1CHARSETS(7)                Linux Programmer's Manual               CHARSETS(7)


6       charsets - character set standards and internationalization


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.
14       Standards discussed include such as ASCII,  GB  2312,  ISO  8859,  JIS,
15       KOI8-R, KS, and Unicode.
17       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.
21   ASCII
22       ASCII (American Standard Code For Information Interchange) is the orig‐
23       inal 7-bit character set, originally  designed  for  American  English.
24       Also  known as US-ASCII.  It is currently described by the ISO 646:1991
25       IRV (International Reference Version) standard.
27       Various ASCII variants replacing the dollar sign  with  other  currency
28       symbols  and  replacing punctuation with non-English alphabetic charac‐
29       ters to cover German, French, Spanish, and others in  7  bits  emerged.
30       All are deprecated; glibc does not support locales whose character sets
31       are not true supersets of ASCII.
33       As Unicode, when using UTF-8, is  ASCII-compatible,  plain  ASCII  text
34       still renders properly on modern UTF-8 using systems.
36   ISO 8859
37       ISO  8859  is  a  series  of 15 8-bit character sets, all of which have
38       ASCII in their low (7-bit) half, invisible control characters in  posi‐
39       tions 128 to 159, and 96 fixed-width graphics in positions 160–255.
41       Of  these,  the  most important is ISO 8859-1 ("Latin Alphabet No .1" /
42       Latin-1).  It was widely adopted and supported  by  different  systems,
43       and  is  gradually being replaced with Unicode.  The ISO 8859-1 charac‐
44       ters are also the first 256 characters of Unicode.
46       Console support for the other 8859 character sets  is  available  under
47       Linux through user-mode utilities (such as setfont(8)) that modify key‐
48       board bindings and the EGA graphics table and employ the "user mapping"
49       font table in the console driver.
51       Here are brief descriptions of each set:
53       8859-1 (Latin-1)
54              Latin-1  covers  many  West European languages such as Albanian,
55              Basque, Danish, English, Faroese,  Galician,  Icelandic,  Irish,
56              Italian,  Norwegian, Portuguese, Spanish, and Swedish.  The lack
57              of the ligatures Dutch IJ/ij, French  œ,  and  old-style  „German“
58              quotation marks was considered tolerable.
60       8859-2 (Latin-2)
61              Latin-2  supports  many  Latin-written Central and East European
62              languages such as Bosnian, Croatian, Czech,  German,  Hungarian,
63              Polish,  Slovak,  and  Slovene.  Replacing Romanian ș/ț with ş/ţ
64              was considered tolerable.
66       8859-3 (Latin-3)
67              Latin-3 was designed to cover of Esperanto, Maltese,  and  Turk‐
68              ish, but 8859-9 later superseded it for Turkish.
70       8859-4 (Latin-4)
71              Latin-4  introduced letters for North European languages such as
72              Estonian, Latvian, and Lithuanian, but was superseded by 8859-10
73              and 8859-13.
75       8859-5 Cyrillic letters supporting Bulgarian, Byelorussian, Macedonian,
76              Russian, Serbian, and (almost  completely)  Ukrainian.   It  was
77              never widely used, see the discussion of KOI8-R/KOI8-U below.
79       8859-6 Was  created for Arabic.  The 8859-6 glyph table is a fixed font
80              of separate letter forms, but a  proper  display  engine  should
81              combine these using the proper initial, medial, and final forms.
83       8859-7 Was created for Modern Greek in 1987, updated in 2003.
85       8859-8 Supports Modern Hebrew without niqud (punctuation signs).  Niqud
86              and full-fledged Biblical Hebrew were outside the scope of  this
87              character set.
89       8859-9 (Latin-5)
90              This  is  a  variant  of Latin-1 that replaces Icelandic letters
91              with Turkish ones.
93       8859-10 (Latin-6)
94              Latin-6 added the Inuit (Greenlandic) and Sami (Lappish) letters
95              that were missing in Latin-4 to cover the entire Nordic area.
97       8859-11
98              Supports  the  Thai  alphabet  and  is  nearly  identical to the
99              TIS-620 standard.
101       8859-12
102              This set does not exist.
104       8859-13 (Latin-7)
105              Supports the Baltic Rim languages; in  particular,  it  includes
106              Latvian characters not found in Latin-4.
108       8859-14 (Latin-8)
109              This  is  the  Celtic  character  set, covering Old Irish, Manx,
110              Gaelic, Welsh, Cornish, and Breton.
112       8859-15 (Latin-9)
113              Latin-9 is similar to the widely used Latin-1 but replaces  some
114              less  common  symbols  with the Euro sign and French and Finnish
115              letters that were missing in Latin-1.
