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1 | =head1 NAME |
2 | |
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3 | perluniintro - Perl Unicode introduction |
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4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | This document gives a general idea of Unicode and how to use Unicode |
8 | in Perl. |
9 | |
10 | =head2 Unicode |
11 | |
12 | Unicode is a character set standard with plans to cover all of the |
13 | writing systems of the world, plus many other symbols. |
14 | |
15 | Unicode and ISO/IEC 10646 are coordinated standards that provide code |
16 | points for the 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 | |
23 | A Unicode I<character> is an abstract entity. It is not bound to any |
24 | particular integer width, and especially not to the C language C<char>. |
25 | Unicode is language neutral and display neutral: it doesn't encode the |
26 | language of the text, and it doesn't define fonts or other graphical |
27 | layout details. Unicode operates on characters and on text built from |
28 | those characters. |
29 | |
30 | Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK |
31 | SMALL LETTER ALPHA>, and then unique numbers for those, hexadecimal |
32 | 0x0041 or 0x03B1 for those particular characters. Such unique |
33 | numbers are called I<code points>. |
34 | |
35 | The Unicode standard prefers using hexadecimal notation for the code |
36 | points. (In case this notation, numbers like 0x0041, is unfamiliar to |
37 | you, take a peek at a later section, L</"Hexadecimal Notation">.) |
38 | The Unicode standard uses the notation C<U+0041 LATIN CAPITAL LETTER A>, |
39 | which gives the hexadecimal code point, and the normative name of |
40 | the character. |
41 | |
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. |
47 | |
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 | a base character and modifiers is called a I<combining character |
52 | sequence>. |
53 | |
54 | Whether to call these combining character sequences, as a whole, |
55 | "characters" depends on your point of view. If you are a programmer, you |
56 | probably would tend towards seeing each element in the sequences as one |
57 | unit, one "character", but from the user viewpoint, the sequence as a |
58 | whole is probably considered one "character", since that's probably what |
59 | it looks like in the context of the user's language. |
60 | |
61 | With this "as a whole" view of characters, the number of characters is |
62 | open-ended. But in the programmer's "one unit is one character" point of |
63 | view, the concept of "characters" is more deterministic, and so we take |
64 | that point of view in this document: one "character" is one Unicode |
65 | code point, be it a base character or a combining character. |
66 | |
67 | For some of the combinations there are I<precomposed> characters, |
68 | for example C<LATIN CAPITAL LETTER A WITH ACUTE> is defined as |
69 | a single code point. These precomposed characters are, however, |
70 | often available only for some combinations, and mainly they are |
71 | meant to support round-trip conversions between Unicode and legacy |
72 | standards (like the ISO 8859), and in general case the composing |
73 | method is more extensible. To support conversion between the |
74 | different compositions of the characters, various I<normalization |
75 | forms> are also defined. |
76 | |
77 | Because of backward compatibility with legacy encodings, the "a unique |
78 | number for every character" breaks down a bit: "at least one number |
79 | for every character" is closer to truth. (This happens when the same |
80 | character has been encoded in several legacy encodings.) The converse |
81 | is also not true: not every code point has an assigned character. |
82 | Firstly, there are unallocated code points within otherwise used |
83 | blocks. Secondly, there are special Unicode control characters that |
84 | do not represent true characters. |
85 | |
86 | A common myth about Unicode is that it would be "16-bit", that is, |
87 | 0x10000 (or 65536) characters from 0x0000 to 0xFFFF. B<This is untrue.> |
88 | Since Unicode 2.0 Unicode has been defined all the way up to 21 bits |
89 | (0x10FFFF), and since 3.1 characters have been defined beyond 0xFFFF. |
90 | The first 0x10000 characters are called the I<Plane 0>, or the I<Basic |
