1CHARSETS(7) Linux Programmer's Manual CHARSETS(7)
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6 charsets - programmer's view of character sets and internationalization
7
9 Linux is an international operating system. Various of its utilities
10 and device drivers (including the console driver) support multilingual
11 character sets including Latin-alphabet letters with diacritical marks,
12 accents, ligatures, and entire non-Latin alphabets including Greek,
13 Cyrillic, Arabic, and Hebrew.
14 This manual page presents a programmer's-eye view of different charac‐
16 ter-set standards and how they fit together on Linux. Standards dis‐
17 cussed include ASCII, ISO 8859, KOI8-R, Unicode, ISO 2022 and ISO 4873.
18 The primary emphasis is on character sets actually used as locale char‐
19 acter sets, not the myriad others that can be found in data from other
20 systems.
21 A complete list of charsets used in an officially supported locale in
23 glibc 2.2.3 is: ISO-8859-{1,2,3,5,6,7,8,9,13,15}, CP1251, UTF-8,
24 EUC-{KR,JP,TW}, KOI8-{R,U}, GB2312, GB18030, GBK, BIG5, BIG5-HKSCS and
25 TIS-620 (in no particular order.) (Romanian may be switching to
26 ISO-8859-16.)
27 ASCII
29 ASCII (American Standard Code For Information Interchange) is the orig‐
30 inal 7-bit character set, originally designed for American English. It
31 is currently described by the ECMA-6 standard.
32 Various ASCII variants replacing the dollar sign with other currency
34 symbols and replacing punctuation with non-English alphabetic charac‐
35 ters to cover German, French, Spanish and others in 7 bits exist. All
36 are deprecated; glibc doesn't support locales whose character sets
37 aren't true supersets of ASCII. (These sets are also known as ISO-646,
38 a close relative of ASCII that permitted replacing these characters.)
39 As Linux was written for hardware designed in the US, it natively sup‐
41 ports ASCII.
42 ISO 8859
44 ISO 8859 is a series of 15 8-bit character sets all of which have US
45 ASCII in their low (7-bit) half, invisible control characters in posi‐
46 tions 128 to 159, and 96 fixed-width graphics in positions 160-255.
47 Of these, the most important is ISO 8859-1 (Latin-1). It is natively
49 supported in the Linux console driver, fairly well supported in X11R6,
50 and is the base character set of HTML.
51 Console support for the other 8859 character sets is available under
53 Linux through user-mode utilities (such as setfont(8)) that modify key‐
54 board bindings and the EGA graphics table and employ the "user mapping"
55 font table in the console driver.
56 Here are brief descriptions of each set:
58 8859-1 (Latin-1)
60 Latin-1 covers most Western European languages such as Albanian,
61 Catalan, Danish, Dutch, English, Faroese, Finnish, French, Ger‐
62 man, Galician, Irish, Icelandic, Italian, Norwegian, Portuguese,
63 Spanish, and Swedish. The lack of the ligatures Dutch ij,
64 French oe and old-style ,,German`` quotation marks is considered
65 tolerable.
66 8859-2 (Latin-2)
68 Latin-2 supports most Latin-written Slavic and Central European
69 languages: Croatian, Czech, German, Hungarian, Polish, Rumanian,
70 Slovak, and Slovene.
71 8859-3 (Latin-3)
73 Latin-3 is popular with authors of Esperanto, Galician, and Mal‐
74 tese. (Turkish is now written with 8859-9 instead.)
75 8859-4 (Latin-4)
77 Latin-4 introduced letters for Estonian, Latvian, and Lithua‐
78 nian. It is essentially obsolete; see 8859-10 (Latin-6) and
79 8859-13 (Latin-7).
80 8859-5 Cyrillic letters supporting Bulgarian, Byelorussian, Macedonian,
82 Russian, Serbian and Ukrainian. Ukrainians read the letter
83 "ghe" with downstroke as "heh" and would need a ghe with
84 upstroke to write a correct ghe. See the discussion of KOI8-R
85 below.
86 8859-6 Supports Arabic. The 8859-6 glyph table is a fixed font of sep‐
88 arate letter forms, but a proper display engine should combine
89 these using the proper initial, medial, and final forms.
90 8859-7 Supports Modern Greek.
92 8859-8 Supports modern Hebrew without niqud (punctuation signs). Niqud
94 and full-fledged Biblical Hebrew are outside the scope of this
95 character set; under Linux, UTF-8 is the preferred encoding for
96 these.
97 8859-9 (Latin-5)
99 This is a variant of Latin-1 that replaces Icelandic letters
100 with Turkish ones.
101 8859-10 (Latin-6)
103 Latin 6 adds the last Inuit (Greenlandic) and Sami (Lappish)
104 letters that were missing in Latin 4 to cover the entire Nordic
105 area. RFC 1345 listed a preliminary and different "latin6".
106 Skolt Sami still needs a few more accents than these.
107 8859-11
109 This only exists as a rejected draft standard. The draft stan‐
110 dard was identical to TIS-620, which is used under Linux for
111 Thai.
112 8859-12
114 This set does not exist. While Vietnamese has been suggested
115 for this space, it does not fit within the 96 (noncombining)
116 characters ISO 8859 offers. UTF-8 is the preferred character
117 set for Vietnamese use under Linux.
