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Rev Author # Line
1 perry 1 CHARSETS
2 !!!CHARSETS
3 NAME
4 DESCRIPTION
5 ASCII
6 ISO 8859
7 KOI8-R
8 JIS X 0208
9 KS X 1001
10 GB 2312
11 Big5
12 TIS 620
13 UNICODE
14 ISO 2022 AND ISO 4873
15 SEE ALSO
16 ----
17 !!NAME
18
19
20 charsets - programmer's view of character sets and internationalization
21 !!DESCRIPTION
22
23
24 Linux is an international operating system. Various of its
25 utilities and device drivers (including the console driver)
26 support multilingual character sets including Latin-alphabet
27 letters with diacritical marks, accents, ligatures, and
28 entire non-Latin alphabets including Greek, Cyrillic,
29 Arabic, and Hebrew.
30
31
32 This manual page presents a programmer's-eye view of
33 different character-set standards and how they fit together
34 on Linux. Standards discussed include ASCII, ISO 8859,
35 KOI8-R, Unicode, ISO 2022 and ISO 4873. The primary emphasis
36 is on character sets actually used as locale character sets,
37 not the myriad others that can be found in data from other
38 systems.
39
40
41 A complete list of charsets used in a officially supported
42 locale in glibc 2.2.3 is: ISO-8859-{1,2,3,5,6,7,8,9,13,15},
43 CP1251, UTF-8, EUC-{KR,JP,TW}, KOI8-{R,U}, GB2312, GB18030,
44 GBK, BIG5, BIG5-HKSCS and TIS-620 (in no particular order.)
45 (Romanian may be switching to ISO-8859-16.)
46 !!ASCII
47
48
49 ASCII (American Standard Code For Information Interchange)
50 is the original 7-bit character set, originally designed for
51 American English. It is currently described by the ECMA-6
52 standard.
53
54
55 Various ASCII variants replacing the dollar sign with other
56 currency symbols and replacing punctuation with non-English
57 alphabetic characters to cover German, French, Spanish and
58 others in 7 bits exist. All are deprecated; GNU libc doesn't
59 support locales whose character sets aren't true supersets
60 of ASCII. (These sets are also known as ISO-646, a close
61 relative of ASCII that permitted replacing these
62 characters.)
63
64
65 As Linux was written for hardware designed in the US, it
66 natively supports ASCII.
67 !!ISO 8859
68
69
70 ISO 8859 is a series of 15 8-bit character sets all of which
71 have US ASCII in their low (7-bit) half, invisible control
72 characters in positions 128 to 159, and 96 fixed-width
73 graphics in positions 160-255.
74
75
76 Of these, the most important is ISO 8859-1 (Latin-1). It is
77 natively supported in the Linux console driver, fairly well
78 supported in X11R6, and is the base character set of
79 HTML.
80
81
82 Console support for the other 8859 character sets is
83 available under Linux through user-mode utilities (such as
84 consolechars(8)) that modify keyboard bindings and
85 the EGA graphics table and employ the
86 __
87
88
89 Here are brief descriptions of each set:
90
91
92 8859-1 (Latin-1)
93
94
95 Latin-1 covers most Western European languages such as
96 Albanian, Catalan, Danish, Dutch, English, Faroese, Finnish,
97 French, German, Galician, Irish, Icelandic, Italian,
98 Norwegian, Portuguese, Spanish, and Swedish. The lack of the
99 ligatures Dutch ij, French oe and old-style ,,German``
100 quotation marks is considered tolerable.
101
102
103 8859-2 (Latin-2)
104
105
106 Latin-2 supports most Latin-written Slavic and Central
107 European languages: Croatian, Czech, German, Hungarian,
108 Polish, Rumanian, Slovak, and Slovene.
109
110
111 8859-3 (Latin-3)
112
113
114 Latin-3 is popular with authors of Esperanto, Galician, and
115 Maltese. (Turkish is now written with 8859-9
116 instead.)
117
118
119 8859-4 (Latin-4)
120
121
122 Latin-4 introduced letters for Estonian, Latvian, and
123 Lithuanian. It is essentially obsolete; see 8859-13
124 (Latin-7).
