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1 | =head1 NAME |
2 | ||
07fcf8ff | 3 | perluniintro - Perl Unicode introduction |
ba62762e JH |
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 | ||
142 | The internal encoding of Unicode in Perl is UTF-8. The internal | |
143 | encoding is normally hidden, however, and one need not and should not | |
144 | worry about the internal encoding at all: it is all just characters. | |
145 | ||
146 | Perl 5.8.0 will also support Unicode on EBCDIC platforms. There the | |
147 | support is somewhat harder to implement since additional conversions | |
148 | are needed at every step. Because of these difficulties the Unicode | |
149 | support won't be quite as full as in other, mainly ASCII-based, | |
150 | platforms (the Unicode support will be better than in the 5.6 series, | |
151 | which didn't work much at all for EBCDIC platform). On EBCDIC | |
152 | platforms the internal encoding form used is UTF-EBCDIC. | |
153 | ||
154 | =head2 Creating Unicode | |
155 | ||
156 | To create Unicode literals, use the C<\x{...}> notation in | |
157 | doublequoted strings: | |
158 | ||
159 | my $smiley = "\x{263a}"; | |
160 | ||
161 | Similarly for regular expression literals | |
162 | ||
163 | $smiley =~ /\x{263a}/; | |
164 | ||
165 | At run-time you can use C<chr()>: | |
166 | ||
167 | my $hebrew_alef = chr(0x05d0); | |
168 | ||
169 | (See L</"Further Resources"> for how to find all these numeric codes.) | |
170 | ||
171 | Naturally, C<ord()> will do the reverse: turn a character to a code point. | |
172 | ||
8a5e5dd5 JH |
173 | Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}> |
174 | and C<chr(...)> for arguments less than 0x100 (decimal 256) will | |
175 | generate an eight-bit character for backward compatibility with older | |
176 | Perls. For arguments of 0x100 or more, Unicode will always be | |
177 | produced. If you want UTF-8 always, use C<pack("U", ...)> instead of | |
178 | C<\x..>, C<\x{...}>, or C<chr()>. | |
ba62762e JH |
179 | |
180 | You can also use the C<charnames> pragma to invoke characters | |
181 | by name in doublequoted strings: | |
182 | ||
183 | use charnames ':full'; | |
184 | my $arabic_alef = "\N{ARABIC LETTER ALEF}"; | |
185 | ||
186 | And, as mentioned above, you can also C<pack()> numbers into Unicode | |
187 | characters: | |
188 | ||
189 | my $georgian_an = pack("U", 0x10a0); | |
190 | ||
8a5e5dd5 JH |
191 | Note that both C<\x{...}> and C<\N{...}> are compile-time string |
192 | constants: you cannot use variables in them. if you want similar | |
193 | run-time functionality, use C<chr()> and C<charnames::vianame()>. | |
194 | ||
ba62762e JH |
195 | =head2 Handling Unicode |
196 | ||
197 | Handling Unicode is for the most part transparent: just use the | |
198 | strings as usual. Functions like C<index()>, C<length()>, and | |
199 | C<substr()> will work on the Unicode characters; regular expressions | |
200 | will work on the Unicode characters (see L<perlunicode> and L<perlretut>). | |
201 | ||
202 | Note that Perl does B<not> consider combining character sequences | |
203 | to be characters, such for example | |
204 | ||
205 | use charnames ':full'; | |
206 | print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; | |
207 | ||
208 | will print 2, not 1. The only exception is that regular expressions | |
209 | have C<\X> for matching a combining character sequence. | |
210 | ||
211 | When life is not quite so transparent is working with legacy | |
212 | encodings, and I/O, and certain special cases. | |
213 | ||
214 | =head2 Legacy Encodings | |
215 | ||
