A '''terminal''' is a display unit that is part of the user interface to a
computer system.  The word carries the connotation of being text-only.



** See Also **

   [ANSI]:   Various ANSI standards govern terminal behaviour.

   [xterm]:   A terminal emulator.

   [curses]:   A [C] library for controlling terminals.

   [handling of ANSI terminals using Expect]:   

   [pty]:   Short for '''pseudo teletype''', but commonly referred to as '''pseudo terminal'''

   [stty]:   The [Units%|%*nix] command to configure and manage a terminal.

   [terminal control sequence]:   



** Reference **

   [http://vt100.net/%|%VT100.net]:   Dedicated to the range of video terminals produced by Digital Equipment Corporation (DEC) from 1970 to 1995.  The most famous of these is the VT100.

   [http://www.linusakesson.net/programming/tty/index.php%|%The TTY demystified], Linus Åkesson, 2008-07-25:   



** Description **

Terminal emulators for [Linux] have support for ANSI escape codes built in.



** Checking for a Terminal **

`[chan configure]` can be used to determine whether a channel is connecte to a terminal:

======
proc isatty chan {
        expr {[catch {chan configure $chan -mode}] == 0}
}
======

Credit to [http://www.sqlite.org/src/info/559835e54e0715f2b4d207d056199a8268af739e] for the idea.

However, this doesn't work on [Microsoft Windows%|%Windows].


[AMG]: To check if stdin is connected to a terminal, run:

======
if {![catch {exec /usr/bin/tty -s}]} {
    # stdin is a terminal
}
======

Checking for stdout/stderr is harder because `[exec]` does not allow stdout/stderr to be redirected to stdin because stdout/stderr are not considered readable.  Instead, let the shell do the redirection.  Furthermore, instruct [[exec]] to not intercept stdout/stderr.

======
if {![catch {exec /bin/sh -c {/usr/bin/