This is a live mirror of the Perl 5 development currently hosted at https://github.com/perl/perl5
Small doc tweaks.
[perl5.git] / pod / perluniintro.pod
CommitLineData
ba62762e
JH
1=head1 NAME
2
07fcf8ff 3perluniintro - Perl Unicode introduction
ba62762e
JH
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
a5f0baef
JH
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.
ba62762e
JH
61
62With this "as a whole" view of characters, the number of characters is
a5f0baef
JH
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.
ba62762e
JH
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
ba62762e
JH
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
JH
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.)
ba62762e
JH
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
4192de81
JH
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
a5f0baef
JH
1470xFF or less, Perl uses the native eight-bit character set.
148Otherwise, it uses UTF-8.
4192de81
JH
149
150A user of Perl does not normally need to know nor care how Perl happens
151to encodes its internal strings, but it becomes relevant when outputting
152Unicode strings to a stream without a discipline (one with the "default
153default"). In such a case, the raw bytes used internally (the native
154character set or UTF-8, as appropriate for each string) will be used,
155and if warnings are turned on, a "Wide character" warning will be issued
156if those strings contain a character beyond 0x00FF.
157
158For example,
159
160 perl -w -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
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
a5f0baef
JH
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").
ba62762e
JH
181
182=head2 Creating Unicode
183
a5f0baef
JH
184To create Unicode characters in literals for code points above 0xFF,
185use the C<\x{...}> notation in doublequoted strings:
ba62762e
JH
186
187 my $smiley = "\x{263a}";
188
8baee566 189Similarly in regular expression literals
ba62762e
JH
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
a5f0baef
JH
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()>.
ba62762e
JH
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
8a5e5dd5
JH
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
ba62762e
JH
224=head2 Handling Unicode
225
226Handling Unicode is for the most part transparent: just use the
227strings as usual. Functions like C<index()>, C<length()>, and
228C<substr()> will work on the Unicode characters; regular expressions
229will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
230
231Note that Perl does B<not> consider combining character sequences
232to be characters, such for example
233
234 use charnames ':full';
235 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
236
237will print 2, not 1. The only exception is that regular expressions
238have C<\X> for matching a combining character sequence.
239
240When life is not quite so transparent is working with legacy
241encodings, and I/O, and certain special cases.
242
243=head2 Legacy Encodings
244
245When you combine legacy data and Unicode the legacy data needs
246to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
247applicable) is assumed. You can override this assumption by
248using the C<encoding> pragma, for example
249
250 use encoding 'latin2'; # ISO 8859-2
251
252in which case literals (string or regular expression) and chr/ord
253in your whole script are assumed to produce Unicode characters from
254ISO 8859-2 code points. Note that the matching for the encoding
255names is forgiving: instead of C<latin2> you could have said
256C<Latin 2>, or C<iso8859-2>, and so forth. With just
257
258 use encoding;
259
260first the environment variable C<PERL_ENCODING> will be consulted,
261and if that doesn't exist, ISO 8859-1 (Latin 1) will be assumed.
262
263The C<Encode> module knows about many encodings and it has interfaces
264for doing conversions between those encodings:
265
266 use Encode 'from_to';
267 from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8
268
269=head2 Unicode I/O
270
8baee566 271Normally, writing out Unicode data
ba62762e 272
8baee566 273 print FH $some_string_with_unicode, "\n";
ba62762e 274
8baee566 275produces raw bytes that Perl happens to use to internally encode the
a5f0baef
JH
276Unicode string (which depends on the system, as well as what
277characters happen to be in the string at the time). If any of the
278characters are at code points 0x100 or above, you will get a warning
279if you use C<-w> or C<use warnings>. To ensure that the output is
280explicitly rendered in the encoding you desire (and to avoid the
281warning), open the stream with the desired encoding. Some examples:
ba62762e 282
8baee566
JF
283 open FH, ">:ucs2", "file"
284 open FH, ">:utf8", "file";
285 open FH, ">:Shift-JIS", "file";
1d7919c5
JH
286
287and on already open streams use C<binmode()>:
288
8baee566 289 binmode(STDOUT, ":ucs2");
1d7919c5 290 binmode(STDOUT, ":utf8");
8baee566 291 binmode(STDOUT, ":Shift-JIS");
1d7919c5 292
8baee566 293See documentation for the C<Encode> module for many supported encodings.
