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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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175You can enable automatic UTF-8-ification of your standard file
176handles, default C<open()> layer, and C<@ARGV> by using either
177the C<-C> command line switch or the C<PERL_UNICODE> environment
178variable, see L<perlrun> for the documentation of the C<-C> switch.
179
180Note that this means that Perl expects other software to work, too:
181if Perl has been led to believe that STDIN should be UTF-8, but then
182STDIN coming in from another command is not UTF-8, Perl will complain
183about the malformed UTF-8.
b310b053 184
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185All features that combine Unicode and I/O also require using the new
186PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though:
187you can see whether yours is by running "perl -V" and looking for
188C<useperlio=define>.
189
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190=head2 Unicode and EBCDIC
191
192Perl 5.8.0 also supports Unicode on EBCDIC platforms. There,
376d9008 193Unicode support is somewhat more complex to implement since
64c66fb6 194additional conversions are needed at every step. Some problems
dc4af4bb 195remain, see L<perlebcdic> for details.
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196
197In any case, the Unicode support on EBCDIC platforms is better than
198in the 5.6 series, which didn't work much at all for EBCDIC platform.
199On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
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200instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in
201that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is
202"EBCDIC-safe".
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203
204=head2 Creating Unicode
205
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206To create Unicode characters in literals for code points above C<0xFF>,
207use the C<\x{...}> notation in double-quoted strings:
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208
209 my $smiley = "\x{263a}";
210
376d9008 211Similarly, it can be used in regular expression literals
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212
213 $smiley =~ /\x{263a}/;
214
215At run-time you can use C<chr()>:
216
217 my $hebrew_alef = chr(0x05d0);
218
376d9008 219See L</"Further Resources"> for how to find all these numeric codes.
ba62762e 220
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221Naturally, C<ord()> will do the reverse: it turns a character into
222a code point.
ba62762e 223
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224Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>,
225and C<chr(...)> for arguments less than C<0x100> (decimal 256)
226generate an eight-bit character for backward compatibility with older
227Perls. For arguments of C<0x100> or more, Unicode characters are
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228always produced. If you want to force the production of Unicode
229characters regardless of the numeric value, use C<pack("U", ...)>
230instead of C<\x..>, C<\x{...}>, or C<chr()>.
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231
232You can also use the C<charnames> pragma to invoke characters
376d9008 233by name in double-quoted strings:
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234
235 use charnames ':full';
236 my $arabic_alef = "\N{ARABIC LETTER ALEF}";
237
238And, as mentioned above, you can also C<pack()> numbers into Unicode
239characters:
240
241 my $georgian_an = pack("U", 0x10a0);
242
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243Note that both C<\x{...}> and C<\N{...}> are compile-time string
244constants: you cannot use variables in them. if you want similar
245run-time functionality, use C<chr()> and C<charnames::vianame()>.
246
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247Also note that if all the code points for pack "U" are below 0x100,
248bytes will be generated, just like if you were using C<chr()>.
249
250 my $bytes = pack("U*", 0x80, 0xFF);
251
252If you want to force the result to Unicode characters, use the special
253C<"U0"> prefix. It consumes no arguments but forces the result to be
254in Unicode characters, instead of bytes.
255
256 my $chars = pack("U0U*", 0x80, 0xFF);
257
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258=head2 Handling Unicode
259
260Handling Unicode is for the most part transparent: just use the
261strings as usual. Functions like C<index()>, C<length()>, and
262C<substr()> will work on the Unicode characters; regular expressions
263will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
264
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265Note that Perl considers combining character sequences to be
266characters, so for example
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267
268 use charnames ':full';
269 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
270
271will print 2, not 1. The only exception is that regular expressions
272have C<\X> for matching a combining character sequence.
273
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274Life is not quite so transparent, however, when working with legacy
275encodings, I/O, and certain special cases:
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276
277=head2 Legacy Encodings
278
279When you combine legacy data and Unicode the legacy data needs
280to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
281applicable) is assumed. You can override this assumption by
282using the C<encoding> pragma, for example
283
284 use encoding 'latin2'; # ISO 8859-2
285
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286in which case literals (string or regular expressions), C<chr()>,
287and C<ord()> in your whole script are assumed to produce Unicode
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288characters from ISO 8859-2 code points. Note that the matching for
289encoding names is forgiving: instead of C<latin2> you could have
290said C<Latin 2>, or C<iso8859-2>, or other variations. With just
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291
292 use encoding;
293
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294the environment variable C<PERL_ENCODING> will be consulted.
