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1 | =head1 NAME |
2 | |
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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 | |
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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 |
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16 | points for characters in almost all modern character set standards, |
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17 | covering more than 30 writing systems and hundreds of languages, |
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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. |
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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 |
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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, |
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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 |
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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 |
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70 | a single code point. These precomposed characters are, however, |
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71 | only available for some combinations, and are mainly |
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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 |
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75 | different compositions of the characters, various I<normalization |
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76 | forms> to standardize representations are also defined. |
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77 | |
78 | Because of backward compatibility with legacy encodings, the "a unique |
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79 | number for every character" idea breaks down a bit: instead, there is |
80 | "at least one number for every character". The same character could |
81 | be represented differently in several legacy encodings. The |
82 | converse is also not true: some code points do not have an assigned |
83 | character. Firstly, there are unallocated code points within |
84 | otherwise used blocks. Secondly, there are special Unicode control |
85 | characters that do not represent true characters. |
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86 | |
87 | A common myth about Unicode is that it would be "16-bit", that is, |
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88 | Unicode is only represented as C<0x10000> (or 65536) characters from |
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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. |
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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. |
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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 |
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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. |
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131 | This model was found to be wrong, or at least clumsy: the "Unicodeness" |
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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 |
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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. |
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146 | |
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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. |
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152 | |
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153 | A user of Perl does not normally need to know nor care how Perl |
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154 | happens to encode its internal strings, but it becomes relevant when |
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155 | outputting Unicode strings to a stream without a PerlIO layer -- one with |
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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 | |
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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 |
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166 | as a warning: |
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167 | |
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168 | Wide character in print at ... |
169 | |
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170 | To output UTF-8, use the C<:utf8> output layer. Prepending |
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171 | |
172 | binmode(STDOUT, ":utf8"); |
173 | |
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174 | to this sample program ensures that the output is completely UTF-8, |
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175 | and removes the program's warning. |