216 | When you combine legacy data and Unicode the legacy data needs | |
217 | to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if | |
218 | applicable) is assumed. You can override this assumption by | |
219 | using the C<encoding> pragma, for example | |
220 | ||
221 | use encoding 'latin2'; # ISO 8859-2 | |
222 | ||
223 | in which case literals (string or regular expression) and chr/ord | |
224 | in your whole script are assumed to produce Unicode characters from | |
225 | ISO 8859-2 code points. Note that the matching for the encoding | |
226 | names is forgiving: instead of C<latin2> you could have said | |
227 | C<Latin 2>, or C<iso8859-2>, and so forth. With just | |
228 | ||
229 | use encoding; | |
230 | ||
231 | first the environment variable C<PERL_ENCODING> will be consulted, | |
232 | and if that doesn't exist, ISO 8859-1 (Latin 1) will be assumed. | |
233 | ||
234 | The C<Encode> module knows about many encodings and it has interfaces | |
235 | for doing conversions between those encodings: | |
236 | ||
237 | use Encode 'from_to'; | |
238 | from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8 | |
239 | ||
240 | =head2 Unicode I/O | |
241 | ||
242 | Normally writing out Unicode data | |
243 | ||
1d7919c5 | 244 | print FH chr(0x100), "\n"; |
ba62762e | 245 | |
1d7919c5 JH |
246 | will print out the raw UTF-8 bytes, but you will get a warning |
247 | out of that if you use C<-w> or C<use warnings>. To avoid the | |
248 | warning open the stream explicitly in UTF-8: | |
ba62762e | 249 | |
1d7919c5 JH |
250 | open FH, ">:utf8", "file"; |
251 | ||
252 | and on already open streams use C<binmode()>: | |
253 | ||
254 | binmode(STDOUT, ":utf8"); | |
255 | ||
256 | Reading in correctly formed UTF-8 data will not magically turn | |
ba62762e JH |
257 | the data into Unicode in Perl's eyes. |
258 | ||
259 | You can use either the C<':utf8'> I/O discipline when opening files | |
260 | ||
261 | open(my $fh,'<:utf8', 'anything'); | |
262 | my $line_of_utf8 = <$fh>; | |
263 | ||
264 | The I/O disciplines can also be specified more flexibly with | |
265 | the C<open> pragma; see L<open>: | |
266 | ||
1d7919c5 JH |
267 | use open ':utf8'; # input and output default discipline will be UTF-8 |
268 | open X, ">file"; | |
269 | print X chr(0x100), "\n"; | |
ba62762e | 270 | close X; |
1d7919c5 | 271 | open Y, "<file"; |
ba62762e JH |
272 | printf "%#x\n", ord(<Y>); # this should print 0x100 |
273 | close Y; | |
274 | ||
275 | With the C<open> pragma you can use the C<:locale> discipline | |
276 | ||
1ecefa54 JH |
277 | $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R'; |
278 | # the :locale will probe the locale environment variables like LC_ALL | |
ba62762e JH |
279 | use open OUT => ':locale'; # russki parusski |
280 | open(O, ">koi8"); | |
281 | print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 | |
282 | close O; | |
283 | open(I, "<koi8"); | |
284 | printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1 | |
285 | close I; | |
286 | ||
287 | or you can also use the C<':encoding(...)'> discipline | |
288 | ||
289 | open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); | |
290 | my $line_of_iliad = <$epic>; | |
291 | ||
292 | Both of these methods install a transparent filter on the I/O stream that | |
293 | will convert data from the specified encoding when it is read in from the | |
294 | stream. In the first example the F<anything> file is assumed to be UTF-8 | |
295 | encoded Unicode, in the second example the F<iliad.greek> file is assumed | |
296 | to be ISO-8858-7 encoded Greek, but the lines read in will be in both | |
297 | cases Unicode. | |
298 | ||