295If that variable isn't set, the encoding pragma will fail.
ba62762e 296
376d9008 297The C<Encode> module knows about many encodings and has interfaces
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298for doing conversions between those encodings:
299
300 use Encode 'from_to';
301 from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8
302
303=head2 Unicode I/O
304
8baee566 305Normally, writing out Unicode data
ba62762e 306
8baee566 307 print FH $some_string_with_unicode, "\n";
ba62762e 308
8baee566 309produces raw bytes that Perl happens to use to internally encode the
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310Unicode string. Perl's internal encoding depends on the system as
311well as what characters happen to be in the string at the time. If
312any of the characters are at code points C<0x100> or above, you will get
313a warning. To ensure that the output is explicitly rendered in the
314encoding you desire--and to avoid the warning--open the stream with
315the desired encoding. Some examples:
ba62762e 316
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317 open FH, ">:utf8", "file";
318
319 open FH, ">:encoding(ucs2)", "file";
320 open FH, ">:encoding(UTF-8)", "file";
321 open FH, ">:encoding(shift_jis)", "file";
1d7919c5 322
376d9008 323and on already open streams, use C<binmode()>:
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324
325 binmode(STDOUT, ":utf8");
326
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327 binmode(STDOUT, ":encoding(ucs2)");
328 binmode(STDOUT, ":encoding(UTF-8)");
329 binmode(STDOUT, ":encoding(shift_jis)");
330
b5d8778e 331The matching of encoding names is loose: case does not matter, and
fae2c0fb 332many encodings have several aliases. Note that the C<:utf8> layer
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333must always be specified exactly like that; it is I<not> subject to
334the loose matching of encoding names.
b5d8778e 335
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336See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
337L<Encode::PerlIO> for the C<:encoding()> layer, and
338L<Encode::Supported> for many encodings supported by the C<Encode>
339module.
ba62762e 340
a5f0baef 341Reading in a file that you know happens to be encoded in one of the
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342Unicode or legacy encodings does not magically turn the data into
343Unicode in Perl's eyes. To do that, specify the appropriate
fae2c0fb 344layer when opening files
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345
346 open(my $fh,'<:utf8', 'anything');
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347 my $line_of_unicode = <$fh>;
348
ec90690f 349 open(my $fh,'<:encoding(Big5)', 'anything');
8baee566 350 my $line_of_unicode = <$fh>;
ba62762e 351
fae2c0fb 352The I/O layers can also be specified more flexibly with
376d9008 353the C<open> pragma. See L<open>, or look at the following example.
ba62762e 354
fae2c0fb 355 use open ':utf8'; # input and output default layer will be UTF-8
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356 open X, ">file";
357 print X chr(0x100), "\n";
ba62762e 358 close X;
1d7919c5 359 open Y, "<file";
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360 printf "%#x\n", ord(<Y>); # this should print 0x100
361 close Y;
362
fae2c0fb 363With the C<open> pragma you can use the C<:locale> layer
ba62762e 364
12f98225 365 BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
1ecefa54 366 # the :locale will probe the locale environment variables like LC_ALL
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367 use open OUT => ':locale'; # russki parusski
368 open(O, ">koi8");
369 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
370 close O;
371 open(I, "<koi8");
372 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
373 close I;
374
fae2c0fb 375or you can also use the C<':encoding(...)'> layer
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376
377 open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
8baee566 378 my $line_of_unicode = <$epic>;
ba62762e 379
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380These methods install a transparent filter on the I/O stream that
381converts data from the specified encoding when it is read in from the
a5f0baef 382stream. The result is always Unicode.
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383
384The L<open> pragma affects all the C<open()> calls after the pragma by
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385setting default layers. If you want to affect only certain
386streams, use explicit layers directly in the C<open()> call.