ba62762e 294
a5f0baef
JH
295Reading in a file that you know happens to be encoded in one of the
296Unicode encodings does not magically turn the data into Unicode in
297Perl's eyes. To do that, specify the appropriate discipline when
298opening files
ba62762e
JH
299
300 open(my $fh,'<:utf8', 'anything');
8baee566
JF
301 my $line_of_unicode = <$fh>;
302
303 open(my $fh,'<:Big5', 'anything');
304 my $line_of_unicode = <$fh>;
ba62762e
JH
305
306The I/O disciplines can also be specified more flexibly with
307the C<open> pragma; see L<open>:
308
1d7919c5
JH
309 use open ':utf8'; # input and output default discipline will be UTF-8
310 open X, ">file";
311 print X chr(0x100), "\n";
ba62762e 312 close X;
1d7919c5 313 open Y, "<file";
ba62762e
JH
314 printf "%#x\n", ord(<Y>); # this should print 0x100
315 close Y;
316
317With the C<open> pragma you can use the C<:locale> discipline
318
1ecefa54
JH
319 $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R';
320 # the :locale will probe the locale environment variables like LC_ALL
ba62762e
JH
321 use open OUT => ':locale'; # russki parusski
322 open(O, ">koi8");
323 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
324 close O;
325 open(I, "<koi8");
326 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
327 close I;
328
329or you can also use the C<':encoding(...)'> discipline
330
331 open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
8baee566 332 my $line_of_unicode = <$epic>;
ba62762e 333
8baee566
JF
334These methods install a transparent filter on the I/O stream that
335converts data from the specified encoding when it is read in from the
a5f0baef 336stream. The result is always Unicode.
ba62762e
JH
337
338The L<open> pragma affects all the C<open()> calls after the pragma by
339setting default disciplines. If you want to affect only certain
340streams, use explicit disciplines directly in the C<open()> call.
341
342You can switch encodings on an already opened stream by using
8baee566 343C<binmode()>; see L<perlfunc/binmode>.
ba62762e 344
1ecefa54
JH
345The C<:locale> does not currently (as of Perl 5.8.0) work with
346C<open()> and C<binmode()>, only with the C<open> pragma. The
8baee566 347C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
1ecefa54 348C<binmode()>, and the C<open> pragma.
ba62762e 349
8baee566 350Similarly, you may use these I/O disciplines on output streams to
a5f0baef
JH
351automatically convert Unicode to the specified encoding when it is
352written to the stream. For example, the following snippet copies the
353contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
354the file "text.utf8", encoded as UTF-8:
ba62762e 355
8baee566
JF
356 open(my $nihongo, '<:encoding(iso2022-jp)', 'text.jis');
357 open(my $unicode, '>:utf8', 'text.utf8');
358 while (<$nihongo>) { print $unicode }
ba62762e
JH
359
360The naming of encodings, both by the C<open()> and by the C<open>
361pragma, is similarly understanding as with the C<encoding> pragma:
362C<koi8-r> and C<KOI8R> will both be understood.
363
364Common encodings recognized by ISO, MIME, IANA, and various other
8baee566 365standardisation organisations are recognised; for a more detailed
ba62762e
JH
366list see L<Encode>.
367
368C<read()> reads characters and returns the number of characters.
369C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
370and C<sysseek()>.
