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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 | |
27 | language of the text and it does not 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. |
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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, | |
376d9008 | 88 | Unicode is only represented as C<0x10000> (or 65536) characters from |
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89 | C<0x0000> to C<0xFFFF>. B<This is untrue.> Since Unicode 2.0 (July |
90 | 1996), Unicode has been defined all the way up to 21 bits (C<0x10FFFF>), | |
91 | and since Unicode 3.1 (March 2001), characters have been defined | |
92 | beyond C<0xFFFF>. The first C<0x10000> characters are called the | |
93 | I<Plane 0>, or the I<Basic Multilingual Plane> (BMP). With Unicode | |
94 | 3.1, 17 (yes, seventeen) planes in all were defined--but they are | |
95 | nowhere near full of defined characters, yet. | |
ba62762e | 96 | |
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97 | Another myth is that the 256-character blocks have something to |
98 | do with languages--that each block would define the characters used | |
99 | by a language or a set of languages. B<This is also untrue.> | |
100 | The division into blocks exists, but it is almost completely | |
101 | accidental--an artifact of how the characters have been and | |
102 | still are allocated. Instead, there is a concept called I<scripts>, | |
103 | which is more useful: there is C<Latin> script, C<Greek> script, and | |
104 | so on. Scripts usually span varied parts of several blocks. | |
105 | For further information see L<Unicode::UCD>. | |
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106 | |
107 | The Unicode code points are just abstract numbers. To input and | |
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108 | output these abstract numbers, the numbers must be I<encoded> or |
109 | I<serialised> somehow. Unicode defines several I<character encoding | |
110 | forms>, of which I<UTF-8> is perhaps the most popular. UTF-8 is a | |
111 | variable length encoding that encodes Unicode characters as 1 to 6 | |
112 | bytes (only 4 with the currently defined characters). Other encodings | |
113 | include UTF-16 and UTF-32 and their big- and little-endian variants | |
114 | (UTF-8 is byte-order independent) The ISO/IEC 10646 defines the UCS-2 | |
115 | and UCS-4 encoding forms. | |
ba62762e | 116 | |
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117 | For more information about encodings--for instance, to learn what |
118 | I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>. | |
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119 | |
120 | =head2 Perl's Unicode Support | |
121 | ||
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122 | Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode |
123 | natively. Perl 5.8.0, however, is the first recommended release for | |
124 | serious Unicode work. The maintenance release 5.6.1 fixed many of the | |
125 | problems of the initial Unicode implementation, but for example | |
1bfb14c4 | 126 | regular expressions still do not work with Unicode in 5.6.1. |
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127 | |
128 | B<Starting from Perl 5.8.0, the use of C<use utf8> is no longer | |
129 | necessary.> In earlier releases the C<utf8> pragma was used to declare | |
130 | that operations in the current block or file would be Unicode-aware. | |
376d9008 | 131 | This model was found to be wrong, or at least clumsy: the "Unicodeness" |
1bfb14c4 | 132 | is now carried with the data, instead of being attached to the |
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133 | operations. Only one case remains where an explicit C<use utf8> is |
134 | needed: if your Perl script itself is encoded in UTF-8, you can use | |
135 | UTF-8 in your identifier names, and in string and regular expression | |
136 | literals, by saying C<use utf8>. This is not the default because | |
8f8cf39c | 137 | scripts with legacy 8-bit data in them would break. See L<utf8>. |
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138 | |
139 | =head2 Perl's Unicode Model | |
140 | ||
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141 | Perl supports both pre-5.6 strings of eight-bit native bytes, and |
142 | strings of Unicode characters. The principle is that Perl tries to | |
143 | keep its data as eight-bit bytes for as long as possible, but as soon | |
144 | as Unicodeness cannot be avoided, the data is transparently upgraded | |
145 | to Unicode. | |
ba62762e | 146 | |
4192de81 | 147 | Internally, Perl currently uses either whatever the native eight-bit |
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148 | character set of the platform (for example Latin-1) is, defaulting to |
149 | UTF-8, to encode Unicode strings. Specifically, if all code points in | |
150 | the string are C<0xFF> or less, Perl uses the native eight-bit | |
151 | character set. Otherwise, it uses UTF-8. | |
4192de81 | 152 | |
7ca610e8 | 153 | A user of Perl does not normally need to know nor care how Perl |