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387
388You can switch encodings on an already opened stream by using
8baee566 389C<binmode()>; see L<perlfunc/binmode>.
ba62762e 390
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391The C<:locale> does not currently (as of Perl 5.8.0) work with
392C<open()> and C<binmode()>, only with the C<open> pragma. The
8baee566 393C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
1ecefa54 394C<binmode()>, and the C<open> pragma.
ba62762e 395
fae2c0fb 396Similarly, you may use these I/O layers on output streams to
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397automatically convert Unicode to the specified encoding when it is
398written to the stream. For example, the following snippet copies the
399contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
400the file "text.utf8", encoded as UTF-8:
ba62762e 401
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402 open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis');
403 open(my $unicode, '>:utf8', 'text.utf8');
0cf8a8d9 404 while (<$nihongo>) { print $unicode $_ }
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405
406The naming of encodings, both by the C<open()> and by the C<open>
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407pragma, is similar to the C<encoding> pragma in that it allows for
408flexible names: C<koi8-r> and C<KOI8R> will both be understood.
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409
410Common encodings recognized by ISO, MIME, IANA, and various other
8baee566 411standardisation organisations are recognised; for a more detailed
1bfb14c4 412list see L<Encode::Supported>.
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413
414C<read()> reads characters and returns the number of characters.
415C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
416and C<sysseek()>.
417
8baee566 418Notice that because of the default behaviour of not doing any
fae2c0fb 419conversion upon input if there is no default layer,
ba62762e 420it is easy to mistakenly write code that keeps on expanding a file
1bfb14c4 421by repeatedly encoding the data:
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422
423 # BAD CODE WARNING
424 open F, "file";
8baee566 425 local $/; ## read in the whole file of 8-bit characters
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426 $t = <F>;
427 close F;
428 open F, ">:utf8", "file";
8baee566 429 print F $t; ## convert to UTF-8 on output
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430 close F;
431
432If you run this code twice, the contents of the F<file> will be twice
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433UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or
434explicitly opening also the F<file> for input as UTF-8.
ba62762e 435
0c901d84 436B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
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437Perl has been built with the new PerlIO feature (which is the default
438on most systems).
0c901d84 439
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440=head2 Displaying Unicode As Text
441
442Sometimes you might want to display Perl scalars containing Unicode as
8baee566 443simple ASCII (or EBCDIC) text. The following subroutine converts
1ecefa54 444its argument so that Unicode characters with code points greater than
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445255 are displayed as C<\x{...}>, control characters (like C<\n>) are
446displayed as C<\x..>, and the rest of the characters as themselves:
1ecefa54 447
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448 sub nice_string {
449 join("",
450 map { $_ > 255 ? # if wide character...
8baee566 451 sprintf("\\x{%04X}", $_) : # \x{...}
58c274a1 452 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
8baee566 453 sprintf("\\x%02X", $_) : # \x..
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454 chr($_) # else as themselves
455 } unpack("U*", $_[0])); # unpack Unicode characters
456 }
457
458For example,
459
460 nice_string("foo\x{100}bar\n")
461
8baee566 462returns:
58c274a1 463
8baee566 464 "foo\x{0100}bar\x0A"
1ecefa54 465
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466=head2 Special Cases
467
468=over 4
469
470=item *
471
472Bit Complement Operator ~ And vec()
473
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474The bit complement operator C<~> may produce surprising results if
475used on strings containing characters with ordinal values above
476255. In such a case, the results are consistent with the internal
477encoding of the characters, but not with much else. So don't do
478that. Similarly for C<vec()>: you will be operating on the
479internally-encoded bit patterns of the Unicode characters, not on
480the code point values, which is very probably not what you want.
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481
482=item *
483
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484Peeking At Perl's Internal Encoding
485
486Normal users of Perl should never care how Perl encodes any particular
a5f0baef 487Unicode string (because the normal ways to get at the contents of a
376d9008 488string with Unicode--via input and output--should always be via
fae2c0fb 489explicitly-defined I/O layers). But if you must, there are two
a5f0baef 490ways of looking behind the scenes.
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491
492One way of peeking inside the internal encoding of Unicode characters
376d9008 493is to use C<unpack("C*", ...> to get the bytes or C<unpack("H*", ...)>
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494to display the bytes:
495
8baee566 496 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
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497 print join(" ", unpack("H*", pack("U", 0x100))), "\n";
498
499Yet another way would be to use the Devel::Peek module:
500
501 perl -MDevel::Peek -e 'Dump(chr(0x100))'
502
8baee566 503That shows the UTF8 flag in FLAGS and both the UTF-8 bytes
376d9008 504and Unicode characters in C<PV>. See also later in this document
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505the discussion about the C<is_utf8> function of the C<Encode> module.
