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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. | |
4c496f0c | 22 | Unicode 1.0 was released in October 1991, and 4.0 in April 2003. |
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23 | |
24 | A Unicode I<character> is an abstract entity. It is not bound to any | |
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25 | particular integer width, especially not to the C language C<char>. |
26 | Unicode is language-neutral and display-neutral: it does not encode the | |
e1b711da | 27 | language of the text, and it does not generally define fonts or other graphical |
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28 | layout details. Unicode operates on characters and on text built from |
29 | those characters. | |
30 | ||
31 | Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK | |
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32 | SMALL LETTER ALPHA> and unique numbers for the characters, in this |
33 | case 0x0041 and 0x03B1, respectively. These unique numbers are called | |
34 | I<code points>. | |
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35 | |
36 | The Unicode standard prefers using hexadecimal notation for the code | |
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37 | points. If numbers like C<0x0041> are unfamiliar to you, take a peek |
38 | at a later section, L</"Hexadecimal Notation">. The Unicode standard | |
39 | uses the notation C<U+0041 LATIN CAPITAL LETTER A>, to give the | |
40 | hexadecimal code point and the normative name of the character. | |
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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. |
ba62762e | 47 | |
0111a78f KW |
48 | A Unicode I<logical> "character" can actually consist of more than one internal |
49 | I<actual> "character" or code point. For Western languages, this is adequately | |
c670e63a | 50 | modelled by a I<base character> (like C<LATIN CAPITAL LETTER A>) followed |
0111a78f | 51 | by one or more I<modifiers> (like C<COMBINING ACUTE ACCENT>). This sequence of |
376d9008 | 52 | base character and modifiers is called a I<combining character |
0111a78f | 53 | sequence>. Some non-western languages require more complicated |
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54 | models, so Unicode created the I<grapheme cluster> concept, and then the |
55 | I<extended grapheme cluster>. For example, a Korean Hangul syllable is | |
0111a78f | 56 | considered a single logical character, but most often consists of three actual |
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57 | Unicode characters: a leading consonant followed by an interior vowel followed |
58 | by a trailing consonant. | |
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59 | |
60 | Whether to call these extended grapheme clusters "characters" depends on your | |
61 | point of view. If you are a programmer, you probably would tend towards seeing | |
62 | each element in the sequences as one unit, or "character". The whole sequence | |
63 | could be seen as one "character", however, from the user's point of view, since | |
64 | that's probably what it looks like in the context of the user's language. | |
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65 | |
66 | With this "whole sequence" view of characters, the total number of | |
67 | characters is open-ended. But in the programmer's "one unit is one | |
68 | character" point of view, the concept of "characters" is more | |
f7d1603d | 69 | deterministic. In this document, we take that second point of view: |
0111a78f | 70 | one "character" is one Unicode code point. |
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71 | |
72 | For some combinations, there are I<precomposed> characters. | |
73 | C<LATIN CAPITAL LETTER A WITH ACUTE>, for example, is defined as | |
ba62762e | 74 | a single code point. These precomposed characters are, however, |
376d9008 | 75 | only available for some combinations, and are mainly |
ba62762e | 76 | meant to support round-trip conversions between Unicode and legacy |
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77 | standards (like the ISO 8859). In the general case, the composing |
78 | method is more extensible. To support conversion between | |
ba62762e | 79 | different compositions of the characters, various I<normalization |
376d9008 | 80 | forms> to standardize representations are also defined. |
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81 | |
82 | Because of backward compatibility with legacy encodings, the "a unique | |
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83 | number for every character" idea breaks down a bit: instead, there is |
84 | "at least one number for every character". The same character could | |
85 | be represented differently in several legacy encodings. The | |
86 | converse is also not true: some code points do not have an assigned | |
87 | character. Firstly, there are unallocated code points within | |
88 | otherwise used blocks. Secondly, there are special Unicode control | |
89 | characters that do not represent true characters. | |
ba62762e | 90 | |
e1b711da | 91 | A common myth about Unicode is that it is "16-bit", that is, |
376d9008 | 92 | Unicode is only represented as C<0x10000> (or 65536) characters from |
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93 | C<0x0000> to C<0xFFFF>. B<This is untrue.> Since Unicode 2.0 (July |
94 | 1996), Unicode has been defined all the way up to 21 bits (C<0x10FFFF>), | |
95 | and since Unicode 3.1 (March 2001), characters have been defined | |
96 | beyond C<0xFFFF>. The first C<0x10000> characters are called the | |