91 | Multilingual Plane> (BMP). With the Unicode 3.1, 17 planes in all are |
92 | defined (but nowhere near full of defined characters yet). |
93 | |
94 | Another myth is that the 256-character blocks have something to do |
95 | with languages: a block per language. B<Also this is untrue.> |
96 | The division into the blocks exists but it is almost completely |
97 | accidental, an artifact of how the characters have been historically |
98 | allocated. Instead, there is a concept called I<scripts>, which may |
99 | be more useful: there is C<Latin> script, C<Greek> script, and so on. |
100 | Scripts usually span several parts of several blocks. For further |
101 | information see L<Unicode::UCD>. |
102 | |
103 | The Unicode code points are just abstract numbers. To input and |
104 | output these abstract numbers, the numbers must be I<encoded> somehow. |
105 | Unicode defines several I<character encoding forms>, of which I<UTF-8> |
106 | is perhaps the most popular. UTF-8 is a variable length encoding that |
107 | encodes Unicode characters as 1 to 6 bytes (only 4 with the currently |
108 | defined characters). Other encodings are UTF-16 and UTF-32 and their |
109 | big and little endian variants (UTF-8 is byteorder independent). |
110 | The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms. |
111 | |
112 | For more information about encodings, for example to learn what |
113 | I<surrogates> and I<byte order marks> (BOMs) are, see L<perlunicode>. |
114 | |
115 | =head2 Perl's Unicode Support |
116 | |
117 | Starting from Perl 5.6.0, Perl has had the capability of handling |
118 | Unicode natively. The first recommended release for serious Unicode |
119 | work is Perl 5.8.0, however. The maintenance release 5.6.1 fixed many |
120 | of the problems of the initial implementation of Unicode, but for |
121 | example regular expressions didn't really work with Unicode. |
122 | |
123 | B<Starting from Perl 5.8.0, the use of C<use utf8> is no longer |
124 | necessary.> In earlier releases the C<utf8> pragma was used to declare |
125 | that operations in the current block or file would be Unicode-aware. |
126 | This model was found to be wrong, or at least clumsy: the Unicodeness |
127 | is now carried with the data, not attached to the operations. (There |
128 | is one remaining case where an explicit C<use utf8> is needed: if your |
129 | Perl script is in UTF-8, you can use UTF-8 in your variable and |
130 | subroutine names, and in your string and regular expression literals, |
131 | by saying C<use utf8>. This is not the default because that would |
132 | break existing scripts having legacy 8-bit data in them.) |
133 | |
134 | =head2 Perl's Unicode Model |
135 | |
136 | Perl supports both the old, pre-5.6, model of strings of eight-bit |
137 | native bytes, and strings of Unicode characters. The principle is |
138 | that Perl tries to keep its data as eight-bit bytes for as long as |
139 | possible, but as soon as Unicodeness cannot be avoided, the data is |
140 | transparently upgraded to Unicode. |
141 | |
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142 | Internally, Perl currently uses either whatever the native eight-bit |
143 | character set of the platform (for example Latin-1) or UTF-8 to encode |
144 | Unicode strings. Specifically, if all code points in the string are |
145 | 0xFF or less, Perl uses Latin-1. Otherwise, it uses UTF-8. |
146 | |
147 | A user of Perl does not normally need to know nor care how Perl happens |
148 | to encodes its internal strings, but it becomes relevant when outputting |
149 | Unicode strings to a stream without a discipline (one with the "default |
150 | default"). In such a case, the raw bytes used internally (the native |
151 | character set or UTF-8, as appropriate for each string) will be used, |
152 | and if warnings are turned on, a "Wide character" warning will be issued |
153 | if those strings contain a character beyond 0x00FF. |
154 | |
155 | For example, |
156 | |
157 | perl -w -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"' |
158 | |
159 | produces a fairly useless mixture of native bytes and UTF-8, as well |
160 | as a warning. |
161 | |
162 | To output UTF-8 always, use the ":utf8" output discipline. Prepending |
163 | |
164 | binmode(STDOUT, ":utf8"); |
165 | |
166 | to this sample program ensures the output is completely UTF-8, and |