506
507=back
508
509=head2 Advanced Topics
510
511=over 4
512
513=item *
514
515String Equivalence
516
517The question of string equivalence turns somewhat complicated
376d9008 518in Unicode: what do you mean by "equal"?
ba62762e 519
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520(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
521C<LATIN CAPITAL LETTER A>?)
ba62762e 522
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523The short answer is that by default Perl compares equivalence (C<eq>,
524C<ne>) based only on code points of the characters. In the above
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525case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any
526CAPITAL LETTER As should be considered equal, or even As of any case.
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527
528The long answer is that you need to consider character normalization
376d9008 529and casing issues: see L<Unicode::Normalize>, Unicode Technical
ba62762e 530Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
376d9008
JB
531Mappings>, http://www.unicode.org/unicode/reports/tr15/ and
532http://www.unicode.org/unicode/reports/tr21/
ba62762e 533
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534As of Perl 5.8.0, the "Full" case-folding of I<Case
535Mappings/SpecialCasing> is implemented.
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536
537=item *
538
539String Collation
540
376d9008 541People like to see their strings nicely sorted--or as Unicode
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542parlance goes, collated. But again, what do you mean by collate?
543
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544(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
545C<LATIN CAPITAL LETTER A WITH GRAVE>?)
ba62762e 546
58c274a1 547The short answer is that by default, Perl compares strings (C<lt>,
ba62762e 548C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
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549characters. In the above case, the answer is "after", since
550C<0x00C1> > C<0x00C0>.
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551
552The long answer is that "it depends", and a good answer cannot be
553given without knowing (at the very least) the language context.
554See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
555http://www.unicode.org/unicode/reports/tr10/
556
557=back
558
559=head2 Miscellaneous
560
561=over 4
562
563=item *
564
3ff56b75 565Character Ranges and Classes
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566
567Character ranges in regular expression character classes (C</[a-z]/>)
568and in the C<tr///> (also known as C<y///>) operator are not magically
58c274a1 569Unicode-aware. What this means that C<[A-Za-z]> will not magically start
376d9008
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570to mean "all alphabetic letters"; not that it does mean that even for
5718-bit characters, you should be using C</[[:alpha:]]/> in that case.
ba62762e 572
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573For specifying character classes like that in regular expressions,
574you can use the various Unicode properties--C<\pL>, or perhaps
575C<\p{Alphabetic}>, in this particular case. You can use Unicode
576code points as the end points of character ranges, but there is no
577magic associated with specifying a certain range. For further
578information--there are dozens of Unicode character classes--see
579L<perlunicode>.
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580
581=item *
582
583String-To-Number Conversions
584
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585Unicode does define several other decimal--and numeric--characters
586besides the familiar 0 to 9, such as the Arabic and Indic digits.
ba62762e 587Perl does not support string-to-number conversion for digits other
58c274a1 588than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
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589
590=back
591
592=head2 Questions With Answers
593
594=over 4
595
818c4caa 596=item *
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597
598Will My Old Scripts Break?
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599
600Very probably not. Unless you are generating Unicode characters
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601somehow, old behaviour should be preserved. About the only behaviour
602that has changed and which could start generating Unicode is the old
603behaviour of C<chr()> where supplying an argument more than 255
604produced a character modulo 255. C<chr(300)>, for example, was equal
605to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
606BREVE.
ba62762e 607
818c4caa 608=item *
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609
610How Do I Make My Scripts Work With Unicode?
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611
612Very little work should be needed since nothing changes until you
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613generate Unicode data. The most important thing is getting input as
614Unicode; for that, see the earlier I/O discussion.
ba62762e 615
818c4caa 616=item *
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617
618How Do I Know Whether My String Is In Unicode?
ba62762e 619
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620You shouldn't care. No, you really shouldn't. No, really. If you
621have to care--beyond the cases described above--it means that we
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622didn't get the transparency of Unicode quite right.
