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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
12Unicode is a character set standard with plans to cover all of the
13writing systems of the world, plus many other symbols.
14
15Unicode and ISO/IEC 10646 are coordinated standards that provide code
16points for the characters in almost all modern character set standards,
17covering more than 30 writing systems and hundreds of languages,
18including all commercially important modern languages. All characters
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
24particular integer width, and especially not to the C language C<char>.
25Unicode is language neutral and display neutral: it doesn't encode the
26language of the text, and it doesn't define fonts or other graphical
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
31SMALL LETTER ALPHA>, and then unique numbers for those, hexadecimal
320x0041 or 0x03B1 for those particular characters. Such unique
33numbers are called I<code points>.
34
35The Unicode standard prefers using hexadecimal notation for the code
36points. (In case this notation, numbers like 0x0041, is unfamiliar to
37you, take a peek at a later section, L</"Hexadecimal Notation">.)
38The Unicode standard uses the notation C<U+0041 LATIN CAPITAL LETTER A>,
39which gives the hexadecimal code point, and the normative name of
40the character.
41
42Unicode also defines various I<properties> for the characters, like
43"uppercase" or "lowercase", "decimal digit", or "punctuation":
44these properties are independent of the names of the characters.
45Furthermore, various operations on the characters like uppercasing,
46lowercasing, and collating (sorting), are defined.
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
51a base character and modifiers is called a I<combining character
52sequence>.
53
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54Whether to call these combining character sequences, as a whole,
55"characters" depends on your point of view. If you are a programmer,
56you probably would tend towards seeing each element in the sequences
57as one unit, one "character", but from the user viewpoint, the
58sequence as a whole is probably considered one "character", since
59that's probably what it looks like in the context of the user's
60language.
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61
62With this "as a whole" view of characters, the number of characters is
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63open-ended. But in the programmer's "one unit is one character" point
64of view, the concept of "characters" is more deterministic, and so we
65take that point of view in this document: one "character" is one
66Unicode code point, be it a base character or a combining character.
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67
68For some of the combinations there are I<precomposed> characters,
69for example C<LATIN CAPITAL LETTER A WITH ACUTE> is defined as
70a single code point. These precomposed characters are, however,
71often available only for some combinations, and mainly they are
72meant to support round-trip conversions between Unicode and legacy
73standards (like the ISO 8859), and in general case the composing
74method is more extensible. To support conversion between the
75different compositions of the characters, various I<normalization
76forms> are also defined.
77
78Because of backward compatibility with legacy encodings, the "a unique
79number for every character" breaks down a bit: "at least one number
80for every character" is closer to truth. (This happens when the same
81character has been encoded in several legacy encodings.) The converse
82is also not true: not every code point has an assigned character.
83Firstly, there are unallocated code points within otherwise used
84blocks. Secondly, there are special Unicode control characters that
85do not represent true characters.
86
87A common myth about Unicode is that it would be "16-bit", that is,
880x10000 (or 65536) characters from 0x0000 to 0xFFFF. B<This is untrue.>
89Since Unicode 2.0 Unicode has been defined all the way up to 21 bits
90(0x10FFFF), and since 3.1 characters have been defined beyond 0xFFFF.
91The first 0x10000 characters are called the I<Plane 0>, or the I<Basic
92Multilingual Plane> (BMP). With the Unicode 3.1, 17 planes in all are
93defined (but nowhere near full of defined characters yet).
94
95Another myth is that the 256-character blocks have something to do
96with languages: a block per language. B<Also this is untrue.>
97The division into the blocks exists but it is almost completely
98accidental, an artifact of how the characters have been historically
99allocated. Instead, there is a concept called I<scripts>, which may
100be more useful: there is C<Latin> script, C<Greek> script, and so on.
101Scripts usually span several parts of several blocks. For further
102information see L<Unicode::UCD>.
103
104The Unicode code points are just abstract numbers. To input and
105output these abstract numbers, the numbers must be I<encoded> somehow.