97 | I<Plane 0>, or the I<Basic Multilingual Plane> (BMP). With Unicode | |
98 | 3.1, 17 (yes, seventeen) planes in all were defined--but they are | |
99 | nowhere near full of defined characters, yet. | |
ba62762e | 100 | |
e1b711da | 101 | Another myth is about Unicode blocks--that they have something to |
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102 | do with languages--that each block would define the characters used |
103 | by a language or a set of languages. B<This is also untrue.> | |
104 | The division into blocks exists, but it is almost completely | |
105 | accidental--an artifact of how the characters have been and | |
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106 | still are allocated. Instead, there is a concept called I<scripts>, which is |
107 | more useful: there is C<Latin> script, C<Greek> script, and so on. Scripts | |
108 | usually span varied parts of several blocks. For more information about | |
109 | scripts, see L<perlunicode/Scripts>. | |
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110 | |
111 | The Unicode code points are just abstract numbers. To input and | |
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112 | output these abstract numbers, the numbers must be I<encoded> or |
113 | I<serialised> somehow. Unicode defines several I<character encoding | |
114 | forms>, of which I<UTF-8> is perhaps the most popular. UTF-8 is a | |
115 | variable length encoding that encodes Unicode characters as 1 to 6 | |
e1b711da | 116 | bytes. Other encodings |
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117 | include UTF-16 and UTF-32 and their big- and little-endian variants |
118 | (UTF-8 is byte-order independent) The ISO/IEC 10646 defines the UCS-2 | |
119 | and UCS-4 encoding forms. | |
ba62762e | 120 | |
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121 | For more information about encodings--for instance, to learn what |
122 | I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>. | |
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123 | |
124 | =head2 Perl's Unicode Support | |
125 | ||
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126 | Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode |
127 | natively. Perl 5.8.0, however, is the first recommended release for | |
128 | serious Unicode work. The maintenance release 5.6.1 fixed many of the | |
129 | problems of the initial Unicode implementation, but for example | |
1bfb14c4 | 130 | regular expressions still do not work with Unicode in 5.6.1. |
ba62762e | 131 | |
2bbc8d55 | 132 | B<Starting from Perl 5.8.0, the use of C<use utf8> is needed only in much more restricted circumstances.> In earlier releases the C<utf8> pragma was used to declare |
ba62762e | 133 | that operations in the current block or file would be Unicode-aware. |
376d9008 | 134 | This model was found to be wrong, or at least clumsy: the "Unicodeness" |
1bfb14c4 | 135 | is now carried with the data, instead of being attached to the |
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136 | operations. Only one case remains where an explicit C<use utf8> is |
137 | needed: if your Perl script itself is encoded in UTF-8, you can use | |
138 | UTF-8 in your identifier names, and in string and regular expression | |
139 | literals, by saying C<use utf8>. This is not the default because | |
8f8cf39c | 140 | scripts with legacy 8-bit data in them would break. See L<utf8>. |
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141 | |
142 | =head2 Perl's Unicode Model | |
143 | ||
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144 | Perl supports both pre-5.6 strings of eight-bit native bytes, and |
145 | strings of Unicode characters. The principle is that Perl tries to | |
146 | keep its data as eight-bit bytes for as long as possible, but as soon | |
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147 | as Unicodeness cannot be avoided, the data is (mostly) transparently upgraded |
148 | to Unicode. There are some problems--see L<perlunicode/The "Unicode Bug">. | |
ba62762e | 149 | |
4192de81 | 150 | Internally, Perl currently uses either whatever the native eight-bit |
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151 | character set of the platform (for example Latin-1) is, defaulting to |
152 | UTF-8, to encode Unicode strings. Specifically, if all code points in | |
153 | the string are C<0xFF> or less, Perl uses the native eight-bit | |
154 | character set. Otherwise, it uses UTF-8. | |
4192de81 | 155 | |
7ca610e8 | 156 | A user of Perl does not normally need to know nor care how Perl |
20ba30f4 | 157 | happens to encode its internal strings, but it becomes relevant when |
ac036724 | 158 | outputting Unicode strings to a stream without a PerlIO layer (one with |
159 | the "default" encoding). In such a case, the raw bytes used internally | |
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160 | (the native character set or UTF-8, as appropriate for each string) |
161 | will be used, and a "Wide character" warning will be issued if those | |
162 | strings contain a character beyond 0x00FF. | |
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163 | |
164 | For example, | |
165 | ||
ae5648b3 | 166 | perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"' |
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167 | |
168 | produces a fairly useless mixture of native bytes and UTF-8, as well | |
1bfb14c4 | 169 | as a warning: |
4192de81 | 170 | |
1bfb14c4 JH |
171 | Wide character in print at ... |
172 | ||
740d4bb2 | 173 | To output UTF-8, use the C<:encoding> or C<:utf8> output layer. Prepending |
4192de81 JH |
174 | |
175 | binmode(STDOUT, ":utf8"); | |