623
624Okay, if you insist:
625
626 use Encode 'is_utf8';
627 print is_utf8($string) ? 1 : 0, "\n";
628
629But note that this doesn't mean that any of the characters in the
630string are necessary UTF-8 encoded, or that any of the characters have
631code points greater than 0xFF (255) or even 0x80 (128), or that the
632string has any characters at all. All the C<is_utf8()> does is to
633return the value of the internal "utf8ness" flag attached to the
376d9008 634C<$string>. If the flag is off, the bytes in the scalar are interpreted
3c1c8017 635as a single byte encoding. If the flag is on, the bytes in the scalar
376d9008 636are interpreted as the (multi-byte, variable-length) UTF-8 encoded code
3c1c8017
AT
637points of the characters. Bytes added to an UTF-8 encoded string are
638automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars
376d9008 639are merged (double-quoted interpolation, explicit concatenation, and
3c1c8017
AT
640printf/sprintf parameter substitution), the result will be UTF-8 encoded
641as if copies of the byte strings were upgraded to UTF-8: for example,
642
643 $a = "ab\x80c";
644 $b = "\x{100}";
645 print "$a = $b\n";
646
1bfb14c4 647the output string will be UTF-8-encoded C<ab\x80c\x{100}\n>, but note
376d9008 648that C<$a> will stay byte-encoded.
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649
650Sometimes you might really need to know the byte length of a string
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651instead of the character length. For that use either the
652C<Encode::encode_utf8()> function or the C<bytes> pragma and its only
653defined function C<length()>:
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654
655 my $unicode = chr(0x100);
656 print length($unicode), "\n"; # will print 1
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657 require Encode;
658 print length(Encode::encode_utf8($unicode)), "\n"; # will print 2
ba62762e 659 use bytes;
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660 print length($unicode), "\n"; # will also print 2
661 # (the 0xC4 0x80 of the UTF-8)
ba62762e 662
818c4caa 663=item *
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664
665How Do I Detect Data That's Not Valid In a Particular Encoding?
ba62762e 666
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667Use the C<Encode> package to try converting it.
668For example,
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669
670 use Encode 'encode_utf8';
8baee566 671 if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) {
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672 # valid
673 } else {
674 # invalid
675 }
676
8baee566 677For UTF-8 only, you can use:
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678
679 use warnings;
8baee566 680 @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
ba62762e 681
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682If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack>
683warning is produced. The "U0" means "expect strictly UTF-8 encoded
684Unicode". Without that the C<unpack("U*", ...)> would accept also
685data like C<chr(0xFF>), similarly to the C<pack> as we saw earlier.
ba62762e 686
818c4caa 687=item *
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688
689How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
ba62762e 690
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691This probably isn't as useful as you might think.
692Normally, you shouldn't need to.
ba62762e 693
1bfb14c4 694In one sense, what you are asking doesn't make much sense: encodings
376d9008 695are for characters, and binary data are not "characters", so converting
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696"data" into some encoding isn't meaningful unless you know in what
697character set and encoding the binary data is in, in which case it's
376d9008 698not just binary data, now is it?
8baee566 699
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700If you have a raw sequence of bytes that you know should be
701interpreted via a particular encoding, you can use C<Encode>:
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702
703 use Encode 'from_to';
704 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
705
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706The call to C<from_to()> changes the bytes in C<$data>, but nothing
707material about the nature of the string has changed as far as Perl is
708concerned. Both before and after the call, the string C<$data>
709contains just a bunch of 8-bit bytes. As far as Perl is concerned,
710the encoding of the string remains as "system-native 8-bit bytes".
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711
712You might relate this to a fictional 'Translate' module:
713
714 use Translate;
715 my $phrase = "Yes";
716 Translate::from_to($phrase, 'english', 'deutsch');
717 ## phrase now contains "Ja"
ba62762e 718
8baee566 719The contents of the string changes, but not the nature of the string.
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720Perl doesn't know any more after the call than before that the
721contents of the string indicates the affirmative.
ba62762e 722
376d9008 723Back to converting data. If you have (or want) data in your system's
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724native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
725pack/unpack to convert to/from Unicode.
ba62762e 726
8baee566
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727 $native_string = pack("C*", unpack("U*", $Unicode_string));
728 $Unicode_string = pack("U*", unpack("C*", $native_string));
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729
730If you have a sequence of bytes you B<know> is valid UTF-8,
731but Perl doesn't know it yet, you can make Perl a believer, too:
732
733 use Encode 'decode_utf8';
8baee566 734 $Unicode = decode_utf8($bytes);
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735
736You can convert well-formed UTF-8 to a sequence of bytes, but if
737you just want to convert random binary data into UTF-8, you can't.