106Unicode defines several I<character encoding forms>, of which I<UTF-8>
107is perhaps the most popular. UTF-8 is a variable length encoding that
108encodes Unicode characters as 1 to 6 bytes (only 4 with the currently
8baee566 109defined characters). Other encodings include UTF-16 and UTF-32 and their
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110big and little endian variants (UTF-8 is byteorder independent).
111The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms.
112
113For more information about encodings, for example to learn what
114I<surrogates> and I<byte order marks> (BOMs) are, see L<perlunicode>.
115
116=head2 Perl's Unicode Support
117
118Starting from Perl 5.6.0, Perl has had the capability of handling
119Unicode natively. The first recommended release for serious Unicode
120work is Perl 5.8.0, however. The maintenance release 5.6.1 fixed many
121of the problems of the initial implementation of Unicode, but for
122example regular expressions didn't really work with Unicode.
123
124B<Starting from Perl 5.8.0, the use of C<use utf8> is no longer
125necessary.> In earlier releases the C<utf8> pragma was used to declare
126that operations in the current block or file would be Unicode-aware.
127This model was found to be wrong, or at least clumsy: the Unicodeness
128is now carried with the data, not attached to the operations. (There
129is one remaining case where an explicit C<use utf8> is needed: if your
a5f0baef 130Perl script itself is encoded in UTF-8, you can use UTF-8 in your
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131identifier names, and in your string and regular expression literals,
132by saying C<use utf8>. This is not the default because that would
133break existing scripts having legacy 8-bit data in them.)
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134
135=head2 Perl's Unicode Model
136
137Perl supports both the old, pre-5.6, model of strings of eight-bit
138native bytes, and strings of Unicode characters. The principle is
139that Perl tries to keep its data as eight-bit bytes for as long as
140possible, but as soon as Unicodeness cannot be avoided, the data is
141transparently upgraded to Unicode.
142
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143Internally, Perl currently uses either whatever the native eight-bit
144character set of the platform (for example Latin-1) or UTF-8 to encode
145Unicode strings. Specifically, if all code points in the string are
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1460xFF or less, Perl uses the native eight-bit character set.
147Otherwise, it uses UTF-8.
4192de81 148
7ca610e8 149A user of Perl does not normally need to know nor care how Perl
20ba30f4 150happens to encode its internal strings, but it becomes relevant when
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151outputting Unicode strings to a stream without a discipline (one with
152the "default default"). In such a case, the raw bytes used internally
153(the native character set or UTF-8, as appropriate for each string)
154will be used, and a "Wide character" warning will be issued if those
155strings contain a character beyond 0x00FF.
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156
157For example,
158
7ca610e8 159 perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
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160
161produces a fairly useless mixture of native bytes and UTF-8, as well
162as a warning.
163
164To output UTF-8 always, use the ":utf8" output discipline. Prepending
165
166 binmode(STDOUT, ":utf8");
167
168to this sample program ensures the output is completely UTF-8, and
4049dcd4 169of course, removes the warning.
ba62762e 170
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171If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG)
172contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching),
173the default encoding of your STDIN, STDOUT, and STDERR, and of
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174B<any subsequent file open>, is UTF-8. Note that this means
175that Perl expects other software to work, too: if STDIN coming
176in from another command is not UTF-8, Perl will complain about
177malformed UTF-8.
b310b053 178
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179=head2 Unicode and EBCDIC
180
181Perl 5.8.0 also supports Unicode on EBCDIC platforms. There,
182the Unicode support is somewhat more complex to implement since
183additional conversions are needed at every step. Some problems
dc4af4bb 184remain, see L<perlebcdic> for details.
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185
186In any case, the Unicode support on EBCDIC platforms is better than
187in the 5.6 series, which didn't work much at all for EBCDIC platform.
