Commit | Line | Data |
ba62762e |
1 | =head1 NAME |
2 | |
07fcf8ff |
3 | perluniintro - Perl Unicode introduction |
ba62762e |
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 | |
376d9008 |
12 | Unicode is a character set standard which plans to codify all of the |
ba62762e |
13 | writing systems of the world, plus many other symbols. |
14 | |
15 | Unicode and ISO/IEC 10646 are coordinated standards that provide code |
376d9008 |
16 | points for characters in almost all modern character set standards, |
ba62762e |
17 | covering more than 30 writing systems and hundreds of languages, |
376d9008 |
18 | including all commercially-important modern languages. All characters |
ba62762e |
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 |
376d9008 |
24 | particular integer width, especially not to the C language C<char>. |
25 | Unicode is language-neutral and display-neutral: it does not encode the |
26 | language of the text and it does not define fonts or other graphical |
ba62762e |
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 |
376d9008 |
31 | SMALL LETTER ALPHA> and unique numbers for the characters, in this |
32 | case 0x0041 and 0x03B1, respectively. These unique numbers are called |
33 | I<code points>. |
ba62762e |
34 | |
35 | The Unicode standard prefers using hexadecimal notation for the code |
1bfb14c4 |
36 | points. If numbers like C<0x0041> are unfamiliar to |
376d9008 |
37 | you, take a peek at a later section, L</"Hexadecimal Notation">. |
ba62762e |
38 | The Unicode standard uses the notation C<U+0041 LATIN CAPITAL LETTER A>, |
376d9008 |
39 | to give the hexadecimal code point and the normative name of |
ba62762e |
40 | the character. |
41 | |
42 | Unicode also defines various I<properties> for the characters, like |
376d9008 |
43 | "uppercase" or "lowercase", "decimal digit", or "punctuation"; |
ba62762e |
44 | these properties are independent of the names of the characters. |
45 | Furthermore, various operations on the characters like uppercasing, |
376d9008 |
46 | lowercasing, and collating (sorting) are defined. |
ba62762e |
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 |
376d9008 |
51 | base character and modifiers is called a I<combining character |
ba62762e |
52 | sequence>. |
53 | |
376d9008 |
54 | Whether to call these combining character sequences "characters" |
55 | depends on your point of view. If you are a programmer, you probably |
56 | would tend towards seeing each element in the sequences as one unit, |
57 | or "character". The whole sequence could be seen as one "character", |
58 | however, from the user's point of view, since that's probably what it |
59 | looks like in the context of the user's language. |
60 | |
61 | With this "whole sequence" view of characters, the total number of |
62 | characters is open-ended. But in the programmer's "one unit is one |
63 | character" point of view, the concept of "characters" is more |
1bfb14c4 |
64 | deterministic. In this document, we take that second point of view: |
65 | one "character" is one Unicode code point, be it a base character or |
66 | a combining character. |
376d9008 |
67 | |
68 | For some combinations, there are I<precomposed> characters. |
69 | C<LATIN CAPITAL LETTER A WITH ACUTE>, for example, is defined as |
ba62762e |
70 | a single code point. These precomposed characters are, however, |
376d9008 |
71 | only available for some combinations, and are mainly |
ba62762e |
72 | meant to support round-trip conversions between Unicode and legacy |
376d9008 |
73 | standards (like the ISO 8859). In the general case, the composing |
74 | method is more extensible. To support conversion between |
ba62762e |
75 | different compositions of the characters, various I<normalization |
376d9008 |
76 | forms> to standardize representations are also defined. |
ba62762e |
77 | |
78 | Because of backward compatibility with legacy encodings, the "a unique |
376d9008 |
79 | number for every character" idea breaks down a bit: instead, there is |
80 | "at least one number for every character". The same character could |
81 | be represented differently in several legacy encodings. The |
82 | converse is also not true: some code points do not have an assigned |
83 | character. Firstly, there are unallocated code points within |
84 | otherwise used blocks. Secondly, there are special Unicode control |
85 | characters that do not represent true characters. |
ba62762e |
86 | |
87 | A common myth about Unicode is that it would be "16-bit", that is, |
376d9008 |
88 | Unicode is only represented as C<0x10000> (or 65536) characters from |
89 | C<0x0000> to C<0xFFFF>. B<This is untrue.> Since Unicode 2.0, Unicode |
90 | has been defined all the way up to 21 bits (C<0x10FFFF>), and since |
91 | Unicode 3.1, characters have been defined beyond C<0xFFFF>. The first |
92 | C<0x10000> characters are called the I<Plane 0>, or the I<Basic |
93 | Multilingual Plane> (BMP). With Unicode 3.1, 17 planes in all are |
94 | defined--but nowhere near full of defined characters, yet. |
ba62762e |
95 | |
1bfb14c4 |
96 | Another myth is that the 256-character blocks have something to |
97 | do with languages--that each block would define the characters used |