371
8baee566
JF
372Notice that because of the default behaviour of not doing any
373conversion upon input if there is no default discipline,
ba62762e 374it is easy to mistakenly write code that keeps on expanding a file
8baee566 375by repeatedly encoding:
ba62762e
JH
376
377 # BAD CODE WARNING
378 open F, "file";
8baee566 379 local $/; ## read in the whole file of 8-bit characters
ba62762e
JH
380 $t = <F>;
381 close F;
382 open F, ">:utf8", "file";
8baee566 383 print F $t; ## convert to UTF-8 on output
ba62762e
JH
384 close F;
385
386If you run this code twice, the contents of the F<file> will be twice
1d7919c5
JH
387UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or
388explicitly opening also the F<file> for input as UTF-8.
ba62762e 389
0c901d84
JH
390B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
391Perl has been built with the new "perlio" feature. Almost all
392Perl 5.8 platforms do use "perlio", though: you can see whether
393yours is by running "perl -V" and looking for C<useperlio=define>.
394
1ecefa54
JH
395=head2 Displaying Unicode As Text
396
397Sometimes you might want to display Perl scalars containing Unicode as
8baee566 398simple ASCII (or EBCDIC) text. The following subroutine converts
1ecefa54
JH
399its argument so that Unicode characters with code points greater than
400255 are displayed as "\x{...}", control characters (like "\n") are
8baee566 401displayed as "\x..", and the rest of the characters as themselves:
1ecefa54 402
58c274a1
JF
403 sub nice_string {
404 join("",
405 map { $_ > 255 ? # if wide character...
8baee566 406 sprintf("\\x{%04X}", $_) : # \x{...}
58c274a1 407 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
8baee566 408 sprintf("\\x%02X", $_) : # \x..
58c274a1
JF
409 chr($_) # else as themselves
410 } unpack("U*", $_[0])); # unpack Unicode characters
411 }
412
413For example,
414
415 nice_string("foo\x{100}bar\n")
416
8baee566 417returns:
58c274a1 418
8baee566 419 "foo\x{0100}bar\x0A"
1ecefa54 420
ba62762e
JH
421=head2 Special Cases
422
423=over 4
424
425=item *
426
427Bit Complement Operator ~ And vec()
428
1d9bf7bb
JF
429The bit complement operator C<~> may produce surprising results if used on
430strings containing characters with ordinal values above 255. In such a
431case, the results are consistent with the internal encoding of the
432characters, but not with much else. So don't do that. Similarly for vec():
433you will be operating on the internally encoded bit patterns of the Unicode
434characters, not on the code point values, which is very probably not what
435you want.
ba62762e
JH
436
437=item *
438
8baee566
JF
439Peeking At Perl's Internal Encoding
440
441Normal users of Perl should never care how Perl encodes any particular
a5f0baef
JH
442Unicode string (because the normal ways to get at the contents of a
443string with Unicode -- via input and output -- should always be via
444explicitly-defined I/O disciplines). But if you must, there are two
445ways of looking behind the scenes.
ba62762e
JH
446
447One way of peeking inside the internal encoding of Unicode characters
448is to use C<unpack("C*", ...> to get the bytes, or C<unpack("H*", ...)>
449to display the bytes:
450
8baee566 451 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
ba62762e
JH
452 print join(" ", unpack("H*", pack("U", 0x100))), "\n";
453
454Yet another way would be to use the Devel::Peek module:
455
456 perl -MDevel::Peek -e 'Dump(chr(0x100))'
457
8baee566 458That shows the UTF8 flag in FLAGS and both the UTF-8 bytes
ba62762e
JH
459and Unicode characters in PV. See also later in this document
460the discussion about the C<is_utf8> function of the C<Encode> module.
461
462=back
463
464=head2 Advanced Topics
465
466=over 4
467
468=item *
469
470String Equivalence
471
472The question of string equivalence turns somewhat complicated
473in Unicode: what do you mean by equal?
474
07698885
RGS
475(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
476C<LATIN CAPITAL LETTER A>?)
ba62762e 477
a5f0baef
JH
478The short answer is that by default Perl compares equivalence (C<eq>,
479C<ne>) based only on code points of the characters. In the above
480case, the answer is no (because 0x00C1 != 0x0041). But sometimes any
ba62762e
JH
481CAPITAL LETTER As being considered equal, or even any As of any case,
482would be desirable.