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176 | |
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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. |
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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 | |
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192 | =head2 Unicode and EBCDIC |
193 | |
194 | Perl 5.8.0 also supports Unicode on EBCDIC platforms. There, |
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195 | Unicode support is somewhat more complex to implement since |
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196 | additional conversions are needed at every step. Some problems |
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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 | |
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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 | |
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221 | See L</"Further Resources"> for how to find all these numeric codes. |
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222 | |
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223 | Naturally, C<ord()> will do the reverse: it turns a character into |
224 | a code point. |
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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 |
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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 | |
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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 | |
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249 | Also note that if all the code points for pack "U" are below 0x100, |
250 | bytes will be generated, just like if you were using C<chr()>. |
251 | |
252 | my $bytes = pack("U*", 0x80, 0xFF); |
253 | |
254 | If you want to force the result to Unicode characters, use the special |
255 | C<"U0"> prefix. It consumes no arguments but forces the result to be |
256 | in Unicode characters, instead of bytes. |
257 | |
258 | my $chars = pack("U0U*", 0x80, 0xFF); |
259 | |
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260 | =head2 Handling Unicode |
261 | |
262 | Handling Unicode is for the most part transparent: just use the |
263 | strings as usual. Functions like C<index()>, C<length()>, and |
264 | C<substr()> will work on the Unicode characters; regular expressions |
265 | will work on the Unicode characters (see L<perlunicode> and L<perlretut>). |
266 | |
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267 | Note that Perl considers combining character sequences to be |
268 | characters, so for example |
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269 | |
270 | use charnames ':full'; |
271 | print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; |
272 | |
273 | will print 2, not 1. The only exception is that regular expressions |
274 | have C<\X> for matching a combining character sequence. |
275 | |
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276 | Life is not quite so transparent, however, when working with legacy |
277 | encodings, I/O, and certain special cases: |
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278 | |
279 | =head2 Legacy Encodings |
280 | |
281 | When you combine legacy data and Unicode the legacy data needs |
282 | to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if |
283 | applicable) is assumed. You can override this assumption by |
284 | using the C<encoding> pragma, for example |
285 | |
286 | use encoding 'latin2'; # ISO 8859-2 |
287 | |
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288 | in which case literals (string or regular expressions), C<chr()>, |
289 | and C<ord()> in your whole script are assumed to produce Unicode |
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290 | characters from ISO 8859-2 code points. Note that the matching for |
291 | encoding names is forgiving: instead of C<latin2> you could have |
292 | said C<Latin 2>, or C<iso8859-2>, or other variations. With just |
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293 | |
294 | use encoding; |
295 | |
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296 | the environment variable C<PERL_ENCODING> will be consulted. |
297 | If that variable isn't set, the encoding pragma will fail. |
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298 | |
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299 | The C<Encode> module knows about many encodings and has interfaces |
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300 | for doing conversions between those encodings: |
301 | |
302 | use Encode 'from_to'; |
303 | from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8 |
304 | |
305 | =head2 Unicode I/O |
306 | |
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307 | Normally, writing out Unicode data |