98 | by a language or a set of languages. B<This is also untrue.> |
99 | The division into blocks exists, but it is almost completely |
100 | accidental--an artifact of how the characters have been and |
101 | still are allocated. Instead, there is a concept called I<scripts>, |
102 | which is more useful: there is C<Latin> script, C<Greek> script, and |
103 | so on. Scripts usually span varied parts of several blocks. |
104 | For further information see L<Unicode::UCD>. |
ba62762e |
105 | |
106 | The Unicode code points are just abstract numbers. To input and |
107 | output these abstract numbers, the numbers must be I<encoded> somehow. |
108 | Unicode defines several I<character encoding forms>, of which I<UTF-8> |
109 | is perhaps the most popular. UTF-8 is a variable length encoding that |
110 | encodes Unicode characters as 1 to 6 bytes (only 4 with the currently |
8baee566 |
111 | defined characters). Other encodings include UTF-16 and UTF-32 and their |
1bfb14c4 |
112 | big- and little-endian variants (UTF-8 is byte-order independent) |
ba62762e |
113 | The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms. |
114 | |
376d9008 |
115 | For more information about encodings--for instance, to learn what |
116 | I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>. |
ba62762e |
117 | |
118 | =head2 Perl's Unicode Support |
119 | |
376d9008 |
120 | Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode |
121 | natively. Perl 5.8.0, however, is the first recommended release for |
122 | serious Unicode work. The maintenance release 5.6.1 fixed many of the |
123 | problems of the initial Unicode implementation, but for example |
1bfb14c4 |
124 | regular expressions still do not work with Unicode in 5.6.1. |
ba62762e |
125 | |
126 | B<Starting from Perl 5.8.0, the use of C<use utf8> is no longer |
127 | necessary.> In earlier releases the C<utf8> pragma was used to declare |
128 | that operations in the current block or file would be Unicode-aware. |
376d9008 |
129 | This model was found to be wrong, or at least clumsy: the "Unicodeness" |
1bfb14c4 |
130 | is now carried with the data, instead of being attached to the |
376d9008 |
131 | operations. Only one case remains where an explicit C<use utf8> is |
132 | needed: if your Perl script itself is encoded in UTF-8, you can use |
133 | UTF-8 in your identifier names, and in string and regular expression |
134 | literals, by saying C<use utf8>. This is not the default because |
135 | scripts with legacy 8-bit data in them would break. |
ba62762e |
136 | |
137 | =head2 Perl's Unicode Model |
138 | |
376d9008 |
139 | Perl supports both pre-5.6 strings of eight-bit native bytes, and |
140 | strings of Unicode characters. The principle is that Perl tries to |
141 | keep its data as eight-bit bytes for as long as possible, but as soon |
142 | as Unicodeness cannot be avoided, the data is transparently upgraded |
143 | to Unicode. |
ba62762e |
144 | |
4192de81 |
145 | Internally, Perl currently uses either whatever the native eight-bit |
376d9008 |
146 | character set of the platform (for example Latin-1) is, defaulting to |
147 | UTF-8, to encode Unicode strings. Specifically, if all code points in |
148 | the string are C<0xFF> or less, Perl uses the native eight-bit |
149 | character set. Otherwise, it uses UTF-8. |
4192de81 |
150 | |
7ca610e8 |
151 | A user of Perl does not normally need to know nor care how Perl |
20ba30f4 |
152 | happens to encode its internal strings, but it becomes relevant when |
376d9008 |
153 | outputting Unicode strings to a stream without a discipline--one with |
154 | the "default" encoding. In such a case, the raw bytes used internally |
7ca610e8 |
155 | (the native character set or UTF-8, as appropriate for each string) |
156 | will be used, and a "Wide character" warning will be issued if those |
157 | strings contain a character beyond 0x00FF. |
4192de81 |
158 | |
159 | For example, |
160 | |
7ca610e8 |
161 | perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"' |
4192de81 |
162 | |
163 | produces a fairly useless mixture of native bytes and UTF-8, as well |
1bfb14c4 |
164 | as a warning: |
4192de81 |
165 | |
1bfb14c4 |
166 | Wide character in print at ... |
167 | |
168 | To output UTF-8, use the C<:utf8> output discipline. Prepending |
4192de81 |
169 | |
170 | binmode(STDOUT, ":utf8"); |
171 | |
376d9008 |
172 | to this sample program ensures that the output is completely UTF-8, |
1bfb14c4 |
173 | and removes the program's warning. |
ba62762e |
174 | |
376d9008 |
175 | If your locale environment variables (C<LANGUAGE>, C<LC_ALL>, |
176 | C<LC_CTYPE>, C<LANG>) contain the strings 'UTF-8' or 'UTF8', |
177 | regardless of case, then the default encoding of your STDIN, STDOUT, |
178 | and STDERR and of B<any subsequent file open>, is UTF-8. Note that |
1bfb14c4 |
179 | this means that Perl expects other software to work, too: if Perl has |
180 | been led to believe that STDIN should be UTF-8, but then STDIN coming |
181 | in from another command is not UTF-8, Perl will complain about the |
ac730995 |
182 | malformed UTF-8. |
b310b053 |
183 | |
64c66fb6 |
184 | =head2 Unicode and EBCDIC |
