3 perluniintro - Perl Unicode introduction
7 This document gives a general idea of Unicode and how to use Unicode
12 Unicode is a character set standard which plans to codify all of the
13 writing systems of the world, plus many other symbols.
15 Unicode and ISO/IEC 10646 are coordinated standards that provide code
16 points for characters in almost all modern character set standards,
17 covering more than 30 writing systems and hundreds of languages,
18 including all commercially-important modern languages. All characters
19 in the largest Chinese, Japanese, and Korean dictionaries are also
20 encoded. The standards will eventually cover almost all characters in
21 more than 250 writing systems and thousands of languages.
22 Unicode 1.0 was released in October 1991, and 4.0 in April 2003.
24 A Unicode I<character> is an abstract entity. It is not bound to any
25 particular integer width, especially not to the C language C<char>.
26 Unicode is language-neutral and display-neutral: it does not encode the
27 language of the text and it does not define fonts or other graphical
28 layout details. Unicode operates on characters and on text built from
31 Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK
32 SMALL LETTER ALPHA> and unique numbers for the characters, in this
33 case 0x0041 and 0x03B1, respectively. These unique numbers are called
36 The Unicode standard prefers using hexadecimal notation for the code
37 points. If numbers like C<0x0041> are unfamiliar to you, take a peek
38 at a later section, L</"Hexadecimal Notation">. The Unicode standard
39 uses the notation C<U+0041 LATIN CAPITAL LETTER A>, to give the
40 hexadecimal code point and the normative name of the character.
42 Unicode also defines various I<properties> for the characters, like
43 "uppercase" or "lowercase", "decimal digit", or "punctuation";
44 these properties are independent of the names of the characters.
45 Furthermore, various operations on the characters like uppercasing,
46 lowercasing, and collating (sorting) are defined.
48 A Unicode character consists either of a single code point, or a
49 I<base character> (like C<LATIN CAPITAL LETTER A>), followed by one or
50 more I<modifiers> (like C<COMBINING ACUTE ACCENT>). This sequence of
51 base character and modifiers is called a I<combining character
54 Whether to call these combining character sequences "characters"
55 depends on your point of view. If you are a programmer, you probably
56 would tend towards seeing each element in the sequences as one unit,
57 or "character". The whole sequence could be seen as one "character",
58 however, from the user's point of view, since that's probably what it
59 looks like in the context of the user's language.
61 With this "whole sequence" view of characters, the total number of
62 characters is open-ended. But in the programmer's "one unit is one
63 character" point of view, the concept of "characters" is more
64 deterministic. In this document, we take that second point of view:
65 one "character" is one Unicode code point, be it a base character or
66 a combining character.
68 For some combinations, there are I<precomposed> characters.
69 C<LATIN CAPITAL LETTER A WITH ACUTE>, for example, is defined as
70 a single code point. These precomposed characters are, however,
71 only available for some combinations, and are mainly
72 meant to support round-trip conversions between Unicode and legacy
73 standards (like the ISO 8859). In the general case, the composing
74 method is more extensible. To support conversion between
75 different compositions of the characters, various I<normalization
76 forms> to standardize representations are also defined.
78 Because of backward compatibility with legacy encodings, the "a unique
79 number for every character" idea breaks down a bit: instead, there is
80 "at least one number for every character". The same character could
81 be represented differently in several legacy encodings. The
82 converse is also not true: some code points do not have an assigned
83 character. Firstly, there are unallocated code points within
84 otherwise used blocks. Secondly, there are special Unicode control
85 characters that do not represent true characters.
87 A common myth about Unicode is that it would be "16-bit", that is,
88 Unicode is only represented as C<0x10000> (or 65536) characters from
89 C<0x0000> to C<0xFFFF>. B<This is untrue.> Since Unicode 2.0 (July
90 1996), Unicode has been defined all the way up to 21 bits (C<0x10FFFF>),
91 and since Unicode 3.1 (March 2001), characters have been defined
92 beyond C<0xFFFF>. The first C<0x10000> characters are called the
93 I<Plane 0>, or the I<Basic Multilingual Plane> (BMP). With Unicode
94 3.1, 17 (yes, seventeen) planes in all were defined--but they are
95 nowhere near full of defined characters, yet.
