luit - Locale and ISO 2022 support for Unicode terminals
luit [
options ] [
-- ] [
program [
args ] ]
Luit is a filter that can be run between an arbitrary application and a
UTF-8 terminal emulator. It will convert application output from the locale's
encoding into UTF-8, and convert terminal input from UTF-8 into the locale's
encoding.
Luit reads its input from the child process, i.e., an application running
in the terminal.
Luit writes its output to the terminal. The two (input
and output) can have different encodings.
An application may also request switching to a different output encoding using
ISO 2022 and ISO 6429 escape sequences. Use of this feature is
discouraged: multilingual applications should be modified to directly generate
UTF-8 instead.
Luit is usually invoked transparently by the terminal emulator. For
information about running
luit from the command line, see EXAMPLES
below.
- -V
- Print luit's version and quit.
-
-alias filename
- the locale alias file
(default: unknown).
-
-argv0 name
- Set the child's name (as passed in argv[0]).
- -c
- Function as a simple converter from standard input to
standard output.
-
-encoding encoding
- Set up luit to use encoding rather than the
current locale's encoding.
-
-g0 charset
- Set the output charset initially selected in G0. The
default depends on the locale, but is usually ASCII.
-
-g1 charset
- Set the output charset initially selected in G1. The
default depends on the locale.
-
-g2 charset
- Set the output charset initially selected in G2. The
default depends on the locale.
-
-g3 charset
- Set the output charset initially selected in G3. The
default depends on the locale.
-
-gl gn
- Set the initial assignment of GL in the output. The
argument should be one of g0, g1, g2 or g3.
The default depends on the locale, but is usually g0.
-
-gr gk
- Set the initial assignment of GR in the output. The default
depends on the locale, and is usually g2 except for EUC locales,
where it is g1.
- -h
- Display a usage and options message on the standard output
and quit.
-
-ilog filename
- Log into filename all the bytes received from the
child.
- -k7
- Generate seven-bit characters for keyboard input.
-
-kg0 charset
- Set the input charset initially selected in G0. The default
depends on the locale, but is usually ASCII.
-
-kg1 charset
- Set the input charset initially selected in G1. The default
depends on the locale.
-
-kg2 charset
- Set the input charset initially selected in G2. The default
depends on the locale.
-
-kg3 charset
- Set the input charset initially selected in G3. The default
depends on the locale.
-
-kgl gn
- Set the initial assignment of GL in the input. The argument
should be one of g0, g1, g2 or g3. The default
depends on the locale, but is usually g0.
-
-kgr gk
- Set the initial assignment of GR in the input. The default
depends on the locale, and is usually g2 except for EUC locales,
where it is g1.
- -kls
- Generate locking shifts (SO/SI) for keyboard input.
- +kss
- Disable generation of single-shifts for keyboard
input.
- +kssgr
- Use GL codes after a single shift for keyboard input. By
default, GR codes are generated after a single shift when generating
eight-bit keyboard input.
- -list
- List the supported charsets and encodings, then quit.
Luit uses its internal tables for this, which are based on the
fontenc library.
- -list-builtin
- List the built-in encodings used as a fallback when data
from iconv or fontenc is missing.
- This option relies on luit being configured to use
iconv, since the fontenc library does not supply a list of
built-in encodings.
- -list-fontenc
- List the encodings provided by “.enc” files
originally distributed with the fontenc library.
- -list-iconv
- List the encodings and locales supported by the
iconv library. Luit adapts its internal tables of
fontenc names to iconv encodings.
- To make scripting simpler, luit ignores spaces,
underscores and ASCII minus-signs (dash) embedded in the names.
Luit also ignores case when matching charset and encoding
names.
- This option lists only the encodings which are associated
with the locales supported on the current operating system. The portable
iconv application provides a list of its supported encodings with
the -l option. Other implementations may provide similar
functionality. There is no portable library call by which an application
can obtain the same information.
-
-olog filename
- Log into filename all the bytes sent to the terminal
emulator.
- +ols
- Disable interpretation of locking shifts in application
output.
- +osl
- Disable interpretation of character set selection sequences
in application output.
- +oss
- Disable interpretation of single shifts in application
output.
- +ot
- Disable interpretation of all sequences and pass all
sequences in application output to the terminal unchanged. This may lead
to interesting results.
- -p
- In startup, establish a handshake between parent and child
processes. This is needed for some older systems, e.g., to successfully
copy the terminal settings to the pseudo-terminal.
-
-prefer list
- Set the lookup-order preference for character set
information. The parameter is a comma-separated list of keywords. The
default order (listing all keywords) is
- fontenc,builtin,iconv,posix
- The default order uses fontenc first because this
allows luit to start more rapidly (about 0.1 seconds) than using
iconv for complex encodings such as eucJP. However, you may find
that the iconv implementation is more accurate or complete. In that case,
you can use the -show-iconv option to obtain a text file which can
be used as an encoding with the fontenc configuration.
