1CHARSETS(7) Linux Programmer's Manual CHARSETS(7)
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6 charsets - character set standards and internationalization
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9 This manual page gives an overview on different character set standards
10 and how they were used on Linux before Unicode became ubiquitous. Some
11 of this information is still helpful for people working with legacy
12 systems and documents.
13 Standards discussed include such as ASCII, GB 2312, ISO 8859, JIS,
15 KOI8-R, KS, and Unicode.
16 The primary emphasis is on character sets that were actually used by
18 locale character sets, not the myriad others that could be found in
19 data from other systems.
20 The recommended encoding in all settings and locales is UTF-8.
22 ASCII
24 ASCII (American Standard Code For Information Interchange) is the orig‐
25 inal 7-bit character set, originally designed for American English.
26 Also known as US-ASCII. It is currently described by the ISO 646:1991
27 IRV (International Reference Version) standard.
28 Various ASCII variants replacing the dollar sign with other currency
30 symbols and replacing punctuation with non-English alphabetic charac‐
31 ters to cover German, French, Spanish, and others in 7 bits emerged.
32 All are deprecated; glibc does not support locales whose character sets
33 are not true supersets of ASCII.
34 As Unicode, when using UTF-8, is ASCII-compatible, plain ASCII text
36 still renders properly on modern UTF-8 using systems.
37 ISO 8859
39 ISO 8859 is a series of 15 8-bit character sets, all of which have
40 ASCII in their low (7-bit) half, invisible control characters in posi‐
41 tions 128 to 159, and 96 fixed-width graphics in positions 160–255.
42 Of these, the most important is ISO 8859-1 ("Latin Alphabet No .1" /
44 Latin-1). It was widely adopted and supported by different systems,
45 and is gradually being replaced with Unicode. The ISO 8859-1 charac‐
46 ters are also the first 256 characters of Unicode.
47 Console support for the other 8859 character sets is available under
49 Linux through user-mode utilities (such as setfont(8)) that modify key‐
50 board bindings and the EGA graphics table and employ the "user mapping"
51 font table in the console driver.
52 Here are brief descriptions of each set:
54 8859-1 (Latin-1)
56 Latin-1 covers many West European languages such as Albanian,
57 Basque, Danish, English, Faroese, Galician, Icelandic, Irish,
58 Italian, Norwegian, Portuguese, Spanish, and Swedish. The lack
59 of the ligatures Dutch IJ/ij, French œ, and old-style „German“
60 quotation marks was considered tolerable.
61 8859-2 (Latin-2)
63 Latin-2 supports many Latin-written Central and East European
64 languages such as Bosnian, Croatian, Czech, German, Hungarian,
65 Polish, Slovak, and Slovene. Replacing Romanian ș/ț with ş/ţ
66 was considered tolerable.
67 8859-3 (Latin-3)
69 Latin-3 was designed to cover of Esperanto, Maltese, and Turk‐
70 ish, but 8859-9 later superseded it for Turkish.
71 8859-4 (Latin-4)
73 Latin-4 introduced letters for North European languages such as
74 Estonian, Latvian, and Lithuanian, but was superseded by 8859-10
75 and 8859-13.
76 8859-5 Cyrillic letters supporting Bulgarian, Byelorussian, Macedonian,
78 Russian, Serbian, and (almost completely) Ukrainian. It was
79 never widely used, see the discussion of KOI8-R/KOI8-U below.
80 8859-6 Was created for Arabic. The 8859-6 glyph table is a fixed font
82 of separate letter forms, but a proper display engine should
83 combine these using the proper initial, medial, and final forms.
84 8859-7 Was created for Modern Greek in 1987, updated in 2003.
86 8859-8 Supports Modern Hebrew without niqud (punctuation signs). Niqud
88 and full-fledged Biblical Hebrew were outside the scope of this
89 character set.
90 8859-9 (Latin-5)
92 This is a variant of Latin-1 that replaces Icelandic letters
93 with Turkish ones.
94 8859-10 (Latin-6)
96 Latin-6 added the Inuit (Greenlandic) and Sami (Lappish) letters
97 that were missing in Latin-4 to cover the entire Nordic area.
98 8859-11
100 Supports the Thai alphabet and is nearly identical to the
101 TIS-620 standard.
102 8859-12
104 This set does not exist.
105 8859-13 (Latin-7)
107 Supports the Baltic Rim languages; in particular, it includes
108 Latvian characters not found in Latin-4.
109 8859-14 (Latin-8)
111 This is the Celtic character set, covering Old Irish, Manx,
112 Gaelic, Welsh, Cornish, and Breton.
113 8859-15 (Latin-9)
115 Latin-9 is similar to the widely used Latin-1 but replaces some
116 less common symbols with the Euro sign and French and Finnish
117 letters that were missing in Latin-1.