483
484The long answer is that you need to consider character normalization
485and casing issues: see L<Unicode::Normalize>, and Unicode Technical
486Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
487Mappings>, http://www.unicode.org/unicode/reports/tr15/
488http://www.unicode.org/unicode/reports/tr21/
489
58c274a1 490As of Perl 5.8.0, regular expression case-ignoring matching
ba62762e
JH
491implements only 1:1 semantics: one character matches one character.
492In I<Case Mappings> both 1:N and N:1 matches are defined.
493
494=item *
495
496String Collation
497
498People like to see their strings nicely sorted, or as Unicode
499parlance goes, collated. But again, what do you mean by collate?
500
07698885
RGS
501(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
502C<LATIN CAPITAL LETTER A WITH GRAVE>?)
ba62762e 503
58c274a1 504The short answer is that by default, Perl compares strings (C<lt>,
ba62762e 505C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
58c274a1 506characters. In the above case, the answer is "after", since 0x00C1 > 0x00C0.
ba62762e
JH
507
508The long answer is that "it depends", and a good answer cannot be
509given without knowing (at the very least) the language context.
510See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
511http://www.unicode.org/unicode/reports/tr10/
512
513=back
514
515=head2 Miscellaneous
516
517=over 4
518
519=item *
520
3ff56b75 521Character Ranges and Classes
ba62762e
JH
522
523Character ranges in regular expression character classes (C</[a-z]/>)
524and in the C<tr///> (also known as C<y///>) operator are not magically
58c274a1 525Unicode-aware. What this means that C<[A-Za-z]> will not magically start
ba62762e 526to mean "all alphabetic letters" (not that it does mean that even for
3ff56b75 5278-bit characters, you should be using C</[[:alpha:]]/> for that).
ba62762e 528
a5f0baef
JH
529For specifying things like that in regular expressions, you can use
530the various Unicode properties, C<\pL> or perhaps C<\p{Alphabetic}>,
531in this particular case. You can use Unicode code points as the end
532points of character ranges, but that means that particular code point
3ff56b75
JH
533range, nothing more. For further information (there are dozens
534of Unicode character classes), see L<perlunicode>.
ba62762e
JH
535
536=item *
537
538String-To-Number Conversions
539
540Unicode does define several other decimal (and numeric) characters
541than just the familiar 0 to 9, such as the Arabic and Indic digits.
542Perl does not support string-to-number conversion for digits other
58c274a1 543than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
ba62762e
JH
544
545=back
546
547=head2 Questions With Answers
548
549=over 4
550
551=item Will My Old Scripts Break?
552
553Very probably not. Unless you are generating Unicode characters
554somehow, any old behaviour should be preserved. About the only
555behaviour that has changed and which could start generating Unicode
556is the old behaviour of C<chr()> where supplying an argument more
557than 255 produced a character modulo 255 (for example, C<chr(300)>
558was equal to C<chr(45)>).
559
560=item How Do I Make My Scripts Work With Unicode?
561
562Very little work should be needed since nothing changes until you
563somehow generate Unicode data. The greatest trick will be getting
564input as Unicode, and for that see the earlier I/O discussion.
565
566=item How Do I Know Whether My String Is In Unicode?
567
568You shouldn't care. No, you really shouldn't. If you have
569to care (beyond the cases described above), it means that we
570didn't get the transparency of Unicode quite right.
571
572Okay, if you insist:
573
574 use Encode 'is_utf8';
575 print is_utf8($string) ? 1 : 0, "\n";
576
577But note that this doesn't mean that any of the characters in the
578string are necessary UTF-8 encoded, or that any of the characters have
579code points greater than 0xFF (255) or even 0x80 (128), or that the
580string has any characters at all. All the C<is_utf8()> does is to
581return the value of the internal "utf8ness" flag attached to the
582$string. If the flag is on, characters added to that string will be
583automatically upgraded to UTF-8 (and even then only if they really
584need to be upgraded, that is, if their code point is greater than 0xFF).