20ba30f4 | 154 | happens to encode its internal strings, but it becomes relevant when |
fae2c0fb | 155 | outputting Unicode strings to a stream without a PerlIO layer -- one with |
376d9008 | 156 | the "default" encoding. In such a case, the raw bytes used internally |
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157 | (the native character set or UTF-8, as appropriate for each string) |
158 | will be used, and a "Wide character" warning will be issued if those | |
159 | strings contain a character beyond 0x00FF. | |
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160 | |
161 | For example, | |
162 | ||
7ca610e8 | 163 | perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"' |
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164 | |
165 | produces a fairly useless mixture of native bytes and UTF-8, as well | |
1bfb14c4 | 166 | as a warning: |
4192de81 | 167 | |
1bfb14c4 JH |
168 | Wide character in print at ... |
169 | ||
fae2c0fb | 170 | To output UTF-8, use the C<:utf8> output layer. Prepending |
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171 | |
172 | binmode(STDOUT, ":utf8"); | |
173 | ||
376d9008 | 174 | to this sample program ensures that the output is completely UTF-8, |
1bfb14c4 | 175 | and removes the program's warning. |
ba62762e | 176 | |
8aa8f774 JH |
177 | You can enable automatic UTF-8-ification of your standard file |
178 | handles, default C<open()> layer, and C<@ARGV> by using either | |
179 | the C<-C> command line switch or the C<PERL_UNICODE> environment | |
180 | variable, see L<perlrun> for the documentation of the C<-C> switch. | |
181 | ||
182 | Note that this means that Perl expects other software to work, too: | |
183 | if Perl has been led to believe that STDIN should be UTF-8, but then | |
184 | STDIN coming in from another command is not UTF-8, Perl will complain | |
185 | about the malformed UTF-8. | |
b310b053 | 186 | |
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187 | All features that combine Unicode and I/O also require using the new |
188 | PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though: | |
189 | you can see whether yours is by running "perl -V" and looking for | |
190 | C<useperlio=define>. | |
191 | ||
64c66fb6 JH |
192 | =head2 Unicode and EBCDIC |
193 | ||
194 | Perl 5.8.0 also supports Unicode on EBCDIC platforms. There, | |
376d9008 | 195 | Unicode support is somewhat more complex to implement since |
64c66fb6 | 196 | additional conversions are needed at every step. Some problems |
dc4af4bb | 197 | remain, see L<perlebcdic> for details. |
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198 | |
199 | In any case, the Unicode support on EBCDIC platforms is better than | |
200 | in the 5.6 series, which didn't work much at all for EBCDIC platform. | |
201 | On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC | |
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202 | instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in |
203 | that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is | |
204 | "EBCDIC-safe". | |
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205 | |
206 | =head2 Creating Unicode | |
207 | ||
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208 | To create Unicode characters in literals for code points above C<0xFF>, |
209 | use the C<\x{...}> notation in double-quoted strings: | |
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210 | |
211 | my $smiley = "\x{263a}"; | |
212 | ||
376d9008 | 213 | Similarly, it can be used in regular expression literals |
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214 | |
215 | $smiley =~ /\x{263a}/; | |
216 | ||
217 | At run-time you can use C<chr()>: | |
218 | ||
219 | my $hebrew_alef = chr(0x05d0); | |
220 | ||
376d9008 | 221 | See L</"Further Resources"> for how to find all these numeric codes. |
ba62762e | 222 | |
376d9008 JB |
223 | Naturally, C<ord()> will do the reverse: it turns a character into |
224 | a code point. | |
ba62762e | 225 | |
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226 | Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>, |
227 | and C<chr(...)> for arguments less than C<0x100> (decimal 256) | |
228 | generate an eight-bit character for backward compatibility with older | |
229 | Perls. For arguments of C<0x100> or more, Unicode characters are | |
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230 | always produced. If you want to force the production of Unicode |
231 | characters regardless of the numeric value, use C<pack("U", ...)> | |
232 | instead of C<\x..>, C<\x{...}>, or C<chr()>. | |
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233 | |
234 | You can also use the C<charnames> pragma to invoke characters | |
376d9008 | 235 | by name in double-quoted strings: |
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236 | |
237 | use charnames ':full'; | |
238 | my $arabic_alef = "\N{ARABIC LETTER ALEF}"; | |
239 | ||
240 | And, as mentioned above, you can also C<pack()> numbers into Unicode | |
241 | characters: | |
242 | ||
243 | my $georgian_an = pack("U", 0x10a0); | |
244 | ||
8a5e5dd5 JH |
245 | Note that both C<\x{...}> and C<\N{...}> are compile-time string |
