3 perluniintro - Perl Unicode introduction
7 This document gives a general idea of Unicode and how to use Unicode
8 in Perl. See L</Further Resources> for references to more in-depth
13 Unicode is a character set standard which plans to codify all of the
14 writing systems of the world, plus many other symbols.
16 Unicode and ISO/IEC 10646 are coordinated standards that unify
17 almost all other modern character set standards,
18 covering more than 80 writing systems and hundreds of languages,
19 including all commercially-important modern languages. All characters
20 in the largest Chinese, Japanese, and Korean dictionaries are also
21 encoded. The standards will eventually cover almost all characters in
22 more than 250 writing systems and thousands of languages.
23 Unicode 1.0 was released in October 1991, and 6.0 in October 2010.
25 A Unicode I<character> is an abstract entity. It is not bound to any
26 particular integer width, especially not to the C language C<char>.
27 Unicode is language-neutral and display-neutral: it does not encode the
28 language of the text, and it does not generally define fonts or other graphical
29 layout details. Unicode operates on characters and on text built from
32 Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK
33 SMALL LETTER ALPHA> and unique numbers for the characters, in this
34 case 0x0041 and 0x03B1, respectively. These unique numbers are called
35 I<code points>. A code point is essentially the position of the
36 character within the set of all possible Unicode characters, and thus in
37 Perl, the term I<ordinal> is often used interchangeably with it.
39 The Unicode standard prefers using hexadecimal notation for the code
40 points. If numbers like C<0x0041> are unfamiliar to you, take a peek
41 at a later section, L</"Hexadecimal Notation">. The Unicode standard
42 uses the notation C<U+0041 LATIN CAPITAL LETTER A>, to give the
43 hexadecimal code point and the normative name of the character.
45 Unicode also defines various I<properties> for the characters, like
46 "uppercase" or "lowercase", "decimal digit", or "punctuation";
47 these properties are independent of the names of the characters.
48 Furthermore, various operations on the characters like uppercasing,
49 lowercasing, and collating (sorting) are defined.
51 A Unicode I<logical> "character" can actually consist of more than one internal
52 I<actual> "character" or code point. For Western languages, this is adequately
53 modelled by a I<base character> (like C<LATIN CAPITAL LETTER A>) followed
54 by one or more I<modifiers> (like C<COMBINING ACUTE ACCENT>). This sequence of
55 base character and modifiers is called a I<combining character
56 sequence>. Some non-western languages require more complicated
57 models, so Unicode created the I<grapheme cluster> concept, which was
58 later further refined into the I<extended grapheme cluster>. For
59 example, a Korean Hangul syllable is considered a single logical
60 character, but most often consists of three actual
61 Unicode characters: a leading consonant followed by an interior vowel followed
62 by a trailing consonant.
64 Whether to call these extended grapheme clusters "characters" depends on your
65 point of view. If you are a programmer, you probably would tend towards seeing
66 each element in the sequences as one unit, or "character". However from
67 the user's point of view, the whole sequence could be seen as one
68 "character" since that's probably what it looks like in the context of the
69 user's language. In this document, we take the programmer's point of
70 view: one "character" is one Unicode code point.
72 For some combinations of base character and modifiers, there are
73 I<precomposed> characters. There is a single character equivalent, for
74 example, for the sequence C<LATIN CAPITAL LETTER A> followed by
75 C<COMBINING ACUTE ACCENT>. It is called C<LATIN CAPITAL LETTER A WITH
76 ACUTE>. These precomposed characters are, however, only available for
77 some combinations, and are mainly meant to support round-trip
78 conversions between Unicode and legacy standards (like ISO 8859). Using
79 sequences, as Unicode does, allows for needing fewer basic building blocks
80 (code points) to express many more potential grapheme clusters. To
81 support conversion between equivalent forms, various I<normalization
82 forms> are also defined. Thus, C<LATIN CAPITAL LETTER A WITH ACUTE> is
83 in I<Normalization Form Composed>, (abbreviated NFC), and the sequence
84 C<LATIN CAPITAL LETTER A> followed by C<COMBINING ACUTE ACCENT>
85 represents the same character in I<Normalization Form Decomposed> (NFD).