167 | of course, removes the warning. Another way to achieve this is the |
168 | L<encoding> pragma, discussed later in L</Legacy Encodings>. |
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169 | |
170 | Perl 5.8.0 will also support Unicode on EBCDIC platforms. There the |
171 | support is somewhat harder to implement since additional conversions |
172 | are needed at every step. Because of these difficulties the Unicode |
173 | support won't be quite as full as in other, mainly ASCII-based, |
174 | platforms (the Unicode support will be better than in the 5.6 series, |
175 | which didn't work much at all for EBCDIC platform). On EBCDIC |
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176 | platforms the internal encoding form used is UTF-EBCDIC instead |
177 | of UTF-8 (the difference is that as UTF-8 is "ASCII-safe" in that |
178 | ASCII characters encode to UTF-8 as-is, UTF-EBCDIC is "EBCDIC-safe"). |
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179 | |
180 | =head2 Creating Unicode |
181 | |
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182 | To create Unicode literals for code points above 0xFF, use the |
183 | C<\x{...}> notation in doublequoted strings: |
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184 | |
185 | my $smiley = "\x{263a}"; |
186 | |
187 | Similarly for regular expression literals |
188 | |
189 | $smiley =~ /\x{263a}/; |
190 | |
191 | At run-time you can use C<chr()>: |
192 | |
193 | my $hebrew_alef = chr(0x05d0); |
194 | |
195 | (See L</"Further Resources"> for how to find all these numeric codes.) |
196 | |
197 | Naturally, C<ord()> will do the reverse: turn a character to a code point. |
198 | |
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199 | Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}> |
200 | and C<chr(...)> for arguments less than 0x100 (decimal 256) will |
201 | generate an eight-bit character for backward compatibility with older |
202 | Perls. For arguments of 0x100 or more, Unicode will always be |
203 | produced. If you want UTF-8 always, use C<pack("U", ...)> instead of |
204 | C<\x..>, C<\x{...}>, or C<chr()>. |
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205 | |
206 | You can also use the C<charnames> pragma to invoke characters |
207 | by name in doublequoted strings: |
208 | |
209 | use charnames ':full'; |
210 | my $arabic_alef = "\N{ARABIC LETTER ALEF}"; |
211 | |
212 | And, as mentioned above, you can also C<pack()> numbers into Unicode |
213 | characters: |
214 | |
215 | my $georgian_an = pack("U", 0x10a0); |
216 | |
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217 | Note that both C<\x{...}> and C<\N{...}> are compile-time string |
218 | constants: you cannot use variables in them. if you want similar |
219 | run-time functionality, use C<chr()> and C<charnames::vianame()>. |
220 | |
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221 | =head2 Handling Unicode |
222 | |
223 | Handling Unicode is for the most part transparent: just use the |
224 | strings as usual. Functions like C<index()>, C<length()>, and |
225 | C<substr()> will work on the Unicode characters; regular expressions |
226 | will work on the Unicode characters (see L<perlunicode> and L<perlretut>). |
227 | |
228 | Note that Perl does B<not> consider combining character sequences |
229 | to be characters, such for example |
230 | |
231 | use charnames ':full'; |
232 | print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; |
233 | |
234 | will print 2, not 1. The only exception is that regular expressions |
235 | have C<\X> for matching a combining character sequence. |
236 | |
237 | When life is not quite so transparent is working with legacy |
238 | encodings, and I/O, and certain special cases. |
239 | |
240 | =head2 Legacy Encodings |
241 | |
242 | When you combine legacy data and Unicode the legacy data needs |
243 | to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if |
244 | applicable) is assumed. You can override this assumption by |
245 | using the C<encoding> pragma, for example |
246 | |
247 | use encoding 'latin2'; # ISO 8859-2 |
248 | |
249 | in which case literals (string or regular expression) and chr/ord |
250 | in your whole script are assumed to produce Unicode characters from |
251 | ISO 8859-2 code points. Note that the matching for the encoding |
252 | names is forgiving: instead of C<latin2> you could have said |
