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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
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130Perl script itself is encoded in UTF-8, you can use UTF-8 in your
131variable and subroutine names, and in your string and regular
132expression literals, by saying C<use utf8>. This is not the default
133because that would break existing scripts having legacy 8-bit data in
134them.)
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135
136=head2 Perl's Unicode Model
137
138Perl supports both the old, pre-5.6, model of strings of eight-bit
139native bytes, and strings of Unicode characters. The principle is
140that Perl tries to keep its data as eight-bit bytes for as long as
141possible, but as soon as Unicodeness cannot be avoided, the data is
142transparently upgraded to Unicode.
143
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144Internally, Perl currently uses either whatever the native eight-bit
145character set of the platform (for example Latin-1) or UTF-8 to encode
146Unicode strings. Specifically, if all code points in the string are
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1470xFF or less, Perl uses the native eight-bit character set.
148Otherwise, it uses UTF-8.
4192de81 149
7ca610e8 150A user of Perl does not normally need to know nor care how Perl
20ba30f4 151happens to encode its internal strings, but it becomes relevant when
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152outputting Unicode strings to a stream without a discipline (one with
153the "default default"). In such a case, the raw bytes used internally
154(the native character set or UTF-8, as appropriate for each string)
155will be used, and a "Wide character" warning will be issued if those
156strings contain a character beyond 0x00FF.
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157
158For example,
159
7ca610e8 160 perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
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161
162produces a fairly useless mixture of native bytes and UTF-8, as well
163as a warning.
164
165To output UTF-8 always, use the ":utf8" output discipline. Prepending
166
167 binmode(STDOUT, ":utf8");
168
169to this sample program ensures the output is completely UTF-8, and
4049dcd4 170of course, removes the warning.
ba62762e 171
8baee566 172Perl 5.8.0 also supports Unicode on EBCDIC platforms. There, the
ba62762e 173support is somewhat harder to implement since additional conversions
8baee566 174are needed at every step. Because of these difficulties, the Unicode
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175support isn't quite as full as in other, mainly ASCII-based, platforms
176(the Unicode support is better than in the 5.6 series, which didn't
177work much at all for EBCDIC platform). On EBCDIC platforms, the
178internal Unicode encoding form is UTF-EBCDIC instead of UTF-8 (the
179difference is that as UTF-8 is "ASCII-safe" in that ASCII characters
180encode to UTF-8 as-is, UTF-EBCDIC is "EBCDIC-safe").
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181
182=head2 Creating Unicode
183
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184To create Unicode characters in literals for code points above 0xFF,
185use the C<\x{...}> notation in doublequoted strings:
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186
187 my $smiley = "\x{263a}";
188
8baee566 189Similarly in regular expression literals
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190
191 $smiley =~ /\x{263a}/;
192
193At run-time you can use C<chr()>:
194
195 my $hebrew_alef = chr(0x05d0);
196
197(See L</"Further Resources"> for how to find all these numeric codes.)
198
199Naturally, C<ord()> will do the reverse: turn a character to a code point.
200
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201Note that C<\x..> (no C<{}> and only two hexadecimal digits),
202C<\x{...}>, and C<chr(...)> for arguments less than 0x100 (decimal
203256) generate an eight-bit character for backward compatibility with
204older Perls. For arguments of 0x100 or more, Unicode characters are
205always produced. If you want to force the production of Unicode
206characters regardless of the numeric value, use C<pack("U", ...)>
207instead of C<\x..>, C<\x{...}>, or C<chr()>.
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208
209You can also use the C<charnames> pragma to invoke characters
210by name in doublequoted strings:
211
212 use charnames ':full';
213 my $arabic_alef = "\N{ARABIC LETTER ALEF}";
214
215And, as mentioned above, you can also C<pack()> numbers into Unicode
216characters:
217
218 my $georgian_an = pack("U", 0x10a0);
219
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220Note that both C<\x{...}> and C<\N{...}> are compile-time string
221constants: you cannot use variables in them. if you want similar
222run-time functionality, use C<chr()> and C<charnames::vianame()>.
223
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224Also note that if all the code points for pack "U" are below 0x100,
225bytes will be generated, just like if you were using C<chr()>.
