Ubuntu Manpage: tset, reset - initialize or reset terminal state

NAME

       tset, reset - initialize or reset terminal state

SYNOPSIS

       tset [-IQVcqrsw] [-] [-e ch] [-i ch] [-k ch] [-m mapping] [terminal-type]
       reset [-IQVcqrsw] [-] [-e ch] [-i ch] [-k ch] [-m mapping] [terminal-type]

DESCRIPTION

tset — initialization
This program initializes terminals.

First, tset retrieves the current terminal mode settings for your terminal. It does this
by successively testing

• the standard error,

• standard output,

• standard input and

• ultimately “/dev/tty”

to obtain terminal settings. Having retrieved these settings, tset remembers which file
descriptor to use when updating settings.

Next, tset determines the type of terminal that you are using. This determination is done
as follows, using the first terminal type found.

1. The terminal argument specified on the command line.

2. The value of the TERM environment variable.

3. (BSD systems only.) The terminal type associated with the standard error output device
in the /etc/ttys file. (On System V hosts and systems using that convention, getty(8)
does this job by setting TERM according to the type passed to it by /etc/inittab.)

4. The default terminal type, “unknown”, is not suitable for curses applications.

If the terminal type was not specified on the command-line, the -m option mappings are
then applied; see subsection “Terminal Type Mapping”. Then, if the terminal type begins
with a question mark (“?”), the user is prompted for confirmation of the terminal type.
An empty response confirms the type, or, another type can be entered to specify a new
type. Once the terminal type has been determined, the terminal description for the
terminal is retrieved. If no terminal description is found for the type, the user is
prompted for another terminal type.

Once the terminal description is retrieved,

• if the “-w” option is enabled, tset may update the terminal's window size.

If the window size cannot be obtained from the operating system, but the terminal
description (or environment, e.g., LINES and COLUMNS variables specify this), use this
to set the operating system's notion of the window size.

• if the “-c” option is enabled, the backspace, interrupt and line kill characters
(among many other things) are set

• unless the “-I” option is enabled, the terminal and tab initialization strings are
sent to the standard error output, and tset waits one second (in case a hardware reset
was issued).

• Finally, if the erase, interrupt and line kill characters have changed, or are not set
to their default values, their values are displayed to the standard error output.

reset — reinitialization
When invoked as reset, tset sets the terminal modes to “sane” values:

• sets cooked and echo modes,

• turns off cbreak and raw modes,

• turns on newline translation and

• resets any unset special characters to their default values

before doing the terminal initialization described above. Also, rather than using the
terminal initialization strings, it uses the terminal reset strings.

The reset command is useful after a program dies leaving a terminal in an abnormal state:

• you may have to type

<LF>reset<LF>

(the line-feed character is normally control-J) to get the terminal to work, as
carriage-return may no longer work in the abnormal state.

• Also, the terminal will often not echo the command.

Setting the Environment
It is often desirable to enter the terminal type and information about the terminal's
capabilities into the shell's environment. This is done using the -s option.

When the -s option is specified, the commands to enter the information into the shell's
environment are written to the standard output. If the SHELL environment variable ends in
“csh”, the commands are for csh(1), otherwise, they are for sh(1). The csh commands set
and unset the shell variable noglob, leaving it unset. The following line in the .login
or .profile files will initialize the environment correctly:

eval `tset -s options ... `

Terminal Type Mapping
When the terminal is not hardwired into the system (or the current system information is
incorrect) the terminal type derived from the /etc/ttys file or the TERM environment
variable is often something generic like network, dialup, or unknown. When tset is used
in a startup script it is often desirable to provide information about the type of
terminal used on such ports.

The -m options maps from some set of conditions to a terminal type, that is, to tell tset
“If I'm on this port at a particular speed, guess that I'm on that kind of terminal”.

The argument to the -m option consists of an optional port type, an optional operator, an
optional baud rate specification, an optional colon (“:”) character and a terminal type.
The port type is a string (delimited by either the operator or the colon character). The
operator may be any combination of “>”, “<”, “@”, and “!”; “>” means greater than, “<”
means less than, “@” means equal to and “!” inverts the sense of the test. The baud rate
is specified as a number and is compared with the speed of the standard error output
(which should be the control terminal). The terminal type is a string.

If the terminal type is not specified on the command line, the -m mappings are applied to
the terminal type. If the port type and baud rate match the mapping, the terminal type
specified in the mapping replaces the current type. If more than one mapping is
specified, the first applicable mapping is used.

For example, consider the following mapping: dialup>9600:vt100. The port type is dialup ,
the operator is >, the baud rate specification is 9600, and the terminal type is vt100.
The result of this mapping is to specify that if the terminal type is dialup, and the baud
rate is greater than 9600 baud, a terminal type of vt100 will be used.

If no baud rate is specified, the terminal type will match any baud rate. If no port type
is specified, the terminal type will match any port type. For example, -m dialup:vt100 -m
:?xterm will cause any dialup port, regardless of baud rate, to match the terminal type
vt100, and any non-dialup port type to match the terminal type ?xterm. Note, because of
the leading question mark, the user will be queried on a default port as to whether they
are actually using an xterm terminal.

No whitespace characters are permitted in the -m option argument. Also, to avoid problems
with meta-characters, it is suggested that the entire -m option argument be placed within
single quote characters, and that csh users insert a backslash character (“\”) before any
exclamation marks (“!”).

OPTIONS

The options are as follows:

-c Set control characters and modes.

-e ch
Set the erase character to ch.

-I Do not send the terminal or tab initialization strings to the terminal.

-i ch
Set the interrupt character to ch.

-k ch
Set the line kill character to ch.