118 8859-13 (Latin-7)
120 Supports the Baltic Rim languages; in particular, it includes
121 Latvian characters not found in Latin-4.
122 8859-14 (Latin-8)
124 This is the Celtic character set, covering Gaelic and Welsh.
125 This charset also contains the dotted characters needed for Old
126 Irish.
127 8859-15 (Latin-9)
129 This adds the Euro sign and French and Finnish letters that were
130 missing in Latin-1.
131 8859-16 (Latin-10)
133 This set covers many of the languages covered by 8859-2, and
134 supports Romanian more completely then that set does.
135 KOI8-R
137 KOI8-R is a non-ISO character set popular in Russia. The lower half is
138 US ASCII; the upper is a Cyrillic character set somewhat better
139 designed than ISO 8859-5. KOI8-U is a common character set, based off
140 KOI8-R, that has better support for Ukrainian. Neither of these sets
141 are ISO-2022 compatible, unlike the ISO-8859 series.
142 Console support for KOI8-R is available under Linux through user-mode
144 utilities that modify keyboard bindings and the EGA graphics table, and
145 employ the "user mapping" font table in the console driver.
146 JIS X 0208
148 JIS X 0208 is a Japanese national standard character set. Though there
149 are some more Japanese national standard character sets (like JIS X
150 0201, JIS X 0212, and JIS X 0213), this is the most important one.
151 Characters are mapped into a 94x94 two-byte matrix, whose each byte is
152 in the range 0x21-0x7e. Note that JIS X 0208 is a character set, not
153 an encoding. This means that JIS X 0208 itself is not used for
154 expressing text data. JIS X 0208 is used as a component to construct
155 encodings such as EUC-JP, Shift_JIS, and ISO-2022-JP. EUC-JP is the
156 most important encoding for Linux and includes US ASCII and JIS X 0208.
157 In EUC-JP, JIS X 0208 characters are expressed in two bytes, each of
158 which is the JIS X 0208 code plus 0x80.
159 KS X 1001
161 KS X 1001 is a Korean national standard character set. Just as JIS X
162 0208, characters are mapped into a 94x94 two-byte matrix. KS X 1001 is
163 used like JIS X 0208, as a component to construct encodings such as
164 EUC-KR, Johab, and ISO-2022-KR. EUC-KR is the most important encoding
165 for Linux and includes US ASCII and KS X 1001. KS C 5601 is an older
166 name for KS X 1001.
167 GB 2312
169 GB 2312 is a mainland Chinese national standard character set used to
170 express simplified Chinese. Just like JIS X 0208, characters are
171 mapped into a 94x94 two-byte matrix used to construct EUC-CN. EUC-CN
172 is the most important encoding for Linux and includes US ASCII and GB
173 2312. Note that EUC-CN is often called as GB, GB 2312, or CN-GB.
174 Big5
176 Big5 is a popular character set in Taiwan to express traditional Chi‐
177 nese. (Big5 is both a character set and an encoding.) It is a super‐
178 set of US ASCII. Non-ASCII characters are expressed in two bytes.
179 Bytes 0xa1-0xfe are used as leading bytes for two-byte characters.
180 Big5 and its extension is widely used in Taiwan and Hong Kong. It is
181 not ISO 2022-compliant.
182 TIS 620
184 TIS 620 is a Thai national standard character set and a superset of US
185 ASCII. Like ISO 8859 series, Thai characters are mapped into
186 0xa1-0xfe. TIS 620 is the only commonly used character set under Linux
187 besides UTF-8 to have combining characters.
188 UNICODE
190 Unicode (ISO 10646) is a standard which aims to unambiguously represent
191 every character in every human language. Unicode's structure permits
192 20.1 bits to encode every character. Since most computers don't
193 include 20.1-bit integers, Unicode is usually encoded as 32-bit inte‐
194 gers internally and either a series of 16-bit integers (UTF-16) (need‐
195 ing two 16-bit integers only when encoding certain rare characters) or
196 a series of 8-bit bytes (UTF-8). Information on Unicode is available
197 at <http://www.unicode.org>.
198 Linux represents Unicode using the 8-bit Unicode Transformation Format
200 (UTF-8). UTF-8 is a variable length encoding of Unicode. It uses 1
201 byte to code 7 bits, 2 bytes for 11 bits, 3 bytes for 16 bits, 4 bytes
202 for 21 bits, 5 bytes for 26 bits, 6 bytes for 31 bits.
203 Let 0,1,x stand for a zero, one, or arbitrary bit. A byte 0xxxxxxx
205 stands for the Unicode 00000000 0xxxxxxx which codes the same symbol as
206 the ASCII 0xxxxxxx. Thus, ASCII goes unchanged into UTF-8, and people
207 using only ASCII do not notice any change: not in code, and not in file
208 size.
