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NAME

       charsets - programmer's view of character sets and internationalization

DESCRIPTION

       Linux  is  an international operating system.  Various of its utilities
       and device drivers (including the console driver) support  multilingual
       character sets including Latin-alphabet letters with diacritical marks,
       accents, ligatures, and entire  non-Latin  alphabets  including  Greek,
       Cyrillic, Arabic, and Hebrew.

       This   manual  page  presents  a  programmer's-eye  view  of  different
       character-set standards and how they fit together on Linux.   Standards
       discussed  include  ASCII,  ISO 8859, KOI8-R, Unicode, ISO 2022 and ISO
       4873.  The primary emphasis is  on  character  sets  actually  used  as
       locale  character sets, not the myriad others that can be found in data
       from other systems.

       A complete list of charsets used in an officially supported  locale  in
       glibc   2.2.3   is:  ISO-8859-{1,2,3,5,6,7,8,9,13,15},  CP1251,  UTF-8,
       EUC-{KR,JP,TW}, KOI8-{R,U}, GB2312, GB18030, GBK, BIG5, BIG5-HKSCS  and
       TIS-620  (in  no  particular  order.)   (Romanian  may  be switching to
       ISO-8859-16.)

   ASCII
       ASCII (American Standard  Code  For  Information  Interchange)  is  the
       original 7-bit character set, originally designed for American English.
       It is currently described by the ECMA-6 standard.

       Various ASCII variants replacing the dollar sign  with  other  currency
       symbols   and   replacing   punctuation   with  non-English  alphabetic
       characters to cover German, French, Spanish and others in 7 bits exist.
       All  are deprecated; glibc doesn't support locales whose character sets
       aren't true supersets of ASCII.  (These sets are also known as ISO-646,
       a close relative of ASCII that permitted replacing these characters.)

       As  Linux  was  written  for  hardware  designed in the US, it natively
       supports ASCII.

   ISO 8859
       ISO 8859 is a series of 15 8-bit character sets all of  which  have  US
       ASCII  in  their  low  (7-bit)  half,  invisible  control characters in
       positions 128 to 159, and 96 fixed-width graphics in positions 160-255.

       Of these, the most important is ISO 8859-1 (Latin-1).  It  is  natively
       supported  in the Linux console driver, fairly well supported in X11R6,
       and is the base character set of HTML.

       Console support for the other 8859 character sets  is  available  under
       Linux  through  user-mode  utilities  (such  as setfont(8)) that modify
       keyboard bindings and the EGA  graphics  table  and  employ  the  "user
       mapping" font table in the console driver.

       Here are brief descriptions of each set:

       8859-1 (Latin-1)
              Latin-1 covers most Western European languages such as Albanian,
              Catalan,  Danish,  Dutch,  English,  Faroese,  Finnish,  French,
              German,   Galician,   Irish,   Icelandic,   Italian,  Norwegian,
              Portuguese, Spanish, and Swedish.  The  lack  of  the  ligatures
              Dutch  ij, French oe and old-style ,,German`` quotation marks is
              considered tolerable.

       8859-2 (Latin-2)
              Latin-2 supports most Latin-written Slavic and Central  European
              languages: Croatian, Czech, German, Hungarian, Polish, Rumanian,
              Slovak, and Slovene.

       8859-3 (Latin-3)
              Latin-3 is popular with  authors  of  Esperanto,  Galician,  and
              Maltese.  (Turkish is now written with 8859-9 instead.)

       8859-4 (Latin-4)
              Latin-4   introduced   letters   for   Estonian,   Latvian,  and
              Lithuanian.  It is essentially obsolete; see  8859-10  (Latin-6)
              and 8859-13 (Latin-7).

       8859-5 Cyrillic letters supporting Bulgarian, Byelorussian, Macedonian,
              Russian, Serbian and  Ukrainian.   Ukrainians  read  the  letter
              "ghe"  with  downstroke  as  "heh"  and  would  need  a ghe with
              upstroke to write a correct ghe.  See the discussion  of  KOI8-R
              below.

