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 integratable without some gotchas. (There are a few
155 exceptions. Firstly, some differences in L<quotemeta|perlfunc/quotemeta>
156 were fixed starting in Perl 5.16.0. Secondly, some differences in
157 L<the range operator|perlop/Range Operators> were fixed starting in
158 Perl 5.26.0. Thirdly, some differences in L<split|perlfunc/split> were fixed
159 started in Perl 5.28.0.)
162 seamless support, you should C<use feature 'unicode_strings'> (which is
163 automatically selected if you C<use 5.012> or higher). See L<feature>.
164 (5.14 also fixes a number of bugs and departures from the Unicode
167 Before Perl v5.8.0, the use of C<use utf8> was used to declare
168 that operations in the current block or file would be Unicode-aware.
169 This model was found to be wrong, or at least clumsy: the "Unicodeness"
170 is now carried with the data, instead of being attached to the
172 Starting with Perl v5.8.0, only one case remains where an explicit C<use
173 utf8> is needed: if your Perl script itself is encoded in UTF-8, you can
174 use UTF-8 in your identifier names, and in string and regular expression
175 literals, by saying C<use utf8>. This is not the default because
176 scripts with legacy 8-bit data in them would break. See L<utf8>.
178 =head2 Perl's Unicode Model
180 Perl supports both pre-5.6 strings of eight-bit native bytes, and
181 strings of Unicode characters. The general principle is that Perl tries
182 to keep its data as eight-bit bytes for as long as possible, but as soon
183 as Unicodeness cannot be avoided, the data is transparently upgraded
184 to Unicode. Prior to Perl v5.14.0, the upgrade was not completely
185 transparent (see L<perlunicode/The "Unicode Bug">), and for backwards
186 compatibility, full transparency is not gained unless C<use feature
187 'unicode_strings'> (see L<feature>) or C<use 5.012> (or higher) is
190 Internally, Perl currently uses either whatever the native eight-bit
191 character set of the platform (for example Latin-1) is, defaulting to
192 UTF-8, to encode Unicode strings. Specifically, if all code points in
193 the string are C<0xFF> or less, Perl uses the native eight-bit
194 character set. Otherwise, it uses UTF-8.
196 A user of Perl does not normally need to know nor care how Perl
197 happens to encode its internal strings, but it becomes relevant when
198 outputting Unicode strings to a stream without a PerlIO layer (one with
199 the "default" encoding). In such a case, the raw bytes used internally
200 (the native character set or UTF-8, as appropriate for each string)
201 will be used, and a "Wide character" warning will be issued if those
202 strings contain a character beyond 0x00FF.
206 perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
208 produces a fairly useless mixture of native bytes and UTF-8, as well
211 Wide character in print at ...
213 To output UTF-8, use the C<:encoding> or C<:utf8> output layer. Prepending
215 binmode(STDOUT, ":utf8");
217 to this sample program ensures that the output is completely UTF-8,
218 and removes the program's warning.
220 You can enable automatic UTF-8-ification of your standard file
221 handles, default C<open()> layer, and C<@ARGV> by using either
222 the C<-C> command line switch or the C<PERL_UNICODE> environment
223 variable, see L<perlrun|perlrun/-C [numberE<sol>list]> for the
224 documentation of the C<-C> switch.
226 Note that this means that Perl expects other software to work the same
228 if Perl has been led to believe that STDIN should be UTF-8, but then
229 STDIN coming in from another command is not UTF-8, Perl will likely
230 complain about the malformed UTF-8.
232 All features that combine Unicode and I/O also require using the new
233 PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though:
234 you can see whether yours is by running "perl -V" and looking for
237 =head2 Unicode and EBCDIC
239 Perl 5.8.0 added support for Unicode on EBCDIC platforms. This support
240 was allowed to lapse in later releases, but was revived in 5.22.
241 Unicode support is somewhat more complex to implement since additional
242 conversions are needed. See L<perlebcdic> for more information.