246 | constants: you cannot use variables in them. if you want similar | |
247 | run-time functionality, use C<chr()> and C<charnames::vianame()>. | |
248 | ||
1eda90df | 249 | If you want to force the result to Unicode characters, use the special |
f337b084 TH |
250 | C<"U0"> prefix. It consumes no arguments but causes the following bytes |
251 | to be interpreted as the UTF-8 encoding of Unicode characters: | |
1eda90df | 252 | |
f337b084 | 253 | my $chars = pack("U0W*", 0x80, 0x42); |
771cd3b2 | 254 | |
f337b084 | 255 | Likewise, you can stop such UTF-8 interpretation by using the special |
771cd3b2 | 256 | C<"C0"> prefix. |
1eda90df | 257 | |
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258 | =head2 Handling Unicode |
259 | ||
260 | Handling Unicode is for the most part transparent: just use the | |
261 | strings as usual. Functions like C<index()>, C<length()>, and | |
262 | C<substr()> will work on the Unicode characters; regular expressions | |
263 | will work on the Unicode characters (see L<perlunicode> and L<perlretut>). | |
264 | ||
1bfb14c4 | 265 | Note that Perl considers combining character sequences to be |
c0c50798 | 266 | separate characters, so for example |
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267 | |
268 | use charnames ':full'; | |
269 | print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; | |
270 | ||
271 | will print 2, not 1. The only exception is that regular expressions | |
272 | have C<\X> for matching a combining character sequence. | |
273 | ||
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274 | Life is not quite so transparent, however, when working with legacy |
275 | encodings, I/O, and certain special cases: | |
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276 | |
277 | =head2 Legacy Encodings | |
278 | ||
279 | When you combine legacy data and Unicode the legacy data needs | |
280 | to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if | |
281 | applicable) is assumed. You can override this assumption by | |
282 | using the C<encoding> pragma, for example | |
283 | ||
284 | use encoding 'latin2'; # ISO 8859-2 | |
285 | ||
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286 | in which case literals (string or regular expressions), C<chr()>, |
287 | and C<ord()> in your whole script are assumed to produce Unicode | |
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288 | characters from ISO 8859-2 code points. Note that the matching for |
289 | encoding names is forgiving: instead of C<latin2> you could have | |
290 | said C<Latin 2>, or C<iso8859-2>, or other variations. With just | |
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291 | |
292 | use encoding; | |
293 | ||
376d9008 JB |
294 | the environment variable C<PERL_ENCODING> will be consulted. |
295 | If that variable isn't set, the encoding pragma will fail. | |
ba62762e | 296 | |
376d9008 | 297 | The C<Encode> module knows about many encodings and has interfaces |
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298 | for doing conversions between those encodings: |
299 | ||
2c9359a2 RGS |
300 | use Encode 'decode'; |
301 | $data = decode("iso-8859-3", $data); # convert from legacy to utf-8 | |
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302 | |
303 | =head2 Unicode I/O | |
304 | ||
8baee566 | 305 | Normally, writing out Unicode data |
ba62762e | 306 | |
8baee566 | 307 | print FH $some_string_with_unicode, "\n"; |
ba62762e | 308 | |
8baee566 | 309 | produces raw bytes that Perl happens to use to internally encode the |
376d9008 JB |
310 | Unicode string. Perl's internal encoding depends on the system as |
311 | well as what characters happen to be in the string at the time. If | |
312 | any of the characters are at code points C<0x100> or above, you will get | |
313 | a warning. To ensure that the output is explicitly rendered in the | |
314 | encoding you desire--and to avoid the warning--open the stream with | |
315 | the desired encoding. Some examples: | |
ba62762e | 316 | |
ec90690f TS |
317 | open FH, ">:utf8", "file"; |
318 | ||
319 | open FH, ">:encoding(ucs2)", "file"; | |
320 | open FH, ">:encoding(UTF-8)", "file"; | |
321 | open FH, ">:encoding(shift_jis)", "file"; | |
1d7919c5 | 322 | |
376d9008 | 323 | and on already open streams, use C<binmode()>: |
1d7919c5 JH |
324 | |
325 | binmode(STDOUT, ":utf8"); | |
326 | ||
ec90690f TS |
327 | binmode(STDOUT, ":encoding(ucs2)"); |
328 | binmode(STDOUT, ":encoding(UTF-8)"); | |
329 | binmode(STDOUT, ":encoding(shift_jis)"); | |
330 | ||
b5d8778e | 331 | The matching of encoding names is loose: case does not matter, and |
fae2c0fb | 332 | many encodings have several aliases. Note that the C<:utf8> layer |
1bfb14c4 JH |
333 | must always be specified exactly like that; it is I<not> subject to |
334 | the loose matching of encoding names. | |
b5d8778e | 335 | |
376d9008 JB |
336 | See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and |
337 | L<Encode::PerlIO> for the C<:encoding()> layer, and | |
338 | L<Encode::Supported> for many encodings supported by the C<Encode> | |
339 | module. | |
ba62762e | 340 | |
a5f0baef | 341 | Reading in a file that you know happens to be encoded in one of the |