87 Because of backward compatibility with legacy encodings, the "a unique
88 number for every character" idea breaks down a bit: instead, there is
89 "at least one number for every character". The same character could
90 be represented differently in several legacy encodings. The
91 converse is not true: some code points do not have an assigned
92 character. Firstly, there are unallocated code points within
93 otherwise used blocks. Secondly, there are special Unicode control
94 characters that do not represent true characters.
96 When Unicode was first conceived, it was thought that all the world's
97 characters could be represented using a 16-bit word; that is a maximum of
98 C<0x10000> (or 65,536) characters would be needed, from C<0x0000> to
99 C<0xFFFF>. This soon proved to be wrong, and since Unicode 2.0 (July
100 1996), Unicode has been defined all the way up to 21 bits (C<0x10FFFF>),
101 and Unicode 3.1 (March 2001) defined the first characters above C<0xFFFF>.
102 The first C<0x10000> characters are called the I<Plane 0>, or the
103 I<Basic Multilingual Plane> (BMP). With Unicode 3.1, 17 (yes,
104 seventeen) planes in all were defined--but they are nowhere near full of
105 defined characters, yet.
107 When a new language is being encoded, Unicode generally will choose a
108 C<block> of consecutive unallocated code points for its characters. So
109 far, the number of code points in these blocks has always been evenly
110 divisible by 16. Extras in a block, not currently needed, are left
111 unallocated, for future growth. But there have been occasions when
112 a later release needed more code points than the available extras, and a
113 new block had to allocated somewhere else, not contiguous to the initial
114 one, to handle the overflow. Thus, it became apparent early on that
115 "block" wasn't an adequate organizing principle, and so the C<Script>
116 property was created. (Later an improved script property was added as
117 well, the C<Script_Extensions> property.) Those code points that are in
118 overflow blocks can still
119 have the same script as the original ones. The script concept fits more
120 closely with natural language: there is C<Latin> script, C<Greek>
121 script, and so on; and there are several artificial scripts, like
122 C<Common> for characters that are used in multiple scripts, such as
123 mathematical symbols. Scripts usually span varied parts of several
124 blocks. For more information about scripts, see L<perlunicode/Scripts>.
125 The division into blocks exists, but it is almost completely
126 accidental--an artifact of how the characters have been and still are
127 allocated. (Note that this paragraph has oversimplified things for the
128 sake of this being an introduction. Unicode doesn't really encode
129 languages, but the writing systems for them--their scripts; and one
130 script can be used by many languages. Unicode also encodes things that
131 aren't really about languages, such as symbols like C<BAGGAGE CLAIM>.)
133 The Unicode code points are just abstract numbers. To input and
134 output these abstract numbers, the numbers must be I<encoded> or
135 I<serialised> somehow. Unicode defines several I<character encoding
136 forms>, of which I<UTF-8> is the most popular. UTF-8 is a
137 variable length encoding that encodes Unicode characters as 1 to 4
138 bytes. Other encodings
139 include UTF-16 and UTF-32 and their big- and little-endian variants
140 (UTF-8 is byte-order independent). The ISO/IEC 10646 defines the UCS-2
141 and UCS-4 encoding forms.
143 For more information about encodings--for instance, to learn what
144 I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>.
146 =head2 Perl's Unicode Support
148 Starting from Perl v5.6.0, Perl has had the capacity to handle Unicode
149 natively. Perl v5.8.0, however, is the first recommended release for
150 serious Unicode work. The maintenance release 5.6.1 fixed many of the
151 problems of the initial Unicode implementation, but for example
152 regular expressions still do not work with Unicode in 5.6.1.
153 Perl v5.14.0 is the first release where Unicode support is
154 (almost) seamlessly integrable without some gotchas (the exception being
155 some differences in L<quotemeta|perlfunc/quotemeta>, and that is fixed
156 starting in Perl 5.16.0). To enable this
157 seamless support, you should C<use feature 'unicode_strings'> (which is
158 automatically selected if you C<use 5.012> or higher). See L<feature>.
159 (5.14 also fixes a number of bugs and departures from the Unicode
162 Before Perl v5.8.0, the use of C<use utf8> was used to declare
163 that operations in the current block or file would be Unicode-aware.
164 This model was found to be wrong, or at least clumsy: the "Unicodeness"
165 is now carried with the data, instead of being attached to the
167 Starting with Perl v5.8.0, only one case remains where an explicit C<use
168 utf8> is needed: if your Perl script itself is encoded in UTF-8, you can
169 use UTF-8 in your identifier names, and in string and regular expression
170 literals, by saying C<use utf8>. This is not the default because
171 scripts with legacy 8-bit data in them would break. See L<utf8>.