185 | |
186 | Perl 5.8.0 also supports Unicode on EBCDIC platforms. There, |
376d9008 |
187 | Unicode support is somewhat more complex to implement since |
64c66fb6 |
188 | additional conversions are needed at every step. Some problems |
dc4af4bb |
189 | remain, see L<perlebcdic> for details. |
64c66fb6 |
190 | |
191 | In any case, the Unicode support on EBCDIC platforms is better than |
192 | in the 5.6 series, which didn't work much at all for EBCDIC platform. |
193 | On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC |
376d9008 |
194 | instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in |
195 | that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is |
196 | "EBCDIC-safe". |
ba62762e |
197 | |
198 | =head2 Creating Unicode |
199 | |
376d9008 |
200 | To create Unicode characters in literals for code points above C<0xFF>, |
201 | use the C<\x{...}> notation in double-quoted strings: |
ba62762e |
202 | |
203 | my $smiley = "\x{263a}"; |
204 | |
376d9008 |
205 | Similarly, it can be used in regular expression literals |
ba62762e |
206 | |
207 | $smiley =~ /\x{263a}/; |
208 | |
209 | At run-time you can use C<chr()>: |
210 | |
211 | my $hebrew_alef = chr(0x05d0); |
212 | |
376d9008 |
213 | See L</"Further Resources"> for how to find all these numeric codes. |
ba62762e |
214 | |
376d9008 |
215 | Naturally, C<ord()> will do the reverse: it turns a character into |
216 | a code point. |
ba62762e |
217 | |
1bfb14c4 |
218 | Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>, |
219 | and C<chr(...)> for arguments less than C<0x100> (decimal 256) |
220 | generate an eight-bit character for backward compatibility with older |
221 | Perls. For arguments of C<0x100> or more, Unicode characters are |
a5f0baef |
222 | always produced. If you want to force the production of Unicode |
223 | characters regardless of the numeric value, use C<pack("U", ...)> |
224 | instead of C<\x..>, C<\x{...}>, or C<chr()>. |
ba62762e |
225 | |
226 | You can also use the C<charnames> pragma to invoke characters |
376d9008 |
227 | by name in double-quoted strings: |
ba62762e |
228 | |
229 | use charnames ':full'; |
230 | my $arabic_alef = "\N{ARABIC LETTER ALEF}"; |
231 | |
232 | And, as mentioned above, you can also C<pack()> numbers into Unicode |
233 | characters: |
234 | |
235 | my $georgian_an = pack("U", 0x10a0); |
236 | |
8a5e5dd5 |
237 | Note that both C<\x{...}> and C<\N{...}> are compile-time string |
238 | constants: you cannot use variables in them. if you want similar |
239 | run-time functionality, use C<chr()> and C<charnames::vianame()>. |
240 | |
1eda90df |
241 | Also note that if all the code points for pack "U" are below 0x100, |
242 | bytes will be generated, just like if you were using C<chr()>. |
243 | |
244 | my $bytes = pack("U*", 0x80, 0xFF); |
245 | |
246 | If you want to force the result to Unicode characters, use the special |
247 | C<"U0"> prefix. It consumes no arguments but forces the result to be |
248 | in Unicode characters, instead of bytes. |
249 | |
250 | my $chars = pack("U0U*", 0x80, 0xFF); |
251 | |
ba62762e |
252 | =head2 Handling Unicode |
253 | |
254 | Handling Unicode is for the most part transparent: just use the |
255 | strings as usual. Functions like C<index()>, C<length()>, and |
256 | C<substr()> will work on the Unicode characters; regular expressions |
257 | will work on the Unicode characters (see L<perlunicode> and L<perlretut>). |
258 | |
1bfb14c4 |
259 | Note that Perl considers combining character sequences to be |
260 | characters, so for example |
ba62762e |
261 | |
262 | use charnames ':full'; |
263 | print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; |
264 | |
265 | will print 2, not 1. The only exception is that regular expressions |
266 | have C<\X> for matching a combining character sequence. |
267 | |
376d9008 |
268 | Life is not quite so transparent, however, when working with legacy |
269 | encodings, I/O, and certain special cases: |
ba62762e |
270 | |
271 | =head2 Legacy Encodings |
272 | |
273 | When you combine legacy data and Unicode the legacy data needs |
274 | to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if |
275 | applicable) is assumed. You can override this assumption by |
276 | using the C<encoding> pragma, for example |
277 | |
278 | use encoding 'latin2'; # ISO 8859-2 |
279 | |
1bfb14c4 |
280 | in which case literals (string or regular expressions), C<chr()>, |
281 | and C<ord()> in your whole script are assumed to produce Unicode |
376d9008 |
282 | characters from ISO 8859-2 code points. Note that the matching for |
283 | encoding names is forgiving: instead of C<latin2> you could have |
284 | said C<Latin 2>, or C<iso8859-2>, or other variations. With just |
ba62762e |
285 | |
286 | use encoding; |
287 | |
376d9008 |
288 | the environment variable C<PERL_ENCODING> will be consulted. |
289 | If that variable isn't set, the encoding pragma will fail. |
ba62762e |
290 | |
376d9008 |
291 | The C<Encode> module knows about many encodings and has interfaces |
ba62762e |
292 | for doing conversions between those encodings: |
293 | |
294 | use Encode 'from_to'; |
295 | from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8 |
