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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
135scripts with legacy 8-bit data in them would break.
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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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184=head2 Unicode and EBCDIC
185
186Perl 5.8.0 also supports Unicode on EBCDIC platforms. There,
376d9008 187Unicode support is somewhat more complex to implement since
64c66fb6 188additional conversions are needed at every step. Some problems
dc4af4bb 189remain, see L<perlebcdic> for details.
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190
191In any case, the Unicode support on EBCDIC platforms is better than
192in the 5.6 series, which didn't work much at all for EBCDIC platform.
193On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
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194instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in
195that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is
196"EBCDIC-safe".
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197
198=head2 Creating Unicode
199
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200To create Unicode characters in literals for code points above C<0xFF>,
201use the C<\x{...}> notation in double-quoted strings:
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202
203 my $smiley = "\x{263a}";
204
376d9008 205Similarly, it can be used in regular expression literals
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206
207 $smiley =~ /\x{263a}/;
208
209At run-time you can use C<chr()>:
210
211 my $hebrew_alef = chr(0x05d0);
212
376d9008 213See L</"Further Resources"> for how to find all these numeric codes.
ba62762e 214
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215Naturally, C<ord()> will do the reverse: it turns a character into
216a code point.
ba62762e 217
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218Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>,
219and C<chr(...)> for arguments less than C<0x100> (decimal 256)
220generate an eight-bit character for backward compatibility with older
221Perls. For arguments of C<0x100> or more, Unicode characters are
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222always produced. If you want to force the production of Unicode
223characters regardless of the numeric value, use C<pack("U", ...)>
224instead of C<\x..>, C<\x{...}>, or C<chr()>.
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225
226You can also use the C<charnames> pragma to invoke characters
376d9008 227by name in double-quoted strings:
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228
229 use charnames ':full';
230 my $arabic_alef = "\N{ARABIC LETTER ALEF}";
231
232And, as mentioned above, you can also C<pack()> numbers into Unicode
233characters:
234
235 my $georgian_an = pack("U", 0x10a0);
236
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237Note that both C<\x{...}> and C<\N{...}> are compile-time string
238constants: you cannot use variables in them. if you want similar
239run-time functionality, use C<chr()> and C<charnames::vianame()>.
240
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241Also note that if all the code points for pack "U" are below 0x100,
242bytes will be generated, just like if you were using C<chr()>.
243
244 my $bytes = pack("U*", 0x80, 0xFF);
245
246If you want to force the result to Unicode characters, use the special
247C<"U0"> prefix. It consumes no arguments but forces the result to be
248in Unicode characters, instead of bytes.
249
250 my $chars = pack("U0U*", 0x80, 0xFF);
251
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252=head2 Handling Unicode
253
254Handling Unicode is for the most part transparent: just use the
255strings as usual. Functions like C<index()>, C<length()>, and
256C<substr()> will work on the Unicode characters; regular expressions
257will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
258
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259Note that Perl considers combining character sequences to be
260characters, so for example
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261
262 use charnames ':full';
263 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
264
265will print 2, not 1. The only exception is that regular expressions
266have C<\X> for matching a combining character sequence.
267
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268Life is not quite so transparent, however, when working with legacy
269encodings, I/O, and certain special cases:
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270
271=head2 Legacy Encodings
272
273When you combine legacy data and Unicode the legacy data needs
274to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
275applicable) is assumed. You can override this assumption by
276using the C<encoding> pragma, for example
277
278 use encoding 'latin2'; # ISO 8859-2
279
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280in which case literals (string or regular expressions), C<chr()>,
281and C<ord()> in your whole script are assumed to produce Unicode
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282characters from ISO 8859-2 code points. Note that the matching for
283encoding names is forgiving: instead of C<latin2> you could have
284said C<Latin 2>, or C<iso8859-2>, or other variations. With just
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285
286 use encoding;
287
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288the environment variable C<PERL_ENCODING> will be consulted.