125
126
127 8859-5
128
129
130 Cyrillic letters supporting Bulgarian, Byelorussian,
131 Macedonian, Russian, Serbian and Ukrainian. Ukrainians read
132 the letter `ghe' with downstroke as `heh' and would need a
133 ghe with upstroke to write a correct ghe. See the discussion
134 of KOI8-R below.
135
136
137 8859-6
138
139
140 Supports Arabic. The 8859-6 glyph table is a fixed font of
141 separate letter forms, but a proper display engine should
142 combine these using the proper initial, medial, and final
143 forms.
144
145
146 8859-7
147
148
149 Supports Modern Greek.
150
151
152 8859-8
153
154
155 Supports modern Hebrew without niqud (punctuation signs).
156 Niqud and full-fledged Biblical Hebrew are outside the scope
157 of this character set; under Linux, UTF-8 is the preferred
158 encoding for these.
159
160
161 8859-9 (Latin-5)
162
163
164 This is a variant of Latin-1 that replaces Icelandic letters
165 with Turkish ones.
166
167
168 8859-10 (Latin-6)
169
170
171 Latin 6 adds the last Inuit (Greenlandic) and Sami (Lappish)
172 letters that were missing in Latin 4 to cover the entire
173 Nordic area. RFC 1345 listed a preliminary and different
174 `latin6'. Skolt Sami still needs a few more accents than
175 these.
176
177
178 8859-11
179
180
181 This only exists as a rejected draft standard. The draft
182 standard was identical to TIS-620, which is used under Linux
183 for Thai.
184
185
186 8859-12
187
188
189 This set does not exist. While Vietnamese has been suggested
190 for this space, it does not fit within the 96
191 (non-combining) characters ISO 8859 offers. UTF-8 is the
192 preferred character set for Vietnamese use under
193 Linux.
194
195
196 8859-13 (Latin-7)
197
198
199 Supports the Baltic Rim languages; in particular, it
200 includes Latvian characters not found in
201 Latin-4.
202
203
204 8859-14 (Latin-8)
205
206
207 This is the Celtic character set, covering Gaelic and
208 Welsh.
209
210
211 8859-15 (Latin-9)
212
213
214 This adds the Euro sign and French and Finnish letters that
215 were missing in Latin-1.
216
217
218 8859-16 (Latin-10)
219
220
221 This set covers many of the languages covered by 8859-2, and
222 supports Romanian more completely then that set
223 does.
224 !!KOI8-R
225
226
227 KOI8-R is a non-ISO character set popular in Russia. The
228 lower half is US ASCII; the upper is a Cyrillic character
229 set somewhat better designed than ISO 8859-5. KOI8-U is a
230 common character set, based off KOI8-R, that has better
231 support for Ukrainian. Neither of these sets are ISO-2022
232 compatible, unlike the ISO-8859 series.
233
234
235 Console support for KOI8-R is available under Linux through
236 user-mode utilities that modify keyboard bindings and the
237 EGA graphics table, and employ the
238 !!JIS X 0208
239
240
241 JIS X 0208 is a Japanese national standard character set.
242 Though there are some more Japanese national standard
243 character sets (like JIS X 0201, JIS X 0212, and JIS X
244 0213), this is the most important one. Characters are mapped
245 into a 94x94 two-byte matrix, whose each byte is in the
246 range 0x21-0x7e. Note that JIS X 0208 is a character set,
247 not an encoding. This means that JIS X 0208 itself is not
248 used for expressing text data. JIS X 0208 is used as a
249 component to construct encodings such as EUC-JP, Shift_JIS,
250 and ISO-2022-JP. EUC-JP is the most important encoding for
251 Linux and includes US ASCII and JIS X 0208. In EUC-JP, JIS X
252 0208 characters are expressed in two bytes, each of which is
253 the JIS X 0208 code plus 0x80.
254 !!KS X 1001
255
256
257 KS X 1001 is a Korean national standard character set. Just
258 as JIS X 0208, characters are mapped into a 94x94 two-byte
259 matrix. KS X 1001 is used like JIS X 0208, as a component to
260 construct encodings such as EUC-KR, Johab, and ISO-2022-KR.
