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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. |
22 | |
23 | A Unicode I<character> is an abstract entity. It is not bound to any |
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24 | particular integer width, especially not to the C language C<char>. |
25 | Unicode is language-neutral and display-neutral: it does not encode the |
26 | language of the text and it does not define fonts or other graphical |
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27 | layout details. Unicode operates on characters and on text built from |
28 | those characters. |
29 | |
30 | Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK |
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31 | SMALL LETTER ALPHA> and unique numbers for the characters, in this |
32 | case 0x0041 and 0x03B1, respectively. These unique numbers are called |
33 | I<code points>. |
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34 | |
35 | The Unicode standard prefers using hexadecimal notation for the code |
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36 | points. If numbers like C<0x0041> are unfamiliar to |
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37 | you, take a peek at a later section, L</"Hexadecimal Notation">. |
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38 | The Unicode standard uses the notation C<U+0041 LATIN CAPITAL LETTER A>, |
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39 | to give the hexadecimal code point and the normative name of |
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40 | the character. |
41 | |
42 | Unicode also defines various I<properties> for the characters, like |
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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 |
89 | C<0x0000> to C<0xFFFF>. B<This is untrue.> Since Unicode 2.0, Unicode |
90 | has been defined all the way up to 21 bits (C<0x10FFFF>), and since |
91 | Unicode 3.1, characters have been defined beyond C<0xFFFF>. The first |
92 | C<0x10000> characters are called the I<Plane 0>, or the I<Basic |
93 | Multilingual Plane> (BMP). With Unicode 3.1, 17 planes in all are |
94 | defined--but nowhere near full of defined characters, yet. |
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95 | |
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96 | Another myth is that the 256-character blocks have something to |
97 | do with languages--that each block would define the characters used |
98 | by a language or a set of languages. B<This is also untrue.> |
99 | The division into blocks exists, but it is almost completely |
100 | accidental--an artifact of how the characters have been and |
101 | still are allocated. Instead, there is a concept called I<scripts>, |
102 | which is more useful: there is C<Latin> script, C<Greek> script, and |
103 | so on. Scripts usually span varied parts of several blocks. |
104 | For further information see L<Unicode::UCD>. |
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105 | |
106 | The Unicode code points are just abstract numbers. To input and |
107 | output these abstract numbers, the numbers must be I<encoded> somehow. |
108 | Unicode defines several I<character encoding forms>, of which I<UTF-8> |
109 | is perhaps the most popular. UTF-8 is a variable length encoding that |
110 | encodes Unicode characters as 1 to 6 bytes (only 4 with the currently |
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111 | defined characters). Other encodings include UTF-16 and UTF-32 and their |
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112 | big- and little-endian variants (UTF-8 is byte-order independent) |
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113 | The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms. |
114 | |
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115 | For more information about encodings--for instance, to learn what |
116 | I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>. |
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117 | |
118 | =head2 Perl's Unicode Support |
119 | |
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120 | Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode |
121 | natively. Perl 5.8.0, however, is the first recommended release for |
122 | serious Unicode work. The maintenance release 5.6.1 fixed many of the |
123 | problems of the initial Unicode implementation, but for example |
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124 | regular expressions still do not work with Unicode in 5.6.1. |
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125 | |
126 | B<Starting from Perl 5.8.0, the use of C<use utf8> is no longer |
127 | necessary.> In earlier releases the C<utf8> pragma was used to declare |
128 | that operations in the current block or file would be Unicode-aware. |
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129 | This model was found to be wrong, or at least clumsy: the "Unicodeness" |
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130 | is now carried with the data, instead of being attached to the |
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131 | operations. Only one case remains where an explicit C<use utf8> is |
132 | needed: if your Perl script itself is encoded in UTF-8, you can use |
133 | UTF-8 in your identifier names, and in string and regular expression |
134 | literals, by saying C<use utf8>. This is not the default because |
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135 | scripts with legacy 8-bit data in them would break. See L<utf8>. |
