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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
fae2c0fb 153outputting Unicode strings to a stream without a PerlIO layer -- one with
376d9008 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
fae2c0fb 168To output UTF-8, use the C<:utf8> output layer. 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<LC_ALL>, C<LC_CTYPE>, C<LANG>)
176contain the strings 'UTF-8' or 'UTF8' (matched case-insensitively)
177B<and> you enable using UTF-8 either by using the C<-C> command line
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178switch or by setting the PERL_UNICODE environment variable to an empty
179string, C<"">, (see L<perlrun> and the documentation for the C<-C>
180switch for more information about the possible values), then the
181default encoding of your STDIN, STDOUT, and STDERR, and of B<any
182subsequent file open>, will be UTF-8. Note that this means that Perl
183expects other software to work, too: if Perl has been led to believe
184that STDIN should be UTF-8, but then STDIN coming in from another
185command is not UTF-8, Perl will complain about 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
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249Also note that if all the code points for pack "U" are below 0x100,
250bytes will be generated, just like if you were using C<chr()>.
251
252 my $bytes = pack("U*", 0x80, 0xFF);
253
254If you want to force the result to Unicode characters, use the special
255C<"U0"> prefix. It consumes no arguments but forces the result to be
256in Unicode characters, instead of bytes.
257
258 my $chars = pack("U0U*", 0x80, 0xFF);
259
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260=head2 Handling Unicode
261
262Handling Unicode is for the most part transparent: just use the
263strings as usual. Functions like C<index()>, C<length()>, and
264C<substr()> will work on the Unicode characters; regular expressions
265will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
266
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267Note that Perl considers combining character sequences to be
268characters, so for example
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269
270 use charnames ':full';
271 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
272
273will print 2, not 1. The only exception is that regular expressions
274have C<\X> for matching a combining character sequence.
275
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276Life is not quite so transparent, however, when working with legacy
277encodings, I/O, and certain special cases:
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278
279=head2 Legacy Encodings
280
281When you combine legacy data and Unicode the legacy data needs
282to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
283applicable) is assumed. You can override this assumption by
284using the C<encoding> pragma, for example
285
286 use encoding 'latin2'; # ISO 8859-2
287
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288in which case literals (string or regular expressions), C<chr()>,
289and C<ord()> in your whole script are assumed to produce Unicode
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290characters from ISO 8859-2 code points. Note that the matching for
291encoding names is forgiving: instead of C<latin2> you could have
292said C<Latin 2>, or C<iso8859-2>, or other variations. With just
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293
294 use encoding;
295
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296the environment variable C<PERL_ENCODING> will be consulted.
297If that variable isn't set, the encoding pragma will fail.
ba62762e 298
376d9008 299The C<Encode> module knows about many encodings and has interfaces
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300for doing conversions between those encodings:
301
302 use Encode 'from_to';
303 from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8
304
305=head2 Unicode I/O
306
8baee566 307Normally, writing out Unicode data
ba62762e 308
8baee566 309 print FH $some_string_with_unicode, "\n";
ba62762e 310
8baee566 311produces raw bytes that Perl happens to use to internally encode the
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312Unicode string. Perl's internal encoding depends on the system as
313well as what characters happen to be in the string at the time. If
314any of the characters are at code points C<0x100> or above, you will get
315a warning. To ensure that the output is explicitly rendered in the
316encoding you desire--and to avoid the warning--open the stream with
317the desired encoding. Some examples:
ba62762e 318
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319 open FH, ">:utf8", "file";
320
321 open FH, ">:encoding(ucs2)", "file";
322 open FH, ">:encoding(UTF-8)", "file";
323 open FH, ">:encoding(shift_jis)", "file";
1d7919c5 324
376d9008 325and on already open streams, use C<binmode()>:
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326
327 binmode(STDOUT, ":utf8");
328
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329 binmode(STDOUT, ":encoding(ucs2)");
330 binmode(STDOUT, ":encoding(UTF-8)");
331 binmode(STDOUT, ":encoding(shift_jis)");
332
b5d8778e 333The matching of encoding names is loose: case does not matter, and
fae2c0fb 334many encodings have several aliases. Note that the C<:utf8> layer
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335must always be specified exactly like that; it is I<not> subject to
336the loose matching of encoding names.