244 On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
245 instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in
246 that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is
247 "EBCDIC-safe", in that all the basic characters (which includes all
248 those that have ASCII equivalents (like C<"A">, C<"0">, C<"%">, I<etc.>)
249 are the same in both EBCDIC and UTF-EBCDIC. Often, documentation
250 will use the term "UTF-8" to mean UTF-EBCDIC as well. This is the case
253 =head2 Creating Unicode
255 This section applies fully to Perls starting with v5.22. Various
256 caveats for earlier releases are in the L</Earlier releases caveats>
259 To create Unicode characters in literals,
260 use the C<\N{...}> notation in double-quoted strings:
262 my $smiley_from_name = "\N{WHITE SMILING FACE}";
263 my $smiley_from_code_point = "\N{U+263a}";
265 Similarly, they can be used in regular expression literals
267 $smiley =~ /\N{WHITE SMILING FACE}/;
268 $smiley =~ /\N{U+263a}/;
270 or, starting in v5.32:
272 $smiley =~ /\p{Name=WHITE SMILING FACE}/;
273 $smiley =~ /\p{Name=whitesmilingface}/;
275 At run-time you can use:
278 my $hebrew_alef_from_name
279 = charnames::string_vianame("HEBREW LETTER ALEF");
280 my $hebrew_alef_from_code_point = charnames::string_vianame("U+05D0");
282 Naturally, C<ord()> will do the reverse: it turns a character into
285 There are other runtime options as well. You can use C<pack()>:
287 my $hebrew_alef_from_code_point = pack("U", 0x05d0);
289 Or you can use C<chr()>, though it is less convenient in the general
292 $hebrew_alef_from_code_point = chr(utf8::unicode_to_native(0x05d0));
293 utf8::upgrade($hebrew_alef_from_code_point);
295 The C<utf8::unicode_to_native()> and C<utf8::upgrade()> aren't needed if
296 the argument is above 0xFF, so the above could have been written as
298 $hebrew_alef_from_code_point = chr(0x05d0);
300 since 0x5d0 is above 255.
302 C<\x{}> and C<\o{}> can also be used to specify code points at compile
303 time in double-quotish strings, but, for backward compatibility with
304 older Perls, the same rules apply as with C<chr()> for code points less
307 C<utf8::unicode_to_native()> is used so that the Perl code is portable
308 to EBCDIC platforms. You can omit it if you're I<really> sure no one
309 will ever want to use your code on a non-ASCII platform. Starting in
310 Perl v5.22, calls to it on ASCII platforms are optimized out, so there's
311 no performance penalty at all in adding it. Or you can simply use the
312 other constructs that don't require it.
314 See L</"Further Resources"> for how to find all these names and numeric
317 =head3 Earlier releases caveats
319 On EBCDIC platforms, prior to v5.22, using C<\N{U+...}> doesn't work
322 Prior to v5.16, using C<\N{...}> with a character name (as opposed to a
323 C<U+...> code point) required a S<C<use charnames :full>>.
325 Prior to v5.14, there were some bugs in C<\N{...}> with a character name
326 (as opposed to a C<U+...> code point).
328 C<charnames::string_vianame()> was introduced in v5.14. Prior to that,
329 C<charnames::vianame()> should work, but only if the argument is of the
330 form C<"U+...">. Your best bet there for runtime Unicode by character
334 my $hebrew_alef_from_name
335 = pack("U", charnames::vianame("HEBREW LETTER ALEF"));
337 =head2 Handling Unicode
339 Handling Unicode is for the most part transparent: just use the
340 strings as usual. Functions like C<index()>, C<length()>, and
341 C<substr()> will work on the Unicode characters; regular expressions
342 will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
344 Note that Perl considers grapheme clusters to be separate characters, so for
347 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"),
350 will print 2, not 1. The only exception is that regular expressions
351 have C<\X> for matching an extended grapheme cluster. (Thus C<\X> in a
352 regular expression would match the entire sequence of both the example
355 Life is not quite so transparent, however, when working with legacy
356 encodings, I/O, and certain special cases:
358 =head2 Legacy Encodings
360 When you combine legacy data and Unicode, the legacy data needs
361 to be upgraded to Unicode. Normally the legacy data is assumed to be
362 ISO 8859-1 (or EBCDIC, if applicable).
364 The C<Encode> module knows about many encodings and has interfaces
365 for doing conversions between those encodings:
368 $data = decode("iso-8859-3", $data); # convert from legacy
372 Normally, writing out Unicode data
374 print FH $some_string_with_unicode, "\n";
376 produces raw bytes that Perl happens to use to internally encode the
377 Unicode string. Perl's internal encoding depends on the system as
378 well as what characters happen to be in the string at the time. If
379 any of the characters are at code points C<0x100> or above, you will get
380 a warning. To ensure that the output is explicitly rendered in the
381 encoding you desire--and to avoid the warning--open the stream with
382 the desired encoding. Some examples:
384 open FH, ">:utf8", "file";
386 open FH, ">:encoding(ucs2)", "file";
387 open FH, ">:encoding(UTF-8)", "file";
388 open FH, ">:encoding(shift_jis)", "file";
390 and on already open streams, use C<binmode()>:
392 binmode(STDOUT, ":utf8");
394 binmode(STDOUT, ":encoding(ucs2)");
395 binmode(STDOUT, ":encoding(UTF-8)");
396 binmode(STDOUT, ":encoding(shift_jis)");
398 The matching of encoding names is loose: case does not matter, and
399 many encodings have several aliases. Note that the C<:utf8> layer
400 must always be specified exactly like that; it is I<not> subject to
401 the loose matching of encoding names. Also note that currently C<:utf8> is unsafe for
402 input, because it accepts the data without validating that it is indeed valid
403 UTF-8; you should instead use C<:encoding(UTF-8)> (with or without a
406 See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
407 L<Encode::PerlIO> for the C<:encoding()> layer, and
408 L<Encode::Supported> for many encodings supported by the C<Encode>
411 Reading in a file that you know happens to be encoded in one of the
412 Unicode or legacy encodings does not magically turn the data into
413 Unicode in Perl's eyes. To do that, specify the appropriate
414 layer when opening files
416 open(my $fh,'<:encoding(UTF-8)', 'anything');
417 my $line_of_unicode = <$fh>;
419 open(my $fh,'<:encoding(Big5)', 'anything');
420 my $line_of_unicode = <$fh>;
422 The I/O layers can also be specified more flexibly with
423 the C<open> pragma. See L<open>, or look at the following example.
425 use open ':encoding(UTF-8)'; # input/output default encoding will be
428 print X chr(0x100), "\n";
431 printf "%#x\n", ord(<Y>); # this should print 0x100
434 With the C<open> pragma you can use the C<:locale> layer
436 BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
437 # the :locale will probe the locale environment variables like
439 use open OUT => ':locale'; # russki parusski
441 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
444 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
447 These methods install a transparent filter on the I/O stream that
448 converts data from the specified encoding when it is read in from the
449 stream. The result is always Unicode.
451 The L<open> pragma affects all the C<open()> calls after the pragma by
452 setting default layers. If you want to affect only certain
453 streams, use explicit layers directly in the C<open()> call.
455 You can switch encodings on an already opened stream by using
456 C<binmode()>; see L<perlfunc/binmode>.
458 The C<:locale> does not currently work with
459 C<open()> and C<binmode()>, only with the C<open> pragma. The
460 C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
461 C<binmode()>, and the C<open> pragma.
463 Similarly, you may use these I/O layers on output streams to
464 automatically convert Unicode to the specified encoding when it is
465 written to the stream. For example, the following snippet copies the
466 contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
467 the file "text.utf8", encoded as UTF-8:
469 open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis');
470 open(my $unicode, '>:utf8', 'text.utf8');
471 while (<$nihongo>) { print $unicode $_ }
473 The naming of encodings, both by the C<open()> and by the C<open>
474 pragma allows for flexible names: C<koi8-r> and C<KOI8R> will both be
477 Common encodings recognized by ISO, MIME, IANA, and various other
478 standardisation organisations are recognised; for a more detailed
479 list see L<Encode::Supported>.