97 Another myth is that the 256-character blocks have something to
98 do with languages--that each block would define the characters used
99 by a language or a set of languages. B<This is also untrue.>
100 The division into blocks exists, but it is almost completely
101 accidental--an artifact of how the characters have been and
102 still are allocated. Instead, there is a concept called I<scripts>,
103 which is more useful: there is C<Latin> script, C<Greek> script, and
104 so on. Scripts usually span varied parts of several blocks.
105 For further information see L<Unicode::UCD>.
107 The Unicode code points are just abstract numbers. To input and
108 output these abstract numbers, the numbers must be I<encoded> or
109 I<serialised> somehow. Unicode defines several I<character encoding
110 forms>, of which I<UTF-8> is perhaps the most popular. UTF-8 is a
111 variable length encoding that encodes Unicode characters as 1 to 6
112 bytes (only 4 with the currently defined characters). Other encodings
113 include UTF-16 and UTF-32 and their big- and little-endian variants
114 (UTF-8 is byte-order independent) The ISO/IEC 10646 defines the UCS-2
115 and UCS-4 encoding forms.
117 For more information about encodings--for instance, to learn what
118 I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>.
120 =head2 Perl's Unicode Support
122 Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode
123 natively. Perl 5.8.0, however, is the first recommended release for
124 serious Unicode work. The maintenance release 5.6.1 fixed many of the
125 problems of the initial Unicode implementation, but for example
126 regular expressions still do not work with Unicode in 5.6.1.
128 B<Starting from Perl 5.8.0, the use of C<use utf8> is no longer
129 necessary.> In earlier releases the C<utf8> pragma was used to declare
130 that operations in the current block or file would be Unicode-aware.
131 This model was found to be wrong, or at least clumsy: the "Unicodeness"
132 is now carried with the data, instead of being attached to the
133 operations. Only one case remains where an explicit C<use utf8> is
134 needed: if your Perl script itself is encoded in UTF-8, you can use
135 UTF-8 in your identifier names, and in string and regular expression
136 literals, by saying C<use utf8>. This is not the default because
137 scripts with legacy 8-bit data in them would break. See L<utf8>.
139 =head2 Perl's Unicode Model
141 Perl supports both pre-5.6 strings of eight-bit native bytes, and
142 strings of Unicode characters. The principle is that Perl tries to
143 keep its data as eight-bit bytes for as long as possible, but as soon
144 as Unicodeness cannot be avoided, the data is transparently upgraded
147 Internally, Perl currently uses either whatever the native eight-bit
148 character set of the platform (for example Latin-1) is, defaulting to
149 UTF-8, to encode Unicode strings. Specifically, if all code points in
150 the string are C<0xFF> or less, Perl uses the native eight-bit
151 character set. Otherwise, it uses UTF-8.
153 A user of Perl does not normally need to know nor care how Perl
154 happens to encode its internal strings, but it becomes relevant when
155 outputting Unicode strings to a stream without a PerlIO layer -- one with
156 the "default" encoding. In such a case, the raw bytes used internally
157 (the native character set or UTF-8, as appropriate for each string)
158 will be used, and a "Wide character" warning will be issued if those
159 strings contain a character beyond 0x00FF.
163 perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
165 produces a fairly useless mixture of native bytes and UTF-8, as well
168 Wide character in print at ...
170 To output UTF-8, use the C<:encoding> or C<:utf8> output layer. Prepending
172 binmode(STDOUT, ":utf8");
174 to this sample program ensures that the output is completely UTF-8,
175 and removes the program's warning.
177 You can enable automatic UTF-8-ification of your standard file
178 handles, default C<open()> layer, and C<@ARGV> by using either
179 the C<-C> command line switch or the C<PERL_UNICODE> environment
180 variable, see L<perlrun> for the documentation of the C<-C> switch.
182 Note that this means that Perl expects other software to work, too:
183 if Perl has been led to believe that STDIN should be UTF-8, but then
184 STDIN coming in from another command is not UTF-8, Perl will complain
185 about the malformed UTF-8.