209 A byte 110xxxxx is the start of a 2-byte code, and 110xxxxx 10yyyyyy is
211 assembled into 00000xxx xxyyyyyy. A byte 1110xxxx is the start of a
212 3-byte code, and 1110xxxx 10yyyyyy 10zzzzzz is assembled into xxxxyyyy
213 yyzzzzzz. (When UTF-8 is used to code the 31-bit ISO 10646 then this
214 progression continues up to 6-byte codes.)
215 For most people who use ISO-8859 character sets, this means that the
217 characters outside of ASCII are now coded with two bytes. This tends
218 to expand ordinary text files by only one or two percent. For Russian
219 or Greek users, this expands ordinary text files by 100%, since text in
220 those languages is mostly outside of ASCII. For Japanese users this
221 means that the 16-bit codes now in common use will take three bytes.
222 While there are algorithmic conversions from some character sets (esp.
223 ISO-8859-1) to Unicode, general conversion requires carrying around
224 conversion tables, which can be quite large for 16-bit codes.
225 Note that UTF-8 is self-synchronizing: 10xxxxxx is a tail, any other
227 byte is the head of a code. Note that the only way ASCII bytes occur
228 in a UTF-8 stream, is as themselves. In particular, there are no
229 embedded NULs ('\0') or '/'s that form part of some larger code.
230 Since ASCII, and, in particular, NUL and '/', are unchanged, the kernel
232 does not notice that UTF-8 is being used. It does not care at all what
233 the bytes it is handling stand for.
234 Rendering of Unicode data streams is typically handled through "sub‐
236 font" tables which map a subset of Unicode to glyphs. Internally the
237 kernel uses Unicode to describe the subfont loaded in video RAM. This
238 means that in UTF-8 mode one can use a character set with 512 different
239 symbols. This is not enough for Japanese, Chinese and Korean, but it
240 is enough for most other purposes.
241 At the current time, the console driver does not handle combining char‐
243 acters. So Thai, Sioux and any other script needing combining charac‐
244 ters can't be handled on the console.
245 ISO 2022 and ISO 4873
247 The ISO 2022 and 4873 standards describe a font-control model based on
248 VT100 practice. This model is (partially) supported by the Linux ker‐
249 nel and by xterm(1). It is popular in Japan and Korea.
250 There are 4 graphic character sets, called G0, G1, G2 and G3, and one
252 of them is the current character set for codes with high bit zero (ini‐
253 tially G0), and one of them is the current character set for codes with
254 high bit one (initially G1). Each graphic character set has 94 or 96
255 characters, and is essentially a 7-bit character set. It uses codes
256 either 040-0177 (041-0176) or 0240-0377 (0241-0376). G0 always has
257 size 94 and uses codes 041-0176.
258 Switching between character sets is done using the shift functions ^N
260 (SO or LS1), ^O (SI or LS0), ESC n (LS2), ESC o (LS3), ESC N (SS2), ESC
261 O (SS3), ESC ~ (LS1R), ESC } (LS2R), ESC | (LS3R). The function LSn
262 makes character set Gn the current one for codes with high bit zero.
263 The function LSnR makes character set Gn the current one for codes with
264 high bit one. The function SSn makes character set Gn (n=2 or 3) the
265 current one for the next character only (regardless of the value of its
266 high order bit).
267 A 94-character set is designated as Gn character set by an escape
269 sequence ESC ( xx (for G0), ESC ) xx (for G1), ESC * xx (for G2), ESC +
270 xx (for G3), where xx is a symbol or a pair of symbols found in the ISO
271 2375 International Register of Coded Character Sets. For example, ESC
272 ( @ selects the ISO 646 character set as G0, ESC ( A selects the UK
273 standard character set (with pound instead of number sign), ESC ( B
274 selects ASCII (with dollar instead of currency sign), ESC ( M selects a
275 character set for African languages, ESC ( ! A selects the Cuban char‐
276 acter set, etc. etc.
277 A 96-character set is designated as Gn character set by an escape
279 sequence ESC - xx (for G1), ESC . xx (for G2) or ESC / xx (for G3).
280 For example, ESC - G selects the Hebrew alphabet as G1.
281 A multibyte character set is designated as Gn character set by an
283 escape sequence ESC $ xx or ESC $ ( xx (for G0), ESC $ ) xx (for G1),
284 ESC $ * xx (for G2), ESC $ + xx (for G3). For example, ESC $ ( C
285 selects the Korean character set for G0. The Japanese character set
286 selected by ESC $ B has a more recent version selected by ESC & @ ESC $
287 B.
288 ISO 4873 stipulates a narrower use of character sets, where G0 is fixed
290 (always ASCII), so that G1, G2 and G3 can only be invoked for codes
291 with the high order bit set. In particular, ^N and ^O are not used
292 anymore, ESC ( xx can be used only with xx=B, and ESC ) xx, ESC * xx,
293 ESC + xx are equivalent to ESC - xx, ESC . xx, ESC / xx, respectively.
294
296 console(4), console_codes(4), console_ioctl(4), ascii(7),
297 iso_8859-1(7), unicode(7), utf-8(7)
298
300 This page is part of release 3.25 of the Linux man-pages project. A
301 description of the project, and information about reporting bugs, can
302 be found at http://www.kernel.org/doc/man-pages/.
303Linux 2008-06-03 CHARSETS(7)