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1 | =head1 NAME |
2 | ||
07fcf8ff | 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 | ||
376d9008 | 12 | Unicode is a character set standard which plans to codify all of the |
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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 |
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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 | |
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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 | |
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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 | |
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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>. | |
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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 |
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40 | the character. |
41 | ||
42 | Unicode also defines various I<properties> for the characters, like | |
376d9008 | 43 | "uppercase" or "lowercase", "decimal digit", or "punctuation"; |
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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. |
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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 |
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52 | sequence>. |
53 | ||
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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 | |
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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. | |
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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 |
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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. |
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77 | |
78 | Because of backward compatibility with legacy encodings, the "a unique | |
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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. | |
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86 | |
87 | A common myth about Unicode is that it would be "16-bit", that is, | |
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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 | |
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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>. | |
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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) |
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113 | The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms. |
114 | ||
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115 | For more information about encodings--for instance, to learn what |
116 | I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>. | |
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117 | |
118 | =head2 Perl's Unicode Support | |
119 | ||
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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. |
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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 |
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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. | |
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136 | |
137 | =head2 Perl's Unicode Model | |
138 | ||
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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 |
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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 |
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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 | |
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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. | |
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158 | |
159 | For example, | |
160 | ||
7ca610e8 | 161 | perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"' |
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162 | |
163 | produces a fairly useless mixture of native bytes and UTF-8, as well | |
1bfb14c4 | 164 | as a warning: |
4192de81 | 165 | |
1bfb14c4 JH |
166 | Wide character in print at ... |
167 | ||
168 | To output UTF-8, use the C<:utf8> output discipline. Prepending | |
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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 | |
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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 | |
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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 JH |
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. |
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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 | |
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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". | |
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197 | |
198 | =head2 Creating Unicode | |
199 | ||
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200 | To create Unicode characters in literals for code points above C<0xFF>, |
201 | use the C<\x{...}> notation in double-quoted strings: | |
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202 | |
203 | my $smiley = "\x{263a}"; | |
204 | ||
376d9008 | 205 | Similarly, it can be used in regular expression literals |
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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 JB |
215 | Naturally, C<ord()> will do the reverse: it turns a character into |
216 | a code point. | |
ba62762e | 217 | |
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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 | |
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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()>. | |
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225 | |
226 | You can also use the C<charnames> pragma to invoke characters | |
376d9008 | 227 | by name in double-quoted strings: |
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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 JH |