187 All features that combine Unicode and I/O also require using the new
188 PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though:
189 you can see whether yours is by running "perl -V" and looking for
192 =head2 Unicode and EBCDIC
194 Perl 5.8.0 also supports Unicode on EBCDIC platforms. There,
195 Unicode support is somewhat more complex to implement since
196 additional conversions are needed at every step. Some problems
197 remain, see L<perlebcdic> for details.
199 In any case, the Unicode support on EBCDIC platforms is better than
200 in the 5.6 series, which didn't work much at all for EBCDIC platform.
201 On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
202 instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in
203 that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is
206 =head2 Creating Unicode
208 To create Unicode characters in literals for code points above C<0xFF>,
209 use the C<\x{...}> notation in double-quoted strings:
211 my $smiley = "\x{263a}";
213 Similarly, it can be used in regular expression literals
215 $smiley =~ /\x{263a}/;
217 At run-time you can use C<chr()>:
219 my $hebrew_alef = chr(0x05d0);
221 See L</"Further Resources"> for how to find all these numeric codes.
223 Naturally, C<ord()> will do the reverse: it turns a character into
226 Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>,
227 and C<chr(...)> for arguments less than C<0x100> (decimal 256)
228 generate an eight-bit character for backward compatibility with older
229 Perls. For arguments of C<0x100> or more, Unicode characters are
230 always produced. If you want to force the production of Unicode
231 characters regardless of the numeric value, use C<pack("U", ...)>
232 instead of C<\x..>, C<\x{...}>, or C<chr()>.
234 You can also use the C<charnames> pragma to invoke characters
235 by name in double-quoted strings:
237 use charnames ':full';
238 my $arabic_alef = "\N{ARABIC LETTER ALEF}";
240 And, as mentioned above, you can also C<pack()> numbers into Unicode
243 my $georgian_an = pack("U", 0x10a0);
245 Note that both C<\x{...}> and C<\N{...}> are compile-time string
246 constants: you cannot use variables in them. if you want similar
247 run-time functionality, use C<chr()> and C<charnames::vianame()>.
249 If you want to force the result to Unicode characters, use the special
250 C<"U0"> prefix. It consumes no arguments but causes the following bytes
251 to be interpreted as the UTF-8 encoding of Unicode characters:
253 my $chars = pack("U0W*", 0x80, 0x42);
255 Likewise, you can stop such UTF-8 interpretation by using the special
258 =head2 Handling Unicode
260 Handling Unicode is for the most part transparent: just use the
261 strings as usual. Functions like C<index()>, C<length()>, and
262 C<substr()> will work on the Unicode characters; regular expressions
263 will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
265 Note that Perl considers combining character sequences to be
266 separate characters, so for example
268 use charnames ':full';
269 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
271 will print 2, not 1. The only exception is that regular expressions
272 have C<\X> for matching a combining character sequence.
274 Life is not quite so transparent, however, when working with legacy
275 encodings, I/O, and certain special cases:
277 =head2 Legacy Encodings
279 When you combine legacy data and Unicode the legacy data needs
280 to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
281 applicable) is assumed.