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136 | |
137 | =head2 Perl's Unicode Model |
138 | |
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139 | Perl supports both pre-5.6 strings of eight-bit native bytes, and |
140 | strings of Unicode characters. The principle is that Perl tries to |
141 | keep its data as eight-bit bytes for as long as possible, but as soon |
142 | as Unicodeness cannot be avoided, the data is transparently upgraded |
143 | to Unicode. |
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144 | |
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145 | Internally, Perl currently uses either whatever the native eight-bit |
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146 | character set of the platform (for example Latin-1) is, defaulting to |
147 | UTF-8, to encode Unicode strings. Specifically, if all code points in |
148 | the string are C<0xFF> or less, Perl uses the native eight-bit |
149 | character set. Otherwise, it uses UTF-8. |
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150 | |
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151 | A user of Perl does not normally need to know nor care how Perl |
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152 | happens to encode its internal strings, but it becomes relevant when |
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153 | outputting Unicode strings to a stream without a PerlIO layer -- one with |
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154 | the "default" encoding. In such a case, the raw bytes used internally |
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155 | (the native character set or UTF-8, as appropriate for each string) |
156 | will be used, and a "Wide character" warning will be issued if those |
157 | strings contain a character beyond 0x00FF. |
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158 | |
159 | For example, |
160 | |
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161 | perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"' |
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162 | |
163 | produces a fairly useless mixture of native bytes and UTF-8, as well |
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164 | as a warning: |
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165 | |
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166 | Wide character in print at ... |
167 | |
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168 | To output UTF-8, use the C<:utf8> output layer. Prepending |
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169 | |
170 | binmode(STDOUT, ":utf8"); |
171 | |
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172 | to this sample program ensures that the output is completely UTF-8, |
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173 | and removes the program's warning. |
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174 | |
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175 | If your locale environment variables (C<LC_ALL>, C<LC_CTYPE>, C<LANG>) |
176 | contain the strings 'UTF-8' or 'UTF8' (matched case-insensitively) |
177 | B<and> you enable using UTF-8 either by using the C<-C> command line |
178 | switch or by setting the PERL_UTF8_LOCALE environment variable to |
179 | a true value, then the default encoding of your STDIN, STDOUT, and |
180 | STDERR, and of B<any subsequent file open>, is UTF-8. Note that this |
181 | means that Perl expects other software to work, too: if Perl has been |
182 | led to believe that STDIN should be UTF-8, but then STDIN coming in |
183 | from another command is not UTF-8, Perl will complain about the |
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184 | malformed UTF-8. |
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185 | |
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186 | All features that combine Unicode and I/O also require using the new |
187 | PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though: |
188 | you can see whether yours is by running "perl -V" and looking for |
189 | C<useperlio=define>. |
190 | |
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191 | =head2 Unicode and EBCDIC |
192 | |
193 | Perl 5.8.0 also supports Unicode on EBCDIC platforms. There, |
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194 | Unicode support is somewhat more complex to implement since |
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195 | additional conversions are needed at every step. Some problems |
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196 | remain, see L<perlebcdic> for details. |
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197 | |
198 | In any case, the Unicode support on EBCDIC platforms is better than |
199 | in the 5.6 series, which didn't work much at all for EBCDIC platform. |
200 | On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC |
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201 | instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in |
202 | that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is |
203 | "EBCDIC-safe". |
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204 | |
205 | =head2 Creating Unicode |
206 | |
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207 | To create Unicode characters in literals for code points above C<0xFF>, |
208 | use the C<\x{...}> notation in double-quoted strings: |
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209 | |
210 | my $smiley = "\x{263a}"; |
211 | |
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212 | Similarly, it can be used in regular expression literals |