253 | C<Latin 2>, or C<iso8859-2>, and so forth. With just |
254 | |
255 | use encoding; |
256 | |
257 | first the environment variable C<PERL_ENCODING> will be consulted, |
258 | and if that doesn't exist, ISO 8859-1 (Latin 1) will be assumed. |
259 | |
260 | The C<Encode> module knows about many encodings and it has interfaces |
261 | for doing conversions between those encodings: |
262 | |
263 | use Encode 'from_to'; |
264 | from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8 |
265 | |
266 | =head2 Unicode I/O |
267 | |
268 | Normally writing out Unicode data |
269 | |
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270 | print FH chr(0x100), "\n"; |
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271 | |
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272 | will print out the raw UTF-8 bytes, but you will get a warning |
273 | out of that if you use C<-w> or C<use warnings>. To avoid the |
274 | warning open the stream explicitly in UTF-8: |
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275 | |
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276 | open FH, ">:utf8", "file"; |
277 | |
278 | and on already open streams use C<binmode()>: |
279 | |
280 | binmode(STDOUT, ":utf8"); |
281 | |
282 | Reading in correctly formed UTF-8 data will not magically turn |
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283 | the data into Unicode in Perl's eyes. |
284 | |
285 | You can use either the C<':utf8'> I/O discipline when opening files |
286 | |
287 | open(my $fh,'<:utf8', 'anything'); |
288 | my $line_of_utf8 = <$fh>; |
289 | |
290 | The I/O disciplines can also be specified more flexibly with |
291 | the C<open> pragma; see L<open>: |
292 | |
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293 | use open ':utf8'; # input and output default discipline will be UTF-8 |
294 | open X, ">file"; |
295 | print X chr(0x100), "\n"; |
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296 | close X; |
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297 | open Y, "<file"; |
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298 | printf "%#x\n", ord(<Y>); # this should print 0x100 |
299 | close Y; |
300 | |
301 | With the C<open> pragma you can use the C<:locale> discipline |
302 | |
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303 | $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R'; |
304 | # the :locale will probe the locale environment variables like LC_ALL |
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305 | use open OUT => ':locale'; # russki parusski |
306 | open(O, ">koi8"); |
307 | print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 |
308 | close O; |
309 | open(I, "<koi8"); |
310 | printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1 |
311 | close I; |
312 | |
313 | or you can also use the C<':encoding(...)'> discipline |
314 | |
315 | open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); |
316 | my $line_of_iliad = <$epic>; |
317 | |
318 | Both of these methods install a transparent filter on the I/O stream that |
319 | will convert data from the specified encoding when it is read in from the |
320 | stream. In the first example the F<anything> file is assumed to be UTF-8 |
321 | encoded Unicode, in the second example the F<iliad.greek> file is assumed |
322 | to be ISO-8858-7 encoded Greek, but the lines read in will be in both |
323 | cases Unicode. |
324 | |
325 | The L<open> pragma affects all the C<open()> calls after the pragma by |
326 | setting default disciplines. If you want to affect only certain |
327 | streams, use explicit disciplines directly in the C<open()> call. |
328 | |
329 | You can switch encodings on an already opened stream by using |
330 | C<binmode()>, see L<perlfunc/binmode>. |
331 | |
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332 | The C<:locale> does not currently (as of Perl 5.8.0) work with |
333 | C<open()> and C<binmode()>, only with the C<open> pragma. The |
334 | C<:utf8> and C<:encoding(...)> do work with all of C<open()>, |
335 | C<binmode()>, and the C<open> pragma. |
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336 | |
337 | Similarly, you may use these I/O disciplines on input streams to |
338 | automatically convert data from the specified encoding when it is |
339 | written to the stream. |
340 | |
341 | open(my $unicode, '<:utf8', 'japanese.uni'); |