- This option relies on luit being configured to use
iconv, since the fontenc library does not provide this
choice.
-
-show-builtin encoding
- Show a built-in encoding, e.g., from a “.enc”
file using the “.enc” format.
- This option relies on luit being configured to use
iconv, since the fontenc library does not supply a list of
built-in encodings.
-
-show-fontenc encoding
- Show a given encoding, e.g., from a “.enc”
file using the “.enc” format. If luit is configured
to use the fontenc library, it obtains the information using that
library. Otherwise luit reads the file directly.
- Some of fontenc's encodings are built into the
library. The fontenc library uses those in preference to an
external file. Use the -show-builtin option to provide similar
information when luit is configured to use iconv.
-
-show-iconv encoding
- Show a given encoding, using the “.enc”
format. If luit is configured to use iconv, it obtains the
information using that interface. If iconv cannot supply the
information, luit may use a built-in table.
- -t
- Initialize luit using the locale and command-line
options, but do not open a pty connection. This option is used for testing
luit's configuration. It will exit with success if no errors were
detected. Repeat the -t option to cause warning messages to be
treated as errors.
- -v
- Be verbose. Repeating the option, e.g., “
-v -v” makes it more verbose. Luit does not
use getopt, so “-vv” does not work.
- -x
- Exit as soon as the child dies. This may cause luit
to lose data at the end of the child's output.
- --
- End of options.
Luit uses these environment variables:
- FONT_ENCODINGS_DIRECTORY
- overrides the location of the “encodings.dir”
file, which lists encodings in external “.enc” files.
- LC_ALL
- LC_CTYPE
- LANG
- During initialization, luit calls setlocale
to check if the user's locale is supported by the operating system. If
setlocale returns a failure, luit looks instead at these
variables in succession to obtain any clues from the user's environment
for locale preference.
- NCURSES_NO_UTF8_ACS
-
Luit sets this to tell ncurses to not rely upon
VT100 SI/SO controls for line-drawing.
- SHELL
- This is normally set by shells other than the Bourne shell,
as a convention. Luit will use this value (rather than the user's
entry in /etc/passwd) to decide which shell to execute. If SHELL is not
set, luit executes /bin/sh.
The most typical use of
luit is to adapt an instance of
XTerm to
the locale's encoding. Current versions of
XTerm invoke
luit
automatically when it is needed. If you are using an older release of
XTerm, or a different terminal emulator, you may invoke
luit
manually:
- $ xterm -u8 -e luit
If you are running in a UTF-8 locale but need to access a remote machine that
doesn't support UTF-8,
luit can adapt the remote output to your
terminal:
- $ LC_ALL=fr_FR luit ssh legacy-machine
Luit is also useful with applications that hard-wire an encoding that is
different from the one normally used on the system or want to use legacy
escape sequences for multilingual output. In particular, versions of
Emacs that do not speak UTF-8 well can use
luit for multilingual
output:
- $ luit -encoding 'ISO 8859-1' emacs -nw
And then, in
Emacs,
- M-x set-terminal-coding-system RET iso-2022-8bit-ss2
RET
- unknown
- The file mapping locales to locale encodings.
On systems with SVR4 (“Unix-98”) ptys (Linux version 2.2 and
later, SVR4),
luit should be run as the invoking user.
On systems without SVR4 (“Unix-98”) ptys (notably BSD variants),
running
luit as an ordinary user will leave the tty world-writable;
this is a security hole, and
luit will generate a warning (but still
accept to run). A possible solution is to make
luit suid root;
luit should drop privileges sufficiently early to make this safe.
However, the startup code has not been exhaustively audited, and the author
takes no responsibility for any resulting security issues.
Luit will refuse to run if it is installed setuid and cannot safely drop
privileges.
None of this complexity should be necessary. Stateless UTF-8 throughout the
system is the way to go.
Charsets with a non-trivial intermediary byte are not yet supported.
Selecting alternate sets of control characters is not supported and will never
be.
These are portable:
- •
- xterm(1),
- •
- ncurses(3X).
These are Linux-specific:
- •
- unicode(1),
- •
- utf-8(1),
- •
- charsets(1).
These are particularly useful:
- •
-
Character Code Structure and Extension Techniques (ISO 2022, ECMA-35)
- •
-
Control Functions for Coded Character Sets (ISO 6429, ECMA-48)
- •
-
http://czyborra.com/charsets/
Luit was written by Juliusz Chroboczek <
[email protected]> for the
XFree86 project.
Thomas E. Dickey has maintained
luit for use by
xterm since
2006.