117       8859-16 (Latin-10)
118              This set covers many  Southeast  European  languages,  and  most
119              importantly supports Romanian more completely than Latin-2.
121   KOI8-R / KOI8-U
122       KOI8-R  is  a  non-ISO  character set popular in Russia before Unicode.
123       The lower half is ASCII; the upper is a Cyrillic character set somewhat
124       better  designed  than ISO 8859-5.  KOI8-U, based on KOI8-R, has better
125       support for Ukrainian.  Neither of these sets are ISO-2022  compatible,
126       unlike the ISO 8859 series.
128       Console  support  for KOI8-R is available under Linux through user-mode
129       utilities that modify keyboard bindings and the EGA graphics table, and
130       employ the "user mapping" font table in the console driver.
132   GB 2312
133       GB  2312  is a mainland Chinese national standard character set used to
134       express simplified Chinese.  Just  like  JIS  X  0208,  characters  are
135       mapped  into  a 94x94 two-byte matrix used to construct EUC-CN.  EUC-CN
136       is the most important encoding for Linux  and  includes  ASCII  and  GB
137       2312.  Note that EUC-CN is often called as GB, GB 2312, or CN-GB.
139   Big5
140       Big5  was a popular character set in Taiwan to express traditional Chi‐
141       nese.  (Big5 is both a character set and an encoding.)  It is a  super‐
142       set  of ASCII.  Non-ASCII characters are expressed in two bytes.  Bytes
143       0xa1–0xfe are used as leading bytes for two-byte characters.  Big5  and
144       its  extension were widely used in Taiwan and Hong Kong.  It is not ISO
145       2022 compliant.
147   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 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.
160   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 ASCII and KS X 1001.  KS C 5601 is an older name
166       for KS X 1001.
168   ISO 2022 and ISO 4873
169       The  ISO 2022 and 4873 standards describe a font-control model based on
170       VT100 practice.  This model is (partially) supported by the Linux  ker‐
171       nel  and  by xterm(1).  Several ISO 2022-based character encodings have
172       been defined, especially for Japanese.
174       There are 4 graphic character sets, called G0, G1, G2, and G3, and  one
175       of them is the current character set for codes with high bit zero (ini‐
176       tially G0), and one of them is the current character set for codes with
177       high  bit  one (initially G1).  Each graphic character set has 94 or 96
178       characters, and is essentially a 7-bit character set.   It  uses  codes
179       either  040–0177  (041–0176)  or  0240–0377 (0241–0376).  G0 always has
180       size 94 and uses codes 041–0176.
182       Switching between character sets is done using the shift  functions  ^N
183       (SO or LS1), ^O (SI or LS0), ESC n (LS2), ESC o (LS3), ESC N (SS2), ESC
184       O (SS3), ESC ~ (LS1R), ESC } (LS2R), ESC | (LS3R).   The  function  LSn
185       makes  character  set  Gn the current one for codes with high bit zero.
186       The function LSnR makes character set Gn the current one for codes with
187       high  bit  one.  The function SSn makes character set Gn (n=2 or 3) the
188       current one for the next character only (regardless of the value of its
189       high order bit).
191       A  94-character  set  is  designated  as  Gn character set by an escape
192       sequence ESC ( xx (for G0), ESC ) xx (for G1), ESC * xx (for G2), ESC +
193       xx (for G3), where xx is a symbol or a pair of symbols found in the ISO
194       2375 International Register of Coded Character Sets.  For example,  ESC
195       (  @  selects  the  ISO 646 character set as G0, ESC ( A selects the UK
196       standard character set (with pound instead of number  sign),  ESC  (  B
197       selects ASCII (with dollar instead of currency sign), ESC ( M selects a
198       character set for African languages, ESC ( ! A selects the Cuban  char‐
199       acter set, and so on.
201       A  96-character  set  is  designated  as  Gn character set by an escape
202       sequence ESC - xx (for G1), ESC . xx (for G2) or ESC  /  xx  (for  G3).