b5d8778e 337
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338See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
339L<Encode::PerlIO> for the C<:encoding()> layer, and
340L<Encode::Supported> for many encodings supported by the C<Encode>
341module.
ba62762e 342
a5f0baef 343Reading in a file that you know happens to be encoded in one of the
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344Unicode or legacy encodings does not magically turn the data into
345Unicode in Perl's eyes. To do that, specify the appropriate
fae2c0fb 346layer when opening files
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347
348 open(my $fh,'<:utf8', 'anything');
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349 my $line_of_unicode = <$fh>;
350
ec90690f 351 open(my $fh,'<:encoding(Big5)', 'anything');
8baee566 352 my $line_of_unicode = <$fh>;
ba62762e 353
fae2c0fb 354The I/O layers can also be specified more flexibly with
376d9008 355the C<open> pragma. See L<open>, or look at the following example.
ba62762e 356
fae2c0fb 357 use open ':utf8'; # input and output default layer will be UTF-8
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358 open X, ">file";
359 print X chr(0x100), "\n";
ba62762e 360 close X;
1d7919c5 361 open Y, "<file";
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362 printf "%#x\n", ord(<Y>); # this should print 0x100
363 close Y;
364
fae2c0fb 365With the C<open> pragma you can use the C<:locale> layer
ba62762e 366
12f98225 367 BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
1ecefa54 368 # the :locale will probe the locale environment variables like LC_ALL
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369 use open OUT => ':locale'; # russki parusski
370 open(O, ">koi8");
371 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
372 close O;
373 open(I, "<koi8");
374 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
375 close I;
376
fae2c0fb 377or you can also use the C<':encoding(...)'> layer
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378
379 open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
8baee566 380 my $line_of_unicode = <$epic>;
ba62762e 381
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382These methods install a transparent filter on the I/O stream that
383converts data from the specified encoding when it is read in from the
a5f0baef 384stream. The result is always Unicode.
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385
386The L<open> pragma affects all the C<open()> calls after the pragma by
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387setting default layers. If you want to affect only certain
388streams, use explicit layers directly in the C<open()> call.
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389
390You can switch encodings on an already opened stream by using
8baee566 391C<binmode()>; see L<perlfunc/binmode>.
ba62762e 392
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393The C<:locale> does not currently (as of Perl 5.8.0) work with
394C<open()> and C<binmode()>, only with the C<open> pragma. The
8baee566 395C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
1ecefa54 396C<binmode()>, and the C<open> pragma.
ba62762e 397
fae2c0fb 398Similarly, you may use these I/O layers on output streams to
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399automatically convert Unicode to the specified encoding when it is
400written to the stream. For example, the following snippet copies the
401contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
402the file "text.utf8", encoded as UTF-8:
ba62762e 403
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404 open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis');
405 open(my $unicode, '>:utf8', 'text.utf8');
0cf8a8d9 406 while (<$nihongo>) { print $unicode $_ }
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407
408The naming of encodings, both by the C<open()> and by the C<open>
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409pragma, is similar to the C<encoding> pragma in that it allows for
410flexible names: C<koi8-r> and C<KOI8R> will both be understood.
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411
412Common encodings recognized by ISO, MIME, IANA, and various other
8baee566 413standardisation organisations are recognised; for a more detailed
1bfb14c4 414list see L<Encode::Supported>.
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415
416C<read()> reads characters and returns the number of characters.
417C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
418and C<sysseek()>.