176 | ||
376d9008 | 177 | to this sample program ensures that the output is completely UTF-8, |
1bfb14c4 | 178 | and removes the program's warning. |
ba62762e | 179 | |
8aa8f774 JH |
180 | You can enable automatic UTF-8-ification of your standard file |
181 | handles, default C<open()> layer, and C<@ARGV> by using either | |
182 | the C<-C> command line switch or the C<PERL_UNICODE> environment | |
183 | variable, see L<perlrun> for the documentation of the C<-C> switch. | |
184 | ||
185 | Note that this means that Perl expects other software to work, too: | |
186 | if Perl has been led to believe that STDIN should be UTF-8, but then | |
187 | STDIN coming in from another command is not UTF-8, Perl will complain | |
188 | about the malformed UTF-8. | |
b310b053 | 189 | |
ec71e770 JH |
190 | All features that combine Unicode and I/O also require using the new |
191 | PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though: | |
192 | you can see whether yours is by running "perl -V" and looking for | |
193 | C<useperlio=define>. | |
194 | ||
64c66fb6 JH |
195 | =head2 Unicode and EBCDIC |
196 | ||
197 | Perl 5.8.0 also supports Unicode on EBCDIC platforms. There, | |
376d9008 | 198 | Unicode support is somewhat more complex to implement since |
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199 | additional conversions are needed at every step. |
200 | ||
201 | Later Perl releases have added code that will not work on EBCDIC platforms, and | |
202 | no one has complained, so the divergence has continued. If you want to run | |
203 | Perl on an EBCDIC platform, send email to perlbug@perl.org | |
64c66fb6 | 204 | |
64c66fb6 | 205 | On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC |
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206 | instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in |
207 | that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is | |
208 | "EBCDIC-safe". | |
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209 | |
210 | =head2 Creating Unicode | |
211 | ||
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212 | To create Unicode characters in literals for code points above C<0xFF>, |
213 | use the C<\x{...}> notation in double-quoted strings: | |
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214 | |
215 | my $smiley = "\x{263a}"; | |
216 | ||
376d9008 | 217 | Similarly, it can be used in regular expression literals |
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218 | |
219 | $smiley =~ /\x{263a}/; | |
220 | ||
221 | At run-time you can use C<chr()>: | |
222 | ||
223 | my $hebrew_alef = chr(0x05d0); | |
224 | ||
376d9008 | 225 | See L</"Further Resources"> for how to find all these numeric codes. |
ba62762e | 226 | |
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227 | Naturally, C<ord()> will do the reverse: it turns a character into |
228 | a code point. | |
ba62762e | 229 | |
1bfb14c4 JH |
230 | Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>, |
231 | and C<chr(...)> for arguments less than C<0x100> (decimal 256) | |
232 | generate an eight-bit character for backward compatibility with older | |
233 | Perls. For arguments of C<0x100> or more, Unicode characters are | |
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234 | always produced. If you want to force the production of Unicode |
235 | characters regardless of the numeric value, use C<pack("U", ...)> | |
236 | instead of C<\x..>, C<\x{...}>, or C<chr()>. | |
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237 | |
238 | You can also use the C<charnames> pragma to invoke characters | |
376d9008 | 239 | by name in double-quoted strings: |
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240 | |
241 | use charnames ':full'; | |
242 | my $arabic_alef = "\N{ARABIC LETTER ALEF}"; | |
243 | ||
244 | And, as mentioned above, you can also C<pack()> numbers into Unicode | |
245 | characters: | |
246 | ||
247 | my $georgian_an = pack("U", 0x10a0); | |
248 | ||
8a5e5dd5 JH |
249 | Note that both C<\x{...}> and C<\N{...}> are compile-time string |
250 | constants: you cannot use variables in them. if you want similar | |
251 | run-time functionality, use C<chr()> and C<charnames::vianame()>. | |
252 | ||
1eda90df | 253 | If you want to force the result to Unicode characters, use the special |
f337b084 TH |
254 | C<"U0"> prefix. It consumes no arguments but causes the following bytes |
255 | to be interpreted as the UTF-8 encoding of Unicode characters: | |
1eda90df | 256 | |
f337b084 | 257 | my $chars = pack("U0W*", 0x80, 0x42); |
771cd3b2 | 258 | |
ae5648b3 | 259 | Likewise, you can stop such UTF-8 interpretation by using the special |
771cd3b2 | 260 | C<"C0"> prefix. |
1eda90df | 261 | |
ba62762e JH |
262 | =head2 Handling Unicode |
263 | ||
264 | Handling Unicode is for the most part transparent: just use the | |
265 | strings as usual. Functions like C<index()>, C<length()>, and | |
266 | C<substr()> will work on the Unicode characters; regular expressions | |
267 | will work on the Unicode characters (see L<perlunicode> and L<perlretut>). | |
268 | ||
0111a78f KW |
269 | Note that Perl considers grapheme clusters to be separate characters, so for |
270 | example | |
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271 | |
272 | use charnames ':full'; | |
273 | print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; | |
274 | ||
275 | will print 2, not 1. The only exception is that regular expressions | |
0111a78f | 276 | have C<\X> for matching an extended grapheme cluster. |
ba62762e | 277 | |
376d9008 JB |
278 | Life is not quite so transparent, however, when working with legacy |
279 | encodings, I/O, and certain special cases: | |