342 | open(my $nihongo, '>:encoding(iso2022-jp)', 'japanese.jp'); |
343 | while (<$unicode>) { print $nihongo } |
344 | |
345 | The naming of encodings, both by the C<open()> and by the C<open> |
346 | pragma, is similarly understanding as with the C<encoding> pragma: |
347 | C<koi8-r> and C<KOI8R> will both be understood. |
348 | |
349 | Common encodings recognized by ISO, MIME, IANA, and various other |
350 | standardisation organisations are recognised, for a more detailed |
351 | list see L<Encode>. |
352 | |
353 | C<read()> reads characters and returns the number of characters. |
354 | C<seek()> and C<tell()> operate on byte counts, as do C<sysread()> |
355 | and C<sysseek()>. |
356 | |
357 | Notice that because of the default behaviour "input is not UTF-8" |
358 | it is easy to mistakenly write code that keeps on expanding a file |
359 | by repeatedly encoding it in UTF-8: |
360 | |
361 | # BAD CODE WARNING |
362 | open F, "file"; |
363 | local $/; # read in the whole file |
364 | $t = <F>; |
365 | close F; |
366 | open F, ">:utf8", "file"; |
367 | print F $t; |
368 | close F; |
369 | |
370 | If you run this code twice, the contents of the F<file> will be twice |
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371 | UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or |
372 | explicitly opening also the F<file> for input as UTF-8. |
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373 | |
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374 | B<NOTE>: the C<:utf8> and C<:encoding> features work only if your |
375 | Perl has been built with the new "perlio" feature. Almost all |
376 | Perl 5.8 platforms do use "perlio", though: you can see whether |
377 | yours is by running "perl -V" and looking for C<useperlio=define>. |
378 | |
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379 | =head2 Displaying Unicode As Text |
380 | |
381 | Sometimes you might want to display Perl scalars containing Unicode as |
382 | simple ASCII (or EBCDIC) text. The following subroutine will convert |
383 | its argument so that Unicode characters with code points greater than |
384 | 255 are displayed as "\x{...}", control characters (like "\n") are |
385 | displayed as "\x..", and the rest of the characters as themselves. |
386 | |
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387 | sub nice_string { |
388 | join("", |
389 | map { $_ > 255 ? # if wide character... |
390 | sprintf("\\x{%x}", $_) : # \x{...} |
391 | chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... |
392 | sprintf("\\x%02x", $_) : # \x.. |
393 | chr($_) # else as themselves |
394 | } unpack("U*", $_[0])); # unpack Unicode characters |
395 | } |
396 | |
397 | For example, |
398 | |
399 | nice_string("foo\x{100}bar\n") |
400 | |
401 | will return: |
402 | |
403 | "foo\x{100}bar\x0a" |
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404 | |
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405 | =head2 Special Cases |
406 | |
407 | =over 4 |
408 | |
409 | =item * |
410 | |
411 | Bit Complement Operator ~ And vec() |
412 | |
413 | The bit complement operator C<~> will produce surprising results if |
414 | used on strings containing Unicode characters. The results are |
415 | consistent with the internal UTF-8 encoding of the characters, but not |
416 | with much else. So don't do that. Similarly for vec(): you will be |
417 | operating on the UTF-8 bit patterns of the Unicode characters, not on |
418 | the bytes, which is very probably not what you want. |
419 | |
420 | =item * |
421 | |
422 | Peeking At UTF-8 |
423 | |
424 | One way of peeking inside the internal encoding of Unicode characters |
425 | is to use C<unpack("C*", ...> to get the bytes, or C<unpack("H*", ...)> |
426 | to display the bytes: |
427 | |
428 | # this will print c4 80 for the UTF-8 bytes 0xc4 0x80 |
429 | print join(" ", unpack("H*", pack("U", 0x100))), "\n"; |
430 | |
431 | Yet another way would be to use the Devel::Peek module: |
432 | |
433 | perl -MDevel::Peek -e 'Dump(chr(0x100))' |
434 | |
435 | That will show the UTF8 flag in FLAGS and both the UTF-8 bytes |
436 | and Unicode characters in PV. See also later in this document |
437 | the discussion about the C<is_utf8> function of the C<Encode> module. |
438 | |
439 | =back |
440 | |
441 | =head2 Advanced Topics |
442 | |
443 | =over 4 |
444 | |
445 | =item * |
446 | |
447 | String Equivalence |
448 | |