299 | The L<open> pragma affects all the C<open()> calls after the pragma by | |
300 | setting default disciplines. If you want to affect only certain | |
301 | streams, use explicit disciplines directly in the C<open()> call. | |
302 | ||
303 | You can switch encodings on an already opened stream by using | |
304 | C<binmode()>, see L<perlfunc/binmode>. | |
305 | ||
1ecefa54 JH |
306 | The C<:locale> does not currently (as of Perl 5.8.0) work with |
307 | C<open()> and C<binmode()>, only with the C<open> pragma. The | |
308 | C<:utf8> and C<:encoding(...)> do work with all of C<open()>, | |
309 | C<binmode()>, and the C<open> pragma. | |
ba62762e JH |
310 | |
311 | Similarly, you may use these I/O disciplines on input streams to | |
312 | automatically convert data from the specified encoding when it is | |
313 | written to the stream. | |
314 | ||
315 | open(my $unicode, '<:utf8', 'japanese.uni'); | |
316 | open(my $nihongo, '>:encoding(iso2022-jp)', 'japanese.jp'); | |
317 | while (<$unicode>) { print $nihongo } | |
318 | ||
319 | The naming of encodings, both by the C<open()> and by the C<open> | |
320 | pragma, is similarly understanding as with the C<encoding> pragma: | |
321 | C<koi8-r> and C<KOI8R> will both be understood. | |
322 | ||
323 | Common encodings recognized by ISO, MIME, IANA, and various other | |
324 | standardisation organisations are recognised, for a more detailed | |
325 | list see L<Encode>. | |
326 | ||
327 | C<read()> reads characters and returns the number of characters. | |
328 | C<seek()> and C<tell()> operate on byte counts, as do C<sysread()> | |
329 | and C<sysseek()>. | |
330 | ||
331 | Notice that because of the default behaviour "input is not UTF-8" | |
332 | it is easy to mistakenly write code that keeps on expanding a file | |
333 | by repeatedly encoding it in UTF-8: | |
334 | ||
335 | # BAD CODE WARNING | |
336 | open F, "file"; | |
337 | local $/; # read in the whole file | |
338 | $t = <F>; | |
339 | close F; | |
340 | open F, ">:utf8", "file"; | |
341 | print F $t; | |
342 | close F; | |
343 | ||
344 | If you run this code twice, the contents of the F<file> will be twice | |
1d7919c5 JH |
345 | UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or |
346 | explicitly opening also the F<file> for input as UTF-8. | |
ba62762e | 347 | |
0c901d84 JH |
348 | B<NOTE>: the C<:utf8> and C<:encoding> features work only if your |
349 | Perl has been built with the new "perlio" feature. Almost all | |
350 | Perl 5.8 platforms do use "perlio", though: you can see whether | |
351 | yours is by running "perl -V" and looking for C<useperlio=define>. | |
352 | ||
1ecefa54 JH |
353 | =head2 Displaying Unicode As Text |
354 | ||
355 | Sometimes you might want to display Perl scalars containing Unicode as | |
356 | simple ASCII (or EBCDIC) text. The following subroutine will convert | |
357 | its argument so that Unicode characters with code points greater than | |
358 | 255 are displayed as "\x{...}", control characters (like "\n") are | |
359 | displayed as "\x..", and the rest of the characters as themselves. | |
360 | ||
58c274a1 JF |
361 | sub nice_string { |
362 | join("", | |
363 | map { $_ > 255 ? # if wide character... | |
364 | sprintf("\\x{%x}", $_) : # \x{...} | |
365 | chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... | |
366 | sprintf("\\x%02x", $_) : # \x.. | |
367 | chr($_) # else as themselves | |
368 | } unpack("U*", $_[0])); # unpack Unicode characters | |
369 | } | |
370 | ||
371 | For example, | |
372 | ||
373 | nice_string("foo\x{100}bar\n") | |
374 | ||
375 | will return: | |
376 | ||
377 | "foo\x{100}bar\x0a" | |
1ecefa54 | 378 | |