       8859-6 Supports  Arabic.   The  8859-6  glyph  table is a fixed font of
              separate letter  forms,  but  a  proper  display  engine  should
              combine these using the proper initial, medial, and final forms.

       8859-7 Supports Modern Greek.

       8859-8 Supports modern Hebrew without niqud (punctuation signs).  Niqud
              and full-fledged Biblical Hebrew are outside the scope  of  this
              character  set; under Linux, UTF-8 is the preferred encoding for
              these.

       8859-9 (Latin-5)
              This is a variant of Latin-1  that  replaces  Icelandic  letters
              with Turkish ones.

       8859-10 (Latin-6)
              Latin  6  adds  the  last Inuit (Greenlandic) and Sami (Lappish)
              letters that were missing in Latin 4 to cover the entire  Nordic
              area.   RFC  1345  listed  a preliminary and different "latin6".
              Skolt Sami still needs a few more accents than these.

       8859-11
              This only exists  as  a  rejected  draft  standard.   The  draft
              standard was identical to TIS-620, which is used under Linux for
              Thai.

       8859-12
              This set does not exist.  While Vietnamese  has  been  suggested
              for  this  space,  it  does not fit within the 96 (noncombining)
              characters ISO 8859 offers.  UTF-8 is  the  preferred  character
              set for Vietnamese use under Linux.

       8859-13 (Latin-7)
              Supports  the  Baltic  Rim languages; in particular, it includes
              Latvian characters not found in Latin-4.

       8859-14 (Latin-8)
              This is the Celtic character set,  covering  Gaelic  and  Welsh.
              This  charset also contains the dotted characters needed for Old
              Irish.

       8859-15 (Latin-9)
              This adds the Euro sign and French and Finnish letters that were
              missing in Latin-1.

       8859-16 (Latin-10)
              This  set  covers  many  of the languages covered by 8859-2, and
              supports Romanian more completely then that set does.

   KOI8-R
       KOI8-R is a non-ISO character set popular in Russia.  The lower half is
       US  ASCII;  the  upper  is  a  Cyrillic  character  set somewhat better
       designed than ISO 8859-5.  KOI8-U is a common character set, based  off
       KOI8-R,  that  has better support for Ukrainian.  Neither of these sets
       are ISO-2022 compatible, unlike the ISO-8859 series.

       Console support for KOI8-R is available under Linux  through  user-mode
       utilities that modify keyboard bindings and the EGA graphics table, and
       employ the "user mapping" font table in the console driver.

   JIS X 0208
       JIS X 0208 is a Japanese national standard character set.  Though there
       are  some  more  Japanese  national standard character sets (like JIS X
       0201, JIS X 0212, and JIS X 0213), this  is  the  most  important  one.
       Characters  are mapped into a 94x94 two-byte matrix, whose each byte is
       in the range 0x21-0x7e.  Note that JIS X 0208 is a character  set,  not
       an  encoding.   This  means  that  JIS  X  0208  itself is not used for
       expressing text data.  JIS X 0208 is used as a component  to  construct
       encodings  such  as  EUC-JP, Shift_JIS, and ISO-2022-JP.  EUC-JP is the
       most important encoding for Linux and includes US ASCII and JIS X 0208.
       In  EUC-JP,  JIS  X 0208 characters are expressed in two bytes, each of
       which is the JIS X 0208 code plus 0x80.

   KS X 1001
       KS X 1001 is a Korean national standard character set.  Just as  JIS  X
       0208, characters are mapped into a 94x94 two-byte matrix.  KS X 1001 is
       used like JIS X 0208, as a component to  construct  encodings  such  as
       EUC-KR,  Johab, and ISO-2022-KR.  EUC-KR is the most important encoding
       for Linux and includes US ASCII and KS X 1001.  KS C 5601 is  an  older
       name for KS X 1001.