173 =head2 Perl's Unicode Model
175 Perl supports both pre-5.6 strings of eight-bit native bytes, and
176 strings of Unicode characters. The general principle is that Perl tries
177 to keep its data as eight-bit bytes for as long as possible, but as soon
178 as Unicodeness cannot be avoided, the data is transparently upgraded
179 to Unicode. Prior to Perl v5.14.0, the upgrade was not completely
180 transparent (see L<perlunicode/The "Unicode Bug">), and for backwards
181 compatibility, full transparency is not gained unless C<use feature
182 'unicode_strings'> (see L<feature>) or C<use 5.012> (or higher) is
185 Internally, Perl currently uses either whatever the native eight-bit
186 character set of the platform (for example Latin-1) is, defaulting to
187 UTF-8, to encode Unicode strings. Specifically, if all code points in
188 the string are C<0xFF> or less, Perl uses the native eight-bit
189 character set. Otherwise, it uses UTF-8.
191 A user of Perl does not normally need to know nor care how Perl
192 happens to encode its internal strings, but it becomes relevant when
193 outputting Unicode strings to a stream without a PerlIO layer (one with
194 the "default" encoding). In such a case, the raw bytes used internally
195 (the native character set or UTF-8, as appropriate for each string)
196 will be used, and a "Wide character" warning will be issued if those
197 strings contain a character beyond 0x00FF.
201 perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
203 produces a fairly useless mixture of native bytes and UTF-8, as well
206 Wide character in print at ...
208 To output UTF-8, use the C<:encoding> or C<:utf8> output layer. Prepending
210 binmode(STDOUT, ":utf8");
212 to this sample program ensures that the output is completely UTF-8,
213 and removes the program's warning.
215 You can enable automatic UTF-8-ification of your standard file
216 handles, default C<open()> layer, and C<@ARGV> by using either
217 the C<-C> command line switch or the C<PERL_UNICODE> environment
218 variable, see L<perlrun> for the documentation of the C<-C> switch.
220 Note that this means that Perl expects other software to work the same
222 if Perl has been led to believe that STDIN should be UTF-8, but then
223 STDIN coming in from another command is not UTF-8, Perl will likely
224 complain about the malformed UTF-8.
226 All features that combine Unicode and I/O also require using the new
227 PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though:
228 you can see whether yours is by running "perl -V" and looking for
231 =head2 Unicode and EBCDIC
233 Perl 5.8.0 added support for Unicode on EBCDIC platforms. This support
234 was allowed to lapse in later releases, but was revived in 5.22.
235 Unicode support is somewhat more complex to implement since additional
236 conversions are needed. See L<perlebcdic> for more information.
238 On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
239 instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in
240 that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is
241 "EBCDIC-safe", in that all the basic characters (which includes all
242 those that have ASCII equivalents (like C<"A">, C<"0">, C<"%">, I<etc.>)
243 are the same in both EBCDIC and UTF-EBCDIC. Often, documentation
244 will use the term "UTF-8" to mean UTF-EBCDIC as well. This is the case
247 =head2 Creating Unicode
249 This section applies fully to Perls starting with v5.22. Various
250 caveats for earlier releases are in the L</Earlier releases caveats>
253 To create Unicode characters in literals,
254 use the C<\N{...}> notation in double-quoted strings:
256 my $smiley_from_name = "\N{WHITE SMILING FACE}";
257 my $smiley_from_code_point = "\N{U+263a}";
259 Similarly, they can be used in regular expression literals
261 $smiley =~ /\N{WHITE SMILING FACE}/;
262 $smiley =~ /\N{U+263a}/;
264 At run-time you can use:
267 my $hebrew_alef_from_name
268 = charnames::string_vianame("HEBREW LETTER ALEF");
269 my $hebrew_alef_from_code_point = charnames::string_vianame("U+05D0");
271 Naturally, C<ord()> will do the reverse: it turns a character into
274 There are other runtime options as well. You can use C<pack()>:
276 my $hebrew_alef_from_code_point = pack("U", 0x05d0);
278 Or you can use C<chr()>, though it is less convenient in the general
281 $hebrew_alef_from_code_point = chr(utf8::unicode_to_native(0x05d0));
282 utf8::upgrade($hebrew_alef_from_code_point);
284 The C<utf8::unicode_to_native()> and C<utf8::upgrade()> aren't needed if
285 the argument is above 0xFF, so the above could have been written as
287 $hebrew_alef_from_code_point = chr(0x05d0);
289 since 0x5d0 is above 255.