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308 | |
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309 | print FH $some_string_with_unicode, "\n"; |
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310 | |
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311 | produces raw bytes that Perl happens to use to internally encode the |
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312 | Unicode string. Perl's internal encoding depends on the system as |
313 | well as what characters happen to be in the string at the time. If |
314 | any of the characters are at code points C<0x100> or above, you will get |
315 | a warning. To ensure that the output is explicitly rendered in the |
316 | encoding you desire--and to avoid the warning--open the stream with |
317 | the desired encoding. Some examples: |
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318 | |
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319 | open FH, ">:utf8", "file"; |
320 | |
321 | open FH, ">:encoding(ucs2)", "file"; |
322 | open FH, ">:encoding(UTF-8)", "file"; |
323 | open FH, ">:encoding(shift_jis)", "file"; |
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324 | |
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325 | and on already open streams, use C<binmode()>: |
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326 | |
327 | binmode(STDOUT, ":utf8"); |
328 | |
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329 | binmode(STDOUT, ":encoding(ucs2)"); |
330 | binmode(STDOUT, ":encoding(UTF-8)"); |
331 | binmode(STDOUT, ":encoding(shift_jis)"); |
332 | |
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333 | The matching of encoding names is loose: case does not matter, and |
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334 | many encodings have several aliases. Note that the C<:utf8> layer |
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335 | must always be specified exactly like that; it is I<not> subject to |
336 | the loose matching of encoding names. |
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337 | |
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338 | See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and |
339 | L<Encode::PerlIO> for the C<:encoding()> layer, and |
340 | L<Encode::Supported> for many encodings supported by the C<Encode> |
341 | module. |
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342 | |
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343 | Reading in a file that you know happens to be encoded in one of the |
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344 | Unicode or legacy encodings does not magically turn the data into |
345 | Unicode in Perl's eyes. To do that, specify the appropriate |
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346 | layer when opening files |
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347 | |
348 | open(my $fh,'<:utf8', 'anything'); |
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349 | my $line_of_unicode = <$fh>; |
350 | |
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351 | open(my $fh,'<:encoding(Big5)', 'anything'); |
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352 | my $line_of_unicode = <$fh>; |
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353 | |
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354 | The I/O layers can also be specified more flexibly with |
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355 | the C<open> pragma. See L<open>, or look at the following example. |
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356 | |
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357 | use open ':utf8'; # input and output default layer will be UTF-8 |
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358 | open X, ">file"; |
359 | print X chr(0x100), "\n"; |
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360 | close X; |
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361 | open Y, "<file"; |
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362 | printf "%#x\n", ord(<Y>); # this should print 0x100 |
363 | close Y; |
364 | |
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365 | With the C<open> pragma you can use the C<:locale> layer |
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366 | |
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367 | BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' } |
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368 | # the :locale will probe the locale environment variables like LC_ALL |
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369 | use open OUT => ':locale'; # russki parusski |
370 | open(O, ">koi8"); |
371 | print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 |
372 | close O; |
373 | open(I, "<koi8"); |
374 | printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1 |
375 | close I; |