283 The C<Encode> module knows about many encodings and has interfaces
284 for doing conversions between those encodings:
287 $data = decode("iso-8859-3", $data); # convert from legacy to utf-8
291 Normally, writing out Unicode data
293 print FH $some_string_with_unicode, "\n";
295 produces raw bytes that Perl happens to use to internally encode the
296 Unicode string. Perl's internal encoding depends on the system as
297 well as what characters happen to be in the string at the time. If
298 any of the characters are at code points C<0x100> or above, you will get
299 a warning. To ensure that the output is explicitly rendered in the
300 encoding you desire--and to avoid the warning--open the stream with
301 the desired encoding. Some examples:
303 open FH, ">:utf8", "file";
305 open FH, ">:encoding(ucs2)", "file";
306 open FH, ">:encoding(UTF-8)", "file";
307 open FH, ">:encoding(shift_jis)", "file";
309 and on already open streams, use C<binmode()>:
311 binmode(STDOUT, ":utf8");
313 binmode(STDOUT, ":encoding(ucs2)");
314 binmode(STDOUT, ":encoding(UTF-8)");
315 binmode(STDOUT, ":encoding(shift_jis)");
317 The matching of encoding names is loose: case does not matter, and
318 many encodings have several aliases. Note that the C<:utf8> layer
319 must always be specified exactly like that; it is I<not> subject to
320 the loose matching of encoding names. Also note that C<:utf8> is unsafe for
321 input, because it accepts the data without validating that it is indeed valid
324 See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
325 L<Encode::PerlIO> for the C<:encoding()> layer, and
326 L<Encode::Supported> for many encodings supported by the C<Encode>
329 Reading in a file that you know happens to be encoded in one of the
330 Unicode or legacy encodings does not magically turn the data into
331 Unicode in Perl's eyes. To do that, specify the appropriate
332 layer when opening files
334 open(my $fh,'<:encoding(utf8)', 'anything');
335 my $line_of_unicode = <$fh>;
337 open(my $fh,'<:encoding(Big5)', 'anything');
338 my $line_of_unicode = <$fh>;
340 The I/O layers can also be specified more flexibly with
341 the C<open> pragma. See L<open>, or look at the following example.
343 use open ':encoding(utf8)'; # input/output default encoding will be UTF-8
345 print X chr(0x100), "\n";
348 printf "%#x\n", ord(<Y>); # this should print 0x100
351 With the C<open> pragma you can use the C<:locale> layer
353 BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
354 # the :locale will probe the locale environment variables like LC_ALL
355 use open OUT => ':locale'; # russki parusski
357 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
360 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
363 These methods install a transparent filter on the I/O stream that
364 converts data from the specified encoding when it is read in from the
365 stream. The result is always Unicode.
367 The L<open> pragma affects all the C<open()> calls after the pragma by
368 setting default layers. If you want to affect only certain
369 streams, use explicit layers directly in the C<open()> call.
371 You can switch encodings on an already opened stream by using
372 C<binmode()>; see L<perlfunc/binmode>.
374 The C<:locale> does not currently (as of Perl 5.8.0) work with
375 C<open()> and C<binmode()>, only with the C<open> pragma. The
376 C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
377 C<binmode()>, and the C<open> pragma.
379 Similarly, you may use these I/O layers on output streams to
380 automatically convert Unicode to the specified encoding when it is
381 written to the stream. For example, the following snippet copies the
382 contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
383 the file "text.utf8", encoded as UTF-8:
385 open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis');
386 open(my $unicode, '>:utf8', 'text.utf8');
387 while (<$nihongo>) { print $unicode $_ }
389 The naming of encodings, both by the C<open()> and by the C<open>
390 pragma allows for flexible names: C<koi8-r> and C<KOI8R> will both be
393 Common encodings recognized by ISO, MIME, IANA, and various other
394 standardisation organisations are recognised; for a more detailed
395 list see L<Encode::Supported>.
397 C<read()> reads characters and returns the number of characters.
398 C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
401 Notice that because of the default behaviour of not doing any
402 conversion upon input if there is no default layer,
403 it is easy to mistakenly write code that keeps on expanding a file
404 by repeatedly encoding the data:
408 local $/; ## read in the whole file of 8-bit characters
411 open F, ">:encoding(utf8)", "file";
412 print F $t; ## convert to UTF-8 on output
415 If you run this code twice, the contents of the F<file> will be twice
416 UTF-8 encoded. A C<use open ':encoding(utf8)'> would have avoided the
417 bug, or explicitly opening also the F<file> for input as UTF-8.
419 B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
420 Perl has been built with the new PerlIO feature (which is the default
423 =head2 Displaying Unicode As Text
425 Sometimes you might want to display Perl scalars containing Unicode as
426 simple ASCII (or EBCDIC) text. The following subroutine converts
427 its argument so that Unicode characters with code points greater than
428 255 are displayed as C<\x{...}>, control characters (like C<\n>) are
429 displayed as C<\x..>, and the rest of the characters as themselves:
433 map { $_ > 255 ? # if wide character...
434 sprintf("\\x{%04X}", $_) : # \x{...}
435 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
436 sprintf("\\x%02X", $_) : # \x..