291 C<\x{}> and C<\o{}> can also be used to specify code points at compile
292 time in double-quotish strings, but, for backward compatibility with
293 older Perls, the same rules apply as with C<chr()> for code points less
296 C<utf8::unicode_to_native()> is used so that the Perl code is portable
297 to EBCDIC platforms. You can omit it if you're I<really> sure no one
298 will ever want to use your code on a non-ASCII platform. Starting in
299 Perl v5.22, calls to it on ASCII platforms are optimized out, so there's
300 no performance penalty at all in adding it. Or you can simply use the
301 other constructs that don't require it.
303 See L</"Further Resources"> for how to find all these names and numeric
306 =head3 Earlier releases caveats
308 On EBCDIC platforms, prior to v5.22, using C<\N{U+...}> doesn't work
311 Prior to v5.16, using C<\N{...}> with a character name (as opposed to a
312 C<U+...> code point) required a S<C<use charnames :full>>.
314 Prior to v5.14, there were some bugs in C<\N{...}> with a character name
315 (as opposed to a C<U+...> code point).
317 C<charnames::string_vianame()> was introduced in v5.14. Prior to that,
318 C<charnames::vianame()> should work, but only if the argument is of the
319 form C<"U+...">. Your best bet there for runtime Unicode by character
323 my $hebrew_alef_from_name
324 = pack("U", charnames::vianame("HEBREW LETTER ALEF"));
326 =head2 Handling Unicode
328 Handling Unicode is for the most part transparent: just use the
329 strings as usual. Functions like C<index()>, C<length()>, and
330 C<substr()> will work on the Unicode characters; regular expressions
331 will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
333 Note that Perl considers grapheme clusters to be separate characters, so for
336 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"),
339 will print 2, not 1. The only exception is that regular expressions
340 have C<\X> for matching an extended grapheme cluster. (Thus C<\X> in a
341 regular expression would match the entire sequence of both the example
344 Life is not quite so transparent, however, when working with legacy
345 encodings, I/O, and certain special cases:
347 =head2 Legacy Encodings
349 When you combine legacy data and Unicode, the legacy data needs
350 to be upgraded to Unicode. Normally the legacy data is assumed to be
351 ISO 8859-1 (or EBCDIC, if applicable).
353 The C<Encode> module knows about many encodings and has interfaces
354 for doing conversions between those encodings:
357 $data = decode("iso-8859-3", $data); # convert from legacy to utf-8
361 Normally, writing out Unicode data
363 print FH $some_string_with_unicode, "\n";
365 produces raw bytes that Perl happens to use to internally encode the
366 Unicode string. Perl's internal encoding depends on the system as
367 well as what characters happen to be in the string at the time. If
368 any of the characters are at code points C<0x100> or above, you will get
369 a warning. To ensure that the output is explicitly rendered in the
370 encoding you desire--and to avoid the warning--open the stream with
371 the desired encoding. Some examples:
373 open FH, ">:utf8", "file";
375 open FH, ">:encoding(ucs2)", "file";
376 open FH, ">:encoding(UTF-8)", "file";
377 open FH, ">:encoding(shift_jis)", "file";
379 and on already open streams, use C<binmode()>:
381 binmode(STDOUT, ":utf8");
383 binmode(STDOUT, ":encoding(ucs2)");
384 binmode(STDOUT, ":encoding(UTF-8)");
385 binmode(STDOUT, ":encoding(shift_jis)");
387 The matching of encoding names is loose: case does not matter, and
388 many encodings have several aliases. Note that the C<:utf8> layer
389 must always be specified exactly like that; it is I<not> subject to
390 the loose matching of encoding names. Also note that currently C<:utf8> is unsafe for
391 input, because it accepts the data without validating that it is indeed valid
392 UTF-8; you should instead use C<:encoding(utf-8)> (with or without a
395 See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
396 L<Encode::PerlIO> for the C<:encoding()> layer, and
397 L<Encode::Supported> for many encodings supported by the C<Encode>
400 Reading in a file that you know happens to be encoded in one of the
401 Unicode or legacy encodings does not magically turn the data into
402 Unicode in Perl's eyes. To do that, specify the appropriate
403 layer when opening files
405 open(my $fh,'<:encoding(utf8)', 'anything');
406 my $line_of_unicode = <$fh>;
408 open(my $fh,'<:encoding(Big5)', 'anything');
409 my $line_of_unicode = <$fh>;
411 The I/O layers can also be specified more flexibly with
412 the C<open> pragma. See L<open>, or look at the following example.