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213 | |
214 | $smiley =~ /\x{263a}/; |
215 | |
216 | At run-time you can use C<chr()>: |
217 | |
218 | my $hebrew_alef = chr(0x05d0); |
219 | |
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220 | See L</"Further Resources"> for how to find all these numeric codes. |
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221 | |
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222 | Naturally, C<ord()> will do the reverse: it turns a character into |
223 | a code point. |
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224 | |
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225 | Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>, |
226 | and C<chr(...)> for arguments less than C<0x100> (decimal 256) |
227 | generate an eight-bit character for backward compatibility with older |
228 | Perls. For arguments of C<0x100> or more, Unicode characters are |
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229 | always produced. If you want to force the production of Unicode |
230 | characters regardless of the numeric value, use C<pack("U", ...)> |
231 | instead of C<\x..>, C<\x{...}>, or C<chr()>. |
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232 | |
233 | You can also use the C<charnames> pragma to invoke characters |
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234 | by name in double-quoted strings: |
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235 | |
236 | use charnames ':full'; |
237 | my $arabic_alef = "\N{ARABIC LETTER ALEF}"; |
238 | |
239 | And, as mentioned above, you can also C<pack()> numbers into Unicode |
240 | characters: |
241 | |
242 | my $georgian_an = pack("U", 0x10a0); |
243 | |
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244 | Note that both C<\x{...}> and C<\N{...}> are compile-time string |
245 | constants: you cannot use variables in them. if you want similar |
246 | run-time functionality, use C<chr()> and C<charnames::vianame()>. |
247 | |
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248 | Also note that if all the code points for pack "U" are below 0x100, |
249 | bytes will be generated, just like if you were using C<chr()>. |
250 | |
251 | my $bytes = pack("U*", 0x80, 0xFF); |
252 | |
253 | If you want to force the result to Unicode characters, use the special |
254 | C<"U0"> prefix. It consumes no arguments but forces the result to be |
255 | in Unicode characters, instead of bytes. |
256 | |
257 | my $chars = pack("U0U*", 0x80, 0xFF); |
258 | |
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259 | =head2 Handling Unicode |
260 | |
261 | Handling Unicode is for the most part transparent: just use the |
262 | strings as usual. Functions like C<index()>, C<length()>, and |
263 | C<substr()> will work on the Unicode characters; regular expressions |
264 | will work on the Unicode characters (see L<perlunicode> and L<perlretut>). |
265 | |
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266 | Note that Perl considers combining character sequences to be |
267 | characters, so for example |
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268 | |
269 | use charnames ':full'; |
270 | print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; |
271 | |
272 | will print 2, not 1. The only exception is that regular expressions |
273 | have C<\X> for matching a combining character sequence. |
274 | |
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275 | Life is not quite so transparent, however, when working with legacy |
276 | encodings, I/O, and certain special cases: |
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277 | |
278 | =head2 Legacy Encodings |
279 | |
280 | When you combine legacy data and Unicode the legacy data needs |
281 | to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if |
282 | applicable) is assumed. You can override this assumption by |
283 | using the C<encoding> pragma, for example |
284 | |
285 | use encoding 'latin2'; # ISO 8859-2 |
286 | |
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287 | in which case literals (string or regular expressions), C<chr()>, |
288 | and C<ord()> in your whole script are assumed to produce Unicode |
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289 | characters from ISO 8859-2 code points. Note that the matching for |
290 | encoding names is forgiving: instead of C<latin2> you could have |
291 | said C<Latin 2>, or C<iso8859-2>, or other variations. With just |
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292 | |
293 | use encoding; |
294 | |
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295 | the environment variable C<PERL_ENCODING> will be consulted. |
296 | If that variable isn't set, the encoding pragma will fail. |
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297 | |
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298 | The C<Encode> module knows about many encodings and has interfaces |
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299 | for doing conversions between those encodings: |
300 | |
301 | use Encode 'from_to'; |
302 | from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8 |
303 | |
304 | =head2 Unicode I/O |
305 | |
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306 | Normally, writing out Unicode data |
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307 | |
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308 | print FH $some_string_with_unicode, "\n"; |
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309 | |