437 quotemeta(chr($_)) # else quoted or as themselves
438 } unpack("W*", $_[0])); # unpack Unicode characters
443 nice_string("foo\x{100}bar\n")
449 which is ready to be printed.
457 Bit Complement Operator ~ And vec()
459 The bit complement operator C<~> may produce surprising results if
460 used on strings containing characters with ordinal values above
461 255. In such a case, the results are consistent with the internal
462 encoding of the characters, but not with much else. So don't do
463 that. Similarly for C<vec()>: you will be operating on the
464 internally-encoded bit patterns of the Unicode characters, not on
465 the code point values, which is very probably not what you want.
469 Peeking At Perl's Internal Encoding
471 Normal users of Perl should never care how Perl encodes any particular
472 Unicode string (because the normal ways to get at the contents of a
473 string with Unicode--via input and output--should always be via
474 explicitly-defined I/O layers). But if you must, there are two
475 ways of looking behind the scenes.
477 One way of peeking inside the internal encoding of Unicode characters
478 is to use C<unpack("C*", ...> to get the bytes of whatever the string
479 encoding happens to be, or C<unpack("U0..", ...)> to get the bytes of the
482 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
483 print join(" ", unpack("U0(H2)*", pack("U", 0x100))), "\n";
485 Yet another way would be to use the Devel::Peek module:
487 perl -MDevel::Peek -e 'Dump(chr(0x100))'
489 That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes
490 and Unicode characters in C<PV>. See also later in this document
491 the discussion about the C<utf8::is_utf8()> function.
495 =head2 Advanced Topics
503 The question of string equivalence turns somewhat complicated
504 in Unicode: what do you mean by "equal"?
506 (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
507 C<LATIN CAPITAL LETTER A>?)
509 The short answer is that by default Perl compares equivalence (C<eq>,
510 C<ne>) based only on code points of the characters. In the above
511 case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any
512 CAPITAL LETTER As should be considered equal, or even As of any case.
514 The long answer is that you need to consider character normalization
515 and casing issues: see L<Unicode::Normalize>, Unicode Technical
516 Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
517 Mappings>, http://www.unicode.org/unicode/reports/tr15/ and
518 http://www.unicode.org/unicode/reports/tr21/
520 As of Perl 5.8.0, the "Full" case-folding of I<Case
521 Mappings/SpecialCasing> is implemented.
527 People like to see their strings nicely sorted--or as Unicode
528 parlance goes, collated. But again, what do you mean by collate?
530 (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
531 C<LATIN CAPITAL LETTER A WITH GRAVE>?)
533 The short answer is that by default, Perl compares strings (C<lt>,
534 C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
535 characters. In the above case, the answer is "after", since
536 C<0x00C1> > C<0x00C0>.
538 The long answer is that "it depends", and a good answer cannot be
539 given without knowing (at the very least) the language context.
540 See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
541 http://www.unicode.org/unicode/reports/tr10/
551 Character Ranges and Classes
553 Character ranges in regular expression character classes (C</[a-z]/>)
554 and in the C<tr///> (also known as C<y///>) operator are not magically
555 Unicode-aware. What this means that C<[A-Za-z]> will not magically start
556 to mean "all alphabetic letters"; not that it does mean that even for
557 8-bit characters, you should be using C</[[:alpha:]]/> in that case.
559 For specifying character classes like that in regular expressions,
560 you can use the various Unicode properties--C<\pL>, or perhaps
561 C<\p{Alphabetic}>, in this particular case. You can use Unicode
562 code points as the end points of character ranges, but there is no
563 magic associated with specifying a certain range. For further
564 information--there are dozens of Unicode character classes--see
569 String-To-Number Conversions
571 Unicode does define several other decimal--and numeric--characters
572 besides the familiar 0 to 9, such as the Arabic and Indic digits.