289If that variable isn't set, the encoding pragma will fail.
ba62762e 290
376d9008 291The C<Encode> module knows about many encodings and has interfaces
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292for doing conversions between those encodings:
293
294 use Encode 'from_to';
295 from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8
296
297=head2 Unicode I/O
298
8baee566 299Normally, writing out Unicode data
ba62762e 300
8baee566 301 print FH $some_string_with_unicode, "\n";
ba62762e 302
8baee566 303produces raw bytes that Perl happens to use to internally encode the
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304Unicode string. Perl's internal encoding depends on the system as
305well as what characters happen to be in the string at the time. If
306any of the characters are at code points C<0x100> or above, you will get
307a warning. To ensure that the output is explicitly rendered in the
308encoding you desire--and to avoid the warning--open the stream with
309the desired encoding. Some examples:
ba62762e 310
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311 open FH, ">:utf8", "file";
312
313 open FH, ">:encoding(ucs2)", "file";
314 open FH, ">:encoding(UTF-8)", "file";
315 open FH, ">:encoding(shift_jis)", "file";
1d7919c5 316
376d9008 317and on already open streams, use C<binmode()>:
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318
319 binmode(STDOUT, ":utf8");
320
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321 binmode(STDOUT, ":encoding(ucs2)");
322 binmode(STDOUT, ":encoding(UTF-8)");
323 binmode(STDOUT, ":encoding(shift_jis)");
324
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325The matching of encoding names is loose: case does not matter, and
326many encodings have several aliases. Note that C<:utf8> discipline
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327must always be specified exactly like that; it is I<not> subject to
328the loose matching of encoding names.
b5d8778e 329
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330See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
331L<Encode::PerlIO> for the C<:encoding()> layer, and
332L<Encode::Supported> for many encodings supported by the C<Encode>
333module.
ba62762e 334
a5f0baef 335Reading in a file that you know happens to be encoded in one of the
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336Unicode or legacy encodings does not magically turn the data into
337Unicode in Perl's eyes. To do that, specify the appropriate
338discipline when opening files
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339
340 open(my $fh,'<:utf8', 'anything');
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341 my $line_of_unicode = <$fh>;
342
ec90690f 343 open(my $fh,'<:encoding(Big5)', 'anything');
8baee566 344 my $line_of_unicode = <$fh>;
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345
346The I/O disciplines can also be specified more flexibly with
376d9008 347the C<open> pragma. See L<open>, or look at the following example.
ba62762e 348
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349 use open ':utf8'; # input and output default discipline will be UTF-8
350 open X, ">file";
351 print X chr(0x100), "\n";
ba62762e 352 close X;
1d7919c5 353 open Y, "<file";
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354 printf "%#x\n", ord(<Y>); # this should print 0x100
355 close Y;
356
357With the C<open> pragma you can use the C<:locale> discipline
358
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359 $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R';
360 # the :locale will probe the locale environment variables like LC_ALL
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361 use open OUT => ':locale'; # russki parusski
362 open(O, ">koi8");
363 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
364 close O;
365 open(I, "<koi8");
366 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
367 close I;
368
369or you can also use the C<':encoding(...)'> discipline
370
371 open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
8baee566 372 my $line_of_unicode = <$epic>;
ba62762e 373
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374These methods install a transparent filter on the I/O stream that
375converts data from the specified encoding when it is read in from the
a5f0baef 376stream. The result is always Unicode.
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377
378The L<open> pragma affects all the C<open()> calls after the pragma by
379setting default disciplines. If you want to affect only certain
380streams, use explicit disciplines directly in the C<open()> call.
381
382You can switch encodings on an already opened stream by using
8baee566 383C<binmode()>; see L<perlfunc/binmode>.
ba62762e 384
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385The C<:locale> does not currently (as of Perl 5.8.0) work with
386C<open()> and C<binmode()>, only with the C<open> pragma. The
8baee566 387C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
1ecefa54 388C<binmode()>, and the C<open> pragma.
ba62762e 389
8baee566 390Similarly, you may use these I/O disciplines on output streams to
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391automatically convert Unicode to the specified encoding when it is
392written to the stream. For example, the following snippet copies the
393contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
394the file "text.utf8", encoded as UTF-8:
ba62762e 395
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396 open(my $nihongo, '<:encoding(iso2022-jp)', 'text.jis');
397 open(my $unicode, '>:utf8', 'text.utf8');
398 while (<$nihongo>) { print $unicode }
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399
400The naming of encodings, both by the C<open()> and by the C<open>
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401pragma, is similar to the C<encoding> pragma in that it allows for
402flexible names: C<koi8-r> and C<KOI8R> will both be understood.