ba62762e JH |
379 | =head2 Special Cases |
380 | ||
381 | =over 4 | |
382 | ||
383 | =item * | |
384 | ||
385 | Bit Complement Operator ~ And vec() | |
386 | ||
387 | The bit complement operator C<~> will produce surprising results if | |
388 | used on strings containing Unicode characters. The results are | |
389 | consistent with the internal UTF-8 encoding of the characters, but not | |
390 | with much else. So don't do that. Similarly for vec(): you will be | |
391 | operating on the UTF-8 bit patterns of the Unicode characters, not on | |
392 | the bytes, which is very probably not what you want. | |
393 | ||
394 | =item * | |
395 | ||
396 | Peeking At UTF-8 | |
397 | ||
398 | One way of peeking inside the internal encoding of Unicode characters | |
399 | is to use C<unpack("C*", ...> to get the bytes, or C<unpack("H*", ...)> | |
400 | to display the bytes: | |
401 | ||
402 | # this will print c4 80 for the UTF-8 bytes 0xc4 0x80 | |
403 | print join(" ", unpack("H*", pack("U", 0x100))), "\n"; | |
404 | ||
405 | Yet another way would be to use the Devel::Peek module: | |
406 | ||
407 | perl -MDevel::Peek -e 'Dump(chr(0x100))' | |
408 | ||
409 | That will show the UTF8 flag in FLAGS and both the UTF-8 bytes | |
410 | and Unicode characters in PV. See also later in this document | |
411 | the discussion about the C<is_utf8> function of the C<Encode> module. | |
412 | ||
413 | =back | |
414 | ||
415 | =head2 Advanced Topics | |
416 | ||
417 | =over 4 | |
418 | ||
419 | =item * | |
420 | ||
421 | String Equivalence | |
422 | ||
423 | The question of string equivalence turns somewhat complicated | |
424 | in Unicode: what do you mean by equal? | |
425 | ||
07698885 RGS |
426 | (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to |
427 | C<LATIN CAPITAL LETTER A>?) | |
ba62762e JH |
428 | |
429 | The short answer is that by default Perl compares equivalence | |
430 | (C<eq>, C<ne>) based only on code points of the characters. | |
58c274a1 | 431 | In the above case, the answer is no (because 0x00C1 != 0x0041). But sometimes any |
ba62762e JH |
432 | CAPITAL LETTER As being considered equal, or even any As of any case, |
433 | would be desirable. | |
434 | ||
435 | The long answer is that you need to consider character normalization | |
436 | and casing issues: see L<Unicode::Normalize>, and Unicode Technical | |
437 | Reports #15 and #21, I<Unicode Normalization Forms> and I<Case | |
438 | Mappings>, http://www.unicode.org/unicode/reports/tr15/ | |
439 | http://www.unicode.org/unicode/reports/tr21/ | |
440 | ||
58c274a1 | 441 | As of Perl 5.8.0, regular expression case-ignoring matching |
ba62762e JH |
442 | implements only 1:1 semantics: one character matches one character. |
443 | In I<Case Mappings> both 1:N and N:1 matches are defined. | |
444 | ||
445 | =item * | |
446 | ||
447 | String Collation | |
448 | ||
449 | People like to see their strings nicely sorted, or as Unicode | |
450 | parlance goes, collated. But again, what do you mean by collate? | |
451 | ||
07698885 RGS |
452 | (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after |
453 | C<LATIN CAPITAL LETTER A WITH GRAVE>?) | |
ba62762e | 454 | |
58c274a1 | 455 | The short answer is that by default, Perl compares strings (C<lt>, |
ba62762e | 456 | C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the |
58c274a1 | 457 | characters. In the above case, the answer is "after", since 0x00C1 > 0x00C0. |
ba62762e JH |
458 | |
459 | The long answer is that "it depends", and a good answer cannot be | |
460 | given without knowing (at the very least) the language context. | |
461 | See L<Unicode::Collate>, and I<Unicode Collation Algorithm> | |