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310 | produces raw bytes that Perl happens to use to internally encode the |
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311 | Unicode string. Perl's internal encoding depends on the system as |
312 | well as what characters happen to be in the string at the time. If |
313 | any of the characters are at code points C<0x100> or above, you will get |
314 | a warning. To ensure that the output is explicitly rendered in the |
315 | encoding you desire--and to avoid the warning--open the stream with |
316 | the desired encoding. Some examples: |
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317 | |
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318 | open FH, ">:utf8", "file"; |
319 | |
320 | open FH, ">:encoding(ucs2)", "file"; |
321 | open FH, ">:encoding(UTF-8)", "file"; |
322 | open FH, ">:encoding(shift_jis)", "file"; |
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323 | |
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324 | and on already open streams, use C<binmode()>: |
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325 | |
326 | binmode(STDOUT, ":utf8"); |
327 | |
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328 | binmode(STDOUT, ":encoding(ucs2)"); |
329 | binmode(STDOUT, ":encoding(UTF-8)"); |
330 | binmode(STDOUT, ":encoding(shift_jis)"); |
331 | |
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332 | The matching of encoding names is loose: case does not matter, and |
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333 | many encodings have several aliases. Note that the C<:utf8> layer |
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334 | must always be specified exactly like that; it is I<not> subject to |
335 | the loose matching of encoding names. |
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336 | |
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337 | See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and |
338 | L<Encode::PerlIO> for the C<:encoding()> layer, and |
339 | L<Encode::Supported> for many encodings supported by the C<Encode> |
340 | module. |
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341 | |
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342 | Reading in a file that you know happens to be encoded in one of the |
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343 | Unicode or legacy encodings does not magically turn the data into |
344 | Unicode in Perl's eyes. To do that, specify the appropriate |
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345 | layer when opening files |
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346 | |
347 | open(my $fh,'<:utf8', 'anything'); |
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348 | my $line_of_unicode = <$fh>; |
349 | |
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350 | open(my $fh,'<:encoding(Big5)', 'anything'); |
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351 | my $line_of_unicode = <$fh>; |
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352 | |
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353 | The I/O layers can also be specified more flexibly with |
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354 | the C<open> pragma. See L<open>, or look at the following example. |
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355 | |
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356 | use open ':utf8'; # input and output default layer will be UTF-8 |
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357 | open X, ">file"; |
358 | print X chr(0x100), "\n"; |
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359 | close X; |
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360 | open Y, "<file"; |
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361 | printf "%#x\n", ord(<Y>); # this should print 0x100 |
362 | close Y; |
363 | |
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364 | With the C<open> pragma you can use the C<:locale> layer |
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365 | |
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366 | $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R'; |
367 | # the :locale will probe the locale environment variables like LC_ALL |
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368 | use open OUT => ':locale'; # russki parusski |
369 | open(O, ">koi8"); |
370 | print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 |
371 | close O; |
372 | open(I, "<koi8"); |
373 | printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1 |
374 | close I; |
375 | |
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376 | or you can also use the C<':encoding(...)'> layer |
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377 | |
378 | open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); |
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379 | my $line_of_unicode = <$epic>; |
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380 | |
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381 | These methods install a transparent filter on the I/O stream that |
382 | converts data from the specified encoding when it is read in from the |
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383 | stream. The result is always Unicode. |
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384 | |
385 | The L<open> pragma affects all the C<open()> calls after the pragma by |
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386 | setting default layers. If you want to affect only certain |
387 | streams, use explicit layers directly in the C<open()> call. |
