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Unicode(5)
NAME
Unicode, unicode, universal.utf8, UCS-2, UCS-4, UTF-8, UTF-16, UTF-32,
iso10646 - Support for the Unicode and ISO/IEC 10646 standards
DESCRIPTION
The operating system provides locales and codeset converters that support
the following standards:
· The Unicode Standard, Version 3.0, Unicode, Inc., 2000
· The Unicode Standard, Version 3.1, Unicode, Inc., 2001
· Information Technology-Universal Multiple-Octet Coded Character Set,
ISO/IEC 10646:2001
The Basic Multilingual Plane defined by this standard is identical
with the main body of Unicode character encoding.
These standards define generalized character encoding rules that can be
applied to characters in most native language scripts. The Unicode standard
specifies a universal character set (UCS). Version 3.0 of the Unicode
standard contains definitions for 49,194 characters and also includes a
Private Use Area for vendor- or user-defined characters. Version 3.1 of the
Unicode standard adds 44,946 new character definitions, incorporates UTF-32
(32-bit encoding) into the standard, and adds three new planes beyond the
16-bit codespace of Plane 0 (Basic Multilingual Plane). Plane 1
(Supplementary Multilingual Plane) contains code positions U+10000 to
U+1FFFF; Plane 2 (Supplementary Ideographic Plane) contains code positions
U+20000 to U+2FFFF; Plane 14 (Supplementary Special-Purpose Plane) contains
code positions U+E0000 to U+EFFFF.
See the Unicode web site at http://www.unicode.org/ for more information on
the Unicode standard. See the Unicode ReadMe document in
/usr/share/unidata/, which describes the Unicode standard version currently
supported on the operating system.
The following list summarizes the main features of the Unicode character
set:
· Characters have properties, such as base, numeric, spacing,
combination, and directionality. The Unicode standard provides rules
for ordering characters with different properties so that parsing of
character sequences is unambiguous.
· The relationship between Unicode characters and the glyphs in the
native language script that users see, type, or print is not
necessarily one-to-one. A glyph may be mapped to a single abstract
character or to a composed character. Conversely, more than one glyph
can be mapped to a character.
· Certain sequences of Unicode characters in a text stream are
transformed into other characters, called composed characters.
· The ISO 8859-1 character set occupies the first 256 code positions
(and the ASCII character set the first 128 positions) of the UCS.
The Unicode and ISO/IEC 10646 standards specify a universal repertoire of
characters that can be used by all major languages and that allow character
units to be processed for all languages under the same set of rules.
Therefore, system support for the universal character set does not need to
include multiple algorithms (one or more per language) for converting
between file code and internal process code. However, the two different
character sizes (16-bit or 32-bit) that the standards support require
different parsing schemes for data input and output. Universal character
encoding that an implementation parses in 16-bit units (2 octets) is known
as UCS-2. Universal character encoding that an implementation parses in
32-bit units (4 octets) is known as UCS-4. This is the canonical ISO/IEC
10646 encoding that is in use on systems that can support the larger data
unit size.
Because UCS-2 is a subset of UTF-16, the operating system supports UCS-2
with UTF-16 codeset converters. The operating system supports UCS-4 with
both codeset converters and locales. (Keep in mind that UCS-2 cannot be
used to encode characters outside of the Basic Multilingual Plane.)
In terms of locales, the operating system supports both Unicode and dense
code. The two types of locales differ in their manner of wide character
encoding support. See l10n_intro(5) for information comparing the two
locale types and for information on switching between Unicode and dense
code locales.
The Unicode and ISO/IEC 10646 standards define a number of transformation
formats for the universal character set (UTF-8 and UTF-32 are the preferred
transformation formats for the operating system):
· UTF-8, the standard method for transforming UCS-4 process encoding
into a sequence of 8-bit bytes and ensuring interchange transparency
for characters in C0 code positions (0 to 31), the SPACE (32)
character, and the DEL (127) character
The operating system supports UTF-8 with both codeset converters and
locales.
· UTF-7, an obsolete interchange format for environments that strip the
eighth bit from each byte
The operating system does not support UTF-7.
· UTF-1, an obsolete interchange format that is similar to UTF-8 but
also ensures interchange transparency of characters in C1 code
positions (128 to 159)
The operating system does not support UTF-1.
