charsets


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 charac-
       ter-set standards and how they fit together on Linux.   Standards  dis-
       cussed include ASCII, ISO 8859, KOI8-R, Unicode, ISO 2022 and ISO 4873.
       The primary emphasis is on character sets actually used as locale char-
       acter  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 orig-
       inal 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 charac-
       ters 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 sup-
       ports 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 posi-
       tions 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 key-
       board 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,
              Latin-3 is popular with authors of Esperanto, Galician, and Mal-
              tese.  (Turkish is now written with 8859-9 instead.)

       8859-4 (Latin-4)
              Latin-4  introduced  letters  for Estonian, Latvian, and Lithua-
              nian.  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 sep-
              arate 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  stan-
              dard  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.

       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 Chi-
       nese.  (Big5 is both a character set and an encoding.)  It is a  super-
       set  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
       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  "sub-
       font"  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 char-
       acters.  So Thai, Sioux and any other script needing combining  charac-
       ters 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  ker-
       nel 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 (ini-
       tially 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.

       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 char-
       acter 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 3.35 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://man7.org/linux/man-pages/.



Linux                             2008-06-03                       CHARSETS(7)
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