226
227 my $bytes = pack("U*", 0x80, 0xFF);
228
229If you want to force the result to Unicode characters, use the special
230C<"U0"> prefix. It consumes no arguments but forces the result to be
231in Unicode characters, instead of bytes.
232
233 my $chars = pack("U0U*", 0x80, 0xFF);
234
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235=head2 Handling Unicode
236
237Handling Unicode is for the most part transparent: just use the
238strings as usual. Functions like C<index()>, C<length()>, and
239C<substr()> will work on the Unicode characters; regular expressions
240will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
241
242Note that Perl does B<not> consider combining character sequences
243to be characters, such for example
244
245 use charnames ':full';
246 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
247
248will print 2, not 1. The only exception is that regular expressions
249have C<\X> for matching a combining character sequence.
250
251When life is not quite so transparent is working with legacy
252encodings, and I/O, and certain special cases.
253
254=head2 Legacy Encodings
255
256When you combine legacy data and Unicode the legacy data needs
257to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
258applicable) is assumed. You can override this assumption by
259using the C<encoding> pragma, for example
260
261 use encoding 'latin2'; # ISO 8859-2
262
263in which case literals (string or regular expression) and chr/ord
264in your whole script are assumed to produce Unicode characters from
265ISO 8859-2 code points. Note that the matching for the encoding
266names is forgiving: instead of C<latin2> you could have said
267C<Latin 2>, or C<iso8859-2>, and so forth. With just
268
269 use encoding;
270
271first the environment variable C<PERL_ENCODING> will be consulted,
272and if that doesn't exist, ISO 8859-1 (Latin 1) will be assumed.
273
274The C<Encode> module knows about many encodings and it has interfaces
275for doing conversions between those encodings:
276
277 use Encode 'from_to';
278 from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8
279
280=head2 Unicode I/O
281
8baee566 282Normally, writing out Unicode data
ba62762e 283
8baee566 284 print FH $some_string_with_unicode, "\n";
ba62762e 285
8baee566 286produces raw bytes that Perl happens to use to internally encode the
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287Unicode string (which depends on the system, as well as what
288characters happen to be in the string at the time). If any of the
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289characters are at code points 0x100 or above, you will get a warning.
290To ensure that the output is explicitly rendered in the encoding you
291desire (and to avoid the warning), open the stream with the desired
292encoding. Some examples:
ba62762e 293
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294 open FH, ">:ucs2", "file"
295 open FH, ">:utf8", "file";
296 open FH, ">:Shift-JIS", "file";
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297
298and on already open streams use C<binmode()>:
299
8baee566 300 binmode(STDOUT, ":ucs2");
1d7919c5 301 binmode(STDOUT, ":utf8");
8baee566 302 binmode(STDOUT, ":Shift-JIS");
1d7919c5 303
8baee566 304See documentation for the C<Encode> module for many supported encodings.
ba62762e 305
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306Reading in a file that you know happens to be encoded in one of the
307Unicode encodings does not magically turn the data into Unicode in
308Perl's eyes. To do that, specify the appropriate discipline when
309opening files
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310
311 open(my $fh,'<:utf8', 'anything');
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312 my $line_of_unicode = <$fh>;
313
314 open(my $fh,'<:Big5', 'anything');
315 my $line_of_unicode = <$fh>;
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316
317The I/O disciplines can also be specified more flexibly with
318the C<open> pragma; see L<open>:
319
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320 use open ':utf8'; # input and output default discipline will be UTF-8
321 open X, ">file";
322 print X chr(0x100), "\n";
ba62762e 323 close X;
1d7919c5 324 open Y, "<file";
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325 printf "%#x\n", ord(<Y>); # this should print 0x100
326 close Y;
327
328With the C<open> pragma you can use the C<:locale> discipline
329
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330 $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R';
331 # the :locale will probe the locale environment variables like LC_ALL
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332 use open OUT => ':locale'; # russki parusski
333 open(O, ">koi8");
334 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
335 close O;
336 open(I, "<koi8");
337 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
338 close I;
339
340or you can also use the C<':encoding(...)'> discipline
341
342 open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
8baee566 343 my $line_of_unicode = <$epic>;
ba62762e 344
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345These methods install a transparent filter on the I/O stream that
346converts data from the specified encoding when it is read in from the
a5f0baef 347stream. The result is always Unicode.