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280 | |
281 | =head2 Legacy Encodings | |
282 | ||
283 | When you combine legacy data and Unicode the legacy data needs | |
284 | to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if | |
ae5648b3 | 285 | applicable) is assumed. |
ba62762e | 286 | |
376d9008 | 287 | The C<Encode> module knows about many encodings and has interfaces |
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288 | for doing conversions between those encodings: |
289 | ||
2c9359a2 RGS |
290 | use Encode 'decode'; |
291 | $data = decode("iso-8859-3", $data); # convert from legacy to utf-8 | |
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292 | |
293 | =head2 Unicode I/O | |
294 | ||
8baee566 | 295 | Normally, writing out Unicode data |
ba62762e | 296 | |
8baee566 | 297 | print FH $some_string_with_unicode, "\n"; |
ba62762e | 298 | |
8baee566 | 299 | produces raw bytes that Perl happens to use to internally encode the |
376d9008 JB |
300 | Unicode string. Perl's internal encoding depends on the system as |
301 | well as what characters happen to be in the string at the time. If | |
302 | any of the characters are at code points C<0x100> or above, you will get | |
303 | a warning. To ensure that the output is explicitly rendered in the | |
304 | encoding you desire--and to avoid the warning--open the stream with | |
305 | the desired encoding. Some examples: | |
ba62762e | 306 | |
ec90690f TS |
307 | open FH, ">:utf8", "file"; |
308 | ||
309 | open FH, ">:encoding(ucs2)", "file"; | |
310 | open FH, ">:encoding(UTF-8)", "file"; | |
311 | open FH, ">:encoding(shift_jis)", "file"; | |
1d7919c5 | 312 | |
376d9008 | 313 | and on already open streams, use C<binmode()>: |
1d7919c5 JH |
314 | |
315 | binmode(STDOUT, ":utf8"); | |
316 | ||
ec90690f TS |
317 | binmode(STDOUT, ":encoding(ucs2)"); |
318 | binmode(STDOUT, ":encoding(UTF-8)"); | |
319 | binmode(STDOUT, ":encoding(shift_jis)"); | |
320 | ||
b5d8778e | 321 | The matching of encoding names is loose: case does not matter, and |
fae2c0fb | 322 | many encodings have several aliases. Note that the C<:utf8> layer |
1bfb14c4 | 323 | must always be specified exactly like that; it is I<not> subject to |
740d4bb2 JW |
324 | the loose matching of encoding names. Also note that C<:utf8> is unsafe for |
325 | input, because it accepts the data without validating that it is indeed valid | |
326 | UTF8. | |
b5d8778e | 327 | |
376d9008 JB |
328 | See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and |
329 | L<Encode::PerlIO> for the C<:encoding()> layer, and | |
330 | L<Encode::Supported> for many encodings supported by the C<Encode> | |
331 | module. | |
ba62762e | 332 | |
a5f0baef | 333 | Reading in a file that you know happens to be encoded in one of the |
1bfb14c4 JH |
334 | Unicode or legacy encodings does not magically turn the data into |
335 | Unicode in Perl's eyes. To do that, specify the appropriate | |
fae2c0fb | 336 | layer when opening files |
ba62762e | 337 | |
740d4bb2 | 338 | open(my $fh,'<:encoding(utf8)', 'anything'); |
8baee566 JF |
339 | my $line_of_unicode = <$fh>; |
340 | ||
ec90690f | 341 | open(my $fh,'<:encoding(Big5)', 'anything'); |
8baee566 | 342 | my $line_of_unicode = <$fh>; |
ba62762e | 343 | |
fae2c0fb | 344 | The I/O layers can also be specified more flexibly with |
376d9008 | 345 | the C<open> pragma. See L<open>, or look at the following example. |
ba62762e | 346 | |
9e5bbba0 KW |
347 | use open ':encoding(utf8)'; # input/output default encoding will be |
348 | # UTF-8 | |
1d7919c5 JH |
349 | open X, ">file"; |
350 | print X chr(0x100), "\n"; | |
ba62762e | 351 | close X; |
1d7919c5 | 352 | open Y, "<file"; |
ba62762e JH |
353 | printf "%#x\n", ord(<Y>); # this should print 0x100 |
354 | close Y; | |
355 | ||
fae2c0fb | 356 | With the C<open> pragma you can use the C<:locale> layer |
ba62762e | 357 | |
12f98225 | 358 | BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' } |
9e5bbba0 KW |
359 | # the :locale will probe the locale environment variables like |
360 | # LC_ALL | |
ba62762e JH |
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 | ||
8baee566 JF |
369 | These methods install a transparent filter on the I/O stream that |
370 | converts data from the specified encoding when it is read in from the | |
a5f0baef | 371 | stream. The result is always Unicode. |
ba62762e JH |
372 | |
373 | The L<open> pragma affects all the C<open()> calls after the pragma by | |
fae2c0fb RGS |
374 | setting default layers. If you want to affect only certain |
375 | streams, use explicit layers directly in the C<open()> call. | |
ba62762e JH |
376 | |
377 | You can switch encodings on an already opened stream by using | |
8baee566 | 378 | C<binmode()>; see L<perlfunc/binmode>. |
ba62762e | 379 | |
1ecefa54 JH |
380 | The C<:locale> does not currently (as of Perl 5.8.0) work with |
381 | C<open()> and C<binmode()>, only with the C<open> pragma. The | |
8baee566 | 382 | C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>, |
1ecefa54 | 383 | C<binmode()>, and the C<open> pragma. |
ba62762e | 384 | |
fae2c0fb | 385 | Similarly, you may use these I/O layers on output streams to |
a5f0baef JH |
386 | automatically convert Unicode to the specified encoding when it is |
387 | written to the stream. For example, the following snippet copies the | |
388 | contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to | |
389 | the file "text.utf8", encoded as UTF-8: | |
ba62762e | 390 | |
c722ef0a JH |
391 | open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis'); |
392 | open(my $unicode, '>:utf8', 'text.utf8'); | |
0cf8a8d9 | 393 | while (<$nihongo>) { print $unicode $_ } |