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388 | |
389 | You can switch encodings on an already opened stream by using |
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390 | C<binmode()>; see L<perlfunc/binmode>. |
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391 | |
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392 | The C<:locale> does not currently (as of Perl 5.8.0) work with |
393 | C<open()> and C<binmode()>, only with the C<open> pragma. The |
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394 | C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>, |
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395 | C<binmode()>, and the C<open> pragma. |
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396 | |
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397 | Similarly, you may use these I/O layers on output streams to |
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398 | automatically convert Unicode to the specified encoding when it is |
399 | written to the stream. For example, the following snippet copies the |
400 | contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to |
401 | the file "text.utf8", encoded as UTF-8: |
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402 | |
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403 | open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis'); |
404 | open(my $unicode, '>:utf8', 'text.utf8'); |
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405 | while (<$nihongo>) { print $unicode $_ } |
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406 | |
407 | The naming of encodings, both by the C<open()> and by the C<open> |
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408 | pragma, is similar to the C<encoding> pragma in that it allows for |
409 | flexible names: C<koi8-r> and C<KOI8R> will both be understood. |
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410 | |
411 | Common encodings recognized by ISO, MIME, IANA, and various other |
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412 | standardisation organisations are recognised; for a more detailed |
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413 | list see L<Encode::Supported>. |
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414 | |
415 | C<read()> reads characters and returns the number of characters. |
416 | C<seek()> and C<tell()> operate on byte counts, as do C<sysread()> |
417 | and C<sysseek()>. |
418 | |
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419 | Notice that because of the default behaviour of not doing any |
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420 | conversion upon input if there is no default layer, |
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421 | it is easy to mistakenly write code that keeps on expanding a file |
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422 | by repeatedly encoding the data: |
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423 | |
424 | # BAD CODE WARNING |
425 | open F, "file"; |
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426 | local $/; ## read in the whole file of 8-bit characters |
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427 | $t = <F>; |
428 | close F; |
429 | open F, ">:utf8", "file"; |
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430 | print F $t; ## convert to UTF-8 on output |
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431 | close F; |
432 | |
433 | If you run this code twice, the contents of the F<file> will be twice |
1d7919c5 |
434 | UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or |
435 | explicitly opening also the F<file> for input as UTF-8. |
ba62762e |
436 | |
0c901d84 |
437 | B<NOTE>: the C<:utf8> and C<:encoding> features work only if your |
ec71e770 |
438 | Perl has been built with the new PerlIO feature. |
0c901d84 |
439 | |
1ecefa54 |
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 |
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 |
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", $_) : # \x.. |
58c274a1 |
454 | chr($_) # else as themselves |
455 | } unpack("U*", $_[0])); # unpack Unicode characters |
456 | } |
457 | |
458 | For example, |
459 | |
460 | nice_string("foo\x{100}bar\n") |
461 | |
8baee566 |
462 | returns: |
58c274a1 |
463 | |
8baee566 |
464 | "foo\x{0100}bar\x0A" |
1ecefa54 |
465 | |
ba62762e |
466 | =head2 Special Cases |
467 | |
468 | =over 4 |
469 | |
470 | =item * |
471 | |
472 | Bit Complement Operator ~ And vec() |
473 | |
1bfb14c4 |
474 | The bit complement operator C<~> may produce surprising results if |
475 | used on strings containing characters with ordinal values above |
476 | 255. In such a case, the results are consistent with the internal |
477 | encoding of the characters, but not with much else. So don't do |
478 | that. Similarly for C<vec()>: you will be operating on the |
479 | internally-encoded bit patterns of the Unicode characters, not on |
480 | the code point values, which is very probably not what you want. |
ba62762e |
481 | |
482 | =item * |
483 | |
8baee566 |
484 | Peeking At Perl's Internal Encoding |
485 | |
486 | Normal users of Perl should never care how Perl encodes any particular |
a5f0baef |
487 | Unicode string (because the normal ways to get at the contents of a |
376d9008 |
488 | string with Unicode--via input and output--should always be via |
fae2c0fb |
489 | explicitly-defined I/O layers). But if you must, there are two |
a5f0baef |
490 | ways of looking behind the scenes. |
ba62762e |
491 | |
492 | One way of peeking inside the internal encoding of Unicode characters |