481 C<read()> reads characters and returns the number of characters.
482 C<seek()> and C<tell()> operate on byte counts, as does C<sysseek()>.
484 C<sysread()> and C<syswrite()> should not be used on file handles with
485 character encoding layers, they behave badly, and that behaviour has
486 been deprecated since perl 5.24.
488 Notice that because of the default behaviour of not doing any
489 conversion upon input if there is no default layer,
490 it is easy to mistakenly write code that keeps on expanding a file
491 by repeatedly encoding the data:
495 local $/; ## read in the whole file of 8-bit characters
498 open F, ">:encoding(UTF-8)", "file";
499 print F $t; ## convert to UTF-8 on output
502 If you run this code twice, the contents of the F<file> will be twice
503 UTF-8 encoded. A C<use open ':encoding(UTF-8)'> would have avoided the
504 bug, or explicitly opening also the F<file> for input as UTF-8.
506 B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
507 Perl has been built with L<PerlIO>, which is the default
510 =head2 Displaying Unicode As Text
512 Sometimes you might want to display Perl scalars containing Unicode as
513 simple ASCII (or EBCDIC) text. The following subroutine converts
514 its argument so that Unicode characters with code points greater than
515 255 are displayed as C<\x{...}>, control characters (like C<\n>) are
516 displayed as C<\x..>, and the rest of the characters as themselves:
520 map { $_ > 255 # if wide character...
521 ? sprintf("\\x{%04X}", $_) # \x{...}
522 : chr($_) =~ /[[:cntrl:]]/ # else if control character...
523 ? sprintf("\\x%02X", $_) # \x..
524 : quotemeta(chr($_)) # else quoted or as themselves
525 } unpack("W*", $_[0])); # unpack Unicode characters
530 nice_string("foo\x{100}bar\n")
536 which is ready to be printed.
538 (C<\\x{}> is used here instead of C<\\N{}>, since it's most likely that
539 you want to see what the native values are.)
547 Starting in Perl 5.28, it is illegal for bit operators, like C<~>, to
548 operate on strings containing code points above 255.
552 The vec() function may produce surprising results if
553 used on strings containing characters with ordinal values above
554 255. In such a case, the results are consistent with the internal
555 encoding of the characters, but not with much else. So don't do
556 that, and starting in Perl 5.28, a deprecation message is issued if you
557 do so, becoming illegal in Perl 5.32.
561 Peeking At Perl's Internal Encoding
563 Normal users of Perl should never care how Perl encodes any particular
564 Unicode string (because the normal ways to get at the contents of a
565 string with Unicode--via input and output--should always be via
566 explicitly-defined I/O layers). But if you must, there are two
567 ways of looking behind the scenes.
569 One way of peeking inside the internal encoding of Unicode characters
570 is to use C<unpack("C*", ...> to get the bytes of whatever the string
571 encoding happens to be, or C<unpack("U0..", ...)> to get the bytes of the
574 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80
575 print join(" ", unpack("U0(H2)*", pack("U", 0x100))), "\n";
577 Yet another way would be to use the Devel::Peek module:
579 perl -MDevel::Peek -e 'Dump(chr(0x100))'
581 That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes
582 and Unicode characters in C<PV>. See also later in this document
583 the discussion about the C<utf8::is_utf8()> function.
587 =head2 Advanced Topics
595 The question of string equivalence turns somewhat complicated
596 in Unicode: what do you mean by "equal"?
598 (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
599 C<LATIN CAPITAL LETTER A>?)
601 The short answer is that by default Perl compares equivalence (C<eq>,
602 C<ne>) based only on code points of the characters. In the above
603 case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any
604 CAPITAL LETTER A's should be considered equal, or even A's of any case.
606 The long answer is that you need to consider character normalization
607 and casing issues: see L<Unicode::Normalize>, Unicode Technical Report #15,
608 L<Unicode Normalization Forms|https://www.unicode.org/reports/tr15> and
609 sections on case mapping in the L<Unicode Standard|https://www.unicode.org>.