188On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
189instead of UTF-8 (the difference is that as UTF-8 is "ASCII-safe" in
190that ASCII characters encode to UTF-8 as-is, UTF-EBCDIC is
191"EBCDIC-safe").
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192
193=head2 Creating Unicode
194
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195To create Unicode characters in literals for code points above 0xFF,
196use the C<\x{...}> notation in doublequoted strings:
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197
198 my $smiley = "\x{263a}";
199
8baee566 200Similarly in regular expression literals
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201
202 $smiley =~ /\x{263a}/;
203
204At run-time you can use C<chr()>:
205
206 my $hebrew_alef = chr(0x05d0);
207
208(See L</"Further Resources"> for how to find all these numeric codes.)
209
210Naturally, C<ord()> will do the reverse: turn a character to a code point.
211
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212Note that C<\x..> (no C<{}> and only two hexadecimal digits),
213C<\x{...}>, and C<chr(...)> for arguments less than 0x100 (decimal
214256) generate an eight-bit character for backward compatibility with
215older Perls. For arguments of 0x100 or more, Unicode characters are
216always produced. If you want to force the production of Unicode
217characters regardless of the numeric value, use C<pack("U", ...)>
218instead of C<\x..>, C<\x{...}>, or C<chr()>.
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219
220You can also use the C<charnames> pragma to invoke characters
221by name in doublequoted strings:
222
223 use charnames ':full';
224 my $arabic_alef = "\N{ARABIC LETTER ALEF}";
225
226And, as mentioned above, you can also C<pack()> numbers into Unicode
227characters:
228
229 my $georgian_an = pack("U", 0x10a0);
230
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231Note that both C<\x{...}> and C<\N{...}> are compile-time string
232constants: you cannot use variables in them. if you want similar
233run-time functionality, use C<chr()> and C<charnames::vianame()>.
234
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235Also note that if all the code points for pack "U" are below 0x100,
236bytes will be generated, just like if you were using C<chr()>.
237
238 my $bytes = pack("U*", 0x80, 0xFF);
239
240If you want to force the result to Unicode characters, use the special
241C<"U0"> prefix. It consumes no arguments but forces the result to be
242in Unicode characters, instead of bytes.
243
244 my $chars = pack("U0U*", 0x80, 0xFF);
245
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246=head2 Handling Unicode
247
248Handling Unicode is for the most part transparent: just use the
249strings as usual. Functions like C<index()>, C<length()>, and
250C<substr()> will work on the Unicode characters; regular expressions
251will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
252
253Note that Perl does B<not> consider combining character sequences
254to be characters, such for example
255
256 use charnames ':full';
257 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
258
259will print 2, not 1. The only exception is that regular expressions
260have C<\X> for matching a combining character sequence.
261
262When life is not quite so transparent is working with legacy
263encodings, and I/O, and certain special cases.
264
265=head2 Legacy Encodings
266
267When you combine legacy data and Unicode the legacy data needs
268to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
269applicable) is assumed. You can override this assumption by
270using the C<encoding> pragma, for example
271
272 use encoding 'latin2'; # ISO 8859-2
273
274in which case literals (string or regular expression) and chr/ord
275in your whole script are assumed to produce Unicode characters from
276ISO 8859-2 code points. Note that the matching for the encoding
277names is forgiving: instead of C<latin2> you could have said
278C<Latin 2>, or C<iso8859-2>, and so forth. With just
279
280 use encoding;
281
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282the environment variable C<PERL_ENCODING> will be consulted,
283but if that doesn't exist, the encoding pragma fails.
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284
285The C<Encode> module knows about many encodings and it has interfaces
286for doing conversions between those encodings:
287
288 use Encode 'from_to';
289 from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8
290
291=head2 Unicode I/O
292
8baee566 293Normally, writing out Unicode data
ba62762e 294
8baee566 295 print FH $some_string_with_unicode, "\n";
ba62762e 296
8baee566 297produces raw bytes that Perl happens to use to internally encode the
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298Unicode string (which depends on the system, as well as what
299characters happen to be in the string at the time). If any of the
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300characters are at code points 0x100 or above, you will get a warning.