419
8baee566 420Notice that because of the default behaviour of not doing any
fae2c0fb 421conversion upon input if there is no default layer,
ba62762e 422it is easy to mistakenly write code that keeps on expanding a file
1bfb14c4 423by repeatedly encoding the data:
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424
425 # BAD CODE WARNING
426 open F, "file";
8baee566 427 local $/; ## read in the whole file of 8-bit characters
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428 $t = <F>;
429 close F;
430 open F, ">:utf8", "file";
8baee566 431 print F $t; ## convert to UTF-8 on output
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432 close F;
433
434If you run this code twice, the contents of the F<file> will be twice
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435UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or
436explicitly opening also the F<file> for input as UTF-8.
ba62762e 437
0c901d84 438B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
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439Perl has been built with the new PerlIO feature (which is the default
440on most systems).
0c901d84 441
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442=head2 Displaying Unicode As Text
443
444Sometimes you might want to display Perl scalars containing Unicode as
8baee566 445simple ASCII (or EBCDIC) text. The following subroutine converts
1ecefa54 446its argument so that Unicode characters with code points greater than
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447255 are displayed as C<\x{...}>, control characters (like C<\n>) are
448displayed as C<\x..>, and the rest of the characters as themselves:
1ecefa54 449
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450 sub nice_string {
451 join("",
452 map { $_ > 255 ? # if wide character...
8baee566 453 sprintf("\\x{%04X}", $_) : # \x{...}
58c274a1 454 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
8baee566 455 sprintf("\\x%02X", $_) : # \x..
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456 chr($_) # else as themselves
457 } unpack("U*", $_[0])); # unpack Unicode characters
458 }
459
460For example,
461
462 nice_string("foo\x{100}bar\n")
463
8baee566 464returns:
58c274a1 465
8baee566 466 "foo\x{0100}bar\x0A"
1ecefa54 467
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468=head2 Special Cases
469
470=over 4
471
472=item *
473
474Bit Complement Operator ~ And vec()
475
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476The bit complement operator C<~> may produce surprising results if
477used on strings containing characters with ordinal values above
478255. In such a case, the results are consistent with the internal
479encoding of the characters, but not with much else. So don't do
480that. Similarly for C<vec()>: you will be operating on the
481internally-encoded bit patterns of the Unicode characters, not on
482the code point values, which is very probably not what you want.
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483
484=item *
485
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486Peeking At Perl's Internal Encoding
487
488Normal users of Perl should never care how Perl encodes any particular
a5f0baef 489Unicode string (because the normal ways to get at the contents of a
376d9008 490string with Unicode--via input and output--should always be via
fae2c0fb 491explicitly-defined I/O layers). But if you must, there are two
a5f0baef 492ways of looking behind the scenes.
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493
494One way of peeking inside the internal encoding of Unicode characters
376d9008 495is to use C<unpack("C*", ...> to get the bytes or C<unpack("H*", ...)>
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496to display the bytes:
497
8baee566 498 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
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499 print join(" ", unpack("H*", pack("U", 0x100))), "\n";
500
501Yet another way would be to use the Devel::Peek module:
502
503 perl -MDevel::Peek -e 'Dump(chr(0x100))'
504
8baee566 505That shows the UTF8 flag in FLAGS and both the UTF-8 bytes
376d9008 506and Unicode characters in C<PV>. See also later in this document
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507the discussion about the C<is_utf8> function of the C<Encode> module.
508
509=back
510
511=head2 Advanced Topics
512
513=over 4
514
515=item *
516
517String Equivalence
518
519The question of string equivalence turns somewhat complicated
376d9008 520in Unicode: what do you mean by "equal"?
ba62762e 521
07698885
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522(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
523C<LATIN CAPITAL LETTER A>?)
ba62762e 524
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525The short answer is that by default Perl compares equivalence (C<eq>,
526C<ne>) based only on code points of the characters. In the above
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527case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any
528CAPITAL LETTER As should be considered equal, or even As of any case.
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529
530The long answer is that you need to consider character normalization
376d9008 531and casing issues: see L<Unicode::Normalize>, Unicode Technical
ba62762e 532Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
376d9008
JB
533Mappings>, http://www.unicode.org/unicode/reports/tr15/ and
534http://www.unicode.org/unicode/reports/tr21/
ba62762e 535
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536As of Perl 5.8.0, the "Full" case-folding of I<Case
537Mappings/SpecialCasing> is implemented.