573 Perl does not support string-to-number conversion for digits other
574 than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
578 =head2 Questions With Answers
584 Will My Old Scripts Break?
586 Very probably not. Unless you are generating Unicode characters
587 somehow, old behaviour should be preserved. About the only behaviour
588 that has changed and which could start generating Unicode is the old
589 behaviour of C<chr()> where supplying an argument more than 255
590 produced a character modulo 255. C<chr(300)>, for example, was equal
591 to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
596 How Do I Make My Scripts Work With Unicode?
598 Very little work should be needed since nothing changes until you
599 generate Unicode data. The most important thing is getting input as
600 Unicode; for that, see the earlier I/O discussion.
604 How Do I Know Whether My String Is In Unicode?
606 You shouldn't care. No, you really shouldn't. No, really. If you
607 have to care--beyond the cases described above--it means that we
608 didn't get the transparency of Unicode quite right.
612 print utf8::is_utf8($string) ? 1 : 0, "\n";
614 But note that this doesn't mean that any of the characters in the
615 string are necessary UTF-8 encoded, or that any of the characters have
616 code points greater than 0xFF (255) or even 0x80 (128), or that the
617 string has any characters at all. All the C<is_utf8()> does is to
618 return the value of the internal "utf8ness" flag attached to the
619 C<$string>. If the flag is off, the bytes in the scalar are interpreted
620 as a single byte encoding. If the flag is on, the bytes in the scalar
621 are interpreted as the (multi-byte, variable-length) UTF-8 encoded code
622 points of the characters. Bytes added to an UTF-8 encoded string are
623 automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars
624 are merged (double-quoted interpolation, explicit concatenation, and
625 printf/sprintf parameter substitution), the result will be UTF-8 encoded
626 as if copies of the byte strings were upgraded to UTF-8: for example,
632 the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but
633 C<$a> will stay byte-encoded.
635 Sometimes you might really need to know the byte length of a string
636 instead of the character length. For that use either the
637 C<Encode::encode_utf8()> function or the C<bytes> pragma and its only
638 defined function C<length()>:
640 my $unicode = chr(0x100);
641 print length($unicode), "\n"; # will print 1
643 print length(Encode::encode_utf8($unicode)), "\n"; # will print 2
645 print length($unicode), "\n"; # will also print 2
646 # (the 0xC4 0x80 of the UTF-8)
650 How Do I Detect Data That's Not Valid In a Particular Encoding?
652 Use the C<Encode> package to try converting it.
655 use Encode 'decode_utf8';
657 if (eval { decode_utf8($string, Encode::FB_CROAK); 1 }) {
658 # $string is valid utf8
660 # $string is not valid utf8
663 Or use C<unpack> to try decoding it:
666 @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
668 If invalid, a C<Malformed UTF-8 character> warning is produced. The "C0" means
669 "process the string character per character". Without that, the
670 C<unpack("U*", ...)> would work in C<U0> mode (the default if the format
671 string starts with C<U>) and it would return the bytes making up the UTF-8
672 encoding of the target string, something that will always work.
676 How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
678 This probably isn't as useful as you might think.
679 Normally, you shouldn't need to.
681 In one sense, what you are asking doesn't make much sense: encodings
682 are for characters, and binary data are not "characters", so converting
683 "data" into some encoding isn't meaningful unless you know in what
684 character set and encoding the binary data is in, in which case it's
685 not just binary data, now is it?
687 If you have a raw sequence of bytes that you know should be
688 interpreted via a particular encoding, you can use C<Encode>:
690 use Encode 'from_to';
691 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
693 The call to C<from_to()> changes the bytes in C<$data>, but nothing
694 material about the nature of the string has changed as far as Perl is
695 concerned. Both before and after the call, the string C<$data>
696 contains just a bunch of 8-bit bytes. As far as Perl is concerned,
697 the encoding of the string remains as "system-native 8-bit bytes".
699 You might relate this to a fictional 'Translate' module:
703 Translate::from_to($phrase, 'english', 'deutsch');
704 ## phrase now contains "Ja"
706 The contents of the string changes, but not the nature of the string.
707 Perl doesn't know any more after the call than before that the
708 contents of the string indicates the affirmative.
710 Back to converting data. If you have (or want) data in your system's
711 native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
712 pack/unpack to convert to/from Unicode.