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403
404Common encodings recognized by ISO, MIME, IANA, and various other
8baee566 405standardisation organisations are recognised; for a more detailed
1bfb14c4 406list see L<Encode::Supported>.
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407
408C<read()> reads characters and returns the number of characters.
409C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
410and C<sysseek()>.
411
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412Notice that because of the default behaviour of not doing any
413conversion upon input if there is no default discipline,
ba62762e 414it is easy to mistakenly write code that keeps on expanding a file
1bfb14c4 415by repeatedly encoding the data:
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416
417 # BAD CODE WARNING
418 open F, "file";
8baee566 419 local $/; ## read in the whole file of 8-bit characters
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420 $t = <F>;
421 close F;
422 open F, ">:utf8", "file";
8baee566 423 print F $t; ## convert to UTF-8 on output
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424 close F;
425
426If you run this code twice, the contents of the F<file> will be twice
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427UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or
428explicitly opening also the F<file> for input as UTF-8.
ba62762e 429
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430B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
431Perl has been built with the new "perlio" feature. Almost all
432Perl 5.8 platforms do use "perlio", though: you can see whether
433yours is by running "perl -V" and looking for C<useperlio=define>.
434
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435=head2 Displaying Unicode As Text
436
437Sometimes you might want to display Perl scalars containing Unicode as
8baee566 438simple ASCII (or EBCDIC) text. The following subroutine converts
1ecefa54 439its argument so that Unicode characters with code points greater than
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440255 are displayed as C<\x{...}>, control characters (like C<\n>) are
441displayed as C<\x..>, and the rest of the characters as themselves:
1ecefa54 442
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443 sub nice_string {
444 join("",
445 map { $_ > 255 ? # if wide character...
8baee566 446 sprintf("\\x{%04X}", $_) : # \x{...}
58c274a1 447 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
8baee566 448 sprintf("\\x%02X", $_) : # \x..
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449 chr($_) # else as themselves
450 } unpack("U*", $_[0])); # unpack Unicode characters
451 }
452
453For example,
454
455 nice_string("foo\x{100}bar\n")
456
8baee566 457returns:
58c274a1 458
8baee566 459 "foo\x{0100}bar\x0A"
1ecefa54 460
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461=head2 Special Cases
462
463=over 4
464
465=item *
466
467Bit Complement Operator ~ And vec()
468
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469The bit complement operator C<~> may produce surprising results if
470used on strings containing characters with ordinal values above
471255. In such a case, the results are consistent with the internal
472encoding of the characters, but not with much else. So don't do
473that. Similarly for C<vec()>: you will be operating on the
474internally-encoded bit patterns of the Unicode characters, not on
475the code point values, which is very probably not what you want.
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476
477=item *
478
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479Peeking At Perl's Internal Encoding
480
481Normal users of Perl should never care how Perl encodes any particular
a5f0baef 482Unicode string (because the normal ways to get at the contents of a
376d9008 483string with Unicode--via input and output--should always be via
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484explicitly-defined I/O disciplines). But if you must, there are two
485ways of looking behind the scenes.
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486
487One way of peeking inside the internal encoding of Unicode characters
376d9008 488is to use C<unpack("C*", ...> to get the bytes or C<unpack("H*", ...)>
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489to display the bytes:
490
8baee566 491 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
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492 print join(" ", unpack("H*", pack("U", 0x100))), "\n";
493
494Yet another way would be to use the Devel::Peek module:
495
496 perl -MDevel::Peek -e 'Dump(chr(0x100))'
497
8baee566 498That shows the UTF8 flag in FLAGS and both the UTF-8 bytes
376d9008 499and Unicode characters in C<PV>. See also later in this document
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500the discussion about the C<is_utf8> function of the C<Encode> module.