1bfb14c4 JH |
342 | Unicode or legacy encodings does not magically turn the data into |
343 | Unicode in Perl's eyes. To do that, specify the appropriate | |
fae2c0fb | 344 | layer when opening files |
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345 | |
346 | open(my $fh,'<:utf8', 'anything'); | |
8baee566 JF |
347 | my $line_of_unicode = <$fh>; |
348 | ||
ec90690f | 349 | open(my $fh,'<:encoding(Big5)', 'anything'); |
8baee566 | 350 | my $line_of_unicode = <$fh>; |
ba62762e | 351 | |
fae2c0fb | 352 | The I/O layers can also be specified more flexibly with |
376d9008 | 353 | the C<open> pragma. See L<open>, or look at the following example. |
ba62762e | 354 | |
fae2c0fb | 355 | use open ':utf8'; # input and output default layer will be UTF-8 |
1d7919c5 JH |
356 | open X, ">file"; |
357 | print X chr(0x100), "\n"; | |
ba62762e | 358 | close X; |
1d7919c5 | 359 | open Y, "<file"; |
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360 | printf "%#x\n", ord(<Y>); # this should print 0x100 |
361 | close Y; | |
362 | ||
fae2c0fb | 363 | With the C<open> pragma you can use the C<:locale> layer |
ba62762e | 364 | |
12f98225 | 365 | BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' } |
1ecefa54 | 366 | # the :locale will probe the locale environment variables like LC_ALL |
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367 | use open OUT => ':locale'; # russki parusski |
368 | open(O, ">koi8"); | |
369 | print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 | |
370 | close O; | |
371 | open(I, "<koi8"); | |
372 | printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1 | |
373 | close I; | |
374 | ||
fae2c0fb | 375 | or you can also use the C<':encoding(...)'> layer |
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376 | |
377 | open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); | |
8baee566 | 378 | my $line_of_unicode = <$epic>; |
ba62762e | 379 | |
8baee566 JF |
380 | These methods install a transparent filter on the I/O stream that |
381 | converts data from the specified encoding when it is read in from the | |
a5f0baef | 382 | stream. The result is always Unicode. |
ba62762e JH |
383 | |
384 | The L<open> pragma affects all the C<open()> calls after the pragma by | |
fae2c0fb RGS |
385 | setting default layers. If you want to affect only certain |
386 | streams, use explicit layers directly in the C<open()> call. | |
ba62762e JH |
387 | |
388 | You can switch encodings on an already opened stream by using | |
8baee566 | 389 | C<binmode()>; see L<perlfunc/binmode>. |
ba62762e | 390 | |
1ecefa54 JH |
391 | The C<:locale> does not currently (as of Perl 5.8.0) work with |
392 | C<open()> and C<binmode()>, only with the C<open> pragma. The | |
8baee566 | 393 | C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>, |
1ecefa54 | 394 | C<binmode()>, and the C<open> pragma. |
ba62762e | 395 | |
fae2c0fb | 396 | Similarly, you may use these I/O layers on output streams to |
a5f0baef JH |
397 | automatically convert Unicode to the specified encoding when it is |
398 | written to the stream. For example, the following snippet copies the | |
399 | contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to | |
400 | the file "text.utf8", encoded as UTF-8: | |
ba62762e | 401 | |
c722ef0a JH |
402 | open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis'); |
403 | open(my $unicode, '>:utf8', 'text.utf8'); | |
0cf8a8d9 | 404 | while (<$nihongo>) { print $unicode $_ } |
ba62762e JH |
405 | |
406 | The naming of encodings, both by the C<open()> and by the C<open> | |
376d9008 JB |
407 | pragma, is similar to the C<encoding> pragma in that it allows for |
408 | flexible names: C<koi8-r> and C<KOI8R> will both be understood. | |
ba62762e JH |
409 | |
410 | Common encodings recognized by ISO, MIME, IANA, and various other | |
8baee566 | 411 | standardisation organisations are recognised; for a more detailed |
1bfb14c4 | 412 | list see L<Encode::Supported>. |
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413 | |
414 | C<read()> reads characters and returns the number of characters. | |
415 | C<seek()> and C<tell()> operate on byte counts, as do C<sysread()> | |
416 | and C<sysseek()>. | |
417 | ||
8baee566 | 418 | Notice that because of the default behaviour of not doing any |
fae2c0fb | 419 | conversion upon input if there is no default layer, |
ba62762e | 420 | it is easy to mistakenly write code that keeps on expanding a file |
1bfb14c4 | 421 | by repeatedly encoding the data: |
ba62762e JH |
422 | |
423 | # BAD CODE WARNING | |
424 | open F, "file"; | |
8baee566 | 425 | local $/; ## read in the whole file of 8-bit characters |
ba62762e JH |
426 | $t = <F>; |
427 | close F; | |
428 | open F, ">:utf8", "file"; | |
8baee566 | 429 | print F $t; ## convert to UTF-8 on output |
ba62762e JH |
430 | close F; |
431 | ||
432 | If you run this code twice, the contents of the F<file> will be twice | |
1d7919c5 JH |
433 | UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or |
434 | explicitly opening also the F<file> for input as UTF-8. | |
ba62762e | 435 | |
0c901d84 | 436 | B<NOTE>: the C<:utf8> and C<:encoding> features work only if your |
d0fadae5 JH |