414 use open ':encoding(utf8)'; # input/output default encoding will be
417 print X chr(0x100), "\n";
420 printf "%#x\n", ord(<Y>); # this should print 0x100
423 With the C<open> pragma you can use the C<:locale> layer
425 BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
426 # the :locale will probe the locale environment variables like
428 use open OUT => ':locale'; # russki parusski
430 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
433 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
436 These methods install a transparent filter on the I/O stream that
437 converts data from the specified encoding when it is read in from the
438 stream. The result is always Unicode.
440 The L<open> pragma affects all the C<open()> calls after the pragma by
441 setting default layers. If you want to affect only certain
442 streams, use explicit layers directly in the C<open()> call.
444 You can switch encodings on an already opened stream by using
445 C<binmode()>; see L<perlfunc/binmode>.
447 The C<:locale> does not currently work with
448 C<open()> and C<binmode()>, only with the C<open> pragma. The
449 C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
450 C<binmode()>, and the C<open> pragma.
452 Similarly, you may use these I/O layers on output streams to
453 automatically convert Unicode to the specified encoding when it is
454 written to the stream. For example, the following snippet copies the
455 contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
456 the file "text.utf8", encoded as UTF-8:
458 open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis');
459 open(my $unicode, '>:utf8', 'text.utf8');
460 while (<$nihongo>) { print $unicode $_ }
462 The naming of encodings, both by the C<open()> and by the C<open>
463 pragma allows for flexible names: C<koi8-r> and C<KOI8R> will both be
466 Common encodings recognized by ISO, MIME, IANA, and various other
467 standardisation organisations are recognised; for a more detailed
468 list see L<Encode::Supported>.
470 C<read()> reads characters and returns the number of characters.
471 C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
474 Notice that because of the default behaviour of not doing any
475 conversion upon input if there is no default layer,
476 it is easy to mistakenly write code that keeps on expanding a file
477 by repeatedly encoding the data:
481 local $/; ## read in the whole file of 8-bit characters
484 open F, ">:encoding(utf8)", "file";
485 print F $t; ## convert to UTF-8 on output
488 If you run this code twice, the contents of the F<file> will be twice
489 UTF-8 encoded. A C<use open ':encoding(utf8)'> would have avoided the
490 bug, or explicitly opening also the F<file> for input as UTF-8.
492 B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
493 Perl has been built with L<PerlIO>, which is the default
496 =head2 Displaying Unicode As Text
498 Sometimes you might want to display Perl scalars containing Unicode as
499 simple ASCII (or EBCDIC) text. The following subroutine converts
500 its argument so that Unicode characters with code points greater than
501 255 are displayed as C<\x{...}>, control characters (like C<\n>) are
502 displayed as C<\x..>, and the rest of the characters as themselves:
506 map { $_ > 255 # if wide character...
507 ? sprintf("\\x{%04X}", $_) # \x{...}
508 : chr($_) =~ /[[:cntrl:]]/ # else if control character...
509 ? sprintf("\\x%02X", $_) # \x..
510 : quotemeta(chr($_)) # else quoted or as themselves
511 } unpack("W*", $_[0])); # unpack Unicode characters
516 nice_string("foo\x{100}bar\n")
522 which is ready to be printed.
524 (C<\\x{}> is used here instead of C<\\N{}>, since it's most likely that
525 you want to see what the native values are.)
533 Bit Complement Operator ~ And vec()
535 The bit complement operator C<~> may produce surprising results if
536 used on strings containing characters with ordinal values above
537 255. In such a case, the results are consistent with the internal
538 encoding of the characters, but not with much else. So don't do
539 that. Similarly for C<vec()>: you will be operating on the
540 internally-encoded bit patterns of the Unicode characters, not on
541 the code point values, which is very probably not what you want.