449 | The question of string equivalence turns somewhat complicated |
450 | in Unicode: what do you mean by equal? |
451 | |
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452 | (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to |
453 | C<LATIN CAPITAL LETTER A>?) |
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454 | |
455 | The short answer is that by default Perl compares equivalence |
456 | (C<eq>, C<ne>) based only on code points of the characters. |
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457 | In the above case, the answer is no (because 0x00C1 != 0x0041). But sometimes any |
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458 | CAPITAL LETTER As being considered equal, or even any As of any case, |
459 | would be desirable. |
460 | |
461 | The long answer is that you need to consider character normalization |
462 | and casing issues: see L<Unicode::Normalize>, and Unicode Technical |
463 | Reports #15 and #21, I<Unicode Normalization Forms> and I<Case |
464 | Mappings>, http://www.unicode.org/unicode/reports/tr15/ |
465 | http://www.unicode.org/unicode/reports/tr21/ |
466 | |
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467 | As of Perl 5.8.0, regular expression case-ignoring matching |
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468 | implements only 1:1 semantics: one character matches one character. |
469 | In I<Case Mappings> both 1:N and N:1 matches are defined. |
470 | |
471 | =item * |
472 | |
473 | String Collation |
474 | |
475 | People like to see their strings nicely sorted, or as Unicode |
476 | parlance goes, collated. But again, what do you mean by collate? |
477 | |
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478 | (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after |
479 | C<LATIN CAPITAL LETTER A WITH GRAVE>?) |
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480 | |
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481 | The short answer is that by default, Perl compares strings (C<lt>, |
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482 | C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the |
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483 | characters. In the above case, the answer is "after", since 0x00C1 > 0x00C0. |
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484 | |
485 | The long answer is that "it depends", and a good answer cannot be |
486 | given without knowing (at the very least) the language context. |
487 | See L<Unicode::Collate>, and I<Unicode Collation Algorithm> |
488 | http://www.unicode.org/unicode/reports/tr10/ |
489 | |
490 | =back |
491 | |
492 | =head2 Miscellaneous |
493 | |
494 | =over 4 |
495 | |
496 | =item * |
497 | |
498 | Character Ranges |
499 | |
500 | Character ranges in regular expression character classes (C</[a-z]/>) |
501 | and in the C<tr///> (also known as C<y///>) operator are not magically |
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502 | Unicode-aware. What this means that C<[A-Za-z]> will not magically start |
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503 | to mean "all alphabetic letters" (not that it does mean that even for |
504 | 8-bit characters, you should be using C</[[:alpha]]/> for that). |
505 | |
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506 | For specifying things like that in regular expressions, you can use the |
507 | various Unicode properties, C<\pL> or perhaps C<\p{Alphabetic}>, in this particular case. You can |
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508 | use Unicode code points as the end points of character ranges, but |
509 | that means that particular code point range, nothing more. For |
510 | further information, see L<perlunicode>. |
511 | |
512 | =item * |
513 | |
514 | String-To-Number Conversions |
515 | |
516 | Unicode does define several other decimal (and numeric) characters |
517 | than just the familiar 0 to 9, such as the Arabic and Indic digits. |
518 | Perl does not support string-to-number conversion for digits other |
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519 | than ASCII 0 to 9 (and ASCII a to f for hexadecimal). |
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520 | |
521 | =back |
522 | |
523 | =head2 Questions With Answers |
524 | |
525 | =over 4 |
526 | |
527 | =item Will My Old Scripts Break? |
528 | |
529 | Very probably not. Unless you are generating Unicode characters |
