charsets (7) manpage
I noticed that charsets (7) from the manpages package had a number
of inaccuracies, so I did some editing. Before I send it back to
the maintainer, I thought I might send to here, so that any errors
I added could get fixed, and hopefully other errors could be found.
Please note that most of my fixes were in the Unicode and ISO-8859
areas. Someone else is going to have to pick apart the ISO-2022
section. My version of the manpage, and the diff between it and
the old version, are attached.
--
David Starner - dstarner98@aasaa.ofe.org
Pointless website: http://dvdeug.dhis.org
"I don't care if Bill personally has my name and reads my email and
laughs at me. In fact, I'd be rather honored." - Joseph_Greg
.\" Copyright (c) 1996 Eric S. Raymond <esr@thyrsus.com>
.\" and Andries Brouwer <aeb@cwi.nl>
.\"
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" the License, or (at your option) any later version.
.\"
.\" This is combined from many sources, including notes by aeb and
.\" research by esr. Portions derive from a writeup by Roman Czyborra.
.\"
.\" Last changed by David Starner <dstarner98@aasaa.ofe.org>.
.TH CHARSETS 7 "May 7, 2001" "Linux" "Linux Programmer's Manual"
.SH NAME
charsets \- programmer's view of character sets and internationalization
.SH 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.
.LP
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.
.SH 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.
.LP
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; GNU libc doesn't support locales whose character sets aren't
true supersets of ASCII.
.LP
As Linux was written for hardware designed in the US, it natively
supports ASCII.
.SH 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.
.LP
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.
.LP
Console support for the other 8859 character sets is available under
Linux through user-mode utilities (such as
.BR setfont (8))
that modify keyboard bindings and the EGA graphics
table and employ the "user mapping" font table in the console
driver.
.LP
Here are brief descriptions of each set:
.TP
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 tolerable.
.TP
8859-2 (Latin-2)
Latin-2 supports most Latin-written Slavic and Central European
languages: Croatian, Czech, German, Hungarian, Polish, Rumanian,
Slovak, and Slovene.
.TP
8859-3 (Latin-3)
Latin-3 is popular with authors of Esperanto, Galician, Maltese, and Turkish.
.TP
8859-4 (Latin-4)
Latin-4 introduced letters for Estonian, Latvian, and Lithuanian. It
is essentially obsolete; see 8859-13 (Latin-7).
.\" Original manpage referred to 8859-10 (Latin-6). My sources don't
.\" mention 8859-10 in conjuction with those languages, but I'm not
.\" confident enought to be sure it was wrong.
.TP
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.
.TP
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.
.TP
8859-7
Supports Modern Greek.
.TP
8859-8
Supports Hebrew.
.TP
8859-9 (Latin-5)
This is a variant of Latin-1 that replaces rarely-used Icelandic
letters with Turkish ones.
.TP
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.
.TP
8859-11
Supports Thai, and is currently unsupported under Linux.
.TP
8859-12
This set does not exist. While Vietnamese has been suggested for this
space, it does not fit within the 96 characters ISO 8859 offers. UTF-8
is the preferred character set for Vietnamese use under Linux.
.TP
8859-13 (Latin-7)
Supports the Baltic Rim languages; in particular, it includes Latvian
characters not found in Latin-4.
.TP
8859-14 (Latin-8)
This is the Celtic character set, covering Gaelic and Welsh.
.TP
8859-15
This adds the Euro sign and French and Finnish letters that were missing in
Latin-1.
.TP
8859-16
This set covers many of the languages covered by 8859-2, and supports
Romanian more completely then that set does.
.SH 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 Ukranian.
.LP
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.
.SH UNICODE
Unicode (ISO 10646) is a standard which aims to unambiguously represent every
known 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.com>.
.LP
Linux represents Unicode using the 8-bit Unicode Transfer 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, and 4 bytes
for the remainder.
.LP
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.
.LP
A byte 110xxxxx is the start of a 2-byte code, and 110xxxxx 10yyyyyy
is assembled into 00000000 0000000 00000xxx xxyyyyyy. A byte 1110xxxx
is the start of a 3-byte code, and 1110xxxx 10yyyyyy 10zzzzzz is assembled
into 00000000 00000000 xxxxyyyy yyzzzzzz. Lastly, 110110xxx starts a 4-byte
code, and 110110xxx 10xxyyyy 10zzzzzz 10aaaaaa becomes 0000000 000xxxxx
yyyyzzzz zzaaaaaa.
.LP
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.
.LP
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 or '/'s that form part of some larger code.
.LP
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.
.LP
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.
.SH 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
.BR xterm (1).
It is popular in Japan and Korea.
.LP
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.
.LP
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 LS\fIn\fP makes character set G\fIn\fP the current one
for codes with high bit zero.
The function LS\fIn\fPR makes character set G\fIn\fP the current one
for codes with high bit one.
The function SS\fIn\fP makes character set G\fIn\fP (\fIn\fP=2 or 3)
the current one for the next character only (regardless of the value
of its high order bit).
.LP
A 94-character set is designated as G\fIn\fP 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.
.LP
A 96-character set is designated as G\fIn\fP 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.
