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           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
           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
           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)
                  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
           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
           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.
                  This  exists only as a rejected draft standard.  The draft stan-
                  dard was identical to TIS-620, which is  used  under  Linux  for
                  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
           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 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 (ISO 10646) is a standard which aims to unambiguously represent
           every  character  in every human language.  Unicode's structure permits
           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
           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 (espe-
           cially  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.
           (  @  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, and so on.
           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 $
           ISO 4873 stipulates a narrower use of character sets, where G0 is fixed
           (always  ASCII),  so  that  G1, G2 and G3 can be invoked only 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.


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

    Linux 2012-08-05 CHARSETS(7)


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