462 | http://www.unicode.org/unicode/reports/tr10/ | |
463 | ||
464 | =back | |
465 | ||
466 | =head2 Miscellaneous | |
467 | ||
468 | =over 4 | |
469 | ||
470 | =item * | |
471 | ||
472 | Character Ranges | |
473 | ||
474 | Character ranges in regular expression character classes (C</[a-z]/>) | |
475 | and in the C<tr///> (also known as C<y///>) operator are not magically | |
58c274a1 | 476 | Unicode-aware. What this means that C<[A-Za-z]> will not magically start |
ba62762e JH |
477 | to mean "all alphabetic letters" (not that it does mean that even for |
478 | 8-bit characters, you should be using C</[[:alpha]]/> for that). | |
479 | ||
58c274a1 JF |
480 | For specifying things like that in regular expressions, you can use the |
481 | various Unicode properties, C<\pL> or perhaps C<\p{Alphabetic}>, in this particular case. You can | |
ba62762e JH |
482 | use Unicode code points as the end points of character ranges, but |
483 | that means that particular code point range, nothing more. For | |
484 | further information, see L<perlunicode>. | |
485 | ||
486 | =item * | |
487 | ||
488 | String-To-Number Conversions | |
489 | ||
490 | Unicode does define several other decimal (and numeric) characters | |
491 | than just the familiar 0 to 9, such as the Arabic and Indic digits. | |
492 | Perl does not support string-to-number conversion for digits other | |
58c274a1 | 493 | than ASCII 0 to 9 (and ASCII a to f for hexadecimal). |
ba62762e JH |
494 | |
495 | =back | |
496 | ||
497 | =head2 Questions With Answers | |
498 | ||
499 | =over 4 | |
500 | ||
501 | =item Will My Old Scripts Break? | |
502 | ||
503 | Very probably not. Unless you are generating Unicode characters | |
504 | somehow, any old behaviour should be preserved. About the only | |
505 | behaviour that has changed and which could start generating Unicode | |
506 | is the old behaviour of C<chr()> where supplying an argument more | |
507 | than 255 produced a character modulo 255 (for example, C<chr(300)> | |
508 | was equal to C<chr(45)>). | |
509 | ||
510 | =item How Do I Make My Scripts Work With Unicode? | |
511 | ||
512 | Very little work should be needed since nothing changes until you | |
513 | somehow generate Unicode data. The greatest trick will be getting | |
514 | input as Unicode, and for that see the earlier I/O discussion. | |
515 | ||
516 | =item How Do I Know Whether My String Is In Unicode? | |
517 | ||
518 | You shouldn't care. No, you really shouldn't. If you have | |
519 | to care (beyond the cases described above), it means that we | |
520 | didn't get the transparency of Unicode quite right. | |
521 | ||
522 | Okay, if you insist: | |
523 | ||
524 | use Encode 'is_utf8'; | |
525 | print is_utf8($string) ? 1 : 0, "\n"; | |
526 | ||
527 | But note that this doesn't mean that any of the characters in the | |
528 | string are necessary UTF-8 encoded, or that any of the characters have | |
529 | code points greater than 0xFF (255) or even 0x80 (128), or that the | |
530 | string has any characters at all. All the C<is_utf8()> does is to | |
531 | return the value of the internal "utf8ness" flag attached to the | |
532 | $string. If the flag is on, characters added to that string will be | |
533 | automatically upgraded to UTF-8 (and even then only if they really | |
534 | need to be upgraded, that is, if their code point is greater than 0xFF). | |
535 | ||
536 | Sometimes you might really need to know the byte length of a string | |
537 | instead of the character length. For that use the C<bytes> pragma | |
538 | and its only defined function C<length()>: | |
539 | ||