301To ensure that the output is explicitly rendered in the encoding you
302desire (and to avoid the warning), open the stream with the desired
303encoding. Some examples:
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305 open FH, ">:ucs2", "file"
306 open FH, ">:utf8", "file";
307 open FH, ">:Shift-JIS", "file";
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308
309and on already open streams use C<binmode()>:
310
8baee566 311 binmode(STDOUT, ":ucs2");
1d7919c5 312 binmode(STDOUT, ":utf8");
8baee566 313 binmode(STDOUT, ":Shift-JIS");
1d7919c5 314
8baee566 315See documentation for the C<Encode> module for many supported encodings.
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317Reading in a file that you know happens to be encoded in one of the
318Unicode encodings does not magically turn the data into Unicode in
319Perl's eyes. To do that, specify the appropriate discipline when
320opening files
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321
322 open(my $fh,'<:utf8', 'anything');
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323 my $line_of_unicode = <$fh>;
324
325 open(my $fh,'<:Big5', 'anything');
326 my $line_of_unicode = <$fh>;
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327
328The I/O disciplines can also be specified more flexibly with
329the C<open> pragma; see L<open>:
330
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331 use open ':utf8'; # input and output default discipline will be UTF-8
332 open X, ">file";
333 print X chr(0x100), "\n";
ba62762e 334 close X;
1d7919c5 335 open Y, "<file";
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336 printf "%#x\n", ord(<Y>); # this should print 0x100
337 close Y;
338
339With the C<open> pragma you can use the C<:locale> discipline
340
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341 $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R';
342 # the :locale will probe the locale environment variables like LC_ALL
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343 use open OUT => ':locale'; # russki parusski
344 open(O, ">koi8");
345 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
346 close O;
347 open(I, "<koi8");
348 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
349 close I;
350
351or you can also use the C<':encoding(...)'> discipline
352
353 open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
8baee566 354 my $line_of_unicode = <$epic>;
ba62762e 355
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356These methods install a transparent filter on the I/O stream that
357converts data from the specified encoding when it is read in from the
a5f0baef 358stream. The result is always Unicode.
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359
360The L<open> pragma affects all the C<open()> calls after the pragma by
361setting default disciplines. If you want to affect only certain
362streams, use explicit disciplines directly in the C<open()> call.
363
364You can switch encodings on an already opened stream by using
8baee566 365C<binmode()>; see L<perlfunc/binmode>.
ba62762e 366
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367The C<:locale> does not currently (as of Perl 5.8.0) work with
368C<open()> and C<binmode()>, only with the C<open> pragma. The
8baee566 369C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
1ecefa54 370C<binmode()>, and the C<open> pragma.
ba62762e 371
8baee566 372Similarly, you may use these I/O disciplines on output streams to
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373automatically convert Unicode to the specified encoding when it is
374written to the stream. For example, the following snippet copies the
375contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
376the file "text.utf8", encoded as UTF-8:
ba62762e 377
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378 open(my $nihongo, '<:encoding(iso2022-jp)', 'text.jis');
379 open(my $unicode, '>:utf8', 'text.utf8');
380 while (<$nihongo>) { print $unicode }
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381
382The naming of encodings, both by the C<open()> and by the C<open>
383pragma, is similarly understanding as with the C<encoding> pragma:
384C<koi8-r> and C<KOI8R> will both be understood.
385
386Common encodings recognized by ISO, MIME, IANA, and various other
8baee566 387standardisation organisations are recognised; for a more detailed
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388list see L<Encode>.
389
390C<read()> reads characters and returns the number of characters.
391C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
392and C<sysseek()>.