714 $native_string = pack("W*", unpack("U*", $Unicode_string));
715 $Unicode_string = pack("U*", unpack("W*", $native_string));
717 If you have a sequence of bytes you B<know> is valid UTF-8,
718 but Perl doesn't know it yet, you can make Perl a believer, too:
720 use Encode 'decode_utf8';
721 $Unicode = decode_utf8($bytes);
725 $Unicode = pack("U0a*", $bytes);
727 You can convert well-formed UTF-8 to a sequence of bytes, but if
728 you just want to convert random binary data into UTF-8, you can't.
729 B<Any random collection of bytes isn't well-formed UTF-8>. You can
730 use C<unpack("C*", $string)> for the former, and you can create
731 well-formed Unicode data by C<pack("U*", 0xff, ...)>.
735 How Do I Display Unicode? How Do I Input Unicode?
737 See http://www.alanwood.net/unicode/ and
738 http://www.cl.cam.ac.uk/~mgk25/unicode.html
742 How Does Unicode Work With Traditional Locales?
744 In Perl, not very well. Avoid using locales through the C<locale>
745 pragma. Use only one or the other. But see L<perlrun> for the
746 description of the C<-C> switch and its environment counterpart,
747 C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features,
748 for example by using locale settings.
752 =head2 Hexadecimal Notation
754 The Unicode standard prefers using hexadecimal notation because
755 that more clearly shows the division of Unicode into blocks of 256 characters.
756 Hexadecimal is also simply shorter than decimal. You can use decimal
757 notation, too, but learning to use hexadecimal just makes life easier
758 with the Unicode standard. The C<U+HHHH> notation uses hexadecimal,
761 The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
762 a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
763 four bits, or half a byte. C<print 0x..., "\n"> will show a
764 hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
765 show a decimal number in hexadecimal. If you have just the
766 "hex digits" of a hexadecimal number, you can use the C<hex()> function.
768 print 0x0009, "\n"; # 9
769 print 0x000a, "\n"; # 10
770 print 0x000f, "\n"; # 15
771 print 0x0010, "\n"; # 16
772 print 0x0011, "\n"; # 17
773 print 0x0100, "\n"; # 256
775 print 0x0041, "\n"; # 65
777 printf "%x\n", 65; # 41
778 printf "%#x\n", 65; # 0x41
780 print hex("41"), "\n"; # 65
782 =head2 Further Resources
790 http://www.unicode.org/
796 http://www.unicode.org/unicode/faq/
802 http://www.unicode.org/glossary/
806 Unicode Useful Resources
808 http://www.unicode.org/unicode/onlinedat/resources.html
812 Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
814 http://www.alanwood.net/unicode/
818 UTF-8 and Unicode FAQ for Unix/Linux
820 http://www.cl.cam.ac.uk/~mgk25/unicode.html
824 Legacy Character Sets
826 http://www.czyborra.com/
827 http://www.eki.ee/letter/
831 The Unicode support files live within the Perl installation in the
834 $Config{installprivlib}/unicore
836 in Perl 5.8.0 or newer, and
838 $Config{installprivlib}/unicode
840 in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
841 avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
842 The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
843 Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
845 perl "-V:installprivlib"
847 You can explore various information from the Unicode data files using
848 the C<Unicode::UCD> module.
852 =head1 UNICODE IN OLDER PERLS
854 If you cannot upgrade your Perl to 5.8.0 or later, you can still
855 do some Unicode processing by using the modules C<Unicode::String>,
856 C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
857 If you have the GNU recode installed, you can also use the
858 Perl front-end C<Convert::Recode> for character conversions.
860 The following are fast conversions from ISO 8859-1 (Latin-1) bytes
861 to UTF-8 bytes and back, the code works even with older Perl 5 versions.
863 # ISO 8859-1 to UTF-8
864 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
866 # UTF-8 to ISO 8859-1
867 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
871 L<perlunitut>, L<perlunicode>, L<Encode>, L<open>, L<utf8>, L<bytes>,
872 L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>,
875 =head1 ACKNOWLEDGMENTS
877 Thanks to the kind readers of the perl5-porters@perl.org,
878 perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
879 mailing lists for their valuable feedback.
881 =head1 AUTHOR, COPYRIGHT, AND LICENSE
883 Copyright 2001-2002 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>
885 This document may be distributed under the same terms as Perl itself.