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538
539=item *
540
541String Collation
542
376d9008 543People like to see their strings nicely sorted--or as Unicode
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544parlance goes, collated. But again, what do you mean by collate?
545
07698885
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546(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
547C<LATIN CAPITAL LETTER A WITH GRAVE>?)
ba62762e 548
58c274a1 549The short answer is that by default, Perl compares strings (C<lt>,
ba62762e 550C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
1bfb14c4
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551characters. In the above case, the answer is "after", since
552C<0x00C1> > C<0x00C0>.
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553
554The long answer is that "it depends", and a good answer cannot be
555given without knowing (at the very least) the language context.
556See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
557http://www.unicode.org/unicode/reports/tr10/
558
559=back
560
561=head2 Miscellaneous
562
563=over 4
564
565=item *
566
3ff56b75 567Character Ranges and Classes
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568
569Character ranges in regular expression character classes (C</[a-z]/>)
570and in the C<tr///> (also known as C<y///>) operator are not magically
58c274a1 571Unicode-aware. What this means that C<[A-Za-z]> will not magically start
376d9008
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572to mean "all alphabetic letters"; not that it does mean that even for
5738-bit characters, you should be using C</[[:alpha:]]/> in that case.
ba62762e 574
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575For specifying character classes like that in regular expressions,
576you can use the various Unicode properties--C<\pL>, or perhaps
577C<\p{Alphabetic}>, in this particular case. You can use Unicode
578code points as the end points of character ranges, but there is no
579magic associated with specifying a certain range. For further
580information--there are dozens of Unicode character classes--see
581L<perlunicode>.
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582
583=item *
584
585String-To-Number Conversions
586
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587Unicode does define several other decimal--and numeric--characters
588besides the familiar 0 to 9, such as the Arabic and Indic digits.
ba62762e 589Perl does not support string-to-number conversion for digits other
58c274a1 590than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
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591
592=back
593
594=head2 Questions With Answers
595
596=over 4
597
818c4caa 598=item *
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599
600Will My Old Scripts Break?
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601
602Very probably not. Unless you are generating Unicode characters
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603somehow, old behaviour should be preserved. About the only behaviour
604that has changed and which could start generating Unicode is the old
605behaviour of C<chr()> where supplying an argument more than 255
606produced a character modulo 255. C<chr(300)>, for example, was equal
607to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
608BREVE.
ba62762e 609
818c4caa 610=item *
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611
612How Do I Make My Scripts Work With Unicode?
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613
614Very little work should be needed since nothing changes until you
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615generate Unicode data. The most important thing is getting input as
616Unicode; for that, see the earlier I/O discussion.
ba62762e 617
818c4caa 618=item *
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619
620How Do I Know Whether My String Is In Unicode?
ba62762e 621
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622You shouldn't care. No, you really shouldn't. No, really. If you
623have to care--beyond the cases described above--it means that we
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624didn't get the transparency of Unicode quite right.
625
626Okay, if you insist:
627
628 use Encode 'is_utf8';
629 print is_utf8($string) ? 1 : 0, "\n";
630
631But note that this doesn't mean that any of the characters in the
632string are necessary UTF-8 encoded, or that any of the characters have
633code points greater than 0xFF (255) or even 0x80 (128), or that the
634string has any characters at all. All the C<is_utf8()> does is to
635return the value of the internal "utf8ness" flag attached to the
376d9008 636C<$string>. If the flag is off, the bytes in the scalar are interpreted
3c1c8017 637as a single byte encoding. If the flag is on, the bytes in the scalar
376d9008 638are interpreted as the (multi-byte, variable-length) UTF-8 encoded code
3c1c8017
AT
639points of the characters. Bytes added to an UTF-8 encoded string are
640automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars
376d9008 641are merged (double-quoted interpolation, explicit concatenation, and
3c1c8017
AT
642printf/sprintf parameter substitution), the result will be UTF-8 encoded
643as if copies of the byte strings were upgraded to UTF-8: for example,
644
645 $a = "ab\x80c";
646 $b = "\x{100}";
647 print "$a = $b\n";
648
1bfb14c4 649the output string will be UTF-8-encoded C<ab\x80c\x{100}\n>, but note
376d9008 650that C<$a> will stay byte-encoded.