585
586Sometimes you might really need to know the byte length of a string
587instead of the character length. For that use the C<bytes> pragma
588and its only defined function C<length()>:
589
590 my $unicode = chr(0x100);
591 print length($unicode), "\n"; # will print 1
592 use bytes;
593 print length($unicode), "\n"; # will print 2 (the 0xC4 0x80 of the UTF-8)
594
8baee566 595=item How Do I Detect Data That's Not Valid In a Particular Encoding
ba62762e 596
8baee566
JF
597Use the C<Encode> package to try converting it.
598For example,
ba62762e
JH
599
600 use Encode 'encode_utf8';
8baee566 601 if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) {
ba62762e
JH
602 # valid
603 } else {
604 # invalid
605 }
606
8baee566 607For UTF-8 only, you can use:
ba62762e
JH
608
609 use warnings;
8baee566 610 @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
ba62762e 611
8baee566
JF
612If invalid, a C<Malformed UTF-8 character (byte 0x##) in
613unpack> is produced. The "U0" means "expect strictly UTF-8
614encoded Unicode". Without that the C<unpack("U*", ...)>
615would accept also data like C<chr(0xFF>).
ba62762e 616
8baee566 617=item How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
ba62762e 618
8baee566
JF
619This probably isn't as useful as you might think.
620Normally, you shouldn't need to.
ba62762e 621
a5f0baef
JH
622In one sense, what you are asking doesn't make much sense: Encodings
623are for characters, and binary data is not "characters", so converting
624"data" into some encoding isn't meaningful unless you know in what
625character set and encoding the binary data is in, in which case it's
626not binary data, now is it?
8baee566
JF
627
628If you have a raw sequence of bytes that you know should be interpreted via
629a particular encoding, you can use C<Encode>:
ba62762e
JH
630
631 use Encode 'from_to';
632 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
633
8baee566
JF
634The call to from_to() changes the bytes in $data, but nothing material
635about the nature of the string has changed as far as Perl is concerned.
636Both before and after the call, the string $data contains just a bunch of
6378-bit bytes. As far as Perl is concerned, the encoding of the string (as
638Perl sees it) remains as "system-native 8-bit bytes".
639
640You might relate this to a fictional 'Translate' module:
641
642 use Translate;
643 my $phrase = "Yes";
644 Translate::from_to($phrase, 'english', 'deutsch');
645 ## phrase now contains "Ja"
ba62762e 646
8baee566
JF
647The contents of the string changes, but not the nature of the string.
648Perl doesn't know any more after the call than before that the contents
649of the string indicates the affirmative.
ba62762e 650
a5f0baef
JH
651Back to converting data, if you have (or want) data in your system's
652native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
653pack/unpack to convert to/from Unicode.
ba62762e 654
8baee566
JF
655 $native_string = pack("C*", unpack("U*", $Unicode_string));
656 $Unicode_string = pack("U*", unpack("C*", $native_string));
ba62762e
JH
657
658If you have a sequence of bytes you B<know> is valid UTF-8,
659but Perl doesn't know it yet, you can make Perl a believer, too:
660
661 use Encode 'decode_utf8';
8baee566 662 $Unicode = decode_utf8($bytes);
ba62762e
JH
663
664You can convert well-formed UTF-8 to a sequence of bytes, but if
665you just want to convert random binary data into UTF-8, you can't.
666Any random collection of bytes isn't well-formed UTF-8. You can
667use C<unpack("C*", $string)> for the former, and you can create
8baee566 668well-formed Unicode data by C<pack("U*", 0xff, ...)>.
ba62762e
JH
669
670=item How Do I Display Unicode? How Do I Input Unicode?
671
672See http://www.hclrss.demon.co.uk/unicode/ and
673http://www.cl.cam.ac.uk/~mgk25/unicode.html
674
675=item How Does Unicode Work With Traditional Locales?