ba62762e JH |
394 | |
395 | The naming of encodings, both by the C<open()> and by the C<open> | |
2575c402 JW |
396 | pragma allows for flexible names: C<koi8-r> and C<KOI8R> will both be |
397 | understood. | |
ba62762e JH |
398 | |
399 | Common encodings recognized by ISO, MIME, IANA, and various other | |
8baee566 | 400 | standardisation organisations are recognised; for a more detailed |
1bfb14c4 | 401 | list see L<Encode::Supported>. |
ba62762e JH |
402 | |
403 | C<read()> reads characters and returns the number of characters. | |
404 | C<seek()> and C<tell()> operate on byte counts, as do C<sysread()> | |
405 | and C<sysseek()>. | |
406 | ||
8baee566 | 407 | Notice that because of the default behaviour of not doing any |
fae2c0fb | 408 | conversion upon input if there is no default layer, |
ba62762e | 409 | it is easy to mistakenly write code that keeps on expanding a file |
1bfb14c4 | 410 | by repeatedly encoding the data: |
ba62762e JH |
411 | |
412 | # BAD CODE WARNING | |
413 | open F, "file"; | |
8baee566 | 414 | local $/; ## read in the whole file of 8-bit characters |
ba62762e JH |
415 | $t = <F>; |
416 | close F; | |
740d4bb2 | 417 | open F, ">:encoding(utf8)", "file"; |
8baee566 | 418 | print F $t; ## convert to UTF-8 on output |
ba62762e JH |
419 | close F; |
420 | ||
421 | If you run this code twice, the contents of the F<file> will be twice | |
740d4bb2 JW |
422 | UTF-8 encoded. A C<use open ':encoding(utf8)'> would have avoided the |
423 | bug, or explicitly opening also the F<file> for input as UTF-8. | |
ba62762e | 424 | |
0c901d84 | 425 | B<NOTE>: the C<:utf8> and C<:encoding> features work only if your |
d0fadae5 JH |
426 | Perl has been built with the new PerlIO feature (which is the default |
427 | on most systems). | |
0c901d84 | 428 | |
1ecefa54 JH |
429 | =head2 Displaying Unicode As Text |
430 | ||
431 | Sometimes you might want to display Perl scalars containing Unicode as | |
8baee566 | 432 | simple ASCII (or EBCDIC) text. The following subroutine converts |
1ecefa54 | 433 | its argument so that Unicode characters with code points greater than |
1bfb14c4 JH |
434 | 255 are displayed as C<\x{...}>, control characters (like C<\n>) are |
435 | displayed as C<\x..>, and the rest of the characters as themselves: | |
1ecefa54 | 436 | |
9e5bbba0 KW |
437 | sub nice_string { |
438 | join("", | |
439 | map { $_ > 255 ? # if wide character... | |
440 | sprintf("\\x{%04X}", $_) : # \x{...} | |
441 | chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... | |
442 | sprintf("\\x%02X", $_) : # \x.. | |
443 | quotemeta(chr($_)) # else quoted or as themselves | |
f337b084 | 444 | } unpack("W*", $_[0])); # unpack Unicode characters |
58c274a1 JF |
445 | } |
446 | ||
447 | For example, | |
448 | ||
449 | nice_string("foo\x{100}bar\n") | |
450 | ||
d0551e73 | 451 | returns the string |
58c274a1 | 452 | |
d0551e73 JH |
453 | 'foo\x{0100}bar\x0A' |
454 | ||
455 | which is ready to be printed. | |
1ecefa54 | 456 | |
ba62762e JH |
457 | =head2 Special Cases |
458 | ||
459 | =over 4 | |
460 | ||
461 | =item * | |
462 | ||
463 | Bit Complement Operator ~ And vec() | |
464 | ||
1bfb14c4 JH |
465 | The bit complement operator C<~> may produce surprising results if |
466 | used on strings containing characters with ordinal values above | |
467 | 255. In such a case, the results are consistent with the internal | |
468 | encoding of the characters, but not with much else. So don't do | |
469 | that. Similarly for C<vec()>: you will be operating on the | |
470 | internally-encoded bit patterns of the Unicode characters, not on | |
471 | the code point values, which is very probably not what you want. | |
ba62762e JH |
472 | |
473 | =item * | |
474 | ||
8baee566 JF |
475 | Peeking At Perl's Internal Encoding |
476 | ||
477 | Normal users of Perl should never care how Perl encodes any particular | |
a5f0baef | 478 | Unicode string (because the normal ways to get at the contents of a |
376d9008 | 479 | string with Unicode--via input and output--should always be via |
fae2c0fb | 480 | explicitly-defined I/O layers). But if you must, there are two |
a5f0baef | 481 | ways of looking behind the scenes. |
ba62762e JH |
482 | |
483 | One way of peeking inside the internal encoding of Unicode characters | |
f337b084 TH |
484 | is to use C<unpack("C*", ...> to get the bytes of whatever the string |
485 | encoding happens to be, or C<unpack("U0..", ...)> to get the bytes of the | |
486 | UTF-8 encoding: | |
ba62762e | 487 | |
8baee566 | 488 | # this prints c4 80 for the UTF-8 bytes 0xc4 0x80 |
f337b084 | 489 | print join(" ", unpack("U0(H2)*", pack("U", 0x100))), "\n"; |
ba62762e JH |
490 | |
491 | Yet another way would be to use the Devel::Peek module: | |
492 | ||
493 | perl -MDevel::Peek -e 'Dump(chr(0x100))' | |
494 | ||
1e54db1a | 495 | That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes |
376d9008 | 496 | and Unicode characters in C<PV>. See also later in this document |
8800c35a | 497 | the discussion about the C<utf8::is_utf8()> function. |
ba62762e JH |
498 | |
499 | =back | |
500 | ||
501 | =head2 Advanced Topics | |
502 | ||
503 | =over 4 | |
504 | ||
505 | =item * | |
506 | ||
507 | String Equivalence | |
508 | ||
509 | The question of string equivalence turns somewhat complicated | |
376d9008 | 510 | in Unicode: what do you mean by "equal"? |
ba62762e | 511 | |
07698885 RGS |
512 | (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to |
513 | C<LATIN CAPITAL LETTER A>?) | |
ba62762e | 514 | |
a5f0baef JH |
515 | The short answer is that by default Perl compares equivalence (C<eq>, |
516 | C<ne>) based only on code points of the characters. In the above | |
376d9008 JB |