376d9008 |
493 | is to use C<unpack("C*", ...> to get the bytes or C<unpack("H*", ...)> |
ba62762e |
494 | to display the bytes: |
495 | |
8baee566 |
496 | # this prints c4 80 for the UTF-8 bytes 0xc4 0x80 |
ba62762e |
497 | print join(" ", unpack("H*", pack("U", 0x100))), "\n"; |
498 | |
499 | Yet another way would be to use the Devel::Peek module: |
500 | |
501 | perl -MDevel::Peek -e 'Dump(chr(0x100))' |
502 | |
8baee566 |
503 | That shows the UTF8 flag in FLAGS and both the UTF-8 bytes |
376d9008 |
504 | and Unicode characters in C<PV>. See also later in this document |
ba62762e |
505 | the discussion about the C<is_utf8> function of the C<Encode> module. |
506 | |
507 | =back |
508 | |
509 | =head2 Advanced Topics |
510 | |
511 | =over 4 |
512 | |
513 | =item * |
514 | |
515 | String Equivalence |
516 | |
517 | The question of string equivalence turns somewhat complicated |
376d9008 |
518 | in Unicode: what do you mean by "equal"? |
ba62762e |
519 | |
07698885 |
520 | (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to |
521 | C<LATIN CAPITAL LETTER A>?) |
ba62762e |
522 | |
a5f0baef |
523 | The short answer is that by default Perl compares equivalence (C<eq>, |
524 | C<ne>) based only on code points of the characters. In the above |
376d9008 |
525 | case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any |
526 | CAPITAL LETTER As should be considered equal, or even As of any case. |
ba62762e |
527 | |
528 | The long answer is that you need to consider character normalization |
376d9008 |
529 | and casing issues: see L<Unicode::Normalize>, Unicode Technical |
ba62762e |
530 | Reports #15 and #21, I<Unicode Normalization Forms> and I<Case |
376d9008 |
531 | Mappings>, http://www.unicode.org/unicode/reports/tr15/ and |
532 | http://www.unicode.org/unicode/reports/tr21/ |
ba62762e |
533 | |
1bfb14c4 |
534 | As of Perl 5.8.0, the "Full" case-folding of I<Case |
535 | Mappings/SpecialCasing> is implemented. |
ba62762e |
536 | |
537 | =item * |
538 | |
539 | String Collation |
540 | |
376d9008 |
541 | People like to see their strings nicely sorted--or as Unicode |
ba62762e |
542 | parlance goes, collated. But again, what do you mean by collate? |
543 | |
07698885 |
544 | (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after |
545 | C<LATIN CAPITAL LETTER A WITH GRAVE>?) |
ba62762e |
546 | |
58c274a1 |
547 | The short answer is that by default, Perl compares strings (C<lt>, |
ba62762e |
548 | C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the |
1bfb14c4 |
549 | characters. In the above case, the answer is "after", since |
550 | C<0x00C1> > C<0x00C0>. |
ba62762e |
551 | |
552 | The long answer is that "it depends", and a good answer cannot be |
553 | given without knowing (at the very least) the language context. |
554 | See L<Unicode::Collate>, and I<Unicode Collation Algorithm> |
555 | http://www.unicode.org/unicode/reports/tr10/ |
556 | |
557 | =back |
558 | |
559 | =head2 Miscellaneous |
560 | |
561 | =over 4 |
562 | |
563 | =item * |
564 | |
3ff56b75 |
565 | Character Ranges and Classes |
ba62762e |
566 | |
567 | Character ranges in regular expression character classes (C</[a-z]/>) |
568 | and in the C<tr///> (also known as C<y///>) operator are not magically |
58c274a1 |
569 | Unicode-aware. What this means that C<[A-Za-z]> will not magically start |
376d9008 |
570 | to mean "all alphabetic letters"; not that it does mean that even for |
571 | 8-bit characters, you should be using C</[[:alpha:]]/> in that case. |
ba62762e |
572 | |
1bfb14c4 |
573 | For specifying character classes like that in regular expressions, |
574 | you can use the various Unicode properties--C<\pL>, or perhaps |
575 | C<\p{Alphabetic}>, in this particular case. You can use Unicode |
576 | code points as the end points of character ranges, but there is no |
577 | magic associated with specifying a certain range. For further |
578 | information--there are dozens of Unicode character classes--see |
579 | L<perlunicode>. |
ba62762e |
580 | |
581 | =item * |
582 | |
583 | String-To-Number Conversions |
584 | |
376d9008 |
585 | Unicode does define several other decimal--and numeric--characters |
586 | besides the familiar 0 to 9, such as the Arabic and Indic digits. |
ba62762e |
587 | Perl does not support string-to-number conversion for digits other |
58c274a1 |
588 | than ASCII 0 to 9 (and ASCII a to f for hexadecimal). |
ba62762e |
589 | |
590 | =back |
591 | |
592 | =head2 Questions With Answers |
593 | |
594 | =over 4 |
595 | |
818c4caa |
596 | =item * |
5cb3728c |
597 | |
598 | Will My Old Scripts Break? |
ba62762e |
599 | |
600 | Very probably not. Unless you are generating Unicode characters |
1bfb14c4 |
601 | somehow, old behaviour should be preserved. About the only behaviour |
602 | that has changed and which could start generating Unicode is the old |
603 | behaviour of C<chr()> where supplying an argument more than 255 |
604 | produced a character modulo 255. C<chr(300)>, for example, was equal |
605 | to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH |
606 | BREVE. |
ba62762e |
607 | |
818c4caa |
608 | =item * |
5cb3728c |
609 | |
610 | How Do I Make My Scripts Work With Unicode? |
ba62762e |
611 | |
612 | Very little work should be needed since nothing changes until you |
1bfb14c4 |
613 | generate Unicode data. The most important thing is getting input as |
614 | Unicode; for that, see the earlier I/O discussion. |
ba62762e |
615 | |
818c4caa |
616 | =item * |
5cb3728c |
617 | |
618 | How Do I Know Whether My String Is In Unicode? |
ba62762e |
619 | |
1bfb14c4 |