540 | my $unicode = chr(0x100); | |
541 | print length($unicode), "\n"; # will print 1 | |
542 | use bytes; | |
543 | print length($unicode), "\n"; # will print 2 (the 0xC4 0x80 of the UTF-8) | |
544 | ||
545 | =item How Do I Detect Invalid UTF-8? | |
546 | ||
547 | Either | |
548 | ||
549 | use Encode 'encode_utf8'; | |
550 | if (encode_utf8($string)) { | |
551 | # valid | |
552 | } else { | |
553 | # invalid | |
554 | } | |
555 | ||
556 | or | |
557 | ||
558 | use warnings; | |
559 | @chars = unpack("U0U*", "\xFF"); # will warn | |
560 | ||
561 | The warning will be C<Malformed UTF-8 character (byte 0xff) in | |
562 | unpack>. The "U0" means "expect strictly UTF-8 encoded Unicode". | |
563 | Without that the C<unpack("U*", ...)> would accept also data like | |
564 | C<chr(0xFF>). | |
565 | ||
566 | =item How Do I Convert Data Into UTF-8? Or Vice Versa? | |
567 | ||
568 | This probably isn't as useful (or simple) as you might think. | |
569 | Also, normally you shouldn't need to. | |
570 | ||
571 | In one sense what you are asking doesn't make much sense: UTF-8 is | |
572 | (intended as an) Unicode encoding, so converting "data" into UTF-8 | |
573 | isn't meaningful unless you know in what character set and encoding | |
574 | the binary data is in, and in this case you can use C<Encode>. | |
575 | ||
576 | use Encode 'from_to'; | |
577 | from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 | |
578 | ||
579 | If you have ASCII (really 7-bit US-ASCII), you already have valid | |
580 | UTF-8, the lowest 128 characters of UTF-8 encoded Unicode and US-ASCII | |
581 | are equivalent. | |
582 | ||
583 | If you have Latin-1 (or want Latin-1), you can just use pack/unpack: | |
584 | ||
585 | $latin1 = pack("C*", unpack("U*", $utf8)); | |
586 | $utf8 = pack("U*", unpack("C*", $latin1)); | |
587 | ||
588 | (The same works for EBCDIC.) | |
589 | ||
590 | If you have a sequence of bytes you B<know> is valid UTF-8, | |
591 | but Perl doesn't know it yet, you can make Perl a believer, too: | |
592 | ||
593 | use Encode 'decode_utf8'; | |
594 | $utf8 = decode_utf8($bytes); | |
595 | ||
596 | You can convert well-formed UTF-8 to a sequence of bytes, but if | |
597 | you just want to convert random binary data into UTF-8, you can't. | |
598 | Any random collection of bytes isn't well-formed UTF-8. You can | |
599 | use C<unpack("C*", $string)> for the former, and you can create | |
600 | well-formed Unicode/UTF-8 data by C<pack("U*", 0xff, ...)>. | |
601 | ||
602 | =item How Do I Display Unicode? How Do I Input Unicode? | |
603 | ||
604 | See http://www.hclrss.demon.co.uk/unicode/ and | |
605 | http://www.cl.cam.ac.uk/~mgk25/unicode.html | |
606 | ||
607 | =item How Does Unicode Work With Traditional Locales? | |
608 | ||
609 | In Perl, not very well. Avoid using locales through the C<locale> | |
610 | pragma. Use only one or the other. | |
611 | ||
612 | =back | |
613 | ||
614 | =head2 Hexadecimal Notation | |
615 | ||
616 | The Unicode standard prefers using hexadecimal notation because that | |
617 | shows better the division of Unicode into blocks of 256 characters. | |
618 | Hexadecimal is also simply shorter than decimal. You can use decimal | |
619 | notation, too, but learning to use hexadecimal just makes life easier | |
620 | with the Unicode standard. | |
621 | ||
622 | The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and> | |
623 | a-f (or A-F, case doesn't matter). Each hexadecimal digit represents | |
624 | four bits, or half a byte. C<print 0x..., "\n"> will show a | |
625 | hexadecimal number in decimal, and C<printf "%x\n", $decimal> will | |