296 | |
297 | =head2 Unicode I/O |
298 | |
8baee566 |
299 | Normally, writing out Unicode data |
ba62762e |
300 | |
8baee566 |
301 | print FH $some_string_with_unicode, "\n"; |
ba62762e |
302 | |
8baee566 |
303 | produces raw bytes that Perl happens to use to internally encode the |
376d9008 |
304 | Unicode string. Perl's internal encoding depends on the system as |
305 | well as what characters happen to be in the string at the time. If |
306 | any of the characters are at code points C<0x100> or above, you will get |
307 | a warning. To ensure that the output is explicitly rendered in the |
308 | encoding you desire--and to avoid the warning--open the stream with |
309 | the desired encoding. Some examples: |
ba62762e |
310 | |
ec90690f |
311 | open FH, ">:utf8", "file"; |
312 | |
313 | open FH, ">:encoding(ucs2)", "file"; |
314 | open FH, ">:encoding(UTF-8)", "file"; |
315 | open FH, ">:encoding(shift_jis)", "file"; |
1d7919c5 |
316 | |
376d9008 |
317 | and on already open streams, use C<binmode()>: |
1d7919c5 |
318 | |
319 | binmode(STDOUT, ":utf8"); |
320 | |
ec90690f |
321 | binmode(STDOUT, ":encoding(ucs2)"); |
322 | binmode(STDOUT, ":encoding(UTF-8)"); |
323 | binmode(STDOUT, ":encoding(shift_jis)"); |
324 | |
b5d8778e |
325 | The matching of encoding names is loose: case does not matter, and |
326 | many encodings have several aliases. Note that C<:utf8> discipline |
1bfb14c4 |
327 | must always be specified exactly like that; it is I<not> subject to |
328 | the loose matching of encoding names. |
b5d8778e |
329 | |
376d9008 |
330 | See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and |
331 | L<Encode::PerlIO> for the C<:encoding()> layer, and |
332 | L<Encode::Supported> for many encodings supported by the C<Encode> |
333 | module. |
ba62762e |
334 | |
a5f0baef |
335 | Reading in a file that you know happens to be encoded in one of the |
1bfb14c4 |
336 | Unicode or legacy encodings does not magically turn the data into |
337 | Unicode in Perl's eyes. To do that, specify the appropriate |
338 | discipline when opening files |
ba62762e |
339 | |
340 | open(my $fh,'<:utf8', 'anything'); |
8baee566 |
341 | my $line_of_unicode = <$fh>; |
342 | |
ec90690f |
343 | open(my $fh,'<:encoding(Big5)', 'anything'); |
8baee566 |
344 | my $line_of_unicode = <$fh>; |
ba62762e |
345 | |
346 | The I/O disciplines can also be specified more flexibly with |
376d9008 |
347 | the C<open> pragma. See L<open>, or look at the following example. |
ba62762e |
348 | |
1d7919c5 |
349 | use open ':utf8'; # input and output default discipline will be UTF-8 |
350 | open X, ">file"; |
351 | print X chr(0x100), "\n"; |
ba62762e |
352 | close X; |
1d7919c5 |
353 | open Y, "<file"; |
ba62762e |
354 | printf "%#x\n", ord(<Y>); # this should print 0x100 |
355 | close Y; |
356 | |
357 | With the C<open> pragma you can use the C<:locale> discipline |
358 | |
1ecefa54 |
359 | $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R'; |
360 | # the :locale will probe the locale environment variables like LC_ALL |
ba62762e |
361 | use open OUT => ':locale'; # russki parusski |
362 | open(O, ">koi8"); |
363 | print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 |
364 | close O; |
365 | open(I, "<koi8"); |
366 | printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1 |
367 | close I; |
368 | |
369 | or you can also use the C<':encoding(...)'> discipline |
370 | |
371 | open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); |
8baee566 |
372 | my $line_of_unicode = <$epic>; |
ba62762e |
373 | |
8baee566 |
374 | These methods install a transparent filter on the I/O stream that |
375 | converts data from the specified encoding when it is read in from the |
a5f0baef |
376 | stream. The result is always Unicode. |
ba62762e |
377 | |
378 | The L<open> pragma affects all the C<open()> calls after the pragma by |
379 | setting default disciplines. If you want to affect only certain |
380 | streams, use explicit disciplines directly in the C<open()> call. |
381 | |
382 | You can switch encodings on an already opened stream by using |
8baee566 |
383 | C<binmode()>; see L<perlfunc/binmode>. |
ba62762e |
384 | |
1ecefa54 |
385 | The C<:locale> does not currently (as of Perl 5.8.0) work with |
386 | C<open()> and C<binmode()>, only with the C<open> pragma. The |
8baee566 |
387 | C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>, |
1ecefa54 |
388 | C<binmode()>, and the C<open> pragma. |
ba62762e |
389 | |
8baee566 |
390 | Similarly, you may use these I/O disciplines on output streams to |
a5f0baef |
391 | automatically convert Unicode to the specified encoding when it is |
392 | written to the stream. For example, the following snippet copies the |
393 | contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to |
394 | the file "text.utf8", encoded as UTF-8: |
ba62762e |
395 | |
8baee566 |
396 | open(my $nihongo, '<:encoding(iso2022-jp)', 'text.jis'); |
397 | open(my $unicode, '>:utf8', 'text.utf8'); |
398 | while (<$nihongo>) { print $unicode } |
ba62762e |
399 | |
400 | The naming of encodings, both by the C<open()> and by the C<open> |
376d9008 |
401 | pragma, is similar to the C<encoding> pragma in that it allows for |