530 | somehow, any old behaviour should be preserved. About the only |
531 | behaviour that has changed and which could start generating Unicode |
532 | is the old behaviour of C<chr()> where supplying an argument more |
533 | than 255 produced a character modulo 255 (for example, C<chr(300)> |
534 | was equal to C<chr(45)>). |
535 | |
536 | =item How Do I Make My Scripts Work With Unicode? |
537 | |
538 | Very little work should be needed since nothing changes until you |
539 | somehow generate Unicode data. The greatest trick will be getting |
540 | input as Unicode, and for that see the earlier I/O discussion. |
541 | |
542 | =item How Do I Know Whether My String Is In Unicode? |
543 | |
544 | You shouldn't care. No, you really shouldn't. If you have |
545 | to care (beyond the cases described above), it means that we |
546 | didn't get the transparency of Unicode quite right. |
547 | |
548 | Okay, if you insist: |
549 | |
550 | use Encode 'is_utf8'; |
551 | print is_utf8($string) ? 1 : 0, "\n"; |
552 | |
553 | But note that this doesn't mean that any of the characters in the |
554 | string are necessary UTF-8 encoded, or that any of the characters have |
555 | code points greater than 0xFF (255) or even 0x80 (128), or that the |
556 | string has any characters at all. All the C<is_utf8()> does is to |
557 | return the value of the internal "utf8ness" flag attached to the |
558 | $string. If the flag is on, characters added to that string will be |
559 | automatically upgraded to UTF-8 (and even then only if they really |
560 | need to be upgraded, that is, if their code point is greater than 0xFF). |
561 | |
562 | Sometimes you might really need to know the byte length of a string |
563 | instead of the character length. For that use the C<bytes> pragma |
564 | and its only defined function C<length()>: |
565 | |
566 | my $unicode = chr(0x100); |
567 | print length($unicode), "\n"; # will print 1 |
568 | use bytes; |
569 | print length($unicode), "\n"; # will print 2 (the 0xC4 0x80 of the UTF-8) |
570 | |
571 | =item How Do I Detect Invalid UTF-8? |
572 | |
573 | Either |
574 | |
575 | use Encode 'encode_utf8'; |
576 | if (encode_utf8($string)) { |
577 | # valid |
578 | } else { |
579 | # invalid |
580 | } |
581 | |
582 | or |
583 | |
584 | use warnings; |
585 | @chars = unpack("U0U*", "\xFF"); # will warn |
586 | |
587 | The warning will be C<Malformed UTF-8 character (byte 0xff) in |
588 | unpack>. The "U0" means "expect strictly UTF-8 encoded Unicode". |
589 | Without that the C<unpack("U*", ...)> would accept also data like |
590 | C<chr(0xFF>). |
591 | |
592 | =item How Do I Convert Data Into UTF-8? Or Vice Versa? |
593 | |
594 | This probably isn't as useful (or simple) as you might think. |
595 | Also, normally you shouldn't need to. |
596 | |
597 | In one sense what you are asking doesn't make much sense: UTF-8 is |
598 | (intended as an) Unicode encoding, so converting "data" into UTF-8 |
599 | isn't meaningful unless you know in what character set and encoding |
600 | the binary data is in, and in this case you can use C<Encode>. |
601 | |
602 | use Encode 'from_to'; |
603 | from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 |
604 | |
605 | If you have ASCII (really 7-bit US-ASCII), you already have valid |
606 | UTF-8, the lowest 128 characters of UTF-8 encoded Unicode and US-ASCII |
607 | are equivalent. |
608 | |
609 | If you have Latin-1 (or want Latin-1), you can just use pack/unpack: |
610 | |
611 | $latin1 = pack("C*", unpack("U*", $utf8)); |
612 | $utf8 = pack("U*", unpack("C*", $latin1)); |
613 | |
614 | (The same works for EBCDIC.) |
615 | |
616 | If you have a sequence of bytes you B<know> is valid UTF-8, |
617 | but Perl doesn't know it yet, you can make Perl a believer, too: |
618 | |
619 | use Encode 'decode_utf8'; |
620 | $utf8 = decode_utf8($bytes); |
621 | |
622 | You can convert well-formed UTF-8 to a sequence of bytes, but if |
623 | you just want to convert random binary data into UTF-8, you can't. |
624 | Any random collection of bytes isn't well-formed UTF-8. You can |
625 | use C<unpack("C*", $string)> for the former, and you can create |
626 | well-formed Unicode/UTF-8 data by C<pack("U*", 0xff, ...)>. |
627 | |
628 | =item How Do I Display Unicode? How Do I Input Unicode? |
629 | |
630 | See http://www.hclrss.demon.co.uk/unicode/ and |
631 | http://www.cl.cam.ac.uk/~mgk25/unicode.html |