393
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394Notice that because of the default behaviour of not doing any
395conversion upon input if there is no default discipline,
ba62762e 396it is easy to mistakenly write code that keeps on expanding a file
8baee566 397by repeatedly encoding:
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398
399 # BAD CODE WARNING
400 open F, "file";
8baee566 401 local $/; ## read in the whole file of 8-bit characters
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402 $t = <F>;
403 close F;
404 open F, ">:utf8", "file";
8baee566 405 print F $t; ## convert to UTF-8 on output
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406 close F;
407
408If you run this code twice, the contents of the F<file> will be twice
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409UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or
410explicitly opening also the F<file> for input as UTF-8.
ba62762e 411
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412B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
413Perl has been built with the new "perlio" feature. Almost all
414Perl 5.8 platforms do use "perlio", though: you can see whether
415yours is by running "perl -V" and looking for C<useperlio=define>.
416
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417=head2 Displaying Unicode As Text
418
419Sometimes you might want to display Perl scalars containing Unicode as
8baee566 420simple ASCII (or EBCDIC) text. The following subroutine converts
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421its argument so that Unicode characters with code points greater than
422255 are displayed as "\x{...}", control characters (like "\n") are
8baee566 423displayed as "\x..", and the rest of the characters as themselves:
1ecefa54 424
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425 sub nice_string {
426 join("",
427 map { $_ > 255 ? # if wide character...
8baee566 428 sprintf("\\x{%04X}", $_) : # \x{...}
58c274a1 429 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
8baee566 430 sprintf("\\x%02X", $_) : # \x..
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431 chr($_) # else as themselves
432 } unpack("U*", $_[0])); # unpack Unicode characters
433 }
434
435For example,
436
437 nice_string("foo\x{100}bar\n")
438
8baee566 439returns:
58c274a1 440
8baee566 441 "foo\x{0100}bar\x0A"
1ecefa54 442
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443=head2 Special Cases
444
445=over 4
446
447=item *
448
449Bit Complement Operator ~ And vec()
450
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451The bit complement operator C<~> may produce surprising results if used on
452strings containing characters with ordinal values above 255. In such a
453case, the results are consistent with the internal encoding of the
454characters, but not with much else. So don't do that. Similarly for vec():
455you will be operating on the internally encoded bit patterns of the Unicode
456characters, not on the code point values, which is very probably not what
457you want.
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458
459=item *
460
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461Peeking At Perl's Internal Encoding
462
463Normal users of Perl should never care how Perl encodes any particular
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464Unicode string (because the normal ways to get at the contents of a
465string with Unicode -- via input and output -- should always be via
466explicitly-defined I/O disciplines). But if you must, there are two
467ways of looking behind the scenes.
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468
469One way of peeking inside the internal encoding of Unicode characters
470is to use C<unpack("C*", ...> to get the bytes, or C<unpack("H*", ...)>
471to display the bytes:
472
8baee566 473 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
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474 print join(" ", unpack("H*", pack("U", 0x100))), "\n";
475
476Yet another way would be to use the Devel::Peek module:
477
478 perl -MDevel::Peek -e 'Dump(chr(0x100))'
479
8baee566 480That shows the UTF8 flag in FLAGS and both the UTF-8 bytes
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481and Unicode characters in PV. See also later in this document
482the discussion about the C<is_utf8> function of the C<Encode> module.
483
484=back
485
486=head2 Advanced Topics
487
488=over 4
489
490=item *
491
492String Equivalence
493
494The question of string equivalence turns somewhat complicated
495in Unicode: what do you mean by equal?
496
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497(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
498C<LATIN CAPITAL LETTER A>?)
ba62762e 499
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500The short answer is that by default Perl compares equivalence (C<eq>,
501C<ne>) based only on code points of the characters. In the above
502case, the answer is no (because 0x00C1 != 0x0041). But sometimes any
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503CAPITAL LETTER As being considered equal, or even any As of any case,
504would be desirable.