402 | flexible names: C<koi8-r> and C<KOI8R> will both be understood. |
ba62762e |
403 | |
404 | Common encodings recognized by ISO, MIME, IANA, and various other |
8baee566 |
405 | standardisation organisations are recognised; for a more detailed |
1bfb14c4 |
406 | list see L<Encode::Supported>. |
ba62762e |
407 | |
408 | C<read()> reads characters and returns the number of characters. |
409 | C<seek()> and C<tell()> operate on byte counts, as do C<sysread()> |
410 | and C<sysseek()>. |
411 | |
8baee566 |
412 | Notice that because of the default behaviour of not doing any |
413 | conversion upon input if there is no default discipline, |
ba62762e |
414 | it is easy to mistakenly write code that keeps on expanding a file |
1bfb14c4 |
415 | by repeatedly encoding the data: |
ba62762e |
416 | |
417 | # BAD CODE WARNING |
418 | open F, "file"; |
8baee566 |
419 | local $/; ## read in the whole file of 8-bit characters |
ba62762e |
420 | $t = <F>; |
421 | close F; |
422 | open F, ">:utf8", "file"; |
8baee566 |
423 | print F $t; ## convert to UTF-8 on output |
ba62762e |
424 | close F; |
425 | |
426 | If you run this code twice, the contents of the F<file> will be twice |
1d7919c5 |
427 | UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or |
428 | explicitly opening also the F<file> for input as UTF-8. |
ba62762e |
429 | |
0c901d84 |
430 | B<NOTE>: the C<:utf8> and C<:encoding> features work only if your |
431 | Perl has been built with the new "perlio" feature. Almost all |
432 | Perl 5.8 platforms do use "perlio", though: you can see whether |
433 | yours is by running "perl -V" and looking for C<useperlio=define>. |
434 | |
1ecefa54 |
435 | =head2 Displaying Unicode As Text |
436 | |
437 | Sometimes you might want to display Perl scalars containing Unicode as |
8baee566 |
438 | simple ASCII (or EBCDIC) text. The following subroutine converts |
1ecefa54 |
439 | its argument so that Unicode characters with code points greater than |
1bfb14c4 |
440 | 255 are displayed as C<\x{...}>, control characters (like C<\n>) are |
441 | displayed as C<\x..>, and the rest of the characters as themselves: |
1ecefa54 |
442 | |
58c274a1 |
443 | sub nice_string { |
444 | join("", |
445 | map { $_ > 255 ? # if wide character... |
8baee566 |
446 | sprintf("\\x{%04X}", $_) : # \x{...} |
58c274a1 |
447 | chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... |
8baee566 |
448 | sprintf("\\x%02X", $_) : # \x.. |
58c274a1 |
449 | chr($_) # else as themselves |
450 | } unpack("U*", $_[0])); # unpack Unicode characters |
451 | } |
452 | |
453 | For example, |
454 | |
455 | nice_string("foo\x{100}bar\n") |
456 | |
8baee566 |
457 | returns: |
58c274a1 |
458 | |
8baee566 |
459 | "foo\x{0100}bar\x0A" |
1ecefa54 |
460 | |
ba62762e |
461 | =head2 Special Cases |
462 | |
463 | =over 4 |
464 | |
465 | =item * |
466 | |
467 | Bit Complement Operator ~ And vec() |
468 | |
1bfb14c4 |
469 | The bit complement operator C<~> may produce surprising results if |
470 | used on strings containing characters with ordinal values above |
471 | 255. In such a case, the results are consistent with the internal |
472 | encoding of the characters, but not with much else. So don't do |
473 | that. Similarly for C<vec()>: you will be operating on the |
474 | internally-encoded bit patterns of the Unicode characters, not on |
475 | the code point values, which is very probably not what you want. |
ba62762e |
476 | |
477 | =item * |
478 | |
8baee566 |
479 | Peeking At Perl's Internal Encoding |
480 | |
481 | Normal users of Perl should never care how Perl encodes any particular |
a5f0baef |
482 | Unicode string (because the normal ways to get at the contents of a |
376d9008 |
483 | string with Unicode--via input and output--should always be via |
a5f0baef |
484 | explicitly-defined I/O disciplines). But if you must, there are two |
485 | ways of looking behind the scenes. |
ba62762e |
486 | |
487 | One way of peeking inside the internal encoding of Unicode characters |
376d9008 |
488 | is to use C<unpack("C*", ...> to get the bytes or C<unpack("H*", ...)> |
ba62762e |
489 | to display the bytes: |
490 | |
8baee566 |
491 | # this prints c4 80 for the UTF-8 bytes 0xc4 0x80 |
ba62762e |
492 | print join(" ", unpack("H*", pack("U", 0x100))), "\n"; |
493 | |
494 | Yet another way would be to use the Devel::Peek module: |
495 | |
496 | perl -MDevel::Peek -e 'Dump(chr(0x100))' |
497 | |
8baee566 |
498 | That shows the UTF8 flag in FLAGS and both the UTF-8 bytes |
376d9008 |
499 | and Unicode characters in C<PV>. See also later in this document |
ba62762e |
500 | the discussion about the C<is_utf8> function of the C<Encode> module. |
501 | |
502 | =back |
503 | |
504 | =head2 Advanced Topics |
505 | |
506 | =over 4 |
507 | |
508 | =item * |
509 | |
510 | String Equivalence |
511 | |
512 | The question of string equivalence turns somewhat complicated |
376d9008 |
513 | in Unicode: what do you mean by "equal"? |
ba62762e |
514 | |
07698885 |
515 | (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to |
516 | C<LATIN CAPITAL LETTER A>?) |
ba62762e |
517 | |
a5f0baef |
518 | The short answer is that by default Perl compares equivalence (C<eq>, |