437 | Perl has been built with the new PerlIO feature (which is the default |
438 | on most systems). | |
0c901d84 | 439 | |
1ecefa54 JH |
440 | =head2 Displaying Unicode As Text |
441 | ||
442 | Sometimes you might want to display Perl scalars containing Unicode as | |
8baee566 | 443 | simple ASCII (or EBCDIC) text. The following subroutine converts |
1ecefa54 | 444 | its argument so that Unicode characters with code points greater than |
1bfb14c4 JH |
445 | 255 are displayed as C<\x{...}>, control characters (like C<\n>) are |
446 | displayed as C<\x..>, and the rest of the characters as themselves: | |
1ecefa54 | 447 | |
58c274a1 JF |
448 | sub nice_string { |
449 | join("", | |
450 | map { $_ > 255 ? # if wide character... | |
8baee566 | 451 | sprintf("\\x{%04X}", $_) : # \x{...} |
58c274a1 | 452 | chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... |
8baee566 | 453 | sprintf("\\x%02X", $_) : # \x.. |
d0551e73 | 454 | quotemeta(chr($_)) # else quoted or as themselves |
f337b084 | 455 | } unpack("W*", $_[0])); # unpack Unicode characters |
58c274a1 JF |
456 | } |
457 | ||
458 | For example, | |
459 | ||
460 | nice_string("foo\x{100}bar\n") | |
461 | ||
d0551e73 | 462 | returns the string |
58c274a1 | 463 | |
d0551e73 JH |
464 | 'foo\x{0100}bar\x0A' |
465 | ||
466 | which is ready to be printed. | |
1ecefa54 | 467 | |
ba62762e JH |
468 | =head2 Special Cases |
469 | ||
470 | =over 4 | |
471 | ||
472 | =item * | |
473 | ||
474 | Bit Complement Operator ~ And vec() | |
475 | ||
1bfb14c4 JH |
476 | The bit complement operator C<~> may produce surprising results if |
477 | used on strings containing characters with ordinal values above | |
478 | 255. In such a case, the results are consistent with the internal | |
479 | encoding of the characters, but not with much else. So don't do | |
480 | that. Similarly for C<vec()>: you will be operating on the | |
481 | internally-encoded bit patterns of the Unicode characters, not on | |
482 | the code point values, which is very probably not what you want. | |
ba62762e JH |
483 | |
484 | =item * | |
485 | ||
8baee566 JF |
486 | Peeking At Perl's Internal Encoding |
487 | ||
488 | Normal users of Perl should never care how Perl encodes any particular | |
a5f0baef | 489 | Unicode string (because the normal ways to get at the contents of a |
376d9008 | 490 | string with Unicode--via input and output--should always be via |
fae2c0fb | 491 | explicitly-defined I/O layers). But if you must, there are two |
a5f0baef | 492 | ways of looking behind the scenes. |
ba62762e JH |
493 | |
494 | One way of peeking inside the internal encoding of Unicode characters | |
f337b084 TH |
495 | is to use C<unpack("C*", ...> to get the bytes of whatever the string |
496 | encoding happens to be, or C<unpack("U0..", ...)> to get the bytes of the | |
497 | UTF-8 encoding: | |
ba62762e | 498 | |
8baee566 | 499 | # this prints c4 80 for the UTF-8 bytes 0xc4 0x80 |
f337b084 | 500 | print join(" ", unpack("U0(H2)*", pack("U", 0x100))), "\n"; |
ba62762e JH |
501 | |
502 | Yet another way would be to use the Devel::Peek module: | |
503 | ||
504 | perl -MDevel::Peek -e 'Dump(chr(0x100))' | |
505 | ||
1e54db1a | 506 | That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes |
376d9008 | 507 | and Unicode characters in C<PV>. See also later in this document |
8800c35a | 508 | the discussion about the C<utf8::is_utf8()> function. |
ba62762e JH |
509 | |
510 | =back | |
511 | ||
512 | =head2 Advanced Topics | |
513 | ||
514 | =over 4 | |
515 | ||
516 | =item * | |
517 | ||
518 | String Equivalence | |
519 | ||
520 | The question of string equivalence turns somewhat complicated | |
376d9008 | 521 | in Unicode: what do you mean by "equal"? |
ba62762e | 522 | |
07698885 RGS |
523 | (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to |
524 | C<LATIN CAPITAL LETTER A>?) | |
ba62762e | 525 | |
a5f0baef JH |
526 | The short answer is that by default Perl compares equivalence (C<eq>, |
527 | C<ne>) based only on code points of the characters. In the above | |
376d9008 JB |
528 | case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any |
529 | CAPITAL LETTER As should be considered equal, or even As of any case. | |
ba62762e JH |
530 | |
531 | The long answer is that you need to consider character normalization | |
376d9008 | 532 | and casing issues: see L<Unicode::Normalize>, Unicode Technical |
ba62762e | 533 | Reports #15 and #21, I<Unicode Normalization Forms> and I<Case |
376d9008 JB |
534 | Mappings>, http://www.unicode.org/unicode/reports/tr15/ and |
535 | http://www.unicode.org/unicode/reports/tr21/ | |
ba62762e | 536 | |
1bfb14c4 JH |
537 | As of Perl 5.8.0, the "Full" case-folding of I<Case |
538 | Mappings/SpecialCasing> is implemented. | |
ba62762e JH |
539 | |
540 | =item * | |
541 | ||
542 | String Collation | |
543 | ||
376d9008 | 544 | People like to see their strings nicely sorted--or as Unicode |
ba62762e JH |
545 | parlance goes, collated. But again, what do you mean by collate? |
546 | ||
07698885 RGS |
547 | (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after |
548 | C<LATIN CAPITAL LETTER A WITH GRAVE>?) | |
ba62762e | 549 | |