501
502=back
503
504=head2 Advanced Topics
505
506=over 4
507
508=item *
509
510String Equivalence
511
512The question of string equivalence turns somewhat complicated
376d9008 513in Unicode: what do you mean by "equal"?
ba62762e 514
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515(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
516C<LATIN CAPITAL LETTER A>?)
ba62762e 517
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518The short answer is that by default Perl compares equivalence (C<eq>,
519C<ne>) based only on code points of the characters. In the above
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520case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any
521CAPITAL LETTER As should be considered equal, or even As of any case.
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522
523The long answer is that you need to consider character normalization
376d9008 524and casing issues: see L<Unicode::Normalize>, Unicode Technical
ba62762e 525Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
376d9008
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526Mappings>, http://www.unicode.org/unicode/reports/tr15/ and
527http://www.unicode.org/unicode/reports/tr21/
ba62762e 528
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529As of Perl 5.8.0, the "Full" case-folding of I<Case
530Mappings/SpecialCasing> is implemented.
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531
532=item *
533
534String Collation
535
376d9008 536People like to see their strings nicely sorted--or as Unicode
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537parlance goes, collated. But again, what do you mean by collate?
538
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539(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
540C<LATIN CAPITAL LETTER A WITH GRAVE>?)
ba62762e 541
58c274a1 542The short answer is that by default, Perl compares strings (C<lt>,
ba62762e 543C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
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544characters. In the above case, the answer is "after", since
545C<0x00C1> > C<0x00C0>.
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546
547The long answer is that "it depends", and a good answer cannot be
548given without knowing (at the very least) the language context.
549See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
550http://www.unicode.org/unicode/reports/tr10/
551
552=back
553
554=head2 Miscellaneous
555
556=over 4
557
558=item *
559
3ff56b75 560Character Ranges and Classes
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561
562Character ranges in regular expression character classes (C</[a-z]/>)
563and in the C<tr///> (also known as C<y///>) operator are not magically
58c274a1 564Unicode-aware. What this means that C<[A-Za-z]> will not magically start
376d9008
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565to mean "all alphabetic letters"; not that it does mean that even for
5668-bit characters, you should be using C</[[:alpha:]]/> in that case.
ba62762e 567
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568For specifying character classes like that in regular expressions,
569you can use the various Unicode properties--C<\pL>, or perhaps
570C<\p{Alphabetic}>, in this particular case. You can use Unicode
571code points as the end points of character ranges, but there is no
572magic associated with specifying a certain range. For further
573information--there are dozens of Unicode character classes--see
574L<perlunicode>.
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575
576=item *
577
578String-To-Number Conversions
579
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580Unicode does define several other decimal--and numeric--characters
581besides the familiar 0 to 9, such as the Arabic and Indic digits.
ba62762e 582Perl does not support string-to-number conversion for digits other
58c274a1 583than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
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584
585=back
586
587=head2 Questions With Answers
588
589=over 4
590
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591=item
592
593Will My Old Scripts Break?
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594
595Very probably not. Unless you are generating Unicode characters
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596somehow, old behaviour should be preserved. About the only behaviour
597that has changed and which could start generating Unicode is the old
598behaviour of C<chr()> where supplying an argument more than 255
599produced a character modulo 255. C<chr(300)>, for example, was equal
600to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
601BREVE.
ba62762e 602
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603=item
604
605How Do I Make My Scripts Work With Unicode?
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606
607Very little work should be needed since nothing changes until you
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608generate Unicode data. The most important thing is getting input as
609Unicode; for that, see the earlier I/O discussion.
ba62762e 610
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611=item
612
613How Do I Know Whether My String Is In Unicode?
ba62762e 614
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615You shouldn't care. No, you really shouldn't. No, really. If you
616have to care--beyond the cases described above--it means that we
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617didn't get the transparency of Unicode quite right.