376 | |
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377 | or you can also use the C<':encoding(...)'> layer |
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378 | |
379 | open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); |
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380 | my $line_of_unicode = <$epic>; |
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381 | |
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382 | These methods install a transparent filter on the I/O stream that |
383 | converts data from the specified encoding when it is read in from the |
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384 | stream. The result is always Unicode. |
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385 | |
386 | The L<open> pragma affects all the C<open()> calls after the pragma by |
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387 | setting default layers. If you want to affect only certain |
388 | streams, use explicit layers directly in the C<open()> call. |
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389 | |
390 | You can switch encodings on an already opened stream by using |
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391 | C<binmode()>; see L<perlfunc/binmode>. |
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392 | |
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393 | The C<:locale> does not currently (as of Perl 5.8.0) work with |
394 | C<open()> and C<binmode()>, only with the C<open> pragma. The |
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395 | C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>, |
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396 | C<binmode()>, and the C<open> pragma. |
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397 | |
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398 | Similarly, you may use these I/O layers on output streams to |
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399 | automatically convert Unicode to the specified encoding when it is |
400 | written to the stream. For example, the following snippet copies the |
401 | contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to |
402 | the file "text.utf8", encoded as UTF-8: |
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403 | |
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404 | open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis'); |
405 | open(my $unicode, '>:utf8', 'text.utf8'); |
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406 | while (<$nihongo>) { print $unicode $_ } |
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407 | |
408 | The naming of encodings, both by the C<open()> and by the C<open> |
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409 | pragma, is similar to the C<encoding> pragma in that it allows for |
410 | flexible names: C<koi8-r> and C<KOI8R> will both be understood. |
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411 | |
412 | Common encodings recognized by ISO, MIME, IANA, and various other |
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413 | standardisation organisations are recognised; for a more detailed |
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414 | list see L<Encode::Supported>. |
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415 | |
416 | C<read()> reads characters and returns the number of characters. |
417 | C<seek()> and C<tell()> operate on byte counts, as do C<sysread()> |
418 | and C<sysseek()>. |
419 | |
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420 | Notice that because of the default behaviour of not doing any |
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421 | conversion upon input if there is no default layer, |
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422 | it is easy to mistakenly write code that keeps on expanding a file |
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423 | by repeatedly encoding the data: |
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424 | |
425 | # BAD CODE WARNING |
426 | open F, "file"; |
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427 | local $/; ## read in the whole file of 8-bit characters |
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428 | $t = <F>; |
429 | close F; |
430 | open F, ">:utf8", "file"; |
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431 | print F $t; ## convert to UTF-8 on output |
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432 | close F; |
433 | |
434 | If you run this code twice, the contents of the F<file> will be twice |
1d7919c5 |
435 | UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or |
436 | explicitly opening also the F<file> for input as UTF-8. |
ba62762e |
437 | |
0c901d84 |
438 | B<NOTE>: the C<:utf8> and C<:encoding> features work only if your |
d0fadae5 |
439 | Perl has been built with the new PerlIO feature (which is the default |