58c274a1 | 550 | The short answer is that by default, Perl compares strings (C<lt>, |
ba62762e | 551 | C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the |
1bfb14c4 | 552 | characters. In the above case, the answer is "after", since |
da76a1f4 | 553 | C<0x00C1> > C<0x00C0>. |
ba62762e JH |
554 | |
555 | The long answer is that "it depends", and a good answer cannot be | |
556 | given without knowing (at the very least) the language context. | |
557 | See L<Unicode::Collate>, and I<Unicode Collation Algorithm> | |
558 | http://www.unicode.org/unicode/reports/tr10/ | |
559 | ||
560 | =back | |
561 | ||
562 | =head2 Miscellaneous | |
563 | ||
564 | =over 4 | |
565 | ||
566 | =item * | |
567 | ||
3ff56b75 | 568 | Character Ranges and Classes |
ba62762e JH |
569 | |
570 | Character ranges in regular expression character classes (C</[a-z]/>) | |
571 | and in the C<tr///> (also known as C<y///>) operator are not magically | |
58c274a1 | 572 | Unicode-aware. What this means that C<[A-Za-z]> will not magically start |
376d9008 JB |
573 | to mean "all alphabetic letters"; not that it does mean that even for |
574 | 8-bit characters, you should be using C</[[:alpha:]]/> in that case. | |
ba62762e | 575 | |
1bfb14c4 JH |
576 | For specifying character classes like that in regular expressions, |
577 | you can use the various Unicode properties--C<\pL>, or perhaps | |
578 | C<\p{Alphabetic}>, in this particular case. You can use Unicode | |
579 | code points as the end points of character ranges, but there is no | |
580 | magic associated with specifying a certain range. For further | |
581 | information--there are dozens of Unicode character classes--see | |
582 | L<perlunicode>. | |
ba62762e JH |
583 | |
584 | =item * | |
585 | ||
586 | String-To-Number Conversions | |
587 | ||
376d9008 JB |
588 | Unicode does define several other decimal--and numeric--characters |
589 | besides the familiar 0 to 9, such as the Arabic and Indic digits. | |
ba62762e | 590 | Perl does not support string-to-number conversion for digits other |
58c274a1 | 591 | than ASCII 0 to 9 (and ASCII a to f for hexadecimal). |
ba62762e JH |
592 | |
593 | =back | |
594 | ||
595 | =head2 Questions With Answers | |
596 | ||
597 | =over 4 | |
598 | ||
818c4caa | 599 | =item * |
5cb3728c RB |
600 | |
601 | Will My Old Scripts Break? | |
ba62762e JH |
602 | |
603 | Very probably not. Unless you are generating Unicode characters | |
1bfb14c4 JH |
604 | somehow, old behaviour should be preserved. About the only behaviour |
605 | that has changed and which could start generating Unicode is the old | |
606 | behaviour of C<chr()> where supplying an argument more than 255 | |
607 | produced a character modulo 255. C<chr(300)>, for example, was equal | |
608 | to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH | |
609 | BREVE. | |
ba62762e | 610 | |
818c4caa | 611 | =item * |
5cb3728c RB |
612 | |
613 | How Do I Make My Scripts Work With Unicode? | |
ba62762e JH |
614 | |
615 | Very little work should be needed since nothing changes until you | |
1bfb14c4 JH |
616 | generate Unicode data. The most important thing is getting input as |
617 | Unicode; for that, see the earlier I/O discussion. | |
ba62762e | 618 | |
818c4caa | 619 | =item * |
5cb3728c RB |
620 | |
621 | How Do I Know Whether My String Is In Unicode? | |
ba62762e | 622 | |
1bfb14c4 JH |
623 | You shouldn't care. No, you really shouldn't. No, really. If you |
624 | have to care--beyond the cases described above--it means that we | |
ba62762e JH |
625 | didn't get the transparency of Unicode quite right. |
626 | ||
627 | Okay, if you insist: | |
628 | ||
8800c35a | 629 | print utf8::is_utf8($string) ? 1 : 0, "\n"; |
ba62762e JH |
630 | |
631 | But note that this doesn't mean that any of the characters in the | |
632 | string are necessary UTF-8 encoded, or that any of the characters have | |
633 | code points greater than 0xFF (255) or even 0x80 (128), or that the | |
634 | string has any characters at all. All the C<is_utf8()> does is to | |
635 | return the value of the internal "utf8ness" flag attached to the | |
376d9008 | 636 | C<$string>. If the flag is off, the bytes in the scalar are interpreted |
3c1c8017 | 637 | as a single byte encoding. If the flag is on, the bytes in the scalar |
376d9008 | 638 | are interpreted as the (multi-byte, variable-length) UTF-8 encoded code |
3c1c8017 | 639 | points of the characters. Bytes added to an UTF-8 encoded string are |
1e54db1a | 640 | automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars |
376d9008 | 641 | are merged (double-quoted interpolation, explicit concatenation, and |
3c1c8017 AT |
642 | printf/sprintf parameter substitution), the result will be UTF-8 encoded |
643 | as if copies of the byte strings were upgraded to UTF-8: for example, | |
644 | ||
645 | $a = "ab\x80c"; | |
646 | $b = "\x{100}"; | |
647 | print "$a = $b\n"; | |
648 | ||
a02b5feb JH |
649 | the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but |
650 | C<$a> will stay byte-encoded. | |
ba62762e JH |
651 | |
652 | Sometimes you might really need to know the byte length of a string | |
ce7675db A |
653 | instead of the character length. For that use either the |