618
619Okay, if you insist:
620
621 use Encode 'is_utf8';
622 print is_utf8($string) ? 1 : 0, "\n";
623
624But note that this doesn't mean that any of the characters in the
625string are necessary UTF-8 encoded, or that any of the characters have
626code points greater than 0xFF (255) or even 0x80 (128), or that the
627string has any characters at all. All the C<is_utf8()> does is to
628return the value of the internal "utf8ness" flag attached to the
376d9008 629C<$string>. If the flag is off, the bytes in the scalar are interpreted
3c1c8017 630as a single byte encoding. If the flag is on, the bytes in the scalar
376d9008 631are interpreted as the (multi-byte, variable-length) UTF-8 encoded code
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632points of the characters. Bytes added to an UTF-8 encoded string are
633automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars
376d9008 634are merged (double-quoted interpolation, explicit concatenation, and
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635printf/sprintf parameter substitution), the result will be UTF-8 encoded
636as if copies of the byte strings were upgraded to UTF-8: for example,
637
638 $a = "ab\x80c";
639 $b = "\x{100}";
640 print "$a = $b\n";
641
1bfb14c4 642the output string will be UTF-8-encoded C<ab\x80c\x{100}\n>, but note
376d9008 643that C<$a> will stay byte-encoded.
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644
645Sometimes you might really need to know the byte length of a string
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646instead of the character length. For that use either the
647C<Encode::encode_utf8()> function or the C<bytes> pragma and its only
648defined function C<length()>:
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649
650 my $unicode = chr(0x100);
651 print length($unicode), "\n"; # will print 1
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652 require Encode;
653 print length(Encode::encode_utf8($unicode)), "\n"; # will print 2
ba62762e 654 use bytes;
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655 print length($unicode), "\n"; # will also print 2
656 # (the 0xC4 0x80 of the UTF-8)
ba62762e 657
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658=item
659
660How Do I Detect Data That's Not Valid In a Particular Encoding?
ba62762e 661
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662Use the C<Encode> package to try converting it.
663For example,
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664
665 use Encode 'encode_utf8';
8baee566 666 if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) {
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667 # valid
668 } else {
669 # invalid
670 }
671
8baee566 672For UTF-8 only, you can use:
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673
674 use warnings;
8baee566 675 @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
ba62762e 676
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677If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack>
678warning is produced. The "U0" means "expect strictly UTF-8 encoded
679Unicode". Without that the C<unpack("U*", ...)> would accept also
680data like C<chr(0xFF>), similarly to the C<pack> as we saw earlier.
ba62762e 681
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682=item
683
684How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
ba62762e 685
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686This probably isn't as useful as you might think.
687Normally, you shouldn't need to.
ba62762e 688
1bfb14c4 689In one sense, what you are asking doesn't make much sense: encodings
376d9008 690are for characters, and binary data are not "characters", so converting
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691"data" into some encoding isn't meaningful unless you know in what
692character set and encoding the binary data is in, in which case it's
376d9008 693not just binary data, now is it?
8baee566 694
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695If you have a raw sequence of bytes that you know should be
696interpreted via a particular encoding, you can use C<Encode>:
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697
698 use Encode 'from_to';
699 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
700
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701The call to C<from_to()> changes the bytes in C<$data>, but nothing
702material about the nature of the string has changed as far as Perl is
703concerned. Both before and after the call, the string C<$data>
704contains just a bunch of 8-bit bytes. As far as Perl is concerned,
705the encoding of the string remains as "system-native 8-bit bytes".
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706
707You might relate this to a fictional 'Translate' module:
708
709 use Translate;
710 my $phrase = "Yes";
711 Translate::from_to($phrase, 'english', 'deutsch');
712 ## phrase now contains "Ja"
ba62762e 713
8baee566 714The contents of the string changes, but not the nature of the string.
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715Perl doesn't know any more after the call than before that the
716contents of the string indicates the affirmative.
ba62762e 717
376d9008 718Back to converting data. If you have (or want) data in your system's
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719native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
720pack/unpack to convert to/from Unicode.
ba62762e 721
8baee566
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722 $native_string = pack("C*", unpack("U*", $Unicode_string));
723 $Unicode_string = pack("U*", unpack("C*", $native_string));
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724
725If you have a sequence of bytes you B<know> is valid UTF-8,
726but Perl doesn't know it yet, you can make Perl a believer, too:
727
728 use Encode 'decode_utf8';
8baee566 729 $Unicode = decode_utf8($bytes);
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730
731You can convert well-formed UTF-8 to a sequence of bytes, but if
732you just want to convert random binary data into UTF-8, you can't.