517 | case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any |
518 | CAPITAL LETTER As should be considered equal, or even As of any case. | |
ba62762e JH |
519 | |
520 | The long answer is that you need to consider character normalization | |
e1b711da KW |
521 | and casing issues: see L<Unicode::Normalize>, Unicode Technical Report #15, |
522 | L<Unicode Normalization Forms|http://www.unicode.org/unicode/reports/tr15> and | |
523 | sections on case mapping in the L<Unicode Standard|http://www.unicode.org>. | |
ba62762e | 524 | |
1bfb14c4 | 525 | As of Perl 5.8.0, the "Full" case-folding of I<Case |
e1b711da | 526 | Mappings/SpecialCasing> is implemented, but bugs remain in C<qr//i> with them. |
ba62762e JH |
527 | |
528 | =item * | |
529 | ||
530 | String Collation | |
531 | ||
376d9008 | 532 | People like to see their strings nicely sorted--or as Unicode |
ba62762e JH |
533 | parlance goes, collated. But again, what do you mean by collate? |
534 | ||
07698885 RGS |
535 | (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after |
536 | C<LATIN CAPITAL LETTER A WITH GRAVE>?) | |
ba62762e | 537 | |
58c274a1 | 538 | The short answer is that by default, Perl compares strings (C<lt>, |
ba62762e | 539 | C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the |
1bfb14c4 | 540 | characters. In the above case, the answer is "after", since |
da76a1f4 | 541 | C<0x00C1> > C<0x00C0>. |
ba62762e JH |
542 | |
543 | The long answer is that "it depends", and a good answer cannot be | |
544 | given without knowing (at the very least) the language context. | |
545 | See L<Unicode::Collate>, and I<Unicode Collation Algorithm> | |
2bbc8d55 | 546 | L<http://www.unicode.org/unicode/reports/tr10/> |
ba62762e JH |
547 | |
548 | =back | |
549 | ||
550 | =head2 Miscellaneous | |
551 | ||
552 | =over 4 | |
553 | ||
554 | =item * | |
555 | ||
3ff56b75 | 556 | Character Ranges and Classes |
ba62762e | 557 | |
0eb9ada1 KW |
558 | Character ranges in regular expression bracketed character classes ( e.g., |
559 | C</[a-z]/>) and in the C<tr///> (also known as C<y///>) operator are not | |
560 | magically Unicode-aware. What this means is that C<[A-Za-z]> will not | |
561 | magically start to mean "all alphabetic letters" (not that it does mean that | |
562 | even for 8-bit characters; for those, if you are using locales (L<perllocale>), | |
563 | use C</[[:alpha:]]/>; and if not, use the 8-bit-aware property C<\p{alpha}>). | |
564 | ||
565 | All the properties that begin with C<\p> (and its inverse C<\P>) are actually | |
566 | character classes that are Unicode-aware. There are dozens of them, see | |
567 | L<perluniprops>. | |
568 | ||
569 | You can use Unicode code points as the end points of character ranges, and the | |
570 | range will include all Unicode code points that lie between those end points. | |
ba62762e JH |
571 | |
572 | =item * | |
573 | ||
574 | String-To-Number Conversions | |
575 | ||
376d9008 JB |
576 | Unicode does define several other decimal--and numeric--characters |
577 | besides the familiar 0 to 9, such as the Arabic and Indic digits. | |
ba62762e | 578 | Perl does not support string-to-number conversion for digits other |
58c274a1 | 579 | than ASCII 0 to 9 (and ASCII a to f for hexadecimal). |
ba62762e JH |
580 | |
581 | =back | |
582 | ||
583 | =head2 Questions With Answers | |
584 | ||
585 | =over 4 | |
586 | ||
818c4caa | 587 | =item * |
5cb3728c RB |
588 | |
589 | Will My Old Scripts Break? | |
ba62762e JH |
590 | |
591 | Very probably not. Unless you are generating Unicode characters | |
1bfb14c4 JH |
592 | somehow, old behaviour should be preserved. About the only behaviour |
593 | that has changed and which could start generating Unicode is the old | |
594 | behaviour of C<chr()> where supplying an argument more than 255 | |
595 | produced a character modulo 255. C<chr(300)>, for example, was equal | |
596 | to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH | |
597 | BREVE. | |
ba62762e | 598 | |
818c4caa | 599 | =item * |
5cb3728c RB |
600 | |
601 | How Do I Make My Scripts Work With Unicode? | |
ba62762e JH |
602 | |
603 | Very little work should be needed since nothing changes until you | |
1bfb14c4 JH |
604 | generate Unicode data. The most important thing is getting input as |
605 | Unicode; for that, see the earlier I/O discussion. | |
ba62762e | 606 | |
818c4caa | 607 | =item * |
5cb3728c RB |
608 | |
609 | How Do I Know Whether My String Is In Unicode? | |
ba62762e | 610 | |
2bbc8d55 | 611 | You shouldn't have to care. But you may, because currently the semantics of the |
0eb9ada1 | 612 | characters whose ordinals are in the range 128 to 255 are different depending on |
2bbc8d55 | 613 | whether the string they are contained within is in Unicode or not. |
e1b711da | 614 | (See L<perlunicode/When Unicode Does Not Happen>.) |
ba62762e | 615 | |
2bbc8d55 | 616 | To determine if a string is in Unicode, use: |
ba62762e | 617 | |
8800c35a | 618 | print utf8::is_utf8($string) ? 1 : 0, "\n"; |
ba62762e JH |
619 | |
620 | But note that this doesn't mean that any of the characters in the | |
621 | string are necessary UTF-8 encoded, or that any of the characters have | |
622 | code points greater than 0xFF (255) or even 0x80 (128), or that the | |
623 | string has any characters at all. All the C<is_utf8()> does is to | |
624 | return the value of the internal "utf8ness" flag attached to the | |
376d9008 | 625 | C<$string>. If the flag is off, the bytes in the scalar are interpreted |
3c1c8017 | 626 | as a single byte encoding. If the flag is on, the bytes in the scalar |
0eb9ada1 KW |
627 | are interpreted as the (variable-length, potentially multi-byte) UTF-8 encoded |