   GB 2312
       GB  2312  is a mainland Chinese national standard character set used to
       express simplified Chinese.  Just  like  JIS  X  0208,  characters  are
       mapped  into  a 94x94 two-byte matrix used to construct EUC-CN.  EUC-CN
       is the most important encoding for Linux and includes US ASCII  and  GB
       2312.  Note that EUC-CN is often called as GB, GB 2312, or CN-GB.

   Big5
       Big5  is  a  popular  character  set  in  Taiwan to express traditional
       Chinese.  (Big5 is both a character set and  an  encoding.)   It  is  a
       superset of US ASCII.  Non-ASCII characters are expressed in two bytes.
       Bytes 0xa1-0xfe are used as  leading  bytes  for  two-byte  characters.
       Big5  and  its extension is widely used in Taiwan and Hong Kong.  It is
       not ISO 2022-compliant.

   TIS 620
       TIS 620 is a Thai national standard character set and a superset of  US
       ASCII.    Like  ISO  8859  series,  Thai  characters  are  mapped  into
       0xa1-0xfe.  TIS 620 is the only commonly used character set under Linux
       besides UTF-8 to have combining characters.

   UNICODE
       Unicode (ISO 10646) is a standard which aims to unambiguously represent
       every character in every human language.  Unicode's  structure  permits
       20.1  bits  to  encode  every  character.   Since  most computers don't
       include  20.1-bit  integers,  Unicode  is  usually  encoded  as  32-bit
       integers  internally  and  either  a series of 16-bit integers (UTF-16)
       (needing  two  16-bit  integers  only  when   encoding   certain   rare
       characters) or a series of 8-bit bytes (UTF-8).  Information on Unicode
       is available at <http://www.unicode.org>.

       Linux represents Unicode using the 8-bit Unicode Transformation  Format
       (UTF-8).   UTF-8  is  a variable length encoding of Unicode.  It uses 1
       byte to code 7 bits, 2 bytes for 11 bits, 3 bytes for 16 bits, 4  bytes
       for 21 bits, 5 bytes for 26 bits, 6 bytes for 31 bits.

       Let  0,1,x  stand  for  a zero, one, or arbitrary bit.  A byte 0xxxxxxx
       stands for the Unicode 00000000 0xxxxxxx which codes the same symbol as
       the  ASCII 0xxxxxxx.  Thus, ASCII goes unchanged into UTF-8, and people
       using only ASCII do not notice any change: not in code, and not in file
       size.

       A byte 110xxxxx is the start of a 2-byte code, and 110xxxxx 10yyyyyy is
       assembled into 00000xxx xxyyyyyy.  A byte 1110xxxx is the  start  of  a
       3-byte  code, and 1110xxxx 10yyyyyy 10zzzzzz is assembled into xxxxyyyy
       yyzzzzzz.  (When UTF-8 is used to code the 31-bit ISO 10646  then  this
       progression continues up to 6-byte codes.)

       For  most  people  who use ISO-8859 character sets, this means that the
       characters outside of ASCII are now coded with two bytes.   This  tends
       to  expand ordinary text files by only one or two percent.  For Russian
       or Greek users, this expands ordinary text files by 100%, since text in
       those  languages  is  mostly outside of ASCII.  For Japanese users this
       means that the 16-bit codes now in common use will  take  three  bytes.
       While  there are algorithmic conversions from some character sets (esp.
       ISO-8859-1) to Unicode, general  conversion  requires  carrying  around
       conversion tables, which can be quite large for 16-bit codes.

       Note  that  UTF-8  is self-synchronizing: 10xxxxxx is a tail, any other
       byte is the head of a code.  Note that the only way ASCII  bytes  occur
       in  a  UTF-8  stream,  is  as  themselves.  In particular, there are no
       embedded NULs ('\0') or '/'s that form part of some larger code.

       Since ASCII, and, in particular, NUL and '/', are unchanged, the kernel
       does not notice that UTF-8 is being used.  It does not care at all what
       the bytes it is handling stand for.