519 | C<ne>) based only on code points of the characters. In the above |
376d9008 |
520 | case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any |
521 | CAPITAL LETTER As should be considered equal, or even As of any case. |
ba62762e |
522 | |
523 | The long answer is that you need to consider character normalization |
376d9008 |
524 | and casing issues: see L<Unicode::Normalize>, Unicode Technical |
ba62762e |
525 | Reports #15 and #21, I<Unicode Normalization Forms> and I<Case |
376d9008 |
526 | Mappings>, http://www.unicode.org/unicode/reports/tr15/ and |
527 | http://www.unicode.org/unicode/reports/tr21/ |
ba62762e |
528 | |
1bfb14c4 |
529 | As of Perl 5.8.0, the "Full" case-folding of I<Case |
530 | Mappings/SpecialCasing> is implemented. |
ba62762e |
531 | |
532 | =item * |
533 | |
534 | String Collation |
535 | |
376d9008 |
536 | People like to see their strings nicely sorted--or as Unicode |
ba62762e |
537 | parlance goes, collated. But again, what do you mean by collate? |
538 | |
07698885 |
539 | (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after |
540 | C<LATIN CAPITAL LETTER A WITH GRAVE>?) |
ba62762e |
541 | |
58c274a1 |
542 | The short answer is that by default, Perl compares strings (C<lt>, |
ba62762e |
543 | C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the |
1bfb14c4 |
544 | characters. In the above case, the answer is "after", since |
545 | C<0x00C1> > C<0x00C0>. |
ba62762e |
546 | |
547 | The long answer is that "it depends", and a good answer cannot be |
548 | given without knowing (at the very least) the language context. |
549 | See L<Unicode::Collate>, and I<Unicode Collation Algorithm> |
550 | http://www.unicode.org/unicode/reports/tr10/ |
551 | |
552 | =back |
553 | |
554 | =head2 Miscellaneous |
555 | |
556 | =over 4 |
557 | |
558 | =item * |
559 | |
3ff56b75 |
560 | Character Ranges and Classes |
ba62762e |
561 | |
562 | Character ranges in regular expression character classes (C</[a-z]/>) |
563 | and in the C<tr///> (also known as C<y///>) operator are not magically |
58c274a1 |
564 | Unicode-aware. What this means that C<[A-Za-z]> will not magically start |
376d9008 |
565 | to mean "all alphabetic letters"; not that it does mean that even for |
566 | 8-bit characters, you should be using C</[[:alpha:]]/> in that case. |
ba62762e |
567 | |
1bfb14c4 |
568 | For specifying character classes like that in regular expressions, |
569 | you can use the various Unicode properties--C<\pL>, or perhaps |
570 | C<\p{Alphabetic}>, in this particular case. You can use Unicode |
571 | code points as the end points of character ranges, but there is no |
572 | magic associated with specifying a certain range. For further |
573 | information--there are dozens of Unicode character classes--see |
574 | L<perlunicode>. |
ba62762e |
575 | |
576 | =item * |
577 | |
578 | String-To-Number Conversions |
579 | |
376d9008 |
580 | Unicode does define several other decimal--and numeric--characters |
581 | besides the familiar 0 to 9, such as the Arabic and Indic digits. |
ba62762e |
582 | Perl does not support string-to-number conversion for digits other |
58c274a1 |
583 | than ASCII 0 to 9 (and ASCII a to f for hexadecimal). |
ba62762e |
584 | |
585 | =back |
586 | |
587 | =head2 Questions With Answers |
588 | |
589 | =over 4 |
590 | |
818c4caa |
591 | =item * |
5cb3728c |
592 | |
593 | Will My Old Scripts Break? |
ba62762e |
594 | |
595 | Very probably not. Unless you are generating Unicode characters |
1bfb14c4 |
596 | somehow, old behaviour should be preserved. About the only behaviour |
597 | that has changed and which could start generating Unicode is the old |
598 | behaviour of C<chr()> where supplying an argument more than 255 |
599 | produced a character modulo 255. C<chr(300)>, for example, was equal |
600 | to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH |
601 | BREVE. |
ba62762e |
602 | |
818c4caa |
603 | =item * |
5cb3728c |
604 | |
605 | How Do I Make My Scripts Work With Unicode? |
ba62762e |
606 | |
607 | Very little work should be needed since nothing changes until you |
1bfb14c4 |
608 | generate Unicode data. The most important thing is getting input as |
609 | Unicode; for that, see the earlier I/O discussion. |
ba62762e |
610 | |
818c4caa |
611 | =item * |
5cb3728c |
612 | |
613 | How Do I Know Whether My String Is In Unicode? |
ba62762e |
614 | |
1bfb14c4 |
615 | You shouldn't care. No, you really shouldn't. No, really. If you |
616 | have to care--beyond the cases described above--it means that we |
ba62762e |
617 | didn't get the transparency of Unicode quite right. |
618 | |
619 | Okay, if you insist: |
620 | |
621 | use Encode 'is_utf8'; |
622 | print is_utf8($string) ? 1 : 0, "\n"; |
623 | |
624 | But note that this doesn't mean that any of the characters in the |
625 | string are necessary UTF-8 encoded, or that any of the characters have |
626 | code points greater than 0xFF (255) or even 0x80 (128), or that the |
627 | string has any characters at all. All the C<is_utf8()> does is to |
628 | return the value of the internal "utf8ness" flag attached to the |
376d9008 |
629 | C<$string>. If the flag is off, the bytes in the scalar are interpreted |