654 | C<Encode::encode_utf8()> function or the C<bytes> pragma and its only | |
655 | defined function C<length()>: | |
ba62762e JH |
656 | |
657 | my $unicode = chr(0x100); | |
658 | print length($unicode), "\n"; # will print 1 | |
ce7675db A |
659 | require Encode; |
660 | print length(Encode::encode_utf8($unicode)), "\n"; # will print 2 | |
ba62762e | 661 | use bytes; |
1bfb14c4 JH |
662 | print length($unicode), "\n"; # will also print 2 |
663 | # (the 0xC4 0x80 of the UTF-8) | |
ba62762e | 664 | |
818c4caa | 665 | =item * |
5cb3728c RB |
666 | |
667 | How Do I Detect Data That's Not Valid In a Particular Encoding? | |
ba62762e | 668 | |
8baee566 JF |
669 | Use the C<Encode> package to try converting it. |
670 | For example, | |
ba62762e | 671 | |
bb2f379c NC |
672 | use Encode 'decode_utf8'; |
673 | if (decode_utf8($string_of_bytes_that_I_think_is_utf8)) { | |
ba62762e JH |
674 | # valid |
675 | } else { | |
676 | # invalid | |
677 | } | |
678 | ||
f337b084 | 679 | Or use C<unpack> to try decoding it: |
ba62762e JH |
680 | |
681 | use warnings; | |
f337b084 | 682 | @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8); |
ba62762e | 683 | |
1bfb14c4 | 684 | If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack> |
f337b084 TH |
685 | warning is produced. The "C0" means |
686 | "process the string character per character". Without that the | |
687 | C<unpack("U*", ...)> would work in C<U0> mode (the default if the format | |
688 | string starts with C<U>) and it would return the bytes making up the UTF-8 | |
689 | encoding of the target string, something that will always work. | |
ba62762e | 690 | |
818c4caa | 691 | =item * |
5cb3728c RB |
692 | |
693 | How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa? | |
ba62762e | 694 | |
8baee566 JF |
695 | This probably isn't as useful as you might think. |
696 | Normally, you shouldn't need to. | |
ba62762e | 697 | |
1bfb14c4 | 698 | In one sense, what you are asking doesn't make much sense: encodings |
376d9008 | 699 | are for characters, and binary data are not "characters", so converting |
a5f0baef JH |
700 | "data" into some encoding isn't meaningful unless you know in what |
701 | character set and encoding the binary data is in, in which case it's | |
376d9008 | 702 | not just binary data, now is it? |
8baee566 | 703 | |
1bfb14c4 JH |
704 | If you have a raw sequence of bytes that you know should be |
705 | interpreted via a particular encoding, you can use C<Encode>: | |
ba62762e JH |
706 | |
707 | use Encode 'from_to'; | |
708 | from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 | |
709 | ||
1bfb14c4 JH |
710 | The call to C<from_to()> changes the bytes in C<$data>, but nothing |
711 | material about the nature of the string has changed as far as Perl is | |
712 | concerned. Both before and after the call, the string C<$data> | |
713 | contains just a bunch of 8-bit bytes. As far as Perl is concerned, | |
714 | the encoding of the string remains as "system-native 8-bit bytes". | |
8baee566 JF |
715 | |
716 | You might relate this to a fictional 'Translate' module: | |
717 | ||
718 | use Translate; | |
719 | my $phrase = "Yes"; | |
720 | Translate::from_to($phrase, 'english', 'deutsch'); | |
721 | ## phrase now contains "Ja" | |
ba62762e | 722 | |
8baee566 | 723 | The contents of the string changes, but not the nature of the string. |
1bfb14c4 JH |
724 | Perl doesn't know any more after the call than before that the |
725 | contents of the string indicates the affirmative. | |
ba62762e | 726 | |
376d9008 | 727 | Back to converting data. If you have (or want) data in your system's |
a5f0baef JH |
728 | native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use |
729 | pack/unpack to convert to/from Unicode. | |
ba62762e | 730 | |
f337b084 TH |
731 | $native_string = pack("W*", unpack("U*", $Unicode_string)); |
732 | $Unicode_string = pack("U*", unpack("W*", $native_string)); | |
ba62762e JH |
733 | |
734 | If you have a sequence of bytes you B<know> is valid UTF-8, | |
735 | but Perl doesn't know it yet, you can make Perl a believer, too: | |
736 | ||
737 | use Encode 'decode_utf8'; | |
8baee566 | 738 | $Unicode = decode_utf8($bytes); |
ba62762e | 739 | |
f337b084 TH |
740 | or: |
741 | ||
742 | $Unicode = pack("U0a*", $bytes); | |
743 | ||
ba62762e JH |
744 | You can convert well-formed UTF-8 to a sequence of bytes, but if |
745 | you just want to convert random binary data into UTF-8, you can't. | |
1bfb14c4 | 746 | B<Any random collection of bytes isn't well-formed UTF-8>. You can |
ba62762e | 747 | use C<unpack("C*", $string)> for the former, and you can create |
8baee566 | 748 | well-formed Unicode data by C<pack("U*", 0xff, ...)>. |
ba62762e | 749 | |
818c4caa | 750 | =item * |
5cb3728c RB |
751 | |
752 | How Do I Display Unicode? How Do I Input Unicode? | |
ba62762e | 753 | |
076d825e | 754 | See http://www.alanwood.net/unicode/ and |
ba62762e JH |
755 | http://www.cl.cam.ac.uk/~mgk25/unicode.html |
756 | ||
818c4caa | 757 | =item * |
5cb3728c RB |
758 | |
759 | How Does Unicode Work With Traditional Locales? | |
ba62762e JH |
760 | |
761 | In Perl, not very well. Avoid using locales through the C<locale> | |