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348
349The L<open> pragma affects all the C<open()> calls after the pragma by
350setting default disciplines. If you want to affect only certain
351streams, use explicit disciplines directly in the C<open()> call.
352
353You can switch encodings on an already opened stream by using
8baee566 354C<binmode()>; see L<perlfunc/binmode>.
ba62762e 355
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356The C<:locale> does not currently (as of Perl 5.8.0) work with
357C<open()> and C<binmode()>, only with the C<open> pragma. The
8baee566 358C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
1ecefa54 359C<binmode()>, and the C<open> pragma.
ba62762e 360
8baee566 361Similarly, you may use these I/O disciplines on output streams to
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362automatically convert Unicode to the specified encoding when it is
363written to the stream. For example, the following snippet copies the
364contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
365the file "text.utf8", encoded as UTF-8:
ba62762e 366
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367 open(my $nihongo, '<:encoding(iso2022-jp)', 'text.jis');
368 open(my $unicode, '>:utf8', 'text.utf8');
369 while (<$nihongo>) { print $unicode }
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370
371The naming of encodings, both by the C<open()> and by the C<open>
372pragma, is similarly understanding as with the C<encoding> pragma:
373C<koi8-r> and C<KOI8R> will both be understood.
374
375Common encodings recognized by ISO, MIME, IANA, and various other
8baee566 376standardisation organisations are recognised; for a more detailed
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377list see L<Encode>.
378
379C<read()> reads characters and returns the number of characters.
380C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
381and C<sysseek()>.
382
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383Notice that because of the default behaviour of not doing any
384conversion upon input if there is no default discipline,
ba62762e 385it is easy to mistakenly write code that keeps on expanding a file
8baee566 386by repeatedly encoding:
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387
388 # BAD CODE WARNING
389 open F, "file";
8baee566 390 local $/; ## read in the whole file of 8-bit characters
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391 $t = <F>;
392 close F;
393 open F, ">:utf8", "file";
8baee566 394 print F $t; ## convert to UTF-8 on output
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395 close F;
396
397If you run this code twice, the contents of the F<file> will be twice
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398UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or
399explicitly opening also the F<file> for input as UTF-8.
ba62762e 400
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401B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
402Perl has been built with the new "perlio" feature. Almost all
403Perl 5.8 platforms do use "perlio", though: you can see whether
404yours is by running "perl -V" and looking for C<useperlio=define>.
405
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406=head2 Displaying Unicode As Text
407
408Sometimes you might want to display Perl scalars containing Unicode as
8baee566 409simple ASCII (or EBCDIC) text. The following subroutine converts
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410its argument so that Unicode characters with code points greater than
411255 are displayed as "\x{...}", control characters (like "\n") are
8baee566 412displayed as "\x..", and the rest of the characters as themselves:
1ecefa54 413
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414 sub nice_string {
415 join("",
416 map { $_ > 255 ? # if wide character...
8baee566 417 sprintf("\\x{%04X}", $_) : # \x{...}
58c274a1 418 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
8baee566 419 sprintf("\\x%02X", $_) : # \x..
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420 chr($_) # else as themselves
421 } unpack("U*", $_[0])); # unpack Unicode characters
422 }
423
424For example,
425
426 nice_string("foo\x{100}bar\n")
427
8baee566 428returns:
58c274a1 429
8baee566 430 "foo\x{0100}bar\x0A"
1ecefa54 431
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432=head2 Special Cases
433
434=over 4
435
436=item *
437
438Bit Complement Operator ~ And vec()
439
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440The bit complement operator C<~> may produce surprising results if used on
441strings containing characters with ordinal values above 255. In such a
442case, the results are consistent with the internal encoding of the
443characters, but not with much else. So don't do that. Similarly for vec():
444you will be operating on the internally encoded bit patterns of the Unicode
445characters, not on the code point values, which is very probably not what
446you want.
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447
448=item *
449
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450Peeking At Perl's Internal Encoding
451
452Normal users of Perl should never care how Perl encodes any particular
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453Unicode string (because the normal ways to get at the contents of a
454string with Unicode -- via input and output -- should always be via
455explicitly-defined I/O disciplines). But if you must, there are two
456ways of looking behind the scenes.