628 | code points of the characters. Bytes added to a UTF-8 encoded string are | |
1e54db1a | 629 | automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars |
376d9008 | 630 | are merged (double-quoted interpolation, explicit concatenation, and |
3c1c8017 AT |
631 | printf/sprintf parameter substitution), the result will be UTF-8 encoded |
632 | as if copies of the byte strings were upgraded to UTF-8: for example, | |
633 | ||
634 | $a = "ab\x80c"; | |
635 | $b = "\x{100}"; | |
636 | print "$a = $b\n"; | |
637 | ||
a02b5feb JH |
638 | the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but |
639 | C<$a> will stay byte-encoded. | |
ba62762e JH |
640 | |
641 | Sometimes you might really need to know the byte length of a string | |
ce7675db | 642 | instead of the character length. For that use either the |
2bbc8d55 SP |
643 | C<Encode::encode_utf8()> function or the C<bytes> pragma and |
644 | the C<length()> function: | |
ba62762e JH |
645 | |
646 | my $unicode = chr(0x100); | |
647 | print length($unicode), "\n"; # will print 1 | |
ce7675db A |
648 | require Encode; |
649 | print length(Encode::encode_utf8($unicode)), "\n"; # will print 2 | |
ba62762e | 650 | use bytes; |
1bfb14c4 JH |
651 | print length($unicode), "\n"; # will also print 2 |
652 | # (the 0xC4 0x80 of the UTF-8) | |
0eb9ada1 | 653 | no bytes; |
ba62762e | 654 | |
818c4caa | 655 | =item * |
5cb3728c RB |
656 | |
657 | How Do I Detect Data That's Not Valid In a Particular Encoding? | |
ba62762e | 658 | |
8baee566 JF |
659 | Use the C<Encode> package to try converting it. |
660 | For example, | |
ba62762e | 661 | |
bb2f379c | 662 | use Encode 'decode_utf8'; |
2bbc8d55 | 663 | |
228ee848 | 664 | if (eval { decode_utf8($string, Encode::FB_CROAK); 1 }) { |
a365f2ce | 665 | # $string is valid utf8 |
ba62762e | 666 | } else { |
a365f2ce | 667 | # $string is not valid utf8 |
ba62762e JH |
668 | } |
669 | ||
f337b084 | 670 | Or use C<unpack> to try decoding it: |
ba62762e JH |
671 | |
672 | use warnings; | |
f337b084 | 673 | @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8); |
ba62762e | 674 | |
ae5648b3 RGS |
675 | If invalid, a C<Malformed UTF-8 character> warning is produced. The "C0" means |
676 | "process the string character per character". Without that, the | |
677 | C<unpack("U*", ...)> would work in C<U0> mode (the default if the format | |
678 | string starts with C<U>) and it would return the bytes making up the UTF-8 | |
f337b084 | 679 | encoding of the target string, something that will always work. |
ba62762e | 680 | |
818c4caa | 681 | =item * |
5cb3728c RB |
682 | |
683 | How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa? | |
ba62762e | 684 | |
8baee566 JF |
685 | This probably isn't as useful as you might think. |
686 | Normally, you shouldn't need to. | |
ba62762e | 687 | |
1bfb14c4 | 688 | In one sense, what you are asking doesn't make much sense: encodings |
376d9008 | 689 | are for characters, and binary data are not "characters", so converting |
a5f0baef JH |
690 | "data" into some encoding isn't meaningful unless you know in what |
691 | character set and encoding the binary data is in, in which case it's | |
376d9008 | 692 | not just binary data, now is it? |
8baee566 | 693 | |
1bfb14c4 JH |
694 | If you have a raw sequence of bytes that you know should be |
695 | interpreted via a particular encoding, you can use C<Encode>: | |
ba62762e JH |
696 | |
697 | use Encode 'from_to'; | |
698 | from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 | |
699 | ||
1bfb14c4 JH |
700 | The call to C<from_to()> changes the bytes in C<$data>, but nothing |
701 | material about the nature of the string has changed as far as Perl is | |
702 | concerned. Both before and after the call, the string C<$data> | |
703 | contains just a bunch of 8-bit bytes. As far as Perl is concerned, | |
704 | the encoding of the string remains as "system-native 8-bit bytes". | |
8baee566 JF |
705 | |
706 | You might relate this to a fictional 'Translate' module: | |
707 | ||
708 | use Translate; | |
709 | my $phrase = "Yes"; | |
710 | Translate::from_to($phrase, 'english', 'deutsch'); | |
711 | ## phrase now contains "Ja" | |
ba62762e | 712 | |
8baee566 | 713 | The contents of the string changes, but not the nature of the string. |
1bfb14c4 JH |
714 | Perl doesn't know any more after the call than before that the |
715 | contents of the string indicates the affirmative. | |
ba62762e | 716 | |
376d9008 | 717 | Back to converting data. If you have (or want) data in your system's |
a5f0baef JH |
718 | native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use |
719 | pack/unpack to convert to/from Unicode. | |
ba62762e | 720 | |
f337b084 TH |
721 | $native_string = pack("W*", unpack("U*", $Unicode_string)); |
722 | $Unicode_string = pack("U*", unpack("W*", $native_string)); | |
ba62762e JH |
723 | |
724 | If you have a sequence of bytes you B<know> is valid UTF-8, | |
725 | but Perl doesn't know it yet, you can make Perl a believer, too: | |
726 | ||
727 | use Encode 'decode_utf8'; | |
8baee566 | 728 | $Unicode = decode_utf8($bytes); |
ba62762e | 729 | |
f337b084 TH |
730 | or: |
731 | ||
732 | $Unicode = pack("U0a*", $bytes); | |
ae5648b3 | 733 | |
2bbc8d55 SP |
734 | You can find the bytes that make up a UTF-8 sequence with |
735 | ||
9e5bbba0 | 736 | @bytes = unpack("C*", $Unicode_string) |
2bbc8d55 SP |
737 | |
738 | and you can create well-formed Unicode with | |
739 | ||
9e5bbba0 | 740 | $Unicode_string = pack("U*", 0xff, ...) |
ba62762e | 741 | |
818c4caa | 742 | =item * |
5cb3728c RB |
743 | |
744 | How Do I Display Unicode? How Do I Input Unicode? | |
ba62762e | 745 | |
2bbc8d55 SP |