440 | on most systems). |
0c901d84 |
441 | |
1ecefa54 |
442 | =head2 Displaying Unicode As Text |
443 | |
444 | Sometimes you might want to display Perl scalars containing Unicode as |
8baee566 |
445 | simple ASCII (or EBCDIC) text. The following subroutine converts |
1ecefa54 |
446 | its argument so that Unicode characters with code points greater than |
1bfb14c4 |
447 | 255 are displayed as C<\x{...}>, control characters (like C<\n>) are |
448 | displayed as C<\x..>, and the rest of the characters as themselves: |
1ecefa54 |
449 | |
58c274a1 |
450 | sub nice_string { |
451 | join("", |
452 | map { $_ > 255 ? # if wide character... |
8baee566 |
453 | sprintf("\\x{%04X}", $_) : # \x{...} |
58c274a1 |
454 | chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... |
8baee566 |
455 | sprintf("\\x%02X", $_) : # \x.. |
d0551e73 |
456 | quotemeta(chr($_)) # else quoted or as themselves |
58c274a1 |
457 | } unpack("U*", $_[0])); # unpack Unicode characters |
458 | } |
459 | |
460 | For example, |
461 | |
462 | nice_string("foo\x{100}bar\n") |
463 | |
d0551e73 |
464 | returns the string |
58c274a1 |
465 | |
d0551e73 |
466 | 'foo\x{0100}bar\x0A' |
467 | |
468 | which is ready to be printed. |
1ecefa54 |
469 | |
ba62762e |
470 | =head2 Special Cases |
471 | |
472 | =over 4 |
473 | |
474 | =item * |
475 | |
476 | Bit Complement Operator ~ And vec() |
477 | |
1bfb14c4 |
478 | The bit complement operator C<~> may produce surprising results if |
479 | used on strings containing characters with ordinal values above |
480 | 255. In such a case, the results are consistent with the internal |
481 | encoding of the characters, but not with much else. So don't do |
482 | that. Similarly for C<vec()>: you will be operating on the |
483 | internally-encoded bit patterns of the Unicode characters, not on |
484 | the code point values, which is very probably not what you want. |
ba62762e |
485 | |
486 | =item * |
487 | |
8baee566 |
488 | Peeking At Perl's Internal Encoding |
489 | |
490 | Normal users of Perl should never care how Perl encodes any particular |
a5f0baef |
491 | Unicode string (because the normal ways to get at the contents of a |
376d9008 |
492 | string with Unicode--via input and output--should always be via |
fae2c0fb |
493 | explicitly-defined I/O layers). But if you must, there are two |
a5f0baef |
494 | ways of looking behind the scenes. |
ba62762e |
495 | |
496 | One way of peeking inside the internal encoding of Unicode characters |
376d9008 |
497 | is to use C<unpack("C*", ...> to get the bytes or C<unpack("H*", ...)> |
ba62762e |
498 | to display the bytes: |
499 | |
8baee566 |
500 | # this prints c4 80 for the UTF-8 bytes 0xc4 0x80 |
ba62762e |
501 | print join(" ", unpack("H*", pack("U", 0x100))), "\n"; |
502 | |
503 | Yet another way would be to use the Devel::Peek module: |
504 | |
505 | perl -MDevel::Peek -e 'Dump(chr(0x100))' |
506 | |
1e54db1a |
507 | That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes |
376d9008 |
508 | and Unicode characters in C<PV>. See also later in this document |
8800c35a |
509 | the discussion about the C<utf8::is_utf8()> function. |
ba62762e |
510 | |
511 | =back |
512 | |
513 | =head2 Advanced Topics |
514 | |
515 | =over 4 |
516 | |
517 | =item * |
518 | |
519 | String Equivalence |
520 | |
521 | The question of string equivalence turns somewhat complicated |
376d9008 |
522 | in Unicode: what do you mean by "equal"? |
ba62762e |
523 | |
07698885 |
524 | (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to |
525 | C<LATIN CAPITAL LETTER A>?) |
ba62762e |
526 | |
a5f0baef |
527 | The short answer is that by default Perl compares equivalence (C<eq>, |
528 | C<ne>) based only on code points of the characters. In the above |
376d9008 |
529 | case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any |
530 | CAPITAL LETTER As should be considered equal, or even As of any case. |
ba62762e |
531 | |
532 | The long answer is that you need to consider character normalization |
376d9008 |
533 | and casing issues: see L<Unicode::Normalize>, Unicode Technical |
ba62762e |
534 | Reports #15 and #21, I<Unicode Normalization Forms> and I<Case |
376d9008 |
535 | Mappings>, http://www.unicode.org/unicode/reports/tr15/ and |
536 | http://www.unicode.org/unicode/reports/tr21/ |
ba62762e |
537 | |
1bfb14c4 |
538 | As of Perl 5.8.0, the "Full" case-folding of I<Case |
539 | Mappings/SpecialCasing> is implemented. |
ba62762e |
540 | |
541 | =item * |
542 | |
543 | String Collation |
544 | |
376d9008 |
545 | People like to see their strings nicely sorted--or as Unicode |
ba62762e |
546 | parlance goes, collated. But again, what do you mean by collate? |
547 | |
07698885 |
548 | (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after |
549 | C<LATIN CAPITAL LETTER A WITH GRAVE>?) |
ba62762e |
550 | |
58c274a1 |
551 | The short answer is that by default, Perl compares strings (C<lt>, |
