tset - terminal dependent initialization
tset [ options ] [ -m [ident][test baudrate]:type ] ... [ type ]
reset [ options ] [ -m [ident][test baudrate]:type ] ... [ type ]
Tset sets up your terminal when you first log in to a UNIX system. It does terminal
dependent processing such as setting erase and kill characters, setting or resetting
delays, sending any sequences needed to properly initialized the terminal, and the like.
It first determines the type of terminal involved, and then does necessary initializations
and mode settings. The type of terminal attached to each UNIX port is specified in the
/etc/ttys(5) database. Type names for terminals may be found in the termcap(5) database.
If a port is not wired permanently to a specific terminal (not hardwired) it will be given
an appropriate generic identifier such as dialup.
In the case where no arguments are specified, tset simply reads the terminal type out of
the environment variable TERM and re-initializes the terminal. The rest of this manual
concerns itself with mode and environment initialization, typically done once at login,
and options used at initialization time to determine the terminal type and set up terminal
When used in a startup script (.profile for sh(1) users or .login for csh(1) users) it is
desirable to give information about the type of terminal you will usually use on ports
which are not hardwired. These ports are identified in /etc/ttys as dialup or plugboard
or arpanet, etc. To specify what terminal type you usually use on these ports, the -m
(map) option flag is followed by the appropriate port type identifier, an optional baud
rate specification, and the terminal type. (The effect is to ``map'' from some conditions
to a terminal type, that is, to tell tset ``If I'm on this kind of port, guess that I'm on
that kind of terminal''.) If more than one mapping is specified, the first applicable
mapping prevails. A missing port type identifier matches all identifiers. Any of the
alternate generic names given in termcap may be used for the identifier.
A baudrate is specified as with stty(1), and is compared with the speed of the diagnostic
output (which should be the control terminal). The baud rate test may be any combination
of: >, @, <, and !; @ means ``at'' and ! inverts the sense of the test. To avoid prob-
lems with metacharacters, it is best to place the entire argument to -m within ``''' char-
acters; users of csh(1) must also put a ``\'' before any ``!'' used here.
tset -m 'dialup>300:adm3a' -m dialup:dw2 -m 'plugboard:?adm3a'
causes the terminal type to be set to an adm3a if the port in use is a dialup at a speed
greater than 300 baud; to a dw2 if the port is (otherwise) a dialup (i.e. at 300 baud or
less). (NOTE: the examples given here appear to take up more than one line, for text pro-
cessing reasons. When you type in real tset commands, you must enter them entirely on one
line.) If the type finally determined by tset begins with a question mark, the user is
asked if s/he really wants that type. A null response means to use that type; otherwise,
another type can be entered which will be used instead. Thus, in the above case, the user
will be queried on a plugboard port as to whether they are actually using an adm3a.
If no mapping applies and a final type option, not preceded by a -m, is given on the com-
mand line then that type is used; otherwise the type found in the /etc/ttys database will
be taken to be the terminal type. This should always be the case for hardwired ports.
It is usually desirable to return the terminal type, as finally determined by tset, and
information about the terminal's capabilities to a shell's environment. This can be done
using the - option; using the Bourne shell, sh(1):
export TERM; TERM=`tset - options...`
or using the C shell, csh(1):
setenv TERM `tset - options...`
With csh it is preferable to use the following command in your .login file to initialize
the TERM and TERMCAP environment variables at the same time.
eval `tset -s options...`
It is also convenient to make an alias in your .cshrc:
alias tset 'eval `tset -s \!*`'
This allows the command:
to be invoked at any time to set the terminal and environment. Note to Bourne Shell
users: It is not possible to get this aliasing effect with a shell script, because shell
scripts cannot set the environment of their parent. (If a process could set its parent's
environment, none of this nonsense would be necessary in the first place.)
These commands cause tset to place the name of your terminal in the variable TERM in the
environment; see environ(7).
Once the terminal type is known, tset engages in terminal driver mode setting. This nor-
mally involves sending an initialization sequence to the terminal, setting the single
character erase (and optionally the line-kill (full line erase)) characters, and setting
special character delays. Tab and newline expansion are turned off during transmission of
the terminal initialization sequence.
On terminals that can backspace but not overstrike (such as a CRT), and when the erase
character is the default erase character (`#' on standard systems), the erase character is
changed to BACKSPACE (Control-H).
The options are:
-ec set the erase character to be the named character c on all terminals, the default
being the backspace character on the terminal, usually ^H. The character c can
either be typed directly, or entered using the hat notation used here.
-kc is similar to -e but for the line kill character rather than the erase character; c
defaults to ^X (for purely historical reasons). The kill characters is left alone
if -k is not specified. The hat notation can also be used for this option.