.LP
A multibyte character set is designated as G\fIn\fP 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.
.LP
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.
.SH SEE ALSO
.BR console (4),
.BR console_ioctl (4),
.BR console_codes (4),
.BR ascii (7),
.BR iso_8859_1 (7),
.BR unicode (7),
.BR utf-8 (7)
--- charsets.7.orig Mon May 7 01:35:08 2001
+++ charsets.7 Mon May 7 02:54:06 2001
@@ -7,9 +7,10 @@
.\" the License, or (at your option) any later version.
.\"
.\" This is combined from many sources, including notes by aeb and
-.\" research by esr. Portions derive from a writeup by Ramon Czybora.
+.\" research by esr. Portions derive from a writeup by Roman Czyborra.
.\"
-.TH CHARSETS 7 "November 5th, 1996" "Linux" "Linux Programmer's Manual"
+.\" Last changed by David Starner <dstarner98@aasaa.ofe.org>.
+.TH CHARSETS 7 "May 7, 2001" "Linux" "Linux Programmer's Manual"
.SH NAME
charsets \- programmer's view of character sets and internationalization
.SH DESCRIPTION
@@ -29,16 +30,17 @@
7-bit character set, originally designed for American English. It is
currently described by the ECMA-6 standard.
.LP
-An ASCII variant replacing the American crosshatch/octothorpe/hash pound
-symbol with the British pound-sterling symbol is used in Great
-Britain; when needed, the American and British variants may be
-distinguished as "US ASCII" and "UK ASCII".
+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; GNU libc doesn't support locales whose character sets aren't
+true supersets of ASCII.
.LP
As Linux was written for hardware designed in the US, it natively
-supports US ASCII.
+supports ASCII.
.SH ISO 8859
-ISO 8859 is a series of 10 8-bit character sets all of which have US
+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.
.LP
@@ -72,7 +74,10 @@
.TP
8859-4 (Latin-4)
Latin-4 introduced letters for Estonian, Latvian, and Lithuanian. It
-is essentially obsolete; see 8859-10 (Latin-6).
+is essentially obsolete; see 8859-13 (Latin-7).
+.\" Original manpage referred to 8859-10 (Latin-6). My sources don't
+.\" mention 8859-10 in conjuction with those languages, but I'm not
+.\" confident enought to be sure it was wrong.
.TP
8859-5
Cyrillic letters supporting Bulgarian, Byelorussian, Macedonian,
@@ -101,31 +106,50 @@
1345 listed a preliminary and different `latin6'. Skolt Sami still
needs a few more accents than these.
.TP
+8859-11
+Supports Thai, and is currently unsupported under Linux.
+.TP
+8859-12
+This set does not exist. While Vietnamese has been suggested for this
+space, it does not fit within the 96 characters ISO 8859 offers. UTF-8
+is the preferred character set for Vietnamese use under Linux.
+.TP
8859-13 (Latin-7)
+Supports the Baltic Rim languages; in particular, it includes Latvian
+characters not found in Latin-4.
.TP
8859-14 (Latin-8)
+This is the Celtic character set, covering Gaelic and Welsh.
.TP
8859-15
-This adds the Euro sign and French ligatures that were missing in
+This adds the Euro sign and French and Finnish letters that were missing in
Latin-1.
+.TP
+8859-16
+This set covers many of the languages covered by 8859-2, and supports
+Romanian more completely then that set does.
.SH 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.
+designed than ISO 8859-5. KOI8-U is a common character set, based off
+KOI8-R, that has better support for Ukranian.
.LP
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.
.SH UNICODE
Unicode (ISO 10646) is a standard which aims to unambiguously represent every
-known glyph in every human language. Unicode's native encoding
-is 32-bit (older versions used 16 bits). Information on Unicode is
-available at <http://www.unicode.com>.
+known 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.com>.
.LP
Linux represents Unicode using the 8-bit Unicode Transfer 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.
+byte to code 7 bits, 2 bytes for 11 bits, 3 bytes for 16 bits, and 4 bytes
+for the remainder.
.LP
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
@@ -134,19 +158,21 @@
in file size.
.LP
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.)
-.LP
-For ISO-8859-1 users this means that the characters with high bit set
-now are coded with two bytes. This tends to expand ordinary text files
-by one or two percent. There are no conversion problems, however,
-since the Unicode value of ISO-8859-1 symbols equals their ISO-8859-1
-value (extended by eight leading zero bits). For Japanese users this
-means that the 16-bit codes now in common use will take three bytes,
-and extensive mapping tables are required. Many Japanese therefore
-prefer ISO 2022.
+is assembled into 00000000 0000000 00000xxx xxyyyyyy. A byte 1110xxxx
+is the start of a 3-byte code, and 1110xxxx 10yyyyyy 10zzzzzz is assembled
+into 00000000 00000000 xxxxyyyy yyzzzzzz. Lastly, 110110xxx starts a 4-byte
+code, and 110110xxx 10xxyyyy 10zzzzzz 10aaaaaa becomes 0000000 000xxxxx
+yyyyzzzz zzaaaaaa.
+.LP
+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.
.LP
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
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