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457
458One way of peeking inside the internal encoding of Unicode characters
459is to use C<unpack("C*", ...> to get the bytes, or C<unpack("H*", ...)>
460to display the bytes:
461
8baee566 462 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
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463 print join(" ", unpack("H*", pack("U", 0x100))), "\n";
464
465Yet another way would be to use the Devel::Peek module:
466
467 perl -MDevel::Peek -e 'Dump(chr(0x100))'
468
8baee566 469That shows the UTF8 flag in FLAGS and both the UTF-8 bytes
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470and Unicode characters in PV. See also later in this document
471the discussion about the C<is_utf8> function of the C<Encode> module.
472
473=back
474
475=head2 Advanced Topics
476
477=over 4
478
479=item *
480
481String Equivalence
482
483The question of string equivalence turns somewhat complicated
484in Unicode: what do you mean by equal?
485
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486(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
487C<LATIN CAPITAL LETTER A>?)
ba62762e 488
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489The short answer is that by default Perl compares equivalence (C<eq>,
490C<ne>) based only on code points of the characters. In the above
491case, the answer is no (because 0x00C1 != 0x0041). But sometimes any
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492CAPITAL LETTER As being considered equal, or even any As of any case,
493would be desirable.
494
495The long answer is that you need to consider character normalization
496and casing issues: see L<Unicode::Normalize>, and Unicode Technical
497Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
498Mappings>, http://www.unicode.org/unicode/reports/tr15/
499http://www.unicode.org/unicode/reports/tr21/
500
58c274a1 501As of Perl 5.8.0, regular expression case-ignoring matching
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502implements only 1:1 semantics: one character matches one character.
503In I<Case Mappings> both 1:N and N:1 matches are defined.
504
505=item *
506
507String Collation
508
509People like to see their strings nicely sorted, or as Unicode
510parlance goes, collated. But again, what do you mean by collate?
511
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512(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
513C<LATIN CAPITAL LETTER A WITH GRAVE>?)
ba62762e 514
58c274a1 515The short answer is that by default, Perl compares strings (C<lt>,
ba62762e 516C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
58c274a1 517characters. In the above case, the answer is "after", since 0x00C1 > 0x00C0.
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518
519The long answer is that "it depends", and a good answer cannot be
520given without knowing (at the very least) the language context.
521See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
522http://www.unicode.org/unicode/reports/tr10/
523
524=back
525
526=head2 Miscellaneous
527
528=over 4
529
530=item *
531
3ff56b75 532Character Ranges and Classes
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533
534Character ranges in regular expression character classes (C</[a-z]/>)
535and in the C<tr///> (also known as C<y///>) operator are not magically
58c274a1 536Unicode-aware. What this means that C<[A-Za-z]> will not magically start
ba62762e 537to mean "all alphabetic letters" (not that it does mean that even for
3ff56b75 5388-bit characters, you should be using C</[[:alpha:]]/> for that).
ba62762e 539
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540For specifying things like that in regular expressions, you can use
541the various Unicode properties, C<\pL> or perhaps C<\p{Alphabetic}>,
542in this particular case. You can use Unicode code points as the end
543points of character ranges, but that means that particular code point
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544range, nothing more. For further information (there are dozens
545of Unicode character classes), see L<perlunicode>.
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546
547=item *
548
549String-To-Number Conversions
550
551Unicode does define several other decimal (and numeric) characters
552than just the familiar 0 to 9, such as the Arabic and Indic digits.
553Perl does not support string-to-number conversion for digits other
58c274a1 554than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
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555
556=back
557
558=head2 Questions With Answers
559
560=over 4
561
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562=item
563
564Will My Old Scripts Break?
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565
566Very probably not. Unless you are generating Unicode characters
567somehow, any old behaviour should be preserved. About the only
568behaviour that has changed and which could start generating Unicode
569is the old behaviour of C<chr()> where supplying an argument more
570than 255 produced a character modulo 255 (for example, C<chr(300)>
571was equal to C<chr(45)>).
572
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573=item
574
575How Do I Make My Scripts Work With Unicode?
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576
577Very little work should be needed since nothing changes until you
578somehow generate Unicode data. The greatest trick will be getting
579input as Unicode, and for that see the earlier I/O discussion.
580
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581=item
582
583How Do I Know Whether My String Is In Unicode?