620 | You shouldn't care. No, you really shouldn't. No, really. If you |
621 | have to care--beyond the cases described above--it means that we |
ba62762e |
622 | didn't get the transparency of Unicode quite right. |
623 | |
624 | Okay, if you insist: |
625 | |
626 | use Encode 'is_utf8'; |
627 | print is_utf8($string) ? 1 : 0, "\n"; |
628 | |
629 | But note that this doesn't mean that any of the characters in the |
630 | string are necessary UTF-8 encoded, or that any of the characters have |
631 | code points greater than 0xFF (255) or even 0x80 (128), or that the |
632 | string has any characters at all. All the C<is_utf8()> does is to |
633 | return the value of the internal "utf8ness" flag attached to the |
376d9008 |
634 | C<$string>. If the flag is off, the bytes in the scalar are interpreted |
3c1c8017 |
635 | as a single byte encoding. If the flag is on, the bytes in the scalar |
376d9008 |
636 | are interpreted as the (multi-byte, variable-length) UTF-8 encoded code |
3c1c8017 |
637 | points of the characters. Bytes added to an UTF-8 encoded string are |
638 | automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars |
376d9008 |
639 | are merged (double-quoted interpolation, explicit concatenation, and |
3c1c8017 |
640 | printf/sprintf parameter substitution), the result will be UTF-8 encoded |
641 | as if copies of the byte strings were upgraded to UTF-8: for example, |
642 | |
643 | $a = "ab\x80c"; |
644 | $b = "\x{100}"; |
645 | print "$a = $b\n"; |
646 | |
1bfb14c4 |
647 | the output string will be UTF-8-encoded C<ab\x80c\x{100}\n>, but note |
376d9008 |
648 | that C<$a> will stay byte-encoded. |
ba62762e |
649 | |
650 | Sometimes you might really need to know the byte length of a string |
ce7675db |
651 | instead of the character length. For that use either the |
652 | C<Encode::encode_utf8()> function or the C<bytes> pragma and its only |
653 | defined function C<length()>: |
ba62762e |
654 | |
655 | my $unicode = chr(0x100); |
656 | print length($unicode), "\n"; # will print 1 |
ce7675db |
657 | require Encode; |
658 | print length(Encode::encode_utf8($unicode)), "\n"; # will print 2 |
ba62762e |
659 | use bytes; |
1bfb14c4 |
660 | print length($unicode), "\n"; # will also print 2 |
661 | # (the 0xC4 0x80 of the UTF-8) |
ba62762e |
662 | |
818c4caa |
663 | =item * |
5cb3728c |
664 | |
665 | How Do I Detect Data That's Not Valid In a Particular Encoding? |
ba62762e |
666 | |
8baee566 |
667 | Use the C<Encode> package to try converting it. |
668 | For example, |
ba62762e |
669 | |
670 | use Encode 'encode_utf8'; |
8baee566 |
671 | if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) { |
ba62762e |
672 | # valid |
673 | } else { |
674 | # invalid |
675 | } |
676 | |
8baee566 |
677 | For UTF-8 only, you can use: |
ba62762e |
678 | |
679 | use warnings; |
8baee566 |
680 | @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8); |
ba62762e |
681 | |
1bfb14c4 |
682 | If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack> |
683 | warning is produced. The "U0" means "expect strictly UTF-8 encoded |
684 | Unicode". Without that the C<unpack("U*", ...)> would accept also |
685 | data like C<chr(0xFF>), similarly to the C<pack> as we saw earlier. |
ba62762e |
686 | |
818c4caa |
687 | =item * |
5cb3728c |
688 | |
689 | How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa? |
ba62762e |
690 | |
8baee566 |
691 | This probably isn't as useful as you might think. |
692 | Normally, you shouldn't need to. |
ba62762e |
693 | |
1bfb14c4 |
694 | In one sense, what you are asking doesn't make much sense: encodings |
376d9008 |
695 | are for characters, and binary data are not "characters", so converting |
a5f0baef |
696 | "data" into some encoding isn't meaningful unless you know in what |
697 | character set and encoding the binary data is in, in which case it's |
376d9008 |
698 | not just binary data, now is it? |
8baee566 |
699 | |
1bfb14c4 |
700 | If you have a raw sequence of bytes that you know should be |
701 | interpreted via a particular encoding, you can use C<Encode>: |
ba62762e |
702 | |
703 | use Encode 'from_to'; |
704 | from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 |
705 | |
1bfb14c4 |
706 | The call to C<from_to()> changes the bytes in C<$data>, but nothing |
707 | material about the nature of the string has changed as far as Perl is |
708 | concerned. Both before and after the call, the string C<$data> |
709 | contains just a bunch of 8-bit bytes. As far as Perl is concerned, |
710 | the encoding of the string remains as "system-native 8-bit bytes". |
8baee566 |
711 | |
712 | You might relate this to a fictional 'Translate' module: |
713 | |
714 | use Translate; |
715 | my $phrase = "Yes"; |
716 | Translate::from_to($phrase, 'english', 'deutsch'); |
717 | ## phrase now contains "Ja" |
ba62762e |
718 | |
8baee566 |
719 | The contents of the string changes, but not the nature of the string. |
1bfb14c4 |
720 | Perl doesn't know any more after the call than before that the |
721 | contents of the string indicates the affirmative. |
ba62762e |
722 | |
376d9008 |
723 | Back to converting data. If you have (or want) data in your system's |
a5f0baef |
724 | native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use |
725 | pack/unpack to convert to/from Unicode. |
ba62762e |
726 | |
8baee566 |
727 | $native_string = pack("C*", unpack("U*", $Unicode_string)); |
728 | $Unicode_string = pack("U*", unpack("C*", $native_string)); |
ba62762e |
729 | |
730 | If you have a sequence of bytes you B<know> is valid UTF-8, |
731 | but Perl doesn't know it yet, you can make Perl a believer, too: |