-m mapping
Specify a mapping from a port type to a terminal; see subsection “Terminal Type
Mapping”.

-Q Do not display any values for the erase, interrupt and line kill characters.
Normally tset displays the values for control characters which differ from the
system's default values.

-q The terminal type is displayed to the standard output, and the terminal is not
initialized in any way. The option “-” by itself is equivalent but archaic.

-r Print the terminal type to the standard error output.

-s Print the sequence of shell commands to initialize the environment variable TERM to
the standard output; see subsection “Setting the Environment”.

-V reports the version of ncurses which was used in this program, and exits.

-w Resize the window to match the size deduced via setupterm(3NCURSES). Normally this
has no effect, unless setupterm is not able to detect the window size.

The arguments for the -e, -i, and -k options may either be entered as actual characters or
by using the “hat” notation, i.e., control-h may be specified as “^H” or “^h”.

If neither -c or -w is given, both options are assumed.

ENVIRONMENT

       The tset command uses these environment variables:

       SHELL
            tells tset whether to initialize TERM using sh(1) or csh(1) syntax.

       TERM Denotes your terminal type.  Each terminal type is distinct, though many are similar.

       TERMCAP
            may  denote  the  location of a termcap database.  If it is not an absolute pathname,
            e.g., begins with a “/”, tset  removes  the  variable  from  the  environment  before
            looking for the terminal description.

FILES

       /etc/ttys
              system port name to terminal type mapping database (BSD versions only).

       /etc/terminfo
              compiled terminal description database directory

PORTABILITY

Neither IEEE Std 1003.1/The Open Group Base Specifications Issue 7 (POSIX.1-2008) nor
X/Open Curses Issue 7 documents tset or reset.

The AT&T tput utility (AIX, HP-UX, Solaris) incorporated the terminal-mode manipulation as
well as termcap-based features such as resetting tabstops from tset in BSD (4.1c),
presumably with the intention of making tset obsolete. However, each of those systems
still provides tset. In fact, the commonly-used reset utility is always an alias for
tset.

The tset utility provides backward compatibility with BSD environments; under most modern
Unices, /etc/inittab and getty(8) can set TERM appropriately for each dial-up line,
obviating what was tset's most important use. This implementation behaves like 4.4BSD
tset, with a few exceptions we shall consider now.

A few options are different because the TERMCAP variable is no longer supported under
terminfo-based ncurses:

• The -S option of BSD tset no longer works; it prints an error message to the standard
error and dies.

• The -s option only sets TERM, not TERMCAP.

There was an undocumented 4.4BSD feature that invoking tset via a link named “TSET” (or
via any other name beginning with an upper-case letter) set the terminal to use upper-case
only. This feature has been omitted.

The -A, -E, -h, -u and -v options were deleted from the tset utility in 4.4BSD. None of
them were documented in 4.3BSD and all are of limited utility at best. The -a, -d, and -p
options are similarly not documented or useful, but were retained as they appear to be in
widespread use. It is strongly recommended that any usage of these three options be
changed to use the -m option instead. The -a, -d, and -p options are therefore omitted
from the usage summary above.

Very old systems, e.g., 3BSD, used a different terminal driver which was replaced in 4BSD
in the early 1980s. To accommodate these older systems, the 4BSD tset provided a -n
option to specify that the new terminal driver should be used. This implementation does
not provide that choice.

It is still permissible to specify the -e, -i, and -k options without arguments, although
it is strongly recommended that such usage be fixed to explicitly specify the character.

As of 4.4BSD, executing tset as reset no longer implies the -Q option. Also, the
interaction between the - option and the terminal argument in some historic
implementations of tset has been removed.

The -c and -w options are not found in earlier implementations. However, a different
window size-change feature was provided in 4.4BSD.

• In 4.4BSD, tset uses the window size from the termcap description to set the window
size if tset is not able to obtain the window size from the operating system.

• In ncurses, tset obtains the window size using setupterm(3NCURSES), which may be from
the operating system, the LINES and COLUMNS environment variables or the terminal
description.

Obtaining the window size from a terminal's type description is common to both
implementations, but considered obsolescent. Its only practical use is for hardware
terminals. Generally, the window size will remain uninitialized only if there were a
problem obtaining the value from the operating system (and setupterm would still fail).
The LINES and COLUMNS environment variables may thus be useful for working around window-
size problems, but have the drawback that if the window is resized, their values must be
recomputed and reassigned. The resize(1) program distributed with xterm(1) assists this
activity.

HISTORY

       A  reset  command  written by Kurt Shoens appeared in 1BSD (March 1978).  It set the erase
       and kill characters to ^H (backspace) and @ respectively.  Mark Horton improved this reset
       in  3BSD  (October  1979),  adding  intr,  quit, start/stop, and eof characters as well as
       changing the program to avoid modifying any user settings.  That version of reset did  not
       use termcap.

       Eric  Allman  wrote a distinct tset command for 1BSD, using a forerunner of termcap called
       ttycap.  Allman's comments in the source code indicate that he began work in October 1977,
       continuing  development over the next few years.  By late 1979, it had migrated to termcap
       and handled the TERMCAP variable.  Later comments  indicate  that  tset  was  modified  in
       September  1980  to  use logic copied from the 3BSD “reset” program when it was invoked as
       reset.  This version appeared in 4.1cBSD, late in 1982.  Other developers  such  as  Keith
       Bostic and Jim Bloom continued to modify tset until 4.4BSD was released in 1993.

       The ncurses implementation was lightly adapted from the 4.4BSD sources to use the terminfo
       API by Eric S. Raymond <esr@snark.thyrsus.com>.