1bfb14c4 733B<Any random collection of bytes isn't well-formed UTF-8>. You can
ba62762e 734use C<unpack("C*", $string)> for the former, and you can create
8baee566 735well-formed Unicode data by C<pack("U*", 0xff, ...)>.
ba62762e 736
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737=item
738
739How Do I Display Unicode? How Do I Input Unicode?
ba62762e 740
076d825e 741See http://www.alanwood.net/unicode/ and
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742http://www.cl.cam.ac.uk/~mgk25/unicode.html
743
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744=item
745
746How Does Unicode Work With Traditional Locales?
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747
748In Perl, not very well. Avoid using locales through the C<locale>
749pragma. Use only one or the other.
750
751=back
752
753=head2 Hexadecimal Notation
754
376d9008
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755The Unicode standard prefers using hexadecimal notation because
756that more clearly shows the division of Unicode into blocks of 256 characters.
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757Hexadecimal is also simply shorter than decimal. You can use decimal
758notation, too, but learning to use hexadecimal just makes life easier
1bfb14c4 759with the Unicode standard. The C<U+HHHH> notation uses hexadecimal,
076d825e 760for example.
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761
762The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
763a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
764four bits, or half a byte. C<print 0x..., "\n"> will show a
765hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
766show a decimal number in hexadecimal. If you have just the
376d9008 767"hex digits" of a hexadecimal number, you can use the C<hex()> function.
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768
769 print 0x0009, "\n"; # 9
770 print 0x000a, "\n"; # 10
771 print 0x000f, "\n"; # 15
772 print 0x0010, "\n"; # 16
773 print 0x0011, "\n"; # 17
774 print 0x0100, "\n"; # 256
775
776 print 0x0041, "\n"; # 65
777
778 printf "%x\n", 65; # 41
779 printf "%#x\n", 65; # 0x41
780
781 print hex("41"), "\n"; # 65
782
783=head2 Further Resources
784
785=over 4
786
787=item *
788
789Unicode Consortium
790
791 http://www.unicode.org/
792
793=item *
794
795Unicode FAQ
796
797 http://www.unicode.org/unicode/faq/
798
799=item *
800
801Unicode Glossary
802
803 http://www.unicode.org/glossary/
804
805=item *
806
807Unicode Useful Resources
808
809 http://www.unicode.org/unicode/onlinedat/resources.html
810
811=item *
812
813Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
814
076d825e 815 http://www.alanwood.net/unicode/
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816
817=item *
818
819UTF-8 and Unicode FAQ for Unix/Linux
820
821 http://www.cl.cam.ac.uk/~mgk25/unicode.html
822
823=item *
824
825Legacy Character Sets
826
827 http://www.czyborra.com/
828 http://www.eki.ee/letter/
829
830=item *
831
832The Unicode support files live within the Perl installation in the
833directory
834
835 $Config{installprivlib}/unicore
836
837in Perl 5.8.0 or newer, and
838
839 $Config{installprivlib}/unicode
840
841in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
842avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
551b6b6f 843The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
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844Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
845
846 perl "-V:installprivlib"
847
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848You can explore various information from the Unicode data files using
849the C<Unicode::UCD> module.
850
851=back
852
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853=head1 UNICODE IN OLDER PERLS
854
855If you cannot upgrade your Perl to 5.8.0 or later, you can still
856do some Unicode processing by using the modules C<Unicode::String>,
857C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
858If you have the GNU recode installed, you can also use the
376d9008 859Perl front-end C<Convert::Recode> for character conversions.
f6edf83b 860
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861The following are fast conversions from ISO 8859-1 (Latin-1) bytes
862to UTF-8 bytes, the code works even with older Perl 5 versions.
863
864 # ISO 8859-1 to UTF-8
865 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
866
867 # UTF-8 to ISO 8859-1
868 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
869
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870=head1 SEE ALSO
871
872L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>,
873L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD>
874
376d9008 875=head1 ACKNOWLEDGMENTS
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876
877Thanks to the kind readers of the perl5-porters@perl.org,
878perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
879mailing lists for their valuable feedback.
880
881=head1 AUTHOR, COPYRIGHT, AND LICENSE
882
be3c0a43 883Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi>
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884
885This document may be distributed under the same terms as Perl itself.