505
506The long answer is that you need to consider character normalization
507and casing issues: see L<Unicode::Normalize>, and Unicode Technical
508Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
509Mappings>, http://www.unicode.org/unicode/reports/tr15/
510http://www.unicode.org/unicode/reports/tr21/
511
58c274a1 512As of Perl 5.8.0, regular expression case-ignoring matching
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513implements only 1:1 semantics: one character matches one character.
514In I<Case Mappings> both 1:N and N:1 matches are defined.
515
516=item *
517
518String Collation
519
520People like to see their strings nicely sorted, or as Unicode
521parlance goes, collated. But again, what do you mean by collate?
522
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523(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
524C<LATIN CAPITAL LETTER A WITH GRAVE>?)
ba62762e 525
58c274a1 526The short answer is that by default, Perl compares strings (C<lt>,
ba62762e 527C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
58c274a1 528characters. In the above case, the answer is "after", since 0x00C1 > 0x00C0.
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529
530The long answer is that "it depends", and a good answer cannot be
531given without knowing (at the very least) the language context.
532See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
533http://www.unicode.org/unicode/reports/tr10/
534
535=back
536
537=head2 Miscellaneous
538
539=over 4
540
541=item *
542
3ff56b75 543Character Ranges and Classes
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544
545Character ranges in regular expression character classes (C</[a-z]/>)
546and in the C<tr///> (also known as C<y///>) operator are not magically
58c274a1 547Unicode-aware. What this means that C<[A-Za-z]> will not magically start
ba62762e 548to mean "all alphabetic letters" (not that it does mean that even for
3ff56b75 5498-bit characters, you should be using C</[[:alpha:]]/> for that).
ba62762e 550
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551For specifying things like that in regular expressions, you can use
552the various Unicode properties, C<\pL> or perhaps C<\p{Alphabetic}>,
553in this particular case. You can use Unicode code points as the end
554points of character ranges, but that means that particular code point
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555range, nothing more. For further information (there are dozens
556of Unicode character classes), see L<perlunicode>.
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557
558=item *
559
560String-To-Number Conversions
561
562Unicode does define several other decimal (and numeric) characters
563than just the familiar 0 to 9, such as the Arabic and Indic digits.
564Perl does not support string-to-number conversion for digits other
58c274a1 565than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
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566
567=back
568
569=head2 Questions With Answers
570
571=over 4
572
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573=item
574
575Will My Old Scripts Break?
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576
577Very probably not. Unless you are generating Unicode characters
578somehow, any old behaviour should be preserved. About the only
579behaviour that has changed and which could start generating Unicode
580is the old behaviour of C<chr()> where supplying an argument more
581than 255 produced a character modulo 255 (for example, C<chr(300)>
582was equal to C<chr(45)>).
583
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584=item
585
586How Do I Make My Scripts Work With Unicode?
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587
588Very little work should be needed since nothing changes until you
589somehow generate Unicode data. The greatest trick will be getting
590input as Unicode, and for that see the earlier I/O discussion.
591
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592=item
593
594How Do I Know Whether My String Is In Unicode?
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595
596You shouldn't care. No, you really shouldn't. If you have
597to care (beyond the cases described above), it means that we
598didn't get the transparency of Unicode quite right.
599
600Okay, if you insist:
601
602 use Encode 'is_utf8';
603 print is_utf8($string) ? 1 : 0, "\n";
604
605But note that this doesn't mean that any of the characters in the
606string are necessary UTF-8 encoded, or that any of the characters have
607code points greater than 0xFF (255) or even 0x80 (128), or that the
608string has any characters at all. All the C<is_utf8()> does is to
609return the value of the internal "utf8ness" flag attached to the
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610$string. If the flag is off, the bytes in the scalar are interpreted
611as a single byte encoding. If the flag is on, the bytes in the scalar
612are interpreted as the (multibyte, variable-length) UTF-8 encoded code
613points of the characters. Bytes added to an UTF-8 encoded string are
614automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars
615are merged (doublequoted interpolation, explicit concatenation, and
616printf/sprintf parameter substitution), the result will be UTF-8 encoded
617as if copies of the byte strings were upgraded to UTF-8: for example,
618
619 $a = "ab\x80c";
620 $b = "\x{100}";
621 print "$a = $b\n";
622
623the output string will be UTF-8-encoded "ab\x80c\x{100}\n", but note
624that C<$a> will stay single byte encoded.