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 JH |
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 | ||
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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 JH |
259 | Note that Perl considers combining character sequences to be |
260 | characters, so for example | |
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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 | ||
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268 | Life is not quite so transparent, however, when working with legacy |
269 | encodings, I/O, and certain special cases: | |
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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 | ||
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280 | in which case literals (string or regular expressions), C<chr()>, |
281 | and C<ord()> in your whole script are assumed to produce Unicode | |
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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 | |
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285 | |
286 | use encoding; | |
287 | ||
376d9008 JB |
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 |
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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 |
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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 TS |
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 JH |
318 | |
319 | binmode(STDOUT, ":utf8"); | |
320 | ||
ec90690f TS |
321 | binmode(STDOUT, ":encoding(ucs2)"); |
322 | binmode(STDOUT, ":encoding(UTF-8)"); | |
323 | binmode(STDOUT, ":encoding(shift_jis)"); | |
324 | ||
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325 | The matching of encoding names is loose: case does not matter, and |
326 | many encodings have several aliases. Note that C<:utf8> discipline | |
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327 | must always be specified exactly like that; it is I<not> subject to |
328 | the loose matching of encoding names. | |
b5d8778e | 329 | |
376d9008 JB |
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 JH |
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 | |
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339 | |
340 | open(my $fh,'<:utf8', 'anything'); | |
8baee566 JF |
341 | my $line_of_unicode = <$fh>; |
342 | ||
ec90690f | 343 | open(my $fh,'<:encoding(Big5)', 'anything'); |
8baee566 | 344 | my $line_of_unicode = <$fh>; |
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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 | |
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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"; |
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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 JH |
359 | $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R'; |
360 | # the :locale will probe the locale environment variables like LC_ALL | |
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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 JF |
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. |
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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 JH |
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 JH |
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 JF |
396 | open(my $nihongo, '<:encoding(iso2022-jp)', 'text.jis'); |
397 | open(my $unicode, '>:utf8', 'text.utf8'); | |
398 | while (<$nihongo>) { print $unicode } | |
ba62762e JH |
399 | |
400 | The naming of encodings, both by the C<open()> and by the C<open> | |
376d9008 JB |
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 JH |
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 JH |
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 JF |
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 JH |
416 | |
417 | # BAD CODE WARNING | |
418 | open F, "file"; | |
8baee566 | 419 | local $/; ## read in the whole file of 8-bit characters |
ba62762e JH |
420 | $t = <F>; |
421 | close F; | |
422 | open F, ">:utf8", "file"; | |
8baee566 | 423 | print F $t; ## convert to UTF-8 on output |
ba62762e JH |
424 | close F; |
425 | ||
426 | If you run this code twice, the contents of the F<file> will be twice | |
1d7919c5 JH |
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 JH |
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 JH |
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 JH |
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 JF |
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", $_) : # \x.. |
58c274a1 JF |
449 | chr($_) # 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 JH |
461 | =head2 Special Cases |
462 | ||
463 | =over 4 | |
464 | ||
465 | =item * | |
466 | ||
467 | Bit Complement Operator ~ And vec() | |
468 | ||
1bfb14c4 JH |
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 JH |
476 | |
477 | =item * | |
478 | ||
8baee566 JF |
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 JH |
484 | explicitly-defined I/O disciplines). But if you must, there are two |
485 | ways of looking behind the scenes. | |
ba62762e JH |
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 JH |
489 | to display the bytes: |
490 | ||
8baee566 | 491 | # this prints c4 80 for the UTF-8 bytes 0xc4 0x80 |
ba62762e JH |
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 JH |
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 RGS |
515 | (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to |
516 | C<LATIN CAPITAL LETTER A>?) | |
ba62762e | 517 | |
a5f0baef JH |
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 JB |
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 JH |
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 JB |
526 | Mappings>, http://www.unicode.org/unicode/reports/tr15/ and |
527 | http://www.unicode.org/unicode/reports/tr21/ | |
ba62762e | 528 | |
1bfb14c4 JH |
529 | As of Perl 5.8.0, the "Full" case-folding of I<Case |
530 | Mappings/SpecialCasing> is implemented. | |
ba62762e JH |
531 | |
532 | =item * | |
533 | ||
534 | String Collation | |
535 | ||
376d9008 | 536 | People like to see their strings nicely sorted--or as Unicode |
ba62762e JH |