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584
585You shouldn't care. No, you really shouldn't. If you have
586to care (beyond the cases described above), it means that we
587didn't get the transparency of Unicode quite right.
588
589Okay, if you insist:
590
591 use Encode 'is_utf8';
592 print is_utf8($string) ? 1 : 0, "\n";
593
594But note that this doesn't mean that any of the characters in the
595string are necessary UTF-8 encoded, or that any of the characters have
596code points greater than 0xFF (255) or even 0x80 (128), or that the
597string has any characters at all. All the C<is_utf8()> does is to
598return the value of the internal "utf8ness" flag attached to the
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599$string. If the flag is off, the bytes in the scalar are interpreted
600as a single byte encoding. If the flag is on, the bytes in the scalar
601are interpreted as the (multibyte, variable-length) UTF-8 encoded code
602points of the characters. Bytes added to an UTF-8 encoded string are
603automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars
604are merged (doublequoted interpolation, explicit concatenation, and
605printf/sprintf parameter substitution), the result will be UTF-8 encoded
606as if copies of the byte strings were upgraded to UTF-8: for example,
607
608 $a = "ab\x80c";
609 $b = "\x{100}";
610 print "$a = $b\n";
611
612the output string will be UTF-8-encoded "ab\x80c\x{100}\n", but note
613that C<$a> will stay single byte encoded.
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614
615Sometimes you might really need to know the byte length of a string
616instead of the character length. For that use the C<bytes> pragma
617and its only defined function C<length()>:
618
619 my $unicode = chr(0x100);
620 print length($unicode), "\n"; # will print 1
621 use bytes;
622 print length($unicode), "\n"; # will print 2 (the 0xC4 0x80 of the UTF-8)
623
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624=item
625
626How Do I Detect Data That's Not Valid In a Particular Encoding?
ba62762e 627
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628Use the C<Encode> package to try converting it.
629For example,
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630
631 use Encode 'encode_utf8';
8baee566 632 if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) {
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633 # valid
634 } else {
635 # invalid
636 }
637
8baee566 638For UTF-8 only, you can use:
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639
640 use warnings;
8baee566 641 @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
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643If invalid, a C<Malformed UTF-8 character (byte 0x##) in
644unpack> is produced. The "U0" means "expect strictly UTF-8
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645encoded Unicode". Without that the C<unpack("U*", ...)>
646would accept also data like C<chr(0xFF>), similarly to the
647C<pack> as we saw earlier.
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649=item
650
651How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
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653This probably isn't as useful as you might think.
654Normally, you shouldn't need to.
ba62762e 655
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656In one sense, what you are asking doesn't make much sense: Encodings
657are for characters, and binary data is not "characters", so converting
658"data" into some encoding isn't meaningful unless you know in what
659character set and encoding the binary data is in, in which case it's
660not binary data, now is it?
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661
662If you have a raw sequence of bytes that you know should be interpreted via
663a particular encoding, you can use C<Encode>:
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664
665 use Encode 'from_to';
666 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
667
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668The call to from_to() changes the bytes in $data, but nothing material
669about the nature of the string has changed as far as Perl is concerned.
670Both before and after the call, the string $data contains just a bunch of
6718-bit bytes. As far as Perl is concerned, the encoding of the string (as
672Perl sees it) remains as "system-native 8-bit bytes".
673
674You might relate this to a fictional 'Translate' module:
675
676 use Translate;
677 my $phrase = "Yes";
678 Translate::from_to($phrase, 'english', 'deutsch');
679 ## phrase now contains "Ja"
ba62762e 680
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681The contents of the string changes, but not the nature of the string.
682Perl doesn't know any more after the call than before that the contents
683of the string indicates the affirmative.
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685Back to converting data, if you have (or want) data in your system's
686native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
687pack/unpack to convert to/from Unicode.
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689 $native_string = pack("C*", unpack("U*", $Unicode_string));
690 $Unicode_string = pack("U*", unpack("C*", $native_string));
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691
692If you have a sequence of bytes you B<know> is valid UTF-8,
693but Perl doesn't know it yet, you can make Perl a believer, too:
694
695 use Encode 'decode_utf8';
8baee566 696 $Unicode = decode_utf8($bytes);
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697
698You can convert well-formed UTF-8 to a sequence of bytes, but if
699you just want to convert random binary data into UTF-8, you can't.