632 | |
633 | =item How Does Unicode Work With Traditional Locales? |
634 | |
635 | In Perl, not very well. Avoid using locales through the C<locale> |
636 | pragma. Use only one or the other. |
637 | |
638 | =back |
639 | |
640 | =head2 Hexadecimal Notation |
641 | |
642 | The Unicode standard prefers using hexadecimal notation because that |
643 | shows better the division of Unicode into blocks of 256 characters. |
644 | Hexadecimal is also simply shorter than decimal. You can use decimal |
645 | notation, too, but learning to use hexadecimal just makes life easier |
646 | with the Unicode standard. |
647 | |
648 | The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and> |
649 | a-f (or A-F, case doesn't matter). Each hexadecimal digit represents |
650 | four bits, or half a byte. C<print 0x..., "\n"> will show a |
651 | hexadecimal number in decimal, and C<printf "%x\n", $decimal> will |
652 | show a decimal number in hexadecimal. If you have just the |
653 | "hexdigits" of a hexadecimal number, you can use the C<hex()> |
654 | function. |
655 | |
656 | print 0x0009, "\n"; # 9 |
657 | print 0x000a, "\n"; # 10 |
658 | print 0x000f, "\n"; # 15 |
659 | print 0x0010, "\n"; # 16 |
660 | print 0x0011, "\n"; # 17 |
661 | print 0x0100, "\n"; # 256 |
662 | |
663 | print 0x0041, "\n"; # 65 |
664 | |
665 | printf "%x\n", 65; # 41 |
666 | printf "%#x\n", 65; # 0x41 |
667 | |
668 | print hex("41"), "\n"; # 65 |
669 | |
670 | =head2 Further Resources |
671 | |
672 | =over 4 |
673 | |
674 | =item * |
675 | |
676 | Unicode Consortium |
677 | |
678 | http://www.unicode.org/ |
679 | |
680 | =item * |
681 | |
682 | Unicode FAQ |
683 | |
684 | http://www.unicode.org/unicode/faq/ |
685 | |
686 | =item * |
687 | |
688 | Unicode Glossary |
689 | |
690 | http://www.unicode.org/glossary/ |
691 | |
692 | =item * |
693 | |
694 | Unicode Useful Resources |
695 | |
696 | http://www.unicode.org/unicode/onlinedat/resources.html |
697 | |
698 | =item * |
699 | |
700 | Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications |
701 | |
702 | http://www.hclrss.demon.co.uk/unicode/ |
703 | |
704 | =item * |
705 | |
706 | UTF-8 and Unicode FAQ for Unix/Linux |
707 | |
708 | http://www.cl.cam.ac.uk/~mgk25/unicode.html |
709 | |
710 | =item * |
711 | |
712 | Legacy Character Sets |
713 | |
714 | http://www.czyborra.com/ |
715 | http://www.eki.ee/letter/ |
716 | |
717 | =item * |
718 | |
719 | The Unicode support files live within the Perl installation in the |
720 | directory |
721 | |
722 | $Config{installprivlib}/unicore |
723 | |
724 | in Perl 5.8.0 or newer, and |
725 | |
726 | $Config{installprivlib}/unicode |
727 | |
728 | in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to |
729 | avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) |
730 | The main Unicode data file is F<Unicode.txt> (or F<Unicode.301> in |
731 | Perl 5.6.1.) You can find the C<$Config{installprivlib}> by |
732 | |
733 | perl "-V:installprivlib" |
734 | |
735 | Note that some of the files have been renamed from the Unicode |
736 | standard since the Perl installation tries to live by the "8.3" |
737 | filenaming restrictions. The renamings are shown in the |
738 | accompanying F<rename> file. |
739 | |
740 | You can explore various information from the Unicode data files using |
741 | the C<Unicode::UCD> module. |
742 | |
743 | =back |
744 | |
f6edf83b |
745 | =head1 UNICODE IN OLDER PERLS |
746 | |
747 | If you cannot upgrade your Perl to 5.8.0 or later, you can still |
748 | do some Unicode processing by using the modules C<Unicode::String>, |
749 | C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN. |
750 | If you have the GNU recode installed, you can also use the |
751 | Perl frontend C<Convert::Recode> for character conversions. |
752 | |
ba62762e |
753 | =head1 SEE ALSO |
754 | |
755 | L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>, |
756 | L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD> |
757 | |
758 | =head1 ACKNOWLEDGEMENTS |
759 | |
760 | Thanks to the kind readers of the perl5-porters@perl.org, |
761 | perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org |
762 | mailing lists for their valuable feedback. |
763 | |
764 | =head1 AUTHOR, COPYRIGHT, AND LICENSE |
765 | |
766 | Copyright 2001 Jarkko Hietaniemi <jhi@iki.fi> |
767 | |
768 | This document may be distributed under the same terms as Perl itself. |