ba62762e |
552 | C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the |
1bfb14c4 |
553 | characters. In the above case, the answer is "after", since |
da76a1f4 |
554 | C<0x00C1> > C<0x00C0>. |
ba62762e |
555 | |
556 | The long answer is that "it depends", and a good answer cannot be |
557 | given without knowing (at the very least) the language context. |
558 | See L<Unicode::Collate>, and I<Unicode Collation Algorithm> |
559 | http://www.unicode.org/unicode/reports/tr10/ |
560 | |
561 | =back |
562 | |
563 | =head2 Miscellaneous |
564 | |
565 | =over 4 |
566 | |
567 | =item * |
568 | |
3ff56b75 |
569 | Character Ranges and Classes |
ba62762e |
570 | |
571 | Character ranges in regular expression character classes (C</[a-z]/>) |
572 | and in the C<tr///> (also known as C<y///>) operator are not magically |
58c274a1 |
573 | Unicode-aware. What this means that C<[A-Za-z]> will not magically start |
376d9008 |
574 | to mean "all alphabetic letters"; not that it does mean that even for |
575 | 8-bit characters, you should be using C</[[:alpha:]]/> in that case. |
ba62762e |
576 | |
1bfb14c4 |
577 | For specifying character classes like that in regular expressions, |
578 | you can use the various Unicode properties--C<\pL>, or perhaps |
579 | C<\p{Alphabetic}>, in this particular case. You can use Unicode |
580 | code points as the end points of character ranges, but there is no |
581 | magic associated with specifying a certain range. For further |
582 | information--there are dozens of Unicode character classes--see |
583 | L<perlunicode>. |
ba62762e |
584 | |
585 | =item * |
586 | |
587 | String-To-Number Conversions |
588 | |
376d9008 |
589 | Unicode does define several other decimal--and numeric--characters |
590 | besides the familiar 0 to 9, such as the Arabic and Indic digits. |
ba62762e |
591 | Perl does not support string-to-number conversion for digits other |
58c274a1 |
592 | than ASCII 0 to 9 (and ASCII a to f for hexadecimal). |
ba62762e |
593 | |
594 | =back |
595 | |
596 | =head2 Questions With Answers |
597 | |
598 | =over 4 |
599 | |
818c4caa |
600 | =item * |
5cb3728c |
601 | |
602 | Will My Old Scripts Break? |
ba62762e |
603 | |
604 | Very probably not. Unless you are generating Unicode characters |
1bfb14c4 |
605 | somehow, old behaviour should be preserved. About the only behaviour |
606 | that has changed and which could start generating Unicode is the old |
607 | behaviour of C<chr()> where supplying an argument more than 255 |
608 | produced a character modulo 255. C<chr(300)>, for example, was equal |
609 | to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH |
610 | BREVE. |
ba62762e |
611 | |
818c4caa |
612 | =item * |
5cb3728c |
613 | |
614 | How Do I Make My Scripts Work With Unicode? |
ba62762e |
615 | |
616 | Very little work should be needed since nothing changes until you |
1bfb14c4 |
617 | generate Unicode data. The most important thing is getting input as |
618 | Unicode; for that, see the earlier I/O discussion. |
ba62762e |
619 | |
818c4caa |
620 | =item * |
5cb3728c |
621 | |
622 | How Do I Know Whether My String Is In Unicode? |
ba62762e |
623 | |
1bfb14c4 |
624 | You shouldn't care. No, you really shouldn't. No, really. If you |
625 | have to care--beyond the cases described above--it means that we |
ba62762e |
626 | didn't get the transparency of Unicode quite right. |
627 | |
628 | Okay, if you insist: |
629 | |
8800c35a |
630 | print utf8::is_utf8($string) ? 1 : 0, "\n"; |
ba62762e |
631 | |
632 | But note that this doesn't mean that any of the characters in the |
633 | string are necessary UTF-8 encoded, or that any of the characters have |
634 | code points greater than 0xFF (255) or even 0x80 (128), or that the |
635 | string has any characters at all. All the C<is_utf8()> does is to |
636 | return the value of the internal "utf8ness" flag attached to the |
376d9008 |
637 | C<$string>. If the flag is off, the bytes in the scalar are interpreted |
3c1c8017 |
638 | as a single byte encoding. If the flag is on, the bytes in the scalar |
376d9008 |
639 | are interpreted as the (multi-byte, variable-length) UTF-8 encoded code |
3c1c8017 |
640 | points of the characters. Bytes added to an UTF-8 encoded string are |
1e54db1a |
641 | automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars |
376d9008 |
642 | are merged (double-quoted interpolation, explicit concatenation, and |
3c1c8017 |
643 | printf/sprintf parameter substitution), the result will be UTF-8 encoded |
644 | as if copies of the byte strings were upgraded to UTF-8: for example, |
645 | |
646 | $a = "ab\x80c"; |
647 | $b = "\x{100}"; |
648 | print "$a = $b\n"; |
649 | |
a02b5feb |
650 | the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but |
651 | C<$a> will stay byte-encoded. |
ba62762e |
652 | |
653 | Sometimes you might really need to know the byte length of a string |