700Any random collection of bytes isn't well-formed UTF-8. You can
701use C<unpack("C*", $string)> for the former, and you can create
8baee566 702well-formed Unicode data by C<pack("U*", 0xff, ...)>.
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704=item
705
706How Do I Display Unicode? How Do I Input Unicode?
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707
708See http://www.hclrss.demon.co.uk/unicode/ and
709http://www.cl.cam.ac.uk/~mgk25/unicode.html
710
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711=item
712
713How Does Unicode Work With Traditional Locales?
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714
715In Perl, not very well. Avoid using locales through the C<locale>
716pragma. Use only one or the other.
717
718=back
719
720=head2 Hexadecimal Notation
721
722The Unicode standard prefers using hexadecimal notation because that
723shows better the division of Unicode into blocks of 256 characters.
724Hexadecimal is also simply shorter than decimal. You can use decimal
725notation, too, but learning to use hexadecimal just makes life easier
726with the Unicode standard.
727
728The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
729a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
730four bits, or half a byte. C<print 0x..., "\n"> will show a
731hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
732show a decimal number in hexadecimal. If you have just the
a5f0baef 733"hexdigits" of a hexadecimal number, you can use the C<hex()> function.
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734
735 print 0x0009, "\n"; # 9
736 print 0x000a, "\n"; # 10
737 print 0x000f, "\n"; # 15
738 print 0x0010, "\n"; # 16
739 print 0x0011, "\n"; # 17
740 print 0x0100, "\n"; # 256
741
742 print 0x0041, "\n"; # 65
743
744 printf "%x\n", 65; # 41
745 printf "%#x\n", 65; # 0x41
746
747 print hex("41"), "\n"; # 65
748
749=head2 Further Resources
750
751=over 4
752
753=item *
754
755Unicode Consortium
756
757 http://www.unicode.org/
758
759=item *
760
761Unicode FAQ
762
763 http://www.unicode.org/unicode/faq/
764
765=item *
766
767Unicode Glossary
768
769 http://www.unicode.org/glossary/
770
771=item *
772
773Unicode Useful Resources
774
775 http://www.unicode.org/unicode/onlinedat/resources.html
776
777=item *
778
779Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
780
781 http://www.hclrss.demon.co.uk/unicode/
782
783=item *
784
785UTF-8 and Unicode FAQ for Unix/Linux
786
787 http://www.cl.cam.ac.uk/~mgk25/unicode.html
788
789=item *
790
791Legacy Character Sets
792
793 http://www.czyborra.com/
794 http://www.eki.ee/letter/
795
796=item *
797
798The Unicode support files live within the Perl installation in the
799directory
800
801 $Config{installprivlib}/unicore
802
803in Perl 5.8.0 or newer, and
804
805 $Config{installprivlib}/unicode
806
807in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
808avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
551b6b6f 809The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
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810Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
811
812 perl "-V:installprivlib"
813
814Note that some of the files have been renamed from the Unicode
815standard since the Perl installation tries to live by the "8.3"
816filenaming restrictions. The renamings are shown in the
817accompanying F<rename> file.
818
819You can explore various information from the Unicode data files using
820the C<Unicode::UCD> module.
821
822=back
823
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824=head1 UNICODE IN OLDER PERLS
825
826If you cannot upgrade your Perl to 5.8.0 or later, you can still
827do some Unicode processing by using the modules C<Unicode::String>,
828C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
829If you have the GNU recode installed, you can also use the
830Perl frontend C<Convert::Recode> for character conversions.
831
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832The following are fast conversions from ISO 8859-1 (Latin-1) bytes
833to UTF-8 bytes, the code works even with older Perl 5 versions.
834
835 # ISO 8859-1 to UTF-8
836 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
837
838 # UTF-8 to ISO 8859-1
839 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
840
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841=head1 SEE ALSO
842
843L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>,
844L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD>
845
846=head1 ACKNOWLEDGEMENTS
847
848Thanks to the kind readers of the perl5-porters@perl.org,
849perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
850mailing lists for their valuable feedback.
851
852=head1 AUTHOR, COPYRIGHT, AND LICENSE
853
be3c0a43 854Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi>
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855
856This document may be distributed under the same terms as Perl itself.