1bfb14c4 738B<Any random collection of bytes isn't well-formed UTF-8>. You can
ba62762e 739use C<unpack("C*", $string)> for the former, and you can create
8baee566 740well-formed Unicode data by C<pack("U*", 0xff, ...)>.
ba62762e 741
818c4caa 742=item *
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743
744How Do I Display Unicode? How Do I Input Unicode?
ba62762e 745
076d825e 746See http://www.alanwood.net/unicode/ and
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747http://www.cl.cam.ac.uk/~mgk25/unicode.html
748
818c4caa 749=item *
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750
751How Does Unicode Work With Traditional Locales?
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752
753In Perl, not very well. Avoid using locales through the C<locale>
754pragma. Use only one or the other.
755
756=back
757
758=head2 Hexadecimal Notation
759
376d9008
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760The Unicode standard prefers using hexadecimal notation because
761that more clearly shows the division of Unicode into blocks of 256 characters.
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762Hexadecimal is also simply shorter than decimal. You can use decimal
763notation, too, but learning to use hexadecimal just makes life easier
1bfb14c4 764with the Unicode standard. The C<U+HHHH> notation uses hexadecimal,
076d825e 765for example.
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766
767The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
768a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
769four bits, or half a byte. C<print 0x..., "\n"> will show a
770hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
771show a decimal number in hexadecimal. If you have just the
376d9008 772"hex digits" of a hexadecimal number, you can use the C<hex()> function.
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773
774 print 0x0009, "\n"; # 9
775 print 0x000a, "\n"; # 10
776 print 0x000f, "\n"; # 15
777 print 0x0010, "\n"; # 16
778 print 0x0011, "\n"; # 17
779 print 0x0100, "\n"; # 256
780
781 print 0x0041, "\n"; # 65
782
783 printf "%x\n", 65; # 41
784 printf "%#x\n", 65; # 0x41
785
786 print hex("41"), "\n"; # 65
787
788=head2 Further Resources
789
790=over 4
791
792=item *
793
794Unicode Consortium
795
796 http://www.unicode.org/
797
798=item *
799
800Unicode FAQ
801
802 http://www.unicode.org/unicode/faq/
803
804=item *
805
806Unicode Glossary
807
808 http://www.unicode.org/glossary/
809
810=item *
811
812Unicode Useful Resources
813
814 http://www.unicode.org/unicode/onlinedat/resources.html
815
816=item *
817
818Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
819
076d825e 820 http://www.alanwood.net/unicode/
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821
822=item *
823
824UTF-8 and Unicode FAQ for Unix/Linux
825
826 http://www.cl.cam.ac.uk/~mgk25/unicode.html
827
828=item *
829
830Legacy Character Sets
831
832 http://www.czyborra.com/
833 http://www.eki.ee/letter/
834
835=item *
836
837The Unicode support files live within the Perl installation in the
838directory
839
840 $Config{installprivlib}/unicore
841
842in Perl 5.8.0 or newer, and
843
844 $Config{installprivlib}/unicode
845
846in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
847avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
551b6b6f 848The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
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849Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
850
851 perl "-V:installprivlib"
852
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853You can explore various information from the Unicode data files using
854the C<Unicode::UCD> module.
855
856=back
857
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858=head1 UNICODE IN OLDER PERLS
859
860If you cannot upgrade your Perl to 5.8.0 or later, you can still
861do some Unicode processing by using the modules C<Unicode::String>,
862C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
863If you have the GNU recode installed, you can also use the
376d9008 864Perl front-end C<Convert::Recode> for character conversions.
f6edf83b 865
aaef10c5 866The following are fast conversions from ISO 8859-1 (Latin-1) bytes
63de3cb2 867to UTF-8 bytes and back, the code works even with older Perl 5 versions.
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868
869 # ISO 8859-1 to UTF-8
870 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
871
872 # UTF-8 to ISO 8859-1
873 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
874
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875=head1 SEE ALSO
876
877L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>,
878L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD>
879
376d9008 880=head1 ACKNOWLEDGMENTS
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881
882Thanks to the kind readers of the perl5-porters@perl.org,
883perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
884mailing lists for their valuable feedback.
885
886=head1 AUTHOR, COPYRIGHT, AND LICENSE
887
be3c0a43 888Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi>
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889
890This document may be distributed under the same terms as Perl itself.