545 Peeking At Perl's Internal Encoding
547 Normal users of Perl should never care how Perl encodes any particular
548 Unicode string (because the normal ways to get at the contents of a
549 string with Unicode--via input and output--should always be via
550 explicitly-defined I/O layers). But if you must, there are two
551 ways of looking behind the scenes.
553 One way of peeking inside the internal encoding of Unicode characters
554 is to use C<unpack("C*", ...> to get the bytes of whatever the string
555 encoding happens to be, or C<unpack("U0..", ...)> to get the bytes of the
558 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
559 print join(" ", unpack("U0(H2)*", pack("U", 0x100))), "\n";
561 Yet another way would be to use the Devel::Peek module:
563 perl -MDevel::Peek -e 'Dump(chr(0x100))'
565 That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes
566 and Unicode characters in C<PV>. See also later in this document
567 the discussion about the C<utf8::is_utf8()> function.
571 =head2 Advanced Topics
579 The question of string equivalence turns somewhat complicated
580 in Unicode: what do you mean by "equal"?
582 (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
583 C<LATIN CAPITAL LETTER A>?)
585 The short answer is that by default Perl compares equivalence (C<eq>,
586 C<ne>) based only on code points of the characters. In the above
587 case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any
588 CAPITAL LETTER A's should be considered equal, or even A's of any case.
590 The long answer is that you need to consider character normalization
591 and casing issues: see L<Unicode::Normalize>, Unicode Technical Report #15,
592 L<Unicode Normalization Forms|http://www.unicode.org/unicode/reports/tr15> and
593 sections on case mapping in the L<Unicode Standard|http://www.unicode.org>.
595 As of Perl 5.8.0, the "Full" case-folding of I<Case
596 Mappings/SpecialCasing> is implemented, but bugs remain in C<qr//i> with them,
597 mostly fixed by 5.14, and essentially entirely by 5.18.
603 People like to see their strings nicely sorted--or as Unicode
604 parlance goes, collated. But again, what do you mean by collate?
606 (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
607 C<LATIN CAPITAL LETTER A WITH GRAVE>?)
609 The short answer is that by default, Perl compares strings (C<lt>,
610 C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
611 characters. In the above case, the answer is "after", since
612 C<0x00C1> > C<0x00C0>.
614 The long answer is that "it depends", and a good answer cannot be
615 given without knowing (at the very least) the language context.
616 See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
617 L<http://www.unicode.org/unicode/reports/tr10/>
627 Character Ranges and Classes
629 Character ranges in regular expression bracketed character classes ( e.g.,
630 C</[a-z]/>) and in the C<tr///> (also known as C<y///>) operator are not
631 magically Unicode-aware. What this means is that C<[A-Za-z]> will not
632 magically start to mean "all alphabetic letters" (not that it does mean that
633 even for 8-bit characters; for those, if you are using locales (L<perllocale>),
634 use C</[[:alpha:]]/>; and if not, use the 8-bit-aware property C<\p{alpha}>).
636 All the properties that begin with C<\p> (and its inverse C<\P>) are actually
637 character classes that are Unicode-aware. There are dozens of them, see
640 Starting in v5.22, you can use Unicode code points as the end points of
641 regular expression pattern character ranges, and the range will include
642 all Unicode code points that lie between those end points, inclusive.
644 qr/ [\N{U+03]-\N{U+20}] /x
646 includes the code points
647 C<\N{U+03}>, C<\N{U+04}>, ..., C<\N{U+20}>.
649 (It is planned to extend this behavior to ranges in C<tr///> in Perl
654 String-To-Number Conversions
656 Unicode does define several other decimal--and numeric--characters
657 besides the familiar 0 to 9, such as the Arabic and Indic digits.
658 Perl does not support string-to-number conversion for digits other
659 than ASCII C<0> to C<9> (and ASCII C<a> to C<f> for hexadecimal).