611 As of Perl 5.8.0, the "Full" case-folding of I<Case
612 Mappings/SpecialCasing> is implemented, but bugs remain in C<qr//i> with them,
613 mostly fixed by 5.14, and essentially entirely by 5.18.
619 People like to see their strings nicely sorted--or as Unicode
620 parlance goes, collated. But again, what do you mean by collate?
622 (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
623 C<LATIN CAPITAL LETTER A WITH GRAVE>?)
625 The short answer is that by default, Perl compares strings (C<lt>,
626 C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
627 characters. In the above case, the answer is "after", since
628 C<0x00C1> > C<0x00C0>.
630 The long answer is that "it depends", and a good answer cannot be
631 given without knowing (at the very least) the language context.
632 See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
633 L<https://www.unicode.org/reports/tr10/>
643 Character Ranges and Classes
645 Character ranges in regular expression bracketed character classes ( e.g.,
646 C</[a-z]/>) and in the C<tr///> (also known as C<y///>) operator are not
647 magically Unicode-aware. What this means is that C<[A-Za-z]> will not
648 magically start to mean "all alphabetic letters" (not that it does mean that
649 even for 8-bit characters; for those, if you are using locales (L<perllocale>),
650 use C</[[:alpha:]]/>; and if not, use the 8-bit-aware property C<\p{alpha}>).
652 All the properties that begin with C<\p> (and its inverse C<\P>) are actually
653 character classes that are Unicode-aware. There are dozens of them, see
656 Starting in v5.22, you can use Unicode code points as the end points of
657 regular expression pattern character ranges, and the range will include
658 all Unicode code points that lie between those end points, inclusive.
660 qr/ [ \N{U+03} - \N{U+20} ] /xx
662 includes the code points
663 C<\N{U+03}>, C<\N{U+04}>, ..., C<\N{U+20}>.
665 This also works for ranges in C<tr///> starting in Perl v5.24.
669 String-To-Number Conversions
671 Unicode does define several other decimal--and numeric--characters
672 besides the familiar 0 to 9, such as the Arabic and Indic digits.
673 Perl does not support string-to-number conversion for digits other
674 than ASCII C<0> to C<9> (and ASCII C<a> to C<f> for hexadecimal).
675 To get safe conversions from any Unicode string, use
676 L<Unicode::UCD/num()>.
680 =head2 Questions With Answers
686 Will My Old Scripts Break?
688 Very probably not. Unless you are generating Unicode characters
689 somehow, old behaviour should be preserved. About the only behaviour
690 that has changed and which could start generating Unicode is the old
691 behaviour of C<chr()> where supplying an argument more than 255
692 produced a character modulo 255. C<chr(300)>, for example, was equal
693 to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
698 How Do I Make My Scripts Work With Unicode?
700 Very little work should be needed since nothing changes until you
701 generate Unicode data. The most important thing is getting input as
702 Unicode; for that, see the earlier I/O discussion.
703 To get full seamless Unicode support, add
704 C<use feature 'unicode_strings'> (or C<use 5.012> or higher) to your
709 How Do I Know Whether My String Is In Unicode?
711 You shouldn't have to care. But you may if your Perl is before 5.14.0
712 or you haven't specified C<use feature 'unicode_strings'> or C<use
713 5.012> (or higher) because otherwise the rules for the code points
714 in the range 128 to 255 are different depending on
715 whether the string they are contained within is in Unicode or not.
716 (See L<perlunicode/When Unicode Does Not Happen>.)