ce7675db |
654 | instead of the character length. For that use either the |
655 | C<Encode::encode_utf8()> function or the C<bytes> pragma and its only |
656 | defined function C<length()>: |
ba62762e |
657 | |
658 | my $unicode = chr(0x100); |
659 | print length($unicode), "\n"; # will print 1 |
ce7675db |
660 | require Encode; |
661 | print length(Encode::encode_utf8($unicode)), "\n"; # will print 2 |
ba62762e |
662 | use bytes; |
1bfb14c4 |
663 | print length($unicode), "\n"; # will also print 2 |
664 | # (the 0xC4 0x80 of the UTF-8) |
ba62762e |
665 | |
818c4caa |
666 | =item * |
5cb3728c |
667 | |
668 | How Do I Detect Data That's Not Valid In a Particular Encoding? |
ba62762e |
669 | |
8baee566 |
670 | Use the C<Encode> package to try converting it. |
671 | For example, |
ba62762e |
672 | |
673 | use Encode 'encode_utf8'; |
8baee566 |
674 | if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) { |
ba62762e |
675 | # valid |
676 | } else { |
677 | # invalid |
678 | } |
679 | |
8baee566 |
680 | For UTF-8 only, you can use: |
ba62762e |
681 | |
682 | use warnings; |
8baee566 |
683 | @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8); |
ba62762e |
684 | |
1bfb14c4 |
685 | If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack> |
686 | warning is produced. The "U0" means "expect strictly UTF-8 encoded |
687 | Unicode". Without that the C<unpack("U*", ...)> would accept also |
688 | data like C<chr(0xFF>), similarly to the C<pack> as we saw earlier. |
ba62762e |
689 | |
818c4caa |
690 | =item * |
5cb3728c |
691 | |
692 | How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa? |
ba62762e |
693 | |
8baee566 |
694 | This probably isn't as useful as you might think. |
695 | Normally, you shouldn't need to. |
ba62762e |
696 | |
1bfb14c4 |
697 | In one sense, what you are asking doesn't make much sense: encodings |
376d9008 |
698 | are for characters, and binary data are not "characters", so converting |
a5f0baef |
699 | "data" into some encoding isn't meaningful unless you know in what |
700 | character set and encoding the binary data is in, in which case it's |
376d9008 |
701 | not just binary data, now is it? |
8baee566 |
702 | |
1bfb14c4 |
703 | If you have a raw sequence of bytes that you know should be |
704 | interpreted via a particular encoding, you can use C<Encode>: |
ba62762e |
705 | |
706 | use Encode 'from_to'; |
707 | from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 |
708 | |
1bfb14c4 |
709 | The call to C<from_to()> changes the bytes in C<$data>, but nothing |
710 | material about the nature of the string has changed as far as Perl is |
711 | concerned. Both before and after the call, the string C<$data> |
712 | contains just a bunch of 8-bit bytes. As far as Perl is concerned, |
713 | the encoding of the string remains as "system-native 8-bit bytes". |
8baee566 |
714 | |
715 | You might relate this to a fictional 'Translate' module: |
716 | |
717 | use Translate; |
718 | my $phrase = "Yes"; |
719 | Translate::from_to($phrase, 'english', 'deutsch'); |
720 | ## phrase now contains "Ja" |
ba62762e |
721 | |
8baee566 |
722 | The contents of the string changes, but not the nature of the string. |
1bfb14c4 |
723 | Perl doesn't know any more after the call than before that the |
724 | contents of the string indicates the affirmative. |
ba62762e |
725 | |
376d9008 |
726 | Back to converting data. If you have (or want) data in your system's |
a5f0baef |
727 | native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use |
728 | pack/unpack to convert to/from Unicode. |
ba62762e |
729 | |
8baee566 |
730 | $native_string = pack("C*", unpack("U*", $Unicode_string)); |
731 | $Unicode_string = pack("U*", unpack("C*", $native_string)); |
ba62762e |
732 | |
733 | If you have a sequence of bytes you B<know> is valid UTF-8, |
734 | but Perl doesn't know it yet, you can make Perl a believer, too: |
735 | |
736 | use Encode 'decode_utf8'; |
8baee566 |
737 | $Unicode = decode_utf8($bytes); |
ba62762e |
738 | |
739 | You can convert well-formed UTF-8 to a sequence of bytes, but if |
740 | you just want to convert random binary data into UTF-8, you can't. |
1bfb14c4 |
741 | B<Any random collection of bytes isn't well-formed UTF-8>. You can |
ba62762e |
742 | use C<unpack("C*", $string)> for the former, and you can create |
8baee566 |
743 | well-formed Unicode data by C<pack("U*", 0xff, ...)>. |
ba62762e |
744 | |
818c4caa |
745 | =item * |
5cb3728c |
746 | |
747 | How Do I Display Unicode? How Do I Input Unicode? |
ba62762e |
748 | |
076d825e |
749 | See http://www.alanwood.net/unicode/ and |
ba62762e |
750 | http://www.cl.cam.ac.uk/~mgk25/unicode.html |
751 | |
818c4caa |
752 | =item * |
5cb3728c |
753 | |
754 | How Does Unicode Work With Traditional Locales? |
ba62762e |
755 | |
756 | In Perl, not very well. Avoid using locales through the C<locale> |
4c496f0c |