676
677In Perl, not very well. Avoid using locales through the C<locale>
678pragma. Use only one or the other.
679
680=back
681
682=head2 Hexadecimal Notation
683
684The Unicode standard prefers using hexadecimal notation because that
685shows better the division of Unicode into blocks of 256 characters.
686Hexadecimal is also simply shorter than decimal. You can use decimal
687notation, too, but learning to use hexadecimal just makes life easier
688with the Unicode standard.
689
690The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
691a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
692four bits, or half a byte. C<print 0x..., "\n"> will show a
693hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
694show a decimal number in hexadecimal. If you have just the
a5f0baef 695"hexdigits" of a hexadecimal number, you can use the C<hex()> function.
ba62762e
JH
696
697 print 0x0009, "\n"; # 9
698 print 0x000a, "\n"; # 10
699 print 0x000f, "\n"; # 15
700 print 0x0010, "\n"; # 16
701 print 0x0011, "\n"; # 17
702 print 0x0100, "\n"; # 256
703
704 print 0x0041, "\n"; # 65
705
706 printf "%x\n", 65; # 41
707 printf "%#x\n", 65; # 0x41
708
709 print hex("41"), "\n"; # 65
710
711=head2 Further Resources
712
713=over 4
714
715=item *
716
717Unicode Consortium
718
719 http://www.unicode.org/
720
721=item *
722
723Unicode FAQ
724
725 http://www.unicode.org/unicode/faq/
726
727=item *
728
729Unicode Glossary
730
731 http://www.unicode.org/glossary/
732
733=item *
734
735Unicode Useful Resources
736
737 http://www.unicode.org/unicode/onlinedat/resources.html
738
739=item *
740
741Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
742
743 http://www.hclrss.demon.co.uk/unicode/
744
745=item *
746
747UTF-8 and Unicode FAQ for Unix/Linux
748
749 http://www.cl.cam.ac.uk/~mgk25/unicode.html
750
751=item *
752
753Legacy Character Sets
754
755 http://www.czyborra.com/
756 http://www.eki.ee/letter/
757
758=item *
759
760The Unicode support files live within the Perl installation in the
761directory
762
763 $Config{installprivlib}/unicore
764
765in Perl 5.8.0 or newer, and
766
767 $Config{installprivlib}/unicode
768
769in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
770avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
771The main Unicode data file is F<Unicode.txt> (or F<Unicode.301> in
772Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
773
774 perl "-V:installprivlib"
775
776Note that some of the files have been renamed from the Unicode
777standard since the Perl installation tries to live by the "8.3"
778filenaming restrictions. The renamings are shown in the
779accompanying F<rename> file.
780
781You can explore various information from the Unicode data files using
782the C<Unicode::UCD> module.
783
784=back
785
f6edf83b
JH
786=head1 UNICODE IN OLDER PERLS
787
788If you cannot upgrade your Perl to 5.8.0 or later, you can still
789do some Unicode processing by using the modules C<Unicode::String>,
790C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
791If you have the GNU recode installed, you can also use the
792Perl frontend C<Convert::Recode> for character conversions.
793
aaef10c5
JH
794The following are fast conversions from ISO 8859-1 (Latin-1) bytes
795to UTF-8 bytes, the code works even with older Perl 5 versions.
796
797 # ISO 8859-1 to UTF-8
798 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
799
800 # UTF-8 to ISO 8859-1
801 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
802
ba62762e
JH
803=head1 SEE ALSO
804
805L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>,
806L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD>
807
808=head1 ACKNOWLEDGEMENTS
809
810Thanks to the kind readers of the perl5-porters@perl.org,
811perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
812mailing lists for their valuable feedback.
813
814=head1 AUTHOR, COPYRIGHT, AND LICENSE
815
816Copyright 2001 Jarkko Hietaniemi <jhi@iki.fi>
817
818This document may be distributed under the same terms as Perl itself.