537 | parlance goes, collated. But again, what do you mean by collate? |
538 | ||
07698885 RGS |
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 JH |
544 | characters. In the above case, the answer is "after", since |
545 | C<0x00C1> > C<0x00C0>. | |
ba62762e JH |
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 JH |
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 JB |
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 JH |
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 JH |
575 | |
576 | =item * | |
577 | ||
578 | String-To-Number Conversions | |
579 | ||
376d9008 JB |
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 JH |
584 | |
585 | =back | |
586 | ||
587 | =head2 Questions With Answers | |
588 | ||
589 | =over 4 | |
590 | ||
818c4caa | 591 | =item * |
5cb3728c RB |
592 | |
593 | Will My Old Scripts Break? | |
ba62762e JH |
594 | |
595 | Very probably not. Unless you are generating Unicode characters | |
1bfb14c4 JH |
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 RB |
604 | |
605 | How Do I Make My Scripts Work With Unicode? | |
ba62762e JH |
606 | |
607 | Very little work should be needed since nothing changes until you | |
1bfb14c4 JH |
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 RB |
612 | |
613 | How Do I Know Whether My String Is In Unicode? | |
ba62762e | 614 | |
1bfb14c4 JH |
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 JH |
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 AT |
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 AT |
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 JH |
644 | |
645 | Sometimes you might really need to know the byte length of a string | |
ce7675db A |
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 JH |
649 | |
650 | my $unicode = chr(0x100); | |
651 | print length($unicode), "\n"; # will print 1 | |
ce7675db A |
652 | require Encode; |
653 | print length(Encode::encode_utf8($unicode)), "\n"; # will print 2 | |
ba62762e | 654 | use bytes; |
1bfb14c4 JH |
655 | print length($unicode), "\n"; # will also print 2 |
656 | # (the 0xC4 0x80 of the UTF-8) | |
ba62762e | 657 | |
818c4caa | 658 | =item * |
5cb3728c RB |
659 | |
660 | How Do I Detect Data That's Not Valid In a Particular Encoding? | |
ba62762e | 661 | |
8baee566 JF |
662 | Use the C<Encode> package to try converting it. |
663 | For example, | |
ba62762e JH |
664 | |
665 | use Encode 'encode_utf8'; | |
8baee566 | 666 | if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) { |
ba62762e JH |
667 | # valid |
668 | } else { | |
669 | # invalid | |
670 | } | |
671 | ||
8baee566 | 672 | For UTF-8 only, you can use: |
ba62762e JH |
673 | |
674 | use warnings; | |
8baee566 | 675 | @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8); |
ba62762e | 676 | |
1bfb14c4 JH |
677 | If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack> |
678 | warning is produced. The "U0" means "expect strictly UTF-8 encoded | |
679 | Unicode". Without that the C<unpack("U*", ...)> would accept also | |
680 | data like C<chr(0xFF>), similarly to the C<pack> as we saw earlier. | |
ba62762e | 681 | |
818c4caa | 682 | =item * |
5cb3728c RB |
683 | |
684 | How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa? | |
ba62762e | 685 | |
8baee566 JF |
686 | This probably isn't as useful as you might think. |
687 | Normally, you shouldn't need to. | |
ba62762e | 688 | |
1bfb14c4 | 689 | In one sense, what you are asking doesn't make much sense: encodings |
376d9008 | 690 | are for characters, and binary data are not "characters", so converting |
a5f0baef JH |
691 | "data" into some encoding isn't meaningful unless you know in what |
692 | character set and encoding the binary data is in, in which case it's | |
376d9008 | 693 | not just binary data, now is it? |
8baee566 | 694 | |
1bfb14c4 JH |
695 | If you have a raw sequence of bytes that you know should be |
696 | interpreted via a particular encoding, you can use C<Encode>: | |
ba62762e JH |
697 | |
698 | use Encode 'from_to'; | |
699 | from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 | |
700 | ||
1bfb14c4 JH |
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 JF |
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 JH |
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 JH |
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 JF |
722 | $native_string = pack("C*", unpack("U*", $Unicode_string)); |
723 | $Unicode_string = pack("U*", unpack("C*", $native_string)); | |
ba62762e JH |
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 JH |
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 RB |
738 | |
739 | How Do I Display Unicode? How Do I Input Unicode? | |
ba62762e | 740 | |
076d825e | 741 | See http://www.alanwood.net/unicode/ and |
ba62762e JH |
742 | http://www.cl.cam.ac.uk/~mgk25/unicode.html |
743 | ||
818c4caa | 744 | =item * |
5cb3728c RB |
745 | |
746 | How Does Unicode Work With Traditional Locales? | |
ba62762e JH |
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 JB |
755 | The Unicode standard prefers using hexadecimal notation because |
756 | that more clearly shows the division of Unicode into blocks of 256 characters. | |
ba62762e JH |
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 JH |
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 JH |
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 JH |
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 | $Config{installprivlib}/unicode | |
840 | ||
841 | in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to | |
842 | avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) | |
551b6b6f | 843 | The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in |
ba62762e JH |
844 | Perl 5.6.1.) You can find the C<$Config{installprivlib}> by |
845 | ||
846 | perl "-V:installprivlib" | |
847 | ||
ba62762e JH |
848 | You can explore various information from the Unicode data files using |
849 | the C<Unicode::UCD> module. | |
850 | ||
851 | =back | |
852 | ||
f6edf83b JH |
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 JH |
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 JH |
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 JH |
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 JH |
884 | |
885 | This document may be distributed under the same terms as Perl itself. |