261 EUC-KR is the most important encoding for Linux and includes
262 US ASCII and KS X 1001. KS C 5601 is an older name for KS X
263 1001.
264 !!GB 2312
265
266
267 GB 2312 is a mainland Chinese national standard character
268 set used to express simplified Chinese. Just like JIS X
269 0208, characters are mapped into a 94x94 two-byte matrix
270 used to construct EUC-CN. EUC-CN is the most important
271 encoding for Linux and includes US ASCII and GB 2312. Note
272 that EUC-CN is often called as GB, GB 2312, or
273 CN-GB.
274 !!Big5
275
276
277 Big5 is a popular character set in Taiwan to express
278 traditional Chinese. (Big5 is both a character set and an
279 encoding.) It is a superset of US ASCII. Non-ASCII
280 characters are expressed in two bytes. Bytes 0xa1-0xfe are
281 used as leading bytes for two-byte characters. Big5 and its
282 extension is widely used in Taiwan and Hong Kong. It is not
283 ISO 2022-compliant.
284 !!TIS 620
285
286
287 TIS 620 is a Thai national standard character set and a
288 superset of US ASCII. Like ISO 8859 series, Thai characters
289 are mapped into 0xa1-0xfe. TIS 620 is the only commonly used
290 character set under Linux besides UTF-8 to have combining
291 characters.
292 !!UNICODE
293
294
295 Unicode (ISO 10646) is a standard which aims to
296 unambiguously represent every character in every human
297 language. Unicode's structure permits 20.1 bits to encode
298 every character. Since most computers don't include 20.1-bit
299 integers, Unicode is usually encoded as 32-bit integers
300 internally and either a series of 16-bit integers (UTF-16)
301 (needing two 16-bit integers only when encoding certain rare
302 characters) or a series of 8-bit bytes (UTF-8). Information
303 on Unicode is available at
304
305
306 Linux represents Unicode using the 8-bit Unicode
307 Transformation Format (UTF-8). UTF-8 is a variable length
308 encoding of Unicode. It uses 1 byte to code 7 bits, 2 bytes
309 for 11 bits, 3 bytes for 16 bits, and 4 bytes for the
310 remainder.
311
312
313 Let 0,1,x stand for a zero, one, or arbitrary bit. A byte
314 0xxxxxxx stands for the Unicode 00000000 0xxxxxxx which
315 codes the same symbol as the ASCII 0xxxxxxx. Thus, ASCII
316 goes unchanged into UTF-8, and people using only ASCII do
317 not notice any change: not in code, and not in file
318 size.
319
320
321 A byte 110xxxxx is the start of a 2-byte code, and 110xxxxx
322 10yyyyyy is assembled into 00000000 0000000 00000xxx
323 xxyyyyyy. A byte 1110xxxx is the start of a 3-byte code, and
324 1110xxxx 10yyyyyy 10zzzzzz is assembled into 00000000
325 00000000 xxxxyyyy yyzzzzzz. Lastly, 110110xxx starts a
326 4-byte code, and 110110xxx 10xxyyyy 10zzzzzz 10aaaaaa
327 becomes 0000000 000xxxxx yyyyzzzz zzaaaaaa.
328
329
330 For most people who use ISO-8859 character sets, this means
331 that the characters outside of ASCII are now coded with two
332 bytes. This tends to expand ordinary text files by only one
333 or two percent. For Russian or Greek users, this expands
334 ordinary text files by 100%, since text in those languages
335 is mostly outside of ASCII. For Japanese users this means
336 that the 16-bit codes now in common use will take three
337 bytes. While there are algorithmic conversions from some
338 character sets (esp. ISO-8859-1) to Unicode, general
339 conversion requires carrying around conversion tables, which
340 can be quite large for 16-bit codes.
341
342
343 Note that UTF-8 is self-synchronizing: 10xxxxxx is a tail,
344 any other byte is the head of a code. Note that the only way
345 ASCII bytes occur in a UTF-8 stream, is as themselves. In
346 particular, there are no embedded NULs or '/'s that form
347 part of some larger code.