757 | pragma. Use only one or the other. But see L<perlrun> for the |
758 | description of the C<-C> switch and its environment counterpart, |
759 | C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features, |
760 | for example by using locale settings. |
ba62762e |
761 | |
762 | =back |
763 | |
764 | =head2 Hexadecimal Notation |
765 | |
376d9008 |
766 | The Unicode standard prefers using hexadecimal notation because |
767 | that more clearly shows the division of Unicode into blocks of 256 characters. |
ba62762e |
768 | Hexadecimal is also simply shorter than decimal. You can use decimal |
769 | notation, too, but learning to use hexadecimal just makes life easier |
1bfb14c4 |
770 | with the Unicode standard. The C<U+HHHH> notation uses hexadecimal, |
076d825e |
771 | for example. |
ba62762e |
772 | |
773 | The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and> |
774 | a-f (or A-F, case doesn't matter). Each hexadecimal digit represents |
775 | four bits, or half a byte. C<print 0x..., "\n"> will show a |
776 | hexadecimal number in decimal, and C<printf "%x\n", $decimal> will |
777 | show a decimal number in hexadecimal. If you have just the |
376d9008 |
778 | "hex digits" of a hexadecimal number, you can use the C<hex()> function. |
ba62762e |
779 | |
780 | print 0x0009, "\n"; # 9 |
781 | print 0x000a, "\n"; # 10 |
782 | print 0x000f, "\n"; # 15 |
783 | print 0x0010, "\n"; # 16 |
784 | print 0x0011, "\n"; # 17 |
785 | print 0x0100, "\n"; # 256 |
786 | |
787 | print 0x0041, "\n"; # 65 |
788 | |
789 | printf "%x\n", 65; # 41 |
790 | printf "%#x\n", 65; # 0x41 |
791 | |
792 | print hex("41"), "\n"; # 65 |
793 | |
794 | =head2 Further Resources |
795 | |
796 | =over 4 |
797 | |
798 | =item * |
799 | |
800 | Unicode Consortium |
801 | |
802 | http://www.unicode.org/ |
803 | |
804 | =item * |
805 | |
806 | Unicode FAQ |
807 | |
808 | http://www.unicode.org/unicode/faq/ |
809 | |
810 | =item * |
811 | |
812 | Unicode Glossary |
813 | |
814 | http://www.unicode.org/glossary/ |
815 | |
816 | =item * |
817 | |
818 | Unicode Useful Resources |
819 | |
820 | http://www.unicode.org/unicode/onlinedat/resources.html |
821 | |
822 | =item * |
823 | |
824 | Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications |
825 | |
076d825e |
826 | http://www.alanwood.net/unicode/ |
ba62762e |
827 | |
828 | =item * |
829 | |
830 | UTF-8 and Unicode FAQ for Unix/Linux |
831 | |
832 | http://www.cl.cam.ac.uk/~mgk25/unicode.html |
833 | |
834 | =item * |
835 | |
836 | Legacy Character Sets |
837 | |
838 | http://www.czyborra.com/ |
839 | http://www.eki.ee/letter/ |
840 | |
841 | =item * |
842 | |
843 | The Unicode support files live within the Perl installation in the |
844 | directory |
845 | |
846 | $Config{installprivlib}/unicore |
847 | |
848 | in Perl 5.8.0 or newer, and |
849 | |
850 | $Config{installprivlib}/unicode |
851 | |
852 | in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to |
853 | avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) |
551b6b6f |
854 | The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in |
ba62762e |
855 | Perl 5.6.1.) You can find the C<$Config{installprivlib}> by |
856 | |
857 | perl "-V:installprivlib" |
858 | |
ba62762e |
859 | You can explore various information from the Unicode data files using |
860 | the C<Unicode::UCD> module. |
861 | |
862 | =back |
863 | |
f6edf83b |
864 | =head1 UNICODE IN OLDER PERLS |
865 | |
866 | If you cannot upgrade your Perl to 5.8.0 or later, you can still |
867 | do some Unicode processing by using the modules C<Unicode::String>, |
868 | C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN. |
869 | If you have the GNU recode installed, you can also use the |
376d9008 |
870 | Perl front-end C<Convert::Recode> for character conversions. |
f6edf83b |
871 | |
aaef10c5 |
872 | The following are fast conversions from ISO 8859-1 (Latin-1) bytes |
63de3cb2 |
873 | to UTF-8 bytes and back, the code works even with older Perl 5 versions. |
aaef10c5 |
874 | |
875 | # ISO 8859-1 to UTF-8 |
876 | s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg; |
877 | |
878 | # UTF-8 to ISO 8859-1 |
879 | s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg; |
880 | |
ba62762e |
881 | =head1 SEE ALSO |
882 | |
883 | L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>, |
4c496f0c |
884 | L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>, |
885 | L<Unicode::UCD> |
ba62762e |
886 | |
376d9008 |
887 | =head1 ACKNOWLEDGMENTS |
ba62762e |
888 | |
889 | Thanks to the kind readers of the perl5-porters@perl.org, |
890 | perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org |
891 | mailing lists for their valuable feedback. |
892 | |
893 | =head1 AUTHOR, COPYRIGHT, AND LICENSE |
894 | |
0f2f9b7d |
895 | Copyright 2001-2002 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt> |
ba62762e |
896 | |
897 | This document may be distributed under the same terms as Perl itself. |