118 8859-16 (Latin-10)
120 This set covers many Southeast European languages, and most
121 importantly supports Romanian more completely than Latin-2.
122 KOI8-R / KOI8-U
124 KOI8-R is a non-ISO character set popular in Russia before Unicode.
125 The lower half is ASCII; the upper is a Cyrillic character set somewhat
126 better designed than ISO 8859-5. KOI8-U, based on KOI8-R, has better
127 support for Ukrainian. Neither of these sets are ISO-2022 compatible,
128 unlike the ISO 8859 series.
129 Console support for KOI8-R is available under Linux through user-mode
131 utilities that modify keyboard bindings and the EGA graphics table, and
132 employ the "user mapping" font table in the console driver.
133 GB 2312
135 GB 2312 is a mainland Chinese national standard character set used to
136 express simplified Chinese. Just like JIS X 0208, characters are
137 mapped into a 94x94 two-byte matrix used to construct EUC-CN. EUC-CN
138 is the most important encoding for Linux and includes ASCII and GB
139 2312. Note that EUC-CN is often called as GB, GB 2312, or CN-GB.
140 Big5
142 Big5 was a popular character set in Taiwan to express traditional Chi‐
143 nese. (Big5 is both a character set and an encoding.) It is a super‐
144 set of ASCII. Non-ASCII characters are expressed in two bytes. Bytes
145 0xa1–0xfe are used as leading bytes for two-byte characters. Big5 and
146 its extension were widely used in Taiwan and Hong Kong. It is not ISO
147 2022 compliant.
148 JIS X 0208
150 JIS X 0208 is a Japanese national standard character set. Though there
151 are some more Japanese national standard character sets (like JIS X
152 0201, JIS X 0212, and JIS X 0213), this is the most important one.
153 Characters are mapped into a 94x94 two-byte matrix, whose each byte is
154 in the range 0x21–0x7e. Note that JIS X 0208 is a character set, not
155 an encoding. This means that JIS X 0208 itself is not used for
156 expressing text data. JIS X 0208 is used as a component to construct
157 encodings such as EUC-JP, Shift_JIS, and ISO-2022-JP. EUC-JP is the
158 most important encoding for Linux and includes ASCII and JIS X 0208.
159 In EUC-JP, JIS X 0208 characters are expressed in two bytes, each of
160 which is the JIS X 0208 code plus 0x80.
161 KS X 1001
163 KS X 1001 is a Korean national standard character set. Just as JIS X
164 0208, characters are mapped into a 94x94 two-byte matrix. KS X 1001 is
165 used like JIS X 0208, as a component to construct encodings such as
166 EUC-KR, Johab, and ISO-2022-KR. EUC-KR is the most important encoding
167 for Linux and includes ASCII and KS X 1001. KS C 5601 is an older name
168 for KS X 1001.
169 ISO 2022 and ISO 4873
171 The ISO 2022 and 4873 standards describe a font-control model based on
172 VT100 practice. This model is (partially) supported by the Linux ker‐
173 nel and by xterm(1). Several ISO 2022-based character encodings have
174 been defined, especially for Japanese.
175 There are 4 graphic character sets, called G0, G1, G2, and G3, and one
177 of them is the current character set for codes with high bit zero (ini‐
178 tially G0), and one of them is the current character set for codes with
179 high bit one (initially G1). Each graphic character set has 94 or 96
180 characters, and is essentially a 7-bit character set. It uses codes
181 either 040–0177 (041–0176) or 0240–0377 (0241–0376). G0 always has
182 size 94 and uses codes 041–0176.
183 Switching between character sets is done using the shift functions ^N
185 (SO or LS1), ^O (SI or LS0), ESC n (LS2), ESC o (LS3), ESC N (SS2), ESC
186 O (SS3), ESC ~ (LS1R), ESC } (LS2R), ESC | (LS3R). The function LSn
187 makes character set Gn the current one for codes with high bit zero.
188 The function LSnR makes character set Gn the current one for codes with
189 high bit one. The function SSn makes character set Gn (n=2 or 3) the
190 current one for the next character only (regardless of the value of its
191 high order bit).
192 A 94-character set is designated as Gn character set by an escape
194 sequence ESC ( xx (for G0), ESC ) xx (for G1), ESC * xx (for G2), ESC +
195 xx (for G3), where xx is a symbol or a pair of symbols found in the ISO
196 2375 International Register of Coded Character Sets. For example, ESC
197 ( @ selects the ISO 646 character set as G0, ESC ( A selects the UK
198 standard character set (with pound instead of number sign), ESC ( B
199 selects ASCII (with dollar instead of currency sign), ESC ( M selects a
200 character set for African languages, ESC ( ! A selects the Cuban char‐
201 acter set, and so on.