718 To determine if a string is in Unicode, use:
720 print utf8::is_utf8($string) ? 1 : 0, "\n";
722 But note that this doesn't mean that any of the characters in the
723 string are necessary UTF-8 encoded, or that any of the characters have
724 code points greater than 0xFF (255) or even 0x80 (128), or that the
725 string has any characters at all. All the C<is_utf8()> does is to
726 return the value of the internal "utf8ness" flag attached to the
727 C<$string>. If the flag is off, the bytes in the scalar are interpreted
728 as a single byte encoding. If the flag is on, the bytes in the scalar
729 are interpreted as the (variable-length, potentially multi-byte) UTF-8 encoded
730 code points of the characters. Bytes added to a UTF-8 encoded string are
731 automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars
732 are merged (double-quoted interpolation, explicit concatenation, or
733 printf/sprintf parameter substitution), the result will be UTF-8 encoded
734 as if copies of the byte strings were upgraded to UTF-8: for example,
740 the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but
741 C<$a> will stay byte-encoded.
743 Sometimes you might really need to know the byte length of a string
744 instead of the character length. For that use the C<bytes> pragma
745 and the C<length()> function:
747 my $unicode = chr(0x100);
748 print length($unicode), "\n"; # will print 1
750 print length($unicode), "\n"; # will print 2
751 # (the 0xC4 0x80 of the UTF-8)
756 How Do I Find Out What Encoding a File Has?
758 You might try L<Encode::Guess>, but it has a number of limitations.
762 How Do I Detect Data That's Not Valid In a Particular Encoding?
764 Use the C<Encode> package to try converting it.
769 if (eval { decode('UTF-8', $string, Encode::FB_CROAK); 1 }) {
770 # $string is valid UTF-8
772 # $string is not valid UTF-8
775 Or use C<unpack> to try decoding it:
778 @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
780 If invalid, a C<Malformed UTF-8 character> warning is produced. The "C0" means
781 "process the string character per character". Without that, the
782 C<unpack("U*", ...)> would work in C<U0> mode (the default if the format
783 string starts with C<U>) and it would return the bytes making up the UTF-8
784 encoding of the target string, something that will always work.
788 How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
790 This probably isn't as useful as you might think.
791 Normally, you shouldn't need to.
793 In one sense, what you are asking doesn't make much sense: encodings
794 are for characters, and binary data are not "characters", so converting
795 "data" into some encoding isn't meaningful unless you know in what
796 character set and encoding the binary data is in, in which case it's
797 not just binary data, now is it?
799 If you have a raw sequence of bytes that you know should be
800 interpreted via a particular encoding, you can use C<Encode>:
802 use Encode 'from_to';
803 from_to($data, "iso-8859-1", "UTF-8"); # from latin-1 to UTF-8
805 The call to C<from_to()> changes the bytes in C<$data>, but nothing
806 material about the nature of the string has changed as far as Perl is
807 concerned. Both before and after the call, the string C<$data>
808 contains just a bunch of 8-bit bytes. As far as Perl is concerned,
809 the encoding of the string remains as "system-native 8-bit bytes".
811 You might relate this to a fictional 'Translate' module:
815 Translate::from_to($phrase, 'english', 'deutsch');
816 ## phrase now contains "Ja"
818 The contents of the string changes, but not the nature of the string.
819 Perl doesn't know any more after the call than before that the
820 contents of the string indicates the affirmative.
822 Back to converting data. If you have (or want) data in your system's
823 native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
824 pack/unpack to convert to/from Unicode.
826 $native_string = pack("W*", unpack("U*", $Unicode_string));
827 $Unicode_string = pack("U*", unpack("W*", $native_string));
829 If you have a sequence of bytes you B<know> is valid UTF-8,
830 but Perl doesn't know it yet, you can make Perl a believer, too:
833 utf8::decode($Unicode);
837 $Unicode = pack("U0a*", $bytes);
839 You can find the bytes that make up a UTF-8 sequence with
841 @bytes = unpack("C*", $Unicode_string)
843 and you can create well-formed Unicode with
845 $Unicode_string = pack("U*", 0xff, ...)
