You can use decimal
761notation, too, but learning to use hexadecimal just makes life easier
1bfb14c4 762with the Unicode standard. The C<U+HHHH> notation uses hexadecimal,
076d825e 763for example.
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764
765The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
766a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
767four bits, or half a byte. C<print 0x..., "\n"> will show a
768hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
769show a decimal number in hexadecimal. If you have just the
376d9008 770"hex digits" of a hexadecimal number, you can use the C<hex()> function.
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771
772 print 0x0009, "\n"; # 9
773 print 0x000a, "\n"; # 10
774 print 0x000f, "\n"; # 15
775 print 0x0010, "\n"; # 16
776 print 0x0011, "\n"; # 17
777 print 0x0100, "\n"; # 256
778
779 print 0x0041, "\n"; # 65
780
781 printf "%x\n", 65; # 41
782 printf "%#x\n", 65; # 0x41
783
784 print hex("41"), "\n"; # 65
785
786=head2 Further Resources
787
788=over 4
789
790=item *
791
792Unicode Consortium
793
794 http://www.unicode.org/
795
796=item *
797
798Unicode FAQ
799
800 http://www.unicode.org/unicode/faq/
801
802=item *
803
804Unicode Glossary
805
806 http://www.unicode.org/glossary/
807
808=item *
809
810Unicode Useful Resources
811
812 http://www.unicode.org/unicode/onlinedat/resources.html
813
814=item *
815
816Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
817
076d825e 818 http://www.alanwood.net/unicode/
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819
820=item *
821
822UTF-8 and Unicode FAQ for Unix/Linux
823
824 http://www.cl.cam.ac.uk/~mgk25/unicode.html
825
826=item *
827
828Legacy Character Sets
829
830 http://www.czyborra.com/
831 http://www.eki.ee/letter/
832
833=item *
834
835The Unicode support files live within the Perl installation in the
836directory
837
838 $Config{installprivlib}/unicore
839
840in Perl 5.8.0 or newer, and
841
842 $Config{installprivlib}/unicode
843
844in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
845avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
551b6b6f 846The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
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847Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
848
849 perl "-V:installprivlib"
850
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851You can explore various information from the Unicode data files using
852the C<Unicode::UCD> module.
853
854=back
855
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856=head1 UNICODE IN OLDER PERLS
857
858If you cannot upgrade your Perl to 5.8.0 or later, you can still
859do some Unicode processing by using the modules C<Unicode::String>,
860C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
861If you have the GNU recode installed, you can also use the
376d9008 862Perl front-end C<Convert::Recode> for character conversions.
f6edf83b 863
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864The following are fast conversions from ISO 8859-1 (Latin-1) bytes
865to UTF-8 bytes, the code works even with older Perl 5 versions.
866
867 # ISO 8859-1 to UTF-8
868 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
869
870 # UTF-8 to ISO 8859-1
871 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
872
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873=head1 SEE ALSO
874
875L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>,
876L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD>
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
be3c0a43 886Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi>
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887
888This document may be distributed under the same terms as Perl itself.