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625
626Sometimes you might really need to know the byte length of a string
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627instead of the character length. For that use either the
628C<Encode::encode_utf8()> function or the C<bytes> pragma and its only
629defined function C<length()>:
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630
631 my $unicode = chr(0x100);
632 print length($unicode), "\n"; # will print 1
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633 require Encode;
634 print length(Encode::encode_utf8($unicode)), "\n"; # will print 2
ba62762e 635 use bytes;
ce7675db 636 print length($unicode), "\n"; # will also print 2 (the 0xC4 0x80 of the UTF-8)
ba62762e 637
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638=item
639
640How Do I Detect Data That's Not Valid In a Particular Encoding?
ba62762e 641
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642Use the C<Encode> package to try converting it.
643For example,
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644
645 use Encode 'encode_utf8';
8baee566 646 if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) {
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647 # valid
648 } else {
649 # invalid
650 }
651
8baee566 652For UTF-8 only, you can use:
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653
654 use warnings;
8baee566 655 @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
ba62762e 656
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657If invalid, a C<Malformed UTF-8 character (byte 0x##) in
658unpack> is produced. The "U0" means "expect strictly UTF-8
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659encoded Unicode". Without that the C<unpack("U*", ...)>
660would accept also data like C<chr(0xFF>), similarly to the
661C<pack> as we saw earlier.
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663=item
664
665How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
ba62762e 666
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667This probably isn't as useful as you might think.
668Normally, you shouldn't need to.
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670In one sense, what you are asking doesn't make much sense: Encodings
671are for characters, and binary data is not "characters", so converting
672"data" into some encoding isn't meaningful unless you know in what
673character set and encoding the binary data is in, in which case it's
674not binary data, now is it?
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675
676If you have a raw sequence of bytes that you know should be interpreted via
677a particular encoding, you can use C<Encode>:
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678
679 use Encode 'from_to';
680 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
681
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682The call to from_to() changes the bytes in $data, but nothing material
683about the nature of the string has changed as far as Perl is concerned.
684Both before and after the call, the string $data contains just a bunch of
6858-bit bytes. As far as Perl is concerned, the encoding of the string (as
686Perl sees it) remains as "system-native 8-bit bytes".
687
688You might relate this to a fictional 'Translate' module:
689
690 use Translate;
691 my $phrase = "Yes";
692 Translate::from_to($phrase, 'english', 'deutsch');
693 ## phrase now contains "Ja"
ba62762e 694
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695The contents of the string changes, but not the nature of the string.
696Perl doesn't know any more after the call than before that the contents
697of the string indicates the affirmative.
ba62762e 698
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699Back to converting data, if you have (or want) data in your system's
700native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
701pack/unpack to convert to/from Unicode.
ba62762e 702
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703 $native_string = pack("C*", unpack("U*", $Unicode_string));
704 $Unicode_string = pack("U*", unpack("C*", $native_string));
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705
706If you have a sequence of bytes you B<know> is valid UTF-8,
707but Perl doesn't know it yet, you can make Perl a believer, too:
708
709 use Encode 'decode_utf8';
8baee566 710 $Unicode = decode_utf8($bytes);
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711
712You can convert well-formed UTF-8 to a sequence of bytes, but if
713you just want to convert random binary data into UTF-8, you can't.
714Any random collection of bytes isn't well-formed UTF-8. You can
715use C<unpack("C*", $string)> for the former, and you can create
8baee566 716well-formed Unicode data by C<pack("U*", 0xff, ...)>.
ba62762e 717
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718=item
719
720How Do I Display Unicode? How Do I Input Unicode?