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651
652Sometimes you might really need to know the byte length of a string
ce7675db
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653instead of the character length. For that use either the
654C<Encode::encode_utf8()> function or the C<bytes> pragma and its only
655defined function C<length()>:
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656
657 my $unicode = chr(0x100);
658 print length($unicode), "\n"; # will print 1
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659 require Encode;
660 print length(Encode::encode_utf8($unicode)), "\n"; # will print 2
ba62762e 661 use bytes;
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662 print length($unicode), "\n"; # will also print 2
663 # (the 0xC4 0x80 of the UTF-8)
ba62762e 664
818c4caa 665=item *
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666
667How Do I Detect Data That's Not Valid In a Particular Encoding?
ba62762e 668
8baee566
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669Use the C<Encode> package to try converting it.
670For example,
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671
672 use Encode 'encode_utf8';
8baee566 673 if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) {
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674 # valid
675 } else {
676 # invalid
677 }
678
8baee566 679For UTF-8 only, you can use:
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680
681 use warnings;
8baee566 682 @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
ba62762e 683
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684If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack>
685warning is produced. The "U0" means "expect strictly UTF-8 encoded
686Unicode". Without that the C<unpack("U*", ...)> would accept also
687data like C<chr(0xFF>), similarly to the C<pack> as we saw earlier.
ba62762e 688
818c4caa 689=item *
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690
691How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
ba62762e 692
8baee566
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693This probably isn't as useful as you might think.
694Normally, you shouldn't need to.
ba62762e 695
1bfb14c4 696In one sense, what you are asking doesn't make much sense: encodings
376d9008 697are for characters, and binary data are not "characters", so converting
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698"data" into some encoding isn't meaningful unless you know in what
699character set and encoding the binary data is in, in which case it's
376d9008 700not just binary data, now is it?
8baee566 701
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702If you have a raw sequence of bytes that you know should be
703interpreted via a particular encoding, you can use C<Encode>:
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704
705 use Encode 'from_to';
706 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
707
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708The call to C<from_to()> changes the bytes in C<$data>, but nothing
709material about the nature of the string has changed as far as Perl is
710concerned. Both before and after the call, the string C<$data>
711contains just a bunch of 8-bit bytes. As far as Perl is concerned,
712the encoding of the string remains as "system-native 8-bit bytes".
8baee566
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713
714You might relate this to a fictional 'Translate' module:
715
716 use Translate;
717 my $phrase = "Yes";
718 Translate::from_to($phrase, 'english', 'deutsch');
719 ## phrase now contains "Ja"
ba62762e 720
8baee566 721The contents of the string changes, but not the nature of the string.
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722Perl doesn't know any more after the call than before that the
723contents of the string indicates the affirmative.
ba62762e 724
376d9008 725Back to converting data. If you have (or want) data in your system's
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726native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
727pack/unpack to convert to/from Unicode.
ba62762e 728
8baee566
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729 $native_string = pack("C*", unpack("U*", $Unicode_string));
730 $Unicode_string = pack("U*", unpack("C*", $native_string));
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731
732If you have a sequence of bytes you B<know> is valid UTF-8,
733but Perl doesn't know it yet, you can make Perl a believer, too:
734
735 use Encode 'decode_utf8';
8baee566 736 $Unicode = decode_utf8($bytes);
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737
738You can convert well-formed UTF-8 to a sequence of bytes, but if
739you just want to convert random binary data into UTF-8, you can't.