· UTF-16, which uses the surrogate character extension technique defined
by Version 2.0 and later of the Unicode standard and represents
characters in 16-bit units
UTF-16 is a superset of UCS-2. As with UCS-2, UTF-16 encodes
characters in the range U+0000 to U+FFFF as single 16-bit units. For
characters in the range U+10000 to U+10FFFF, UTF-16 transforms them
into a surrogate pair. The result of this transformation is that the
high surrogate (the first of the pair) is in the range U+D800 to
U+DBFF, while the low surrogate (the second part of the pair) is in
the range U+DC00 to U+DFFF. These two 16-bit values represent a single
character.
Although UTF-16 does not support representation of the entire UCS-4
code space (including private-use ranges for character values above
U+10FFFF), it does supports all characters that have been currently
defined for the languages covered by both standards.
Byte orientation in file code can differ and, depending on the
platform on which the file was generated, can be little-endian (LE) or
big-endian (BE). UTF-16 uses a byte order mark (BOM), which is not
part of the file text data, to indicate byte orientation. The code
point of the BOM is U+FEFF. The Unicode standard also defines UTF-16LE
and UTF-16BE, which are specific to the little-endian and big-endian
orientations, respectively, and do not include a byte order mark.
The operating system supports UTF-16, UTF-16LE, and UTF-16BE through
codeset converters. The codeset converter name, UCS-2 is recognized as
an alias for UTF-16*, but with a restricted repertoire of characters.
Note
By default, the operating system uses UTF-16 rather than UTF-16LE or
UTF-16BE.
In an input file, the software first looks for a BOM. If a BOM is
not found, the converter assumes UTF-16BE. This means that you must
explicitly specify UTF-16LE to the converter (convert files
manually) when UTF-16LE applies to an input file.
For an output file, the converter automatically inserts a BOM. This
means that you must explicitly specify UTF-16LE or UTF-16BE (convert
files manually) when you want conversion output to be UTF-16LE or
UTF-16BE rather than UTF-16.
· UTF-32 allows character representation in 4-byte encoding units
UTF-32 is a restricted subset of UCS-4. UTF-32 is restricted in values
to the range U+0000 to U+10FFFF, which precisely matches the range of
character values defined by UTF-16. Like UTF-16, UTF-32 does not
support private-use ranges for character values above U+10FFFF.
UTF-32 uses a BOM to indicate little-endian or big-endian byte
orientation. The Unicode standard also defines UTF-32LE and UTF-32BE,
which are specific to the little-endian and big-endian orientations,
respectively, and do not include a BOM. As with UTF-16, big-endian is
the default byte order when a BOM is not generated.
UTF-32 is almost the same as UCS-4, so you can use UCS-4 codeset
converters to process UTF-32. UCS-4 converter software includes
support for UTF-32, UTF-32LE, or UTF-32BE.
Codeset Conversion
Codeset converters are available to convert data in all the major encoding
formats that the operating system supports to and from UCS-2, UTF-16, UCS-
4, and UTF-8. If the worldwide support subsets are installed on your
system, you can enter the following commands to find the names of these
converters:
% cd /usr/lib/nls/loc/iconv
% ls | grep UTF
% ls | grep UCS
Among the converters listed, you will find some that handle conversion of
data in the code-page format used on PC systems. See code_page(5) for more
information about converting between codeset and code-page formats. You can
use all codeset converters with the iconv command and associated library
functions.
Note
The mapping of Korean Hangul characters changed between Version 1.1
and Version 2.0 of the Unicode standard. By default, UTF-16, UCS-4,
and UTF-8 conversion assumes Version 2.0 character mapping for Hangul
characters. Therefore, if data is in Version 1.1 format, you must
first convert the data to Version 2.0 format before converting from
UTF-16, UCS-4, or UTF-8 to an entirely different format.
The format of a codeset converter name is from-codeset_to-codeset. In
converter names, the Version 1.1 codeset formats for UCS-2, UCS-4, and
UTF-8 are represented by UNICODE-1-1, UNICODE-1-1-UCS-4, and UNICODE-
1-1-UTF-8, respectively. The Version 2.0 codeset names are represented
by UTF-16, UCS-4, and UTF-8.
For example, if Korean data is currently in UCS-4 Version 1.1 format,
the data must first be processed by the UNICODE-1-1-UCS-4_UCS-4
converter before being processed by the UCS-4_deckorean converter.
See iconv_intro(5) for general information on codeset conversion.
Locales
The following locales use UTF-32 as internal processing code:
· universal.UTF-8
This locale is used by applications. It converts data in UTF-8 file
format to UCS-4 process code and can be used to test any UCS-4
character to determine if it is included in one of the following
classes defined for the LC_CTYPE category: alnum, alpha, blank, cntrl,
digit, graph, lower, print, punct, space, upper, or xdigit.