       Rendering  of  Unicode  data  streams  is  typically  handled   through
       "subfont"  tables  which map a subset of Unicode to glyphs.  Internally
       the kernel uses Unicode to describe the subfont loaded  in  video  RAM.
       This  means  that  in  UTF-8  mode one can use a character set with 512
       different symbols.  This  is  not  enough  for  Japanese,  Chinese  and
       Korean, but it is enough for most other purposes.

       At  the  current  time,  the  console  driver does not handle combining
       characters.  So Thai, Sioux and  any  other  script  needing  combining
       characters can't be handled on the console.

   ISO 2022 and ISO 4873
       The  ISO 2022 and 4873 standards describe a font-control model based on
       VT100 practice.  This model  is  (partially)  supported  by  the  Linux
       kernel and by xterm(1).  It is popular in Japan and Korea.

       There  are  4 graphic character sets, called G0, G1, G2 and G3, and one
       of them is the current character set  for  codes  with  high  bit  zero
       (initially  G0), and one of them is the current character set for codes
       with high bit one (initially G1).  Each graphic character set has 94 or
       96 characters, and is essentially a 7-bit character set.  It uses codes
       either 040-0177 (041-0176) or 0240-0377  (0241-0376).   G0  always  has
       size 94 and uses codes 041-0176.

       Switching  between  character sets is done using the shift functions ^N
       (SO or LS1), ^O (SI or LS0), ESC n (LS2), ESC o (LS3), ESC N (SS2), ESC
       O  (SS3),  ESC  ~ (LS1R), ESC } (LS2R), ESC | (LS3R).  The function LSn
       makes character set Gn the current one for codes with  high  bit  zero.
       The function LSnR makes character set Gn the current one for codes with
       high bit one.  The function SSn makes character set Gn (n=2 or  3)  the
       current one for the next character only (regardless of the value of its
       high order bit).

       A 94-character set is designated as  Gn  character  set  by  an  escape
       sequence ESC ( xx (for G0), ESC ) xx (for G1), ESC * xx (for G2), ESC +
       xx (for G3), where xx is a symbol or a pair of symbols found in the ISO
       2375  International Register of Coded Character Sets.  For example, ESC
       ( @ selects the ISO 646 character set as G0, ESC (  A  selects  the  UK
       standard  character  set  (with  pound instead of number sign), ESC ( B
       selects ASCII (with dollar instead of currency sign), ESC ( M selects a
       character  set  for  African  languages,  ESC  (  ! A selects the Cuban
       character set, etc. etc.

       A 96-character set is designated as  Gn  character  set  by  an  escape
       sequence  ESC  -  xx  (for G1), ESC . xx (for G2) or ESC / xx (for G3).
       For example, ESC - G selects the Hebrew alphabet as G1.

       A multibyte character set is designated  as  Gn  character  set  by  an
       escape  sequence  ESC $ xx or ESC $ ( xx (for G0), ESC $ ) xx (for G1),
       ESC $ * xx (for G2), ESC $ + xx (for G3).   For  example,  ESC  $  (  C
       selects  the  Korean  character set for G0.  The Japanese character set
       selected by ESC $ B has a more recent version selected by ESC & @ ESC $
       B.

       ISO 4873 stipulates a narrower use of character sets, where G0 is fixed
       (always ASCII), so that G1, G2 and G3 can only  be  invoked  for  codes
       with  the  high  order  bit set.  In particular, ^N and ^O are not used
       anymore, ESC ( xx can be used only with xx=B, and ESC ) xx, ESC  *  xx,
       ESC + xx are equivalent to ESC - xx, ESC . xx, ESC / xx, respectively.

SEE ALSO

       console(4),      console_codes(4),      console_ioctl(4),     ascii(7),
       iso_8859-1(7), unicode(7), utf-8(7)

COLOPHON

       This page is part of release 3.27 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.