732 | |
733 | use Encode 'decode_utf8'; |
8baee566 |
734 | $Unicode = decode_utf8($bytes); |
ba62762e |
735 | |
736 | You can convert well-formed UTF-8 to a sequence of bytes, but if |
737 | you just want to convert random binary data into UTF-8, you can't. |
1bfb14c4 |
738 | B<Any random collection of bytes isn't well-formed UTF-8>. You can |
ba62762e |
739 | use C<unpack("C*", $string)> for the former, and you can create |
8baee566 |
740 | well-formed Unicode data by C<pack("U*", 0xff, ...)>. |
ba62762e |
741 | |
818c4caa |
742 | =item * |
5cb3728c |
743 | |
744 | How Do I Display Unicode? How Do I Input Unicode? |
ba62762e |
745 | |
076d825e |
746 | See http://www.alanwood.net/unicode/ and |
ba62762e |
747 | http://www.cl.cam.ac.uk/~mgk25/unicode.html |
748 | |
818c4caa |
749 | =item * |
5cb3728c |
750 | |
751 | How Does Unicode Work With Traditional Locales? |
ba62762e |
752 | |
753 | In Perl, not very well. Avoid using locales through the C<locale> |
754 | pragma. Use only one or the other. |
755 | |
756 | =back |
757 | |
758 | =head2 Hexadecimal Notation |
759 | |
376d9008 |
760 | The Unicode standard prefers using hexadecimal notation because |
761 | that more clearly shows the division of Unicode into blocks of 256 characters. |
ba62762e |
762 | Hexadecimal is also simply shorter than decimal. You can use decimal |
763 | notation, too, but learning to use hexadecimal just makes life easier |
1bfb14c4 |
764 | with the Unicode standard. The C<U+HHHH> notation uses hexadecimal, |
076d825e |
765 | for example. |
ba62762e |
766 | |
767 | The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and> |
768 | a-f (or A-F, case doesn't matter). Each hexadecimal digit represents |
769 | four bits, or half a byte. C<print 0x..., "\n"> will show a |
770 | hexadecimal number in decimal, and C<printf "%x\n", $decimal> will |
771 | show a decimal number in hexadecimal. If you have just the |
376d9008 |
772 | "hex digits" of a hexadecimal number, you can use the C<hex()> function. |
ba62762e |
773 | |
774 | print 0x0009, "\n"; # 9 |
775 | print 0x000a, "\n"; # 10 |
776 | print 0x000f, "\n"; # 15 |
777 | print 0x0010, "\n"; # 16 |
778 | print 0x0011, "\n"; # 17 |
779 | print 0x0100, "\n"; # 256 |
780 | |
781 | print 0x0041, "\n"; # 65 |
782 | |
783 | printf "%x\n", 65; # 41 |
784 | printf "%#x\n", 65; # 0x41 |
785 | |
786 | print hex("41"), "\n"; # 65 |
787 | |
788 | =head2 Further Resources |
789 | |
790 | =over 4 |
791 | |
792 | =item * |
793 | |
794 | Unicode Consortium |
795 | |
796 | http://www.unicode.org/ |
797 | |
798 | =item * |
799 | |
800 | Unicode FAQ |
801 | |
802 | http://www.unicode.org/unicode/faq/ |
803 | |
804 | =item * |
805 | |
806 | Unicode Glossary |
807 | |
808 | http://www.unicode.org/glossary/ |
809 | |
810 | =item * |
811 | |
812 | Unicode Useful Resources |
813 | |
814 | http://www.unicode.org/unicode/onlinedat/resources.html |
815 | |
816 | =item * |
817 | |
818 | Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications |
819 | |
076d825e |
820 | http://www.alanwood.net/unicode/ |
ba62762e |
821 | |
822 | =item * |
823 | |
824 | UTF-8 and Unicode FAQ for Unix/Linux |
825 | |
826 | http://www.cl.cam.ac.uk/~mgk25/unicode.html |
827 | |
828 | =item * |
829 | |
830 | Legacy Character Sets |
831 | |
832 | http://www.czyborra.com/ |
833 | http://www.eki.ee/letter/ |
834 | |
835 | =item * |
836 | |
837 | The Unicode support files live within the Perl installation in the |
838 | directory |
839 | |
840 | $Config{installprivlib}/unicore |
841 | |
842 | in Perl 5.8.0 or newer, and |
843 | |
844 | $Config{installprivlib}/unicode |
845 | |
846 | in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to |
847 | avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) |
551b6b6f |
848 | The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in |
ba62762e |
849 | Perl 5.6.1.) You can find the C<$Config{installprivlib}> by |
850 | |
851 | perl "-V:installprivlib" |
852 | |
ba62762e |
853 | You can explore various information from the Unicode data files using |
854 | the C<Unicode::UCD> module. |
855 | |
856 | =back |
857 | |
f6edf83b |
858 | =head1 UNICODE IN OLDER PERLS |
859 | |
860 | If you cannot upgrade your Perl to 5.8.0 or later, you can still |
861 | do some Unicode processing by using the modules C<Unicode::String>, |
862 | C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN. |
863 | If you have the GNU recode installed, you can also use the |
376d9008 |
864 | Perl front-end C<Convert::Recode> for character conversions. |
f6edf83b |
865 | |
aaef10c5 |
866 | The following are fast conversions from ISO 8859-1 (Latin-1) bytes |
63de3cb2 |
867 | to UTF-8 bytes and back, the code works even with older Perl 5 versions. |
aaef10c5 |
868 | |
869 | # ISO 8859-1 to UTF-8 |
870 | s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg; |
871 | |
872 | # UTF-8 to ISO 8859-1 |
873 | s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg; |
874 | |
ba62762e |
875 | =head1 SEE ALSO |
876 | |
877 | L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>, |
878 | L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD> |
879 | |
376d9008 |
880 | =head1 ACKNOWLEDGMENTS |
ba62762e |
881 | |
882 | Thanks to the kind readers of the perl5-porters@perl.org, |
883 | perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org |
884 | mailing lists for their valuable feedback. |
885 | |
886 | =head1 AUTHOR, COPYRIGHT, AND LICENSE |
887 | |
be3c0a43 |
888 | Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi> |
ba62762e |
889 | |
890 | This document may be distributed under the same terms as Perl itself. |