626 | show a decimal number in hexadecimal. If you have just the | |
627 | "hexdigits" of a hexadecimal number, you can use the C<hex()> | |
628 | function. | |
629 | ||
630 | print 0x0009, "\n"; # 9 | |
631 | print 0x000a, "\n"; # 10 | |
632 | print 0x000f, "\n"; # 15 | |
633 | print 0x0010, "\n"; # 16 | |
634 | print 0x0011, "\n"; # 17 | |
635 | print 0x0100, "\n"; # 256 | |
636 | ||
637 | print 0x0041, "\n"; # 65 | |
638 | ||
639 | printf "%x\n", 65; # 41 | |
640 | printf "%#x\n", 65; # 0x41 | |
641 | ||
642 | print hex("41"), "\n"; # 65 | |
643 | ||
644 | =head2 Further Resources | |
645 | ||
646 | =over 4 | |
647 | ||
648 | =item * | |
649 | ||
650 | Unicode Consortium | |
651 | ||
652 | http://www.unicode.org/ | |
653 | ||
654 | =item * | |
655 | ||
656 | Unicode FAQ | |
657 | ||
658 | http://www.unicode.org/unicode/faq/ | |
659 | ||
660 | =item * | |
661 | ||
662 | Unicode Glossary | |
663 | ||
664 | http://www.unicode.org/glossary/ | |
665 | ||
666 | =item * | |
667 | ||
668 | Unicode Useful Resources | |
669 | ||
670 | http://www.unicode.org/unicode/onlinedat/resources.html | |
671 | ||
672 | =item * | |
673 | ||
674 | Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications | |
675 | ||
676 | http://www.hclrss.demon.co.uk/unicode/ | |
677 | ||
678 | =item * | |
679 | ||
680 | UTF-8 and Unicode FAQ for Unix/Linux | |
681 | ||
682 | http://www.cl.cam.ac.uk/~mgk25/unicode.html | |
683 | ||
684 | =item * | |
685 | ||
686 | Legacy Character Sets | |
687 | ||
688 | http://www.czyborra.com/ | |
689 | http://www.eki.ee/letter/ | |
690 | ||
691 | =item * | |
692 | ||
693 | The Unicode support files live within the Perl installation in the | |
694 | directory | |
695 | ||
696 | $Config{installprivlib}/unicore | |
697 | ||
698 | in Perl 5.8.0 or newer, and | |
699 | ||
700 | $Config{installprivlib}/unicode | |
701 | ||
702 | in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to | |
703 | avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) | |
704 | The main Unicode data file is F<Unicode.txt> (or F<Unicode.301> in | |
705 | Perl 5.6.1.) You can find the C<$Config{installprivlib}> by | |
706 | ||
707 | perl "-V:installprivlib" | |
708 | ||
709 | Note that some of the files have been renamed from the Unicode | |
710 | standard since the Perl installation tries to live by the "8.3" | |
711 | filenaming restrictions. The renamings are shown in the | |
712 | accompanying F<rename> file. | |
713 | ||
714 | You can explore various information from the Unicode data files using | |
715 | the C<Unicode::UCD> module. | |
716 | ||
717 | =back | |
718 | ||
f6edf83b JH |
719 | =head1 UNICODE IN OLDER PERLS |
720 | ||
721 | If you cannot upgrade your Perl to 5.8.0 or later, you can still | |
722 | do some Unicode processing by using the modules C<Unicode::String>, | |
723 | C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN. | |
724 | If you have the GNU recode installed, you can also use the | |
725 | Perl frontend C<Convert::Recode> for character conversions. | |
726 | ||
ba62762e JH |
727 | =head1 SEE ALSO |
728 | ||
729 | L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>, | |
730 | L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD> | |
731 | ||
732 | =head1 ACKNOWLEDGEMENTS | |
733 | ||
734 | Thanks to the kind readers of the perl5-porters@perl.org, | |
735 | perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org | |
736 | mailing lists for their valuable feedback. | |
737 | ||
738 | =head1 AUTHOR, COPYRIGHT, AND LICENSE | |
739 | ||
740 | Copyright 2001 Jarkko Hietaniemi <jhi@iki.fi> | |
741 | ||
742 | This document may be distributed under the same terms as Perl itself. |