3c1c8017 |
630 | as a single byte encoding. If the flag is on, the bytes in the scalar |
376d9008 |
631 | are interpreted as the (multi-byte, variable-length) UTF-8 encoded code |
3c1c8017 |
632 | points of the characters. Bytes added to an UTF-8 encoded string are |
633 | automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars |
376d9008 |
634 | are merged (double-quoted interpolation, explicit concatenation, and |
3c1c8017 |
635 | printf/sprintf parameter substitution), the result will be UTF-8 encoded |
636 | as if copies of the byte strings were upgraded to UTF-8: for example, |
637 | |
638 | $a = "ab\x80c"; |
639 | $b = "\x{100}"; |
640 | print "$a = $b\n"; |
641 | |
1bfb14c4 |
642 | the output string will be UTF-8-encoded C<ab\x80c\x{100}\n>, but note |
376d9008 |
643 | that C<$a> will stay byte-encoded. |
ba62762e |
644 | |
645 | Sometimes you might really need to know the byte length of a string |
ce7675db |
646 | instead of the character length. For that use either the |
647 | C<Encode::encode_utf8()> function or the C<bytes> pragma and its only |
648 | defined function C<length()>: |
ba62762e |
649 | |
650 | my $unicode = chr(0x100); |
651 | print length($unicode), "\n"; # will print 1 |
ce7675db |
652 | require Encode; |
653 | print length(Encode::encode_utf8($unicode)), "\n"; # will print 2 |
ba62762e |
654 | use bytes; |
1bfb14c4 |
655 | print length($unicode), "\n"; # will also print 2 |
656 | # (the 0xC4 0x80 of the UTF-8) |
ba62762e |
657 | |
818c4caa |
658 | =item * |
5cb3728c |
659 | |
660 | How Do I Detect Data That's Not Valid In a Particular Encoding? |
ba62762e |
661 | |
8baee566 |
662 | Use the C<Encode> package to try converting it. |
663 | For example, |
ba62762e |
664 | |
665 | use Encode 'encode_utf8'; |
8baee566 |
666 | if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) { |
ba62762e |
667 | # valid |
668 | } else { |
669 | # invalid |
670 | } |
671 | |
8baee566 |
672 | For UTF-8 only, you can use: |
ba62762e |
673 | |
674 | use warnings; |
8baee566 |
675 | @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8); |
ba62762e |
676 | |
1bfb14c4 |
677 | If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack> |
678 | warning is produced. The "U0" means "expect strictly UTF-8 encoded |
679 | Unicode". Without that the C<unpack("U*", ...)> would accept also |
680 | data like C<chr(0xFF>), similarly to the C<pack> as we saw earlier. |
ba62762e |
681 | |
818c4caa |
682 | =item * |
5cb3728c |
683 | |
684 | How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa? |
ba62762e |
685 | |
8baee566 |
686 | This probably isn't as useful as you might think. |
687 | Normally, you shouldn't need to. |
ba62762e |
688 | |
1bfb14c4 |
689 | In one sense, what you are asking doesn't make much sense: encodings |
376d9008 |
690 | are for characters, and binary data are not "characters", so converting |
a5f0baef |
691 | "data" into some encoding isn't meaningful unless you know in what |
692 | character set and encoding the binary data is in, in which case it's |
376d9008 |
693 | not just binary data, now is it? |
8baee566 |
694 | |
1bfb14c4 |
695 | If you have a raw sequence of bytes that you know should be |
696 | interpreted via a particular encoding, you can use C<Encode>: |
ba62762e |
697 | |
698 | use Encode 'from_to'; |
699 | from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 |
700 | |
1bfb14c4 |
701 | The call to C<from_to()> changes the bytes in C<$data>, but nothing |
702 | material about the nature of the string has changed as far as Perl is |
703 | concerned. Both before and after the call, the string C<$data> |
704 | contains just a bunch of 8-bit bytes. As far as Perl is concerned, |
705 | the encoding of the string remains as "system-native 8-bit bytes". |
8baee566 |
706 | |
707 | You might relate this to a fictional 'Translate' module: |
708 | |
709 | use Translate; |
710 | my $phrase = "Yes"; |
711 | Translate::from_to($phrase, 'english', 'deutsch'); |
712 | ## phrase now contains "Ja" |
ba62762e |
713 | |
8baee566 |
714 | The contents of the string changes, but not the nature of the string. |
1bfb14c4 |
715 | Perl doesn't know any more after the call than before that the |
716 | contents of the string indicates the affirmative. |
ba62762e |
717 | |
376d9008 |
718 | Back to converting data. If you have (or want) data in your system's |
a5f0baef |
719 | native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use |
720 | pack/unpack to convert to/from Unicode. |
ba62762e |
721 | |
8baee566 |
722 | $native_string = pack("C*", unpack("U*", $Unicode_string)); |
723 | $Unicode_string = pack("U*", unpack("C*", $native_string)); |
ba62762e |
724 | |
725 | If you have a sequence of bytes you B<know> is valid UTF-8, |
726 | but Perl doesn't know it yet, you can make Perl a believer, too: |
727 | |
728 | use Encode 'decode_utf8'; |
8baee566 |
729 | $Unicode = decode_utf8($bytes); |
ba62762e |
730 | |
731 | You can convert well-formed UTF-8 to a sequence of bytes, but if |
732 | you just want to convert random binary data into UTF-8, you can't. |
1bfb14c4 |
733 | B<Any random collection of bytes isn't well-formed UTF-8>. You can |
ba62762e |