202 A 96-character set is designated as Gn character set by an escape
204 sequence ESC - xx (for G1), ESC . xx (for G2) or ESC / xx (for G3).
205 For example, ESC - G selects the Hebrew alphabet as G1.
206 A multibyte character set is designated as Gn character set by an
208 escape sequence ESC $ xx or ESC $ ( xx (for G0), ESC $ ) xx (for G1),
209 ESC $ * xx (for G2), ESC $ + xx (for G3). For example, ESC $ ( C
210 selects the Korean character set for G0. The Japanese character set
211 selected by ESC $ B has a more recent version selected by ESC & @ ESC $
212 B.
213 ISO 4873 stipulates a narrower use of character sets, where G0 is fixed
215 (always ASCII), so that G1, G2 and G3 can be invoked only for codes
216 with the high order bit set. In particular, ^N and ^O are not used
217 anymore, ESC ( xx can be used only with xx=B, and ESC ) xx, ESC * xx,
218 ESC + xx are equivalent to ESC - xx, ESC . xx, ESC / xx, respectively.
219 TIS-620
221 TIS-620 is a Thai national standard character set and a superset of
222 ASCII. In the same fashion as the ISO 8859 series, Thai characters are
223 mapped into 0xa1–0xfe.
224 Unicode
226 Unicode (ISO 10646) is a standard which aims to unambiguously represent
227 every character in every human language. Unicode's structure permits
228 20.1 bits to encode every character. Since most computers don't
229 include 20.1-bit integers, Unicode is usually encoded as 32-bit inte‐
230 gers internally and either a series of 16-bit integers (UTF-16) (need‐
231 ing two 16-bit integers only when encoding certain rare characters) or
232 a series of 8-bit bytes (UTF-8).
233 Linux represents Unicode using the 8-bit Unicode Transformation Format
235 (UTF-8). UTF-8 is a variable length encoding of Unicode. It uses 1
236 byte to code 7 bits, 2 bytes for 11 bits, 3 bytes for 16 bits, 4 bytes
237 for 21 bits, 5 bytes for 26 bits, 6 bytes for 31 bits.
238 Let 0,1,x stand for a zero, one, or arbitrary bit. A byte 0xxxxxxx
240 stands for the Unicode 00000000 0xxxxxxx which codes the same symbol as
241 the ASCII 0xxxxxxx. Thus, ASCII goes unchanged into UTF-8, and people
242 using only ASCII do not notice any change: not in code, and not in file
243 size.
244 A byte 110xxxxx is the start of a 2-byte code, and 110xxxxx 10yyyyyy is
246 assembled into 00000xxx xxyyyyyy. A byte 1110xxxx is the start of a
247 3-byte code, and 1110xxxx 10yyyyyy 10zzzzzz is assembled into xxxxyyyy
248 yyzzzzzz. (When UTF-8 is used to code the 31-bit ISO 10646 then this
249 progression continues up to 6-byte codes.)
250 For most texts in ISO 8859 character sets, this means that the charac‐
252 ters outside of ASCII are now coded with two bytes. This tends to
253 expand ordinary text files by only one or two percent. For Russian or
254 Greek texts, this expands ordinary text files by 100%, since text in
255 those languages is mostly outside of ASCII. For Japanese users this
256 means that the 16-bit codes now in common use will take three bytes.
257 While there are algorithmic conversions from some character sets (espe‐
258 cially ISO 8859-1) to Unicode, general conversion requires carrying
259 around conversion tables, which can be quite large for 16-bit codes.
260 Note that UTF-8 is self-synchronizing: 10xxxxxx is a tail, any other
262 byte is the head of a code. Note that the only way ASCII bytes occur
263 in a UTF-8 stream, is as themselves. In particular, there are no
264 embedded NULs ('\0') or '/'s that form part of some larger code.
265 Since ASCII, and, in particular, NUL and '/', are unchanged, the kernel
267 does not notice that UTF-8 is being used. It does not care at all what
268 the bytes it is handling stand for.
269 Rendering of Unicode data streams is typically handled through "sub‐
271 font" tables which map a subset of Unicode to glyphs. Internally the
272 kernel uses Unicode to describe the subfont loaded in video RAM. This
273 means that in the Linux console in UTF-8 mode, one can use a character
274 set with 512 different symbols. This is not enough for Japanese, Chi‐
275 nese, and Korean, but it is enough for most other purposes.
276
278 iconv(1), ascii(7), iso_8859-1(7), unicode(7), utf-8(7)
279
281 This page is part of release 4.15 of the Linux man-pages project. A
282 description of the project, information about reporting bugs, and the
283 latest version of this page, can be found at
284 https://www.kernel.org/doc/man-pages/.
285Linux 2017-09-15 CHARSETS(7)