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



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  depre-
       cated; 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, Hun-
              garian, 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 (non-combining) 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 char-
       acter 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  stan-
       dard  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 char-
       acters 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 lan-
       guage.  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 inte-
       gers (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 algo-
       rithmic 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  (par-
       tially) 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  char-
       acter  set  Gn the current one for codes with high bit zero.  The function LSnR makes character set Gn the cur-
       rent 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 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-06-03                       CHARSETS(7)