1bfb14c4 740B<Any random collection of bytes isn't well-formed UTF-8>. You can
ba62762e 741use C<unpack("C*", $string)> for the former, and you can create
8baee566 742well-formed Unicode data by C<pack("U*", 0xff, ...)>.
ba62762e 743
818c4caa 744=item *
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745
746How Do I Display Unicode? How Do I Input Unicode?
ba62762e 747
076d825e 748See http://www.alanwood.net/unicode/ and
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749http://www.cl.cam.ac.uk/~mgk25/unicode.html
750
818c4caa 751=item *
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752
753How Does Unicode Work With Traditional Locales?
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754
755In Perl, not very well. Avoid using locales through the C<locale>
756pragma. Use only one or the other.
757
758=back
759
760=head2 Hexadecimal Notation
761
376d9008
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762The Unicode standard prefers using hexadecimal notation because
763that more clearly shows the division of Unicode into blocks of 256 characters.
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764Hexadecimal is also simply shorter than decimal. You can use decimal
765notation, too, but learning to use hexadecimal just makes life easier
1bfb14c4 766with the Unicode standard. The C<U+HHHH> notation uses hexadecimal,
076d825e 767for example.
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768
769The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
770a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
771four bits, or half a byte. C<print 0x..., "\n"> will show a
772hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
773show a decimal number in hexadecimal. If you have just the
376d9008 774"hex digits" of a hexadecimal number, you can use the C<hex()> function.
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775
776 print 0x0009, "\n"; # 9
777 print 0x000a, "\n"; # 10
778 print 0x000f, "\n"; # 15
779 print 0x0010, "\n"; # 16
780 print 0x0011, "\n"; # 17
781 print 0x0100, "\n"; # 256
782
783 print 0x0041, "\n"; # 65
784
785 printf "%x\n", 65; # 41
786 printf "%#x\n", 65; # 0x41
787
788 print hex("41"), "\n"; # 65
789
790=head2 Further Resources
791
792=over 4
793
794=item *
795
796Unicode Consortium
797
798 http://www.unicode.org/
799
800=item *
801
802Unicode FAQ
803
804 http://www.unicode.org/unicode/faq/
805
806=item *
807
808Unicode Glossary
809
810 http://www.unicode.org/glossary/
811
812=item *
813
814Unicode Useful Resources
815
816 http://www.unicode.org/unicode/onlinedat/resources.html
817
818=item *
819
820Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
821
076d825e 822 http://www.alanwood.net/unicode/
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823
824=item *
825
826UTF-8 and Unicode FAQ for Unix/Linux
827
828 http://www.cl.cam.ac.uk/~mgk25/unicode.html
829
830=item *
831
832Legacy Character Sets
833
834 http://www.czyborra.com/
835 http://www.eki.ee/letter/
836
837=item *
838
839The Unicode support files live within the Perl installation in the
840directory
841
842 $Config{installprivlib}/unicore
843
844in Perl 5.8.0 or newer, and
845
846 $Config{installprivlib}/unicode
847
848in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
849avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
551b6b6f 850The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
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851Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
852
853 perl "-V:installprivlib"
854
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855You can explore various information from the Unicode data files using
856the C<Unicode::UCD> module.
857
858=back
859
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860=head1 UNICODE IN OLDER PERLS
861
862If you cannot upgrade your Perl to 5.8.0 or later, you can still
863do some Unicode processing by using the modules C<Unicode::String>,
864C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
865If you have the GNU recode installed, you can also use the
376d9008 866Perl front-end C<Convert::Recode> for character conversions.
f6edf83b 867
aaef10c5 868The following are fast conversions from ISO 8859-1 (Latin-1) bytes
63de3cb2 869to UTF-8 bytes and back, the code works even with older Perl 5 versions.
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JH
870
871 # ISO 8859-1 to UTF-8
872 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
873
874 # UTF-8 to ISO 8859-1
875 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
876
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877=head1 SEE ALSO
878
879L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>,
880L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD>
881
376d9008 882=head1 ACKNOWLEDGMENTS
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883
884Thanks to the kind readers of the perl5-porters@perl.org,
885perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
886mailing lists for their valuable feedback.
887
888=head1 AUTHOR, COPYRIGHT, AND LICENSE
889
be3c0a43 890Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi>
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891
892This document may be distributed under the same terms as Perl itself.