In the universal.UTF-8 locale, the LC_MESSAGES, LC_MONETARY,
LC_NUMERIC, and LC_TIME category definitions match those for the POSIX
(C) locale.
· language_territory.UTF-8
These locales limit classification information to the characters in a
particular native language, make country-specific data available to
the application, and assume file data follows UTF-8 encoding rules.
The operating system locales that support the euro monetary symbol use
either the UTF-8 or ISO8859-15 codeset. See euro(5) for more
information.
Note
The X locale database file used by applications running in the
universal.UTF-8, en_US.UTF-8, or Asian locales (Chinese, Japanese,
or Korean) contains font definitions that include all the fonts used
with the operating system. This enables applications under
en_US.UTF-8 to display all the font characters installed with
Worldwide Language Software (WLS). Applications under the Asian
locales display all the font characters installed with WLS, except
for ISO8859-2, -4, -5, -7, -8, -9, -15, and TACTIS.
· native_locale_name
These locales are installed in the default Unicode path,
/usr/i18n/lib/nls/ucsloc/ and use UTF-32 as internal processing code.
However, they differ in the following ways:
-- The file code is specified by the codeset portion (for example,
ISO8859-1) of native_locale_name.
-- Classification information is not provided for the full set of
UTF-32 characters, but only for those in a particular native
language (for example, French).
-- Country-specific data is also available to the application. The
LC_COLLATE, LC_MESSAGES, LC_MONETARY, LC_NUMERIC, and LC_TIME
category definitions match those defined in native_locale_name.
· native_locale_name@ucs4
These locales are installed in /usr/i18n/lib/nls/loc/ and are the same
as the native_locale_name locales installed in
/usr/i18n/lib/nls/ucsloc/ except that they are not a complete set of
locales and will not be enhanced in future versions of the operating
system. They are provided for compatibility with existing
applications. You cannot select @ucs4 locales from the CDE login menu;
you must specify the locale name in the LANG environment variable.
CDE desktop users can select .UTF-8 locales by choosing names followed by
(Unicode) from the CDE language menu at session startup. In this case, the
locale setting applies by default to all applications run during the CDE
session.
Unicode Character Database
For the convenience of programmers, the source file for the Unicode
character database is available on line. This source file is the one used
to build the .UTF-8 locales provided in optional software subsets included
with the operating system product. When the .UTF-8 locales are installed on
your system, both the Unicode character database and an associated ReadMe
file are also installed in the /usr/share/unidata directory. The ReadMe
file discusses the character properties supported by Unicode.
Font Support
The operating system provides the following types of bitmap fonts for UCS
characters:
· Public domain Unicode fonts:
-etl-fixed-medium-r-normal--14-140-72-72-c-70-iso10646-1
-etl-fixed-medium-r-normal--16-160-72-72-c-80-iso10646-1
-etl-fixed-medium-r-normal--24-240-72-72-c-120-iso10646-1
· Composite fonts that the libfr_FGC font renderer creates by combining
fonts available for other codesets
· Two sets of monospaced fonts (a 16x18 pixel set and a 24x24 pixel set)
for UTF-8 locales with the following CDE font aliases (where -n is -1,
-2, -3, -4, -5, -7, -8,- 9, or -15):
-dt-interface-*-*-*-*-*-*-*-*-*-*-*-iso8859-n@mono
-dt-interface-*-*-*-*-*-*-*-*-*-*-*-iso10646-1@mono
These fonts currently cover only a subset of the characters in UCS. Each
of the ETL public domain fonts supports about 1000 characters, but does not
include any characters for Chinese, Japanese, or Korean. The composite
fonts created by the font renderer are generated only from fonts available
for the ISO 8859-1 (Latin-1) and ISO 8859-15 (Latin-9) codesets.
See iso8859-1(5) and iso8859-15(5) for the names of fonts available for
Latin-1 and Latin-9 characters. The Latin-9 fonts, which include glyphs for
the euro character, provide the best support for the
language_territory.UTF-8 locales, which also support this character.
See i18n_printing(5) and wwpsof(8) for information on printer support and
converting bitmap font encoding to PostScript.
SEE ALSO
Commands: locale(1), wwpsof(8)
Others: ascii(5), code_page(5), iso8859-1(5), iso8859-15(5), i18n_intro(5),
i18n_printing(5), iconv_intro(5), l10n_intro(5)
Using International Software
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Index for
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Alphabetical
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