-ic is similar to -e but for the interrupt character rather than the erase character; c
defaults to ^C. The hat notation can also be used for this option.
- The name of the terminal finally decided upon is output on the standard output.
This is intended to be captured by the shell and placed in the environment variable
-s Print the sequence of csh commands to initialize the environment variables TERM and
TERMCAP based on the name of the terminal finally decided upon.
-n On systems with the Berkeley 4BSD tty driver, specifies that the new tty driver
modes should be initialized for this terminal. For a CRT, the CRTERASE and CRTKILL
modes are set only if the baud rate is 1200 or greater. See tty(4) for more
-I suppresses transmitting terminal initialization strings.
-Q suppresses printing the ``Erase set to'' and ``Kill set to'' messages.
If tset is invoked as reset, it will set cooked and echo modes, turn off cbreak and raw
modes, turn on newline translation, and restore special characters to a sensible state
before any terminal dependent processing is done. Any special character that is found to
be NULL or ``-1'' is reset to its default value. All arguments to tset may be used with
This is most useful after a program dies leaving a terminal in a funny state. You may have
to type ``<LF>reset<LF>'' to get it to work since <CR> may not work in this state. Often
none of this will echo.
These examples all assume the Bourne shell and use the - option. If you use csh, use one
of the variations described above. Note that a typical use of tset in a .profile or
.login will also use the -e and -k options, and often the -n or -Q options as well. These
options have not been included here to keep the examples small. (NOTE: some of the exam-
ples given here appear to take up more than one line, for text processing reasons. When
you type in real tset commands, you must enter them entirely on one line.)
At the moment, you are on a 2621. This is suitable for typing by hand but not for a .pro-
file, unless you are always on a 2621.
export TERM; TERM=`tset - 2621`
You have an h19 at home which you dial up on, but your office terminal is hardwired and
known in /etc/ttys.
export TERM; TERM=`tset - -m dialup:h19`
You have a switch which connects everything to everything, making it nearly impossible to
key on what port you are coming in on. You use a vt100 in your office at 9600 baud, and
dial up to switch ports at 1200 baud from home on a 2621. Sometimes you use someone elses
terminal at work, so you want it to ask you to make sure what terminal type you have at
high speeds, but at 1200 baud you are always on a 2621. Note the placement of the ques-
tion mark, and the quotes to protect the greater than and question mark from interpreta-
tion by the shell.
export TERM; TERM=`tset - -m 'switch>1200:?vt100' -m 'switch<=1200:2621'
All of the above entries will fall back on the terminal type specified in /etc/ttys if
none of the conditions hold. The following entry is appropriate if you always dial up,
always at the same baud rate, on many different kinds of terminals. Your most common ter-
minal is an adm3a. It always asks you what kind of terminal you are on, defaulting to
export TERM; TERM=`tset - .PP If the file /etc/ttys is not properly installed and
you want to key entirely on the baud rate, the following can be used:
export TERM; TERM=`tset - -m '>1200:vt100' 2621`
Here is a fancy example to illustrate the power of tset and to hopelessly confuse anyone
who has made it this far. You dial up at 1200 baud or less on a concept100, sometimes
over switch ports and sometimes over regular dialups. You use various terminals at speeds
higher than 1200 over switch ports, most often the terminal in your office, which is a
vt100. However, sometimes you log in from the university you used to go to, over the
ARPANET; in this case you are on an ALTO emulating a dm2500. You also often log in on
various hardwired ports, such as the console, all of which are properly entered in
/etc/ttys. You want your erase character set to control H, your kill character set to
control U, and don't want tset to print the ``Erase set to Backspace, Kill set to Control
export TERM; TERM=`tset -e -k^U -Q - -m 'switch<=1200:concept100' -m
'switch:?vt100' -m dialup:concept100 -m arpanet:dm2500`
/etc/ttys port name to terminal type mapping database
/etc/termcap terminal capability database
csh(1), sh(1), stty(1), ttys(5), termcap(5), environ(7)
The tset command is one of the first commands a user must master when getting started on a
UNIX system. Unfortunately, it is one of the most complex, largely because of the extra
effort the user must go through to get the environment of the login shell set. Something
needs to be done to make all this simpler, either the login(1) program should do this
stuff, or a default shell alias should be made, or a way to set the environment of the
parent should exist.
This program can't intuit personal choices for erase, interrupt and line kill characters,
so it leaves these set to the local system standards.
For compatibility with earlier versions of tset a number of flags are accepted whose use
-d type equivalent to -m dialup:type
-p type equivalent to -m plugboard:type
-a type equivalent to -m arpanet:type
- prints the terminal type on the standard output
-r prints the terminal type on the diagnostic output.
4th Berkeley Distribution March 28, 1997 TSET(1)