348
349
350 Since ASCII, and, in particular, NUL and '/', are unchanged,
351 the kernel does not notice that UTF-8 is being used. It does
352 not care at all what the bytes it is handling stand
353 for.
354
355
356 Rendering of Unicode data streams is typically handled
357 through `subfont' tables which map a subset of Unicode to
358 glyphs. Internally the kernel uses Unicode to describe the
359 subfont loaded in video RAM. This means that in UTF-8 mode
360 one can use a character set with 512 different symbols. This
361 is not enough for Japanese, Chinese and Korean, but it is
362 enough for most other purposes.
363
364
365 At the current time, the console driver does not handle
366 combining characters. So Thai, Sioux and any other script
367 needing combining characters can't be handled on the
368 console.
369 !!ISO 2022 AND ISO 4873
370
371
372 The ISO 2022 and 4873 standards describe a font-control
373 model based on VT100 practice. This model is (partially)
374 supported by the Linux kernel and by xterm(1). It is
375 popular in Japan and Korea.
376
377
378 There are 4 graphic character sets, called G0, G1, G2 and
379 G3, and one of them is the current character set for codes
380 with high bit zero (initially G0), and one of them is the
381 current character set for codes with high bit one (initially
382 G1). Each graphic character set has 94 or 96 characters, and
383 is essentially a 7-bit character set. It uses codes either
384 040-0177 (041-0176) or 0240-0377 (0241-0376). G0 always has
385 size 94 and uses codes 041-0176.
386
387
388 Switching between character sets is done using the shift
389 functions ^N (SO or LS1), ^O (SI or LS0), ESC n (LS2), ESC o
390 (LS3), ESC N (SS2), ESC O (SS3), ESC ~ (LS1R), ESC } (LS2R),
391 ESC | (LS3R). The function LS''n'' makes character set
392 G''n'' the current one for codes with high bit zero. The
393 function LS''n''R makes character set G''n'' the
394 current one for codes with high bit one. The function
395 SS''n'' makes character set G''n'' (''n''=2 or 3)
396 the current one for the next character only (regardless of
397 the value of its high order bit).
398
399
400 A 94-character set is designated as G''n'' character set
401 by an escape sequence ESC ( xx (for G0), ESC ) xx (for G1),
402 ESC * xx (for G2), ESC + xx (for G3), where xx is a symbol
403 or a pair of symbols found in the ISO 2375 International
404 Register of Coded Character Sets. For example, ESC ( @
405 selects the ISO 646 character set as G0, ESC ( A selects the
406 UK standard character set (with pound instead of number
407 sign), ESC ( B selects ASCII (with dollar instead of
408 currency sign), ESC ( M selects a character set for African
409 languages, ESC ( ! A selects the Cuban character set, etc.
410 etc.
411
412
413 A 96-character set is designated as G''n'' character set
414 by an escape sequence ESC - xx (for G1), ESC . xx (for G2)
415 or ESC / xx (for G3). For example, ESC - G selects the
416 Hebrew alphabet as G1.
417
418
419 A multibyte character set is designated as G''n''
420 character set by an escape sequence ESC $ xx or ESC $ ( xx
421 (for G0), ESC $ ) xx (for G1), ESC $ * xx (for G2), ESC $ +
422 xx (for G3). For example, ESC $ ( C selects the Korean
423 character set for G0. The Japanese character set selected by
424 ESC $ B has a more recent version selected by ESC
425 ''
426
427
428 ISO 4873 stipulates a narrower use of character sets, where
429 G0 is fixed (always ASCII), so that G1, G2 and G3 can only
430 be invoked for codes with the high order bit set. In
431 particular, ^N and ^O are not used anymore, ESC ( xx can be
432 used only with xx=B, and ESC ) xx, ESC * xx, ESC + xx are
433 equivalent to ESC - xx, ESC . xx, ESC / xx,
434 respectively.
435 !!SEE ALSO
436
437
4 perry 438 console(4), console_ioctl(4),
439 console_codes(4), ascii(7),
440 iso_8859_1(7), unicode(7),
441 utf-8(7)
1 perry 442 ----
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