4c496f0c JH |
762 | pragma. Use only one or the other. But see L<perlrun> for the |
763 | description of the C<-C> switch and its environment counterpart, | |
764 | C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features, | |
765 | for example by using locale settings. | |
ba62762e JH |
766 | |
767 | =back | |
768 | ||
769 | =head2 Hexadecimal Notation | |
770 | ||
376d9008 JB |
771 | The Unicode standard prefers using hexadecimal notation because |
772 | that more clearly shows the division of Unicode into blocks of 256 characters. | |
ba62762e JH |
773 | Hexadecimal is also simply shorter than decimal. You can use decimal |
774 | notation, too, but learning to use hexadecimal just makes life easier | |
1bfb14c4 | 775 | with the Unicode standard. The C<U+HHHH> notation uses hexadecimal, |
076d825e | 776 | for example. |
ba62762e JH |
777 | |
778 | The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and> | |
779 | a-f (or A-F, case doesn't matter). Each hexadecimal digit represents | |
780 | four bits, or half a byte. C<print 0x..., "\n"> will show a | |
781 | hexadecimal number in decimal, and C<printf "%x\n", $decimal> will | |
782 | show a decimal number in hexadecimal. If you have just the | |
376d9008 | 783 | "hex digits" of a hexadecimal number, you can use the C<hex()> function. |
ba62762e JH |
784 | |
785 | print 0x0009, "\n"; # 9 | |
786 | print 0x000a, "\n"; # 10 | |
787 | print 0x000f, "\n"; # 15 | |
788 | print 0x0010, "\n"; # 16 | |
789 | print 0x0011, "\n"; # 17 | |
790 | print 0x0100, "\n"; # 256 | |
791 | ||
792 | print 0x0041, "\n"; # 65 | |
793 | ||
794 | printf "%x\n", 65; # 41 | |
795 | printf "%#x\n", 65; # 0x41 | |
796 | ||
797 | print hex("41"), "\n"; # 65 | |
798 | ||
799 | =head2 Further Resources | |
800 | ||
801 | =over 4 | |
802 | ||
803 | =item * | |
804 | ||
805 | Unicode Consortium | |
806 | ||
807 | http://www.unicode.org/ | |
808 | ||
809 | =item * | |
810 | ||
811 | Unicode FAQ | |
812 | ||
813 | http://www.unicode.org/unicode/faq/ | |
814 | ||
815 | =item * | |
816 | ||
817 | Unicode Glossary | |
818 | ||
819 | http://www.unicode.org/glossary/ | |
820 | ||
821 | =item * | |
822 | ||
823 | Unicode Useful Resources | |
824 | ||
825 | http://www.unicode.org/unicode/onlinedat/resources.html | |
826 | ||
827 | =item * | |
828 | ||
829 | Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications | |
830 | ||
076d825e | 831 | http://www.alanwood.net/unicode/ |
ba62762e JH |
832 | |
833 | =item * | |
834 | ||
835 | UTF-8 and Unicode FAQ for Unix/Linux | |
836 | ||
837 | http://www.cl.cam.ac.uk/~mgk25/unicode.html | |
838 | ||
839 | =item * | |
840 | ||
841 | Legacy Character Sets | |
842 | ||
843 | http://www.czyborra.com/ | |
844 | http://www.eki.ee/letter/ | |
845 | ||
846 | =item * | |
847 | ||
848 | The Unicode support files live within the Perl installation in the | |
849 | directory | |
850 | ||
851 | $Config{installprivlib}/unicore | |
852 | ||
853 | in Perl 5.8.0 or newer, and | |
854 | ||
855 | $Config{installprivlib}/unicode | |
856 | ||
857 | in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to | |
858 | avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) | |
551b6b6f | 859 | The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in |
ba62762e JH |
860 | Perl 5.6.1.) You can find the C<$Config{installprivlib}> by |
861 | ||
862 | perl "-V:installprivlib" | |
863 | ||
ba62762e JH |
864 | You can explore various information from the Unicode data files using |
865 | the C<Unicode::UCD> module. | |
866 | ||
867 | =back | |
868 | ||
f6edf83b JH |
869 | =head1 UNICODE IN OLDER PERLS |
870 | ||
871 | If you cannot upgrade your Perl to 5.8.0 or later, you can still | |
872 | do some Unicode processing by using the modules C<Unicode::String>, | |
873 | C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN. | |
874 | If you have the GNU recode installed, you can also use the | |
376d9008 | 875 | Perl front-end C<Convert::Recode> for character conversions. |
f6edf83b | 876 | |
aaef10c5 | 877 | The following are fast conversions from ISO 8859-1 (Latin-1) bytes |
63de3cb2 | 878 | to UTF-8 bytes and back, the code works even with older Perl 5 versions. |
aaef10c5 JH |
879 | |
880 | # ISO 8859-1 to UTF-8 | |
881 | s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg; | |
882 | ||
883 | # UTF-8 to ISO 8859-1 | |
884 | s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg; | |
885 | ||
ba62762e JH |
886 | =head1 SEE ALSO |
887 | ||
888 | L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>, | |
4c496f0c JH |
889 | L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>, |
890 | L<Unicode::UCD> | |
ba62762e | 891 | |
376d9008 | 892 | =head1 ACKNOWLEDGMENTS |
ba62762e JH |
893 | |
894 | Thanks to the kind readers of the perl5-porters@perl.org, | |
895 | perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org | |
896 | mailing lists for their valuable feedback. | |
897 | ||
898 | =head1 AUTHOR, COPYRIGHT, AND LICENSE | |
899 | ||
0f2f9b7d | 900 | Copyright 2001-2002 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt> |
ba62762e JH |
901 | |
902 | This document may be distributed under the same terms as Perl itself. |