849 How Do I Display Unicode? How Do I Input Unicode?
851 See L<http://www.alanwood.net/unicode/> and
852 L<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
856 How Does Unicode Work With Traditional Locales?
858 If your locale is a UTF-8 locale, starting in Perl v5.26, Perl works
859 well for all categories; before this, starting with Perl v5.20, it works
860 for all categories but C<LC_COLLATE>, which deals with
861 sorting and the C<cmp> operator. But note that the standard
862 C<L<Unicode::Collate>> and C<L<Unicode::Collate::Locale>> modules offer
863 much more powerful solutions to collation issues, and work on earlier
866 For other locales, starting in Perl 5.16, you can specify
868 use locale ':not_characters';
870 to get Perl to work well with them. The catch is that you
871 have to translate from the locale character set to/from Unicode
872 yourself. See L</Unicode IE<sol>O> above for how to
876 to accomplish this, but full details are in L<perllocale/Unicode and
877 UTF-8>, including gotchas that happen if you don't specify
882 =head2 Hexadecimal Notation
884 The Unicode standard prefers using hexadecimal notation because
885 that more clearly shows the division of Unicode into blocks of 256 characters.
886 Hexadecimal is also simply shorter than decimal. You can use decimal
887 notation, too, but learning to use hexadecimal just makes life easier
888 with the Unicode standard. The C<U+HHHH> notation uses hexadecimal,
891 The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
892 a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
893 four bits, or half a byte. C<print 0x..., "\n"> will show a
894 hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
895 show a decimal number in hexadecimal. If you have just the
896 "hex digits" of a hexadecimal number, you can use the C<hex()> function.
898 print 0x0009, "\n"; # 9
899 print 0x000a, "\n"; # 10
900 print 0x000f, "\n"; # 15
901 print 0x0010, "\n"; # 16
902 print 0x0011, "\n"; # 17
903 print 0x0100, "\n"; # 256
905 print 0x0041, "\n"; # 65
907 printf "%x\n", 65; # 41
908 printf "%#x\n", 65; # 0x41
910 print hex("41"), "\n"; # 65
912 =head2 Further Resources
920 L<https://www.unicode.org/>
926 L<https://www.unicode.org/faq/>
932 L<https://www.unicode.org/glossary/>
936 Unicode Recommended Reading List
938 The Unicode Consortium has a list of articles and books, some of which
939 give a much more in depth treatment of Unicode:
940 L<http://unicode.org/resources/readinglist.html>
944 Unicode Useful Resources
946 L<https://www.unicode.org/unicode/onlinedat/resources.html>
950 Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
952 L<http://www.alanwood.net/unicode/>
956 UTF-8 and Unicode FAQ for Unix/Linux
958 L<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
962 Legacy Character Sets
964 L<http://www.czyborra.com/>
965 L<http://www.eki.ee/letter/>
969 You can explore various information from the Unicode data files using
970 the C<Unicode::UCD> module.
974 =head1 UNICODE IN OLDER PERLS
976 If you cannot upgrade your Perl to 5.8.0 or later, you can still
977 do some Unicode processing by using the modules C<Unicode::String>,
978 C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
979 If you have the GNU recode installed, you can also use the
980 Perl front-end C<Convert::Recode> for character conversions.
982 The following are fast conversions from ISO 8859-1 (Latin-1) bytes
983 to UTF-8 bytes and back, the code works even with older Perl 5 versions.
985 # ISO 8859-1 to UTF-8
986 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
988 # UTF-8 to ISO 8859-1
989 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
993 L<perlunitut>, L<perlunicode>, L<Encode>, L<open>, L<utf8>, L<bytes>,
994 L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>,
997 =head1 ACKNOWLEDGMENTS
999 Thanks to the kind readers of the perl5-porters@perl.org,
1000 perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
1001 mailing lists for their valuable feedback.
1003 =head1 AUTHOR, COPYRIGHT, AND LICENSE
1005 Copyright 2001-2011 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>.
1006 Now maintained by Perl 5 Porters.
1008 This document may be distributed under the same terms as Perl itself.