734 | use C<unpack("C*", $string)> for the former, and you can create |
8baee566 |
735 | well-formed Unicode data by C<pack("U*", 0xff, ...)>. |
ba62762e |
736 | |
818c4caa |
737 | =item * |
5cb3728c |
738 | |
739 | How Do I Display Unicode? How Do I Input Unicode? |
ba62762e |
740 | |
076d825e |
741 | See http://www.alanwood.net/unicode/ and |
ba62762e |
742 | http://www.cl.cam.ac.uk/~mgk25/unicode.html |
743 | |
818c4caa |
744 | =item * |
5cb3728c |
745 | |
746 | How Does Unicode Work With Traditional Locales? |
ba62762e |
747 | |
748 | In Perl, not very well. Avoid using locales through the C<locale> |
749 | pragma. Use only one or the other. |
750 | |
751 | =back |
752 | |
753 | =head2 Hexadecimal Notation |
754 | |
376d9008 |
755 | The Unicode standard prefers using hexadecimal notation because |
756 | that more clearly shows the division of Unicode into blocks of 256 characters. |
ba62762e |
757 | Hexadecimal is also simply shorter than decimal. You can use decimal |
758 | notation, too, but learning to use hexadecimal just makes life easier |
1bfb14c4 |
759 | with the Unicode standard. The C<U+HHHH> notation uses hexadecimal, |
076d825e |
760 | for example. |
ba62762e |
761 | |
762 | The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and> |
763 | a-f (or A-F, case doesn't matter). Each hexadecimal digit represents |
764 | four bits, or half a byte. C<print 0x..., "\n"> will show a |
765 | hexadecimal number in decimal, and C<printf "%x\n", $decimal> will |
766 | show a decimal number in hexadecimal. If you have just the |
376d9008 |
767 | "hex digits" of a hexadecimal number, you can use the C<hex()> function. |
ba62762e |
768 | |
769 | print 0x0009, "\n"; # 9 |
770 | print 0x000a, "\n"; # 10 |
771 | print 0x000f, "\n"; # 15 |
772 | print 0x0010, "\n"; # 16 |
773 | print 0x0011, "\n"; # 17 |
774 | print 0x0100, "\n"; # 256 |
775 | |
776 | print 0x0041, "\n"; # 65 |
777 | |
778 | printf "%x\n", 65; # 41 |
779 | printf "%#x\n", 65; # 0x41 |
780 | |
781 | print hex("41"), "\n"; # 65 |
782 | |
783 | =head2 Further Resources |
784 | |
785 | =over 4 |
786 | |
787 | =item * |
788 | |
789 | Unicode Consortium |
790 | |
791 | http://www.unicode.org/ |
792 | |
793 | =item * |
794 | |
795 | Unicode FAQ |
796 | |
797 | http://www.unicode.org/unicode/faq/ |
798 | |
799 | =item * |
800 | |
801 | Unicode Glossary |
802 | |
803 | http://www.unicode.org/glossary/ |
804 | |
805 | =item * |
806 | |
807 | Unicode Useful Resources |
808 | |
809 | http://www.unicode.org/unicode/onlinedat/resources.html |
810 | |
811 | =item * |
812 | |
813 | Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications |
814 | |
076d825e |
815 | http://www.alanwood.net/unicode/ |
ba62762e |
816 | |
817 | =item * |
818 | |
819 | UTF-8 and Unicode FAQ for Unix/Linux |
820 | |
821 | http://www.cl.cam.ac.uk/~mgk25/unicode.html |
822 | |
823 | =item * |
824 | |
825 | Legacy Character Sets |
826 | |
827 | http://www.czyborra.com/ |
828 | http://www.eki.ee/letter/ |
829 | |
830 | =item * |
831 | |
832 | The Unicode support files live within the Perl installation in the |
833 | directory |
834 | |
835 | $Config{installprivlib}/unicore |
836 | |
837 | in Perl 5.8.0 or newer, and |
838 | |
839 | $Config{installprivlib}/unicode |
840 | |
841 | in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to |
842 | avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) |
551b6b6f |
843 | The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in |
ba62762e |
844 | Perl 5.6.1.) You can find the C<$Config{installprivlib}> by |
845 | |
846 | perl "-V:installprivlib" |
847 | |
ba62762e |
848 | You can explore various information from the Unicode data files using |
849 | the C<Unicode::UCD> module. |
850 | |
851 | =back |
852 | |
f6edf83b |
853 | =head1 UNICODE IN OLDER PERLS |
854 | |
855 | If you cannot upgrade your Perl to 5.8.0 or later, you can still |
856 | do some Unicode processing by using the modules C<Unicode::String>, |
857 | C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN. |
858 | If you have the GNU recode installed, you can also use the |
376d9008 |
859 | Perl front-end C<Convert::Recode> for character conversions. |
f6edf83b |
860 | |
aaef10c5 |
861 | The following are fast conversions from ISO 8859-1 (Latin-1) bytes |
862 | to UTF-8 bytes, the code works even with older Perl 5 versions. |
863 | |
864 | # ISO 8859-1 to UTF-8 |
865 | s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg; |
866 | |
867 | # UTF-8 to ISO 8859-1 |
868 | s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg; |
869 | |
ba62762e |
870 | =head1 SEE ALSO |
871 | |
872 | L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>, |
873 | L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD> |
874 | |
376d9008 |
875 | =head1 ACKNOWLEDGMENTS |
ba62762e |
876 | |
877 | Thanks to the kind readers of the perl5-porters@perl.org, |
878 | perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org |
879 | mailing lists for their valuable feedback. |
880 | |
881 | =head1 AUTHOR, COPYRIGHT, AND LICENSE |
882 | |
be3c0a43 |
883 | Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi> |
ba62762e |
884 | |
885 | This document may be distributed under the same terms as Perl itself. |