660 To get safe conversions from any Unicode string, use
661 L<Unicode::UCD/num()>.
665 =head2 Questions With Answers
671 Will My Old Scripts Break?
673 Very probably not. Unless you are generating Unicode characters
674 somehow, old behaviour should be preserved. About the only behaviour
675 that has changed and which could start generating Unicode is the old
676 behaviour of C<chr()> where supplying an argument more than 255
677 produced a character modulo 255. C<chr(300)>, for example, was equal
678 to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
683 How Do I Make My Scripts Work With Unicode?
685 Very little work should be needed since nothing changes until you
686 generate Unicode data. The most important thing is getting input as
687 Unicode; for that, see the earlier I/O discussion.
688 To get full seamless Unicode support, add
689 C<use feature 'unicode_strings'> (or C<use 5.012> or higher) to your
694 How Do I Know Whether My String Is In Unicode?
696 You shouldn't have to care. But you may if your Perl is before 5.14.0
697 or you haven't specified C<use feature 'unicode_strings'> or C<use
698 5.012> (or higher) because otherwise the rules for the code points
699 in the range 128 to 255 are different depending on
700 whether the string they are contained within is in Unicode or not.
701 (See L<perlunicode/When Unicode Does Not Happen>.)
703 To determine if a string is in Unicode, use:
705 print utf8::is_utf8($string) ? 1 : 0, "\n";
707 But note that this doesn't mean that any of the characters in the
708 string are necessary UTF-8 encoded, or that any of the characters have
709 code points greater than 0xFF (255) or even 0x80 (128), or that the
710 string has any characters at all. All the C<is_utf8()> does is to
711 return the value of the internal "utf8ness" flag attached to the
712 C<$string>. If the flag is off, the bytes in the scalar are interpreted
713 as a single byte encoding. If the flag is on, the bytes in the scalar
714 are interpreted as the (variable-length, potentially multi-byte) UTF-8 encoded
715 code points of the characters. Bytes added to a UTF-8 encoded string are
716 automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars
717 are merged (double-quoted interpolation, explicit concatenation, or
718 printf/sprintf parameter substitution), the result will be UTF-8 encoded
719 as if copies of the byte strings were upgraded to UTF-8: for example,
725 the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but
726 C<$a> will stay byte-encoded.
728 Sometimes you might really need to know the byte length of a string
729 instead of the character length. For that use either the
730 C<Encode::encode_utf8()> function or the C<bytes> pragma
731 and the C<length()> function:
733 my $unicode = chr(0x100);
734 print length($unicode), "\n"; # will print 1
736 print length(Encode::encode_utf8($unicode)),"\n"; # will print 2
738 print length($unicode), "\n"; # will also print 2
739 # (the 0xC4 0x80 of the UTF-8)
744 How Do I Find Out What Encoding a File Has?
746 You might try L<Encode::Guess>, but it has a number of limitations.
750 How Do I Detect Data That's Not Valid In a Particular Encoding?
752 Use the C<Encode> package to try converting it.
755 use Encode 'decode_utf8';
757 if (eval { decode_utf8($string, Encode::FB_CROAK); 1 }) {
758 # $string is valid utf8
760 # $string is not valid utf8
763 Or use C<unpack> to try decoding it:
766 @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
768 If invalid, a C<Malformed UTF-8 character> warning is produced. The "C0" means
769 "process the string character per character". Without that, the
770 C<unpack("U*", ...)> would work in C<U0> mode (the default if the format
771 string starts with C<U>) and it would return the bytes making up the UTF-8
772 encoding of the target string, something that will always work.
776 How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
778 This probably isn't as useful as you might think.
779 Normally, you shouldn't need to.
781 In one sense, what you are asking doesn't make much sense: encodings
782 are for characters, and binary data are not "characters", so converting
783 "data" into some encoding isn't meaningful unless you know in what
784 character set and encoding the binary data is in, in which case it's
785 not just binary data, now is it?
787 If you have a raw sequence of bytes that you know should be
788 interpreted via a particular encoding, you can use C<Encode>:
790 use Encode 'from_to';
791 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
793 The call to C<from_to()> changes the bytes in C<$data>, but nothing
794 material about the nature of the string has changed as far as Perl is
795 concerned. Both before and after the call, the string C<$data>
796 contains just a bunch of 8-bit bytes. As far as Perl is concerned,
797 the encoding of the string remains as "system-native 8-bit bytes".
799 You might relate this to a fictional 'Translate' module:
803 Translate::from_to($phrase, 'english', 'deutsch');
804 ## phrase now contains "Ja"
806 The contents of the string changes, but not the nature of the string.
807 Perl doesn't know any more after the call than before that the
808 contents of the string indicates the affirmative.
810 Back to converting data. If you have (or want) data in your system's
811 native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
812 pack/unpack to convert to/from Unicode.