746 | See L<http://www.alanwood.net/unicode/> and |
747 | L<http://www.cl.cam.ac.uk/~mgk25/unicode.html> | |
ba62762e | 748 | |
818c4caa | 749 | =item * |
5cb3728c RB |
750 | |
751 | How Does Unicode Work With Traditional Locales? | |
ba62762e JH |
752 | |
753 | In Perl, not very well. Avoid using locales through the C<locale> | |
4c496f0c JH |
754 | pragma. Use only one or the other. But see L<perlrun> for the |
755 | description of the C<-C> switch and its environment counterpart, | |
756 | C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features, | |
757 | for example by using locale settings. | |
ba62762e JH |
758 | |
759 | =back | |
760 | ||
761 | =head2 Hexadecimal Notation | |
762 | ||
376d9008 JB |
763 | The Unicode standard prefers using hexadecimal notation because |
764 | that more clearly shows the division of Unicode into blocks of 256 characters. | |
ba62762e JH |
765 | Hexadecimal is also simply shorter than decimal. You can use decimal |
766 | notation, too, but learning to use hexadecimal just makes life easier | |
1bfb14c4 | 767 | with the Unicode standard. The C<U+HHHH> notation uses hexadecimal, |
076d825e | 768 | for example. |
ba62762e JH |
769 | |
770 | The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and> | |
771 | a-f (or A-F, case doesn't matter). Each hexadecimal digit represents | |
772 | four bits, or half a byte. C<print 0x..., "\n"> will show a | |
773 | hexadecimal number in decimal, and C<printf "%x\n", $decimal> will | |
774 | show a decimal number in hexadecimal. If you have just the | |
376d9008 | 775 | "hex digits" of a hexadecimal number, you can use the C<hex()> function. |
ba62762e JH |
776 | |
777 | print 0x0009, "\n"; # 9 | |
778 | print 0x000a, "\n"; # 10 | |
779 | print 0x000f, "\n"; # 15 | |
780 | print 0x0010, "\n"; # 16 | |
781 | print 0x0011, "\n"; # 17 | |
782 | print 0x0100, "\n"; # 256 | |
783 | ||
784 | print 0x0041, "\n"; # 65 | |
785 | ||
786 | printf "%x\n", 65; # 41 | |
787 | printf "%#x\n", 65; # 0x41 | |
788 | ||
789 | print hex("41"), "\n"; # 65 | |
790 | ||
791 | =head2 Further Resources | |
792 | ||
793 | =over 4 | |
794 | ||
795 | =item * | |
796 | ||
797 | Unicode Consortium | |
798 | ||
2bbc8d55 | 799 | L<http://www.unicode.org/> |
ba62762e JH |
800 | |
801 | =item * | |
802 | ||
803 | Unicode FAQ | |
804 | ||
2bbc8d55 | 805 | L<http://www.unicode.org/unicode/faq/> |
ba62762e JH |
806 | |
807 | =item * | |
808 | ||
809 | Unicode Glossary | |
810 | ||
2bbc8d55 | 811 | L<http://www.unicode.org/glossary/> |
ba62762e JH |
812 | |
813 | =item * | |
814 | ||
815 | Unicode Useful Resources | |
816 | ||
2bbc8d55 | 817 | L<http://www.unicode.org/unicode/onlinedat/resources.html> |
ba62762e JH |
818 | |
819 | =item * | |
820 | ||
821 | Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications | |
822 | ||
2bbc8d55 | 823 | L<http://www.alanwood.net/unicode/> |
ba62762e JH |
824 | |
825 | =item * | |
826 | ||
827 | UTF-8 and Unicode FAQ for Unix/Linux | |
828 | ||
2bbc8d55 | 829 | L<http://www.cl.cam.ac.uk/~mgk25/unicode.html> |
ba62762e JH |
830 | |
831 | =item * | |
832 | ||
833 | Legacy Character Sets | |
834 | ||
2bbc8d55 SP |
835 | L<http://www.czyborra.com/> |
836 | L<http://www.eki.ee/letter/> | |
ba62762e JH |
837 | |
838 | =item * | |
839 | ||
840 | The Unicode support files live within the Perl installation in the | |
841 | directory | |
842 | ||
843 | $Config{installprivlib}/unicore | |
844 | ||
ae5648b3 | 845 | in Perl 5.8.0 or newer, and |
ba62762e JH |
846 | |
847 | $Config{installprivlib}/unicode | |
848 | ||
849 | in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to | |
850 | avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) | |
551b6b6f | 851 | The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in |
ba62762e JH |
852 | Perl 5.6.1.) You can find the C<$Config{installprivlib}> by |
853 | ||
854 | perl "-V:installprivlib" | |
855 | ||
ba62762e JH |
856 | You can explore various information from the Unicode data files using |
857 | the C<Unicode::UCD> module. | |
858 | ||
859 | =back | |
860 | ||
f6edf83b JH |
861 | =head1 UNICODE IN OLDER PERLS |
862 | ||
863 | If you cannot upgrade your Perl to 5.8.0 or later, you can still | |
864 | do some Unicode processing by using the modules C<Unicode::String>, | |
865 | C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN. | |
866 | If you have the GNU recode installed, you can also use the | |
376d9008 | 867 | Perl front-end C<Convert::Recode> for character conversions. |
f6edf83b | 868 | |
aaef10c5 | 869 | The following are fast conversions from ISO 8859-1 (Latin-1) bytes |
63de3cb2 | 870 | to UTF-8 bytes and back, the code works even with older Perl 5 versions. |
aaef10c5 JH |
871 | |
872 | # ISO 8859-1 to UTF-8 | |
873 | s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg; | |
874 | ||
875 | # UTF-8 to ISO 8859-1 | |
876 | s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg; | |
877 | ||
ba62762e JH |
878 | =head1 SEE ALSO |
879 | ||
2575c402 | 880 | L<perlunitut>, L<perlunicode>, L<Encode>, L<open>, L<utf8>, L<bytes>, |
4c496f0c JH |
881 | L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>, |
882 | L<Unicode::UCD> | |
ba62762e | 883 | |
376d9008 | 884 | =head1 ACKNOWLEDGMENTS |
ba62762e JH |
885 | |
886 | Thanks to the kind readers of the perl5-porters@perl.org, | |
887 | perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org | |
888 | mailing lists for their valuable feedback. | |
889 | ||
890 | =head1 AUTHOR, COPYRIGHT, AND LICENSE | |
891 | ||
0f2f9b7d | 892 | Copyright 2001-2002 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt> |
ba62762e JH |
893 | |
894 | This document may be distributed under the same terms as Perl itself. |