203       For example, ESC - G selects the Hebrew alphabet as G1.
205       A  multibyte  character  set  is  designated  as Gn character set by an
206       escape sequence ESC $ xx or ESC $ ( xx (for G0), ESC $ ) xx  (for  G1),
207       ESC  $  *  xx  (for  G2),  ESC $ + xx (for G3).  For example, ESC $ ( C
208       selects the Korean character set for G0.  The  Japanese  character  set
209       selected by ESC $ B has a more recent version selected by ESC & @ ESC $
210       B.
212       ISO 4873 stipulates a narrower use of character sets, where G0 is fixed
213       (always  ASCII),  so  that  G1, G2 and G3 can be invoked only for codes
214       with the high order bit set.  In particular, ^N and  ^O  are  not  used
215       anymore,  ESC  ( xx can be used only with xx=B, and ESC ) xx, ESC * xx,
216       ESC + xx are equivalent to ESC - xx, ESC . xx, ESC / xx, respectively.
218   TIS-620
219       TIS-620 is a Thai national standard character set  and  a  superset  of
220       ASCII.  In the same fashion as the ISO 8859 series, Thai characters are
221       mapped into 0xa1–0xfe.
223   Unicode
224       Unicode (ISO 10646) is a standard which aims to unambiguously represent
225       every  character  in every human language.  Unicode's structure permits
226       20.1 bits to  encode  every  character.   Since  most  computers  don't
227       include  20.1-bit  integers, Unicode is usually encoded as 32-bit inte‐
228       gers internally and either a series of 16-bit integers (UTF-16)  (need‐
229       ing  two 16-bit integers only when encoding certain rare characters) or
230       a series of 8-bit bytes (UTF-8).
232       Linux represents Unicode using the 8-bit Unicode Transformation  Format
233       (UTF-8).   UTF-8  is  a variable length encoding of Unicode.  It uses 1
234       byte to code 7 bits, 2 bytes for 11 bits, 3 bytes for 16 bits, 4  bytes
235       for 21 bits, 5 bytes for 26 bits, 6 bytes for 31 bits.
237       Let  0,1,x  stand  for  a zero, one, or arbitrary bit.  A byte 0xxxxxxx
238       stands for the Unicode 00000000 0xxxxxxx which codes the same symbol as
239       the  ASCII 0xxxxxxx.  Thus, ASCII goes unchanged into UTF-8, and people
240       using only ASCII do not notice any change: not in code, and not in file
241       size.
243       A byte 110xxxxx is the start of a 2-byte code, and 110xxxxx 10yyyyyy is
244       assembled into 00000xxx xxyyyyyy.  A byte 1110xxxx is the  start  of  a
245       3-byte  code, and 1110xxxx 10yyyyyy 10zzzzzz is assembled into xxxxyyyy
246       yyzzzzzz.  (When UTF-8 is used to code the 31-bit ISO 10646  then  this
247       progression continues up to 6-byte codes.)
249       For  most texts in ISO 8859 character sets, this means that the charac‐
250       ters outside of ASCII are now coded with  two  bytes.   This  tends  to
251       expand  ordinary text files by only one or two percent.  For Russian or
252       Greek texts, this expands ordinary text files by 100%,  since  text  in
253       those  languages  is  mostly outside of ASCII.  For Japanese users this
254       means that the 16-bit codes now in common use will  take  three  bytes.
255       While there are algorithmic conversions from some character sets (espe‐
256       cially ISO 8859-1) to Unicode,  general  conversion  requires  carrying
257       around conversion tables, which can be quite large for 16-bit codes.
259       Note  that  UTF-8  is self-synchronizing: 10xxxxxx is a tail, any other
260       byte is the head of a code.  Note that the only way ASCII  bytes  occur
261       in  a  UTF-8  stream,  is  as  themselves.  In particular, there are no
262       embedded NULs ('\0') or '/'s that form part of some larger code.
264       Since ASCII, and, in particular, NUL and '/', are unchanged, the kernel
265       does not notice that UTF-8 is being used.  It does not care at all what
266       the bytes it is handling stand for.
268       Rendering of Unicode data streams is typically  handled  through  "sub‐
269       font"  tables  which map a subset of Unicode to glyphs.  Internally the
270       kernel uses Unicode to describe the subfont loaded in video RAM.   This
271       means  that in the Linux console in UTF-8 mode, one can use a character
272       set with 512 different symbols.  This is not enough for Japanese,  Chi‐
273       nese, and Korean, but it is enough for most other purposes.


276       iconv(1), ascii(7), iso_8859-1(7), unicode(7), utf-8(7)


279       This  page  is  part of release 4.16 of the Linux man-pages project.  A
280       description of the project, information about reporting bugs,  and  the
281       latest     version     of     this    page,    can    be    found    at
282       https://www.kernel.org/doc/man-pages/.
286Linux                             2017-09-15                       CHARSETS(7)