814 $native_string = pack("W*", unpack("U*", $Unicode_string));
815 $Unicode_string = pack("U*", unpack("W*", $native_string));
817 If you have a sequence of bytes you B<know> is valid UTF-8,
818 but Perl doesn't know it yet, you can make Perl a believer, too:
820 use Encode 'decode_utf8';
821 $Unicode = decode_utf8($bytes);
825 $Unicode = pack("U0a*", $bytes);
827 You can find the bytes that make up a UTF-8 sequence with
829 @bytes = unpack("C*", $Unicode_string)
831 and you can create well-formed Unicode with
833 $Unicode_string = pack("U*", 0xff, ...)
837 How Do I Display Unicode? How Do I Input Unicode?
839 See L<http://www.alanwood.net/unicode/> and
840 L<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
844 How Does Unicode Work With Traditional Locales?
846 If your locale is a UTF-8 locale, starting in Perl v5.20, Perl works
847 well for all categories except C<LC_COLLATE> dealing with sorting and
850 For other locales, starting in Perl 5.16, you can specify
852 use locale ':not_characters';
854 to get Perl to work well with them. The catch is that you
855 have to translate from the locale character set to/from Unicode
856 yourself. See L</Unicode IE<sol>O> above for how to
860 to accomplish this, but full details are in L<perllocale/Unicode and
861 UTF-8>, including gotchas that happen if you don't specify
866 =head2 Hexadecimal Notation
868 The Unicode standard prefers using hexadecimal notation because
869 that more clearly shows the division of Unicode into blocks of 256 characters.
870 Hexadecimal is also simply shorter than decimal. You can use decimal
871 notation, too, but learning to use hexadecimal just makes life easier
872 with the Unicode standard. The C<U+HHHH> notation uses hexadecimal,
875 The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
876 a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
877 four bits, or half a byte. C<print 0x..., "\n"> will show a
878 hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
879 show a decimal number in hexadecimal. If you have just the
880 "hex digits" of a hexadecimal number, you can use the C<hex()> function.
882 print 0x0009, "\n"; # 9
883 print 0x000a, "\n"; # 10
884 print 0x000f, "\n"; # 15
885 print 0x0010, "\n"; # 16
886 print 0x0011, "\n"; # 17
887 print 0x0100, "\n"; # 256
889 print 0x0041, "\n"; # 65
891 printf "%x\n", 65; # 41
892 printf "%#x\n", 65; # 0x41
894 print hex("41"), "\n"; # 65
896 =head2 Further Resources
904 L<http://www.unicode.org/>
910 L<http://www.unicode.org/unicode/faq/>
916 L<http://www.unicode.org/glossary/>
920 Unicode Recommended Reading List
922 The Unicode Consortium has a list of articles and books, some of which
923 give a much more in depth treatment of Unicode:
924 L<http://unicode.org/resources/readinglist.html>
928 Unicode Useful Resources
930 L<http://www.unicode.org/unicode/onlinedat/resources.html>
934 Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
936 L<http://www.alanwood.net/unicode/>
940 UTF-8 and Unicode FAQ for Unix/Linux
942 L<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
946 Legacy Character Sets
948 L<http://www.czyborra.com/>
949 L<http://www.eki.ee/letter/>
953 You can explore various information from the Unicode data files using
954 the C<Unicode::UCD> module.
958 =head1 UNICODE IN OLDER PERLS
960 If you cannot upgrade your Perl to 5.8.0 or later, you can still
961 do some Unicode processing by using the modules C<Unicode::String>,
962 C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
963 If you have the GNU recode installed, you can also use the
964 Perl front-end C<Convert::Recode> for character conversions.
966 The following are fast conversions from ISO 8859-1 (Latin-1) bytes
967 to UTF-8 bytes and back, the code works even with older Perl 5 versions.
969 # ISO 8859-1 to UTF-8
970 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
972 # UTF-8 to ISO 8859-1
973 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
977 L<perlunitut>, L<perlunicode>, L<Encode>, L<open>, L<utf8>, L<bytes>,
978 L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>,
981 =head1 ACKNOWLEDGMENTS
983 Thanks to the kind readers of the perl5-porters@perl.org,
984 perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
985 mailing lists for their valuable feedback.
987 =head1 AUTHOR, COPYRIGHT, AND LICENSE
989 Copyright 2001-2011 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>.
990 Now maintained by Perl 5 Porters.
992 This document may be distributed under the same terms as Perl itself.