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721
722See http://www.hclrss.demon.co.uk/unicode/ and
723http://www.cl.cam.ac.uk/~mgk25/unicode.html
724
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725=item
726
727How Does Unicode Work With Traditional Locales?
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728
729In Perl, not very well. Avoid using locales through the C<locale>
730pragma. Use only one or the other.
731
732=back
733
734=head2 Hexadecimal Notation
735
736The Unicode standard prefers using hexadecimal notation because that
737shows better the division of Unicode into blocks of 256 characters.
738Hexadecimal is also simply shorter than decimal. You can use decimal
739notation, too, but learning to use hexadecimal just makes life easier
740with the Unicode standard.
741
742The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
743a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
744four bits, or half a byte. C<print 0x..., "\n"> will show a
745hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
746show a decimal number in hexadecimal. If you have just the
a5f0baef 747"hexdigits" of a hexadecimal number, you can use the C<hex()> function.
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748
749 print 0x0009, "\n"; # 9
750 print 0x000a, "\n"; # 10
751 print 0x000f, "\n"; # 15
752 print 0x0010, "\n"; # 16
753 print 0x0011, "\n"; # 17
754 print 0x0100, "\n"; # 256
755
756 print 0x0041, "\n"; # 65
757
758 printf "%x\n", 65; # 41
759 printf "%#x\n", 65; # 0x41
760
761 print hex("41"), "\n"; # 65
762
763=head2 Further Resources
764
765=over 4
766
767=item *
768
769Unicode Consortium
770
771 http://www.unicode.org/
772
773=item *
774
775Unicode FAQ
776
777 http://www.unicode.org/unicode/faq/
778
779=item *
780
781Unicode Glossary
782
783 http://www.unicode.org/glossary/
784
785=item *
786
787Unicode Useful Resources
788
789 http://www.unicode.org/unicode/onlinedat/resources.html
790
791=item *
792
793Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
794
795 http://www.hclrss.demon.co.uk/unicode/
796
797=item *
798
799UTF-8 and Unicode FAQ for Unix/Linux
800
801 http://www.cl.cam.ac.uk/~mgk25/unicode.html
802
803=item *
804
805Legacy Character Sets
806
807 http://www.czyborra.com/
808 http://www.eki.ee/letter/
809
810=item *
811
812The Unicode support files live within the Perl installation in the
813directory
814
815 $Config{installprivlib}/unicore
816
817in Perl 5.8.0 or newer, and
818
819 $Config{installprivlib}/unicode
820
821in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
822avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
551b6b6f 823The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
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824Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
825
826 perl "-V:installprivlib"
827
828Note that some of the files have been renamed from the Unicode
829standard since the Perl installation tries to live by the "8.3"
830filenaming restrictions. The renamings are shown in the
831accompanying F<rename> file.
832
833You can explore various information from the Unicode data files using
834the C<Unicode::UCD> module.
835
836=back
837
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838=head1 UNICODE IN OLDER PERLS
839
840If you cannot upgrade your Perl to 5.8.0 or later, you can still
841do some Unicode processing by using the modules C<Unicode::String>,
842C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
843If you have the GNU recode installed, you can also use the
844Perl frontend C<Convert::Recode> for character conversions.
845
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846The following are fast conversions from ISO 8859-1 (Latin-1) bytes
847to UTF-8 bytes, the code works even with older Perl 5 versions.
848
849 # ISO 8859-1 to UTF-8
850 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
851
852 # UTF-8 to ISO 8859-1
853 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
854
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855=head1 SEE ALSO
856
857L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>,
858L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD>
859
860=head1 ACKNOWLEDGEMENTS
861
862Thanks to the kind readers of the perl5-porters@perl.org,
863perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
864mailing lists for their valuable feedback.
865
866=head1 AUTHOR, COPYRIGHT, AND LICENSE
867
be3c0a43 868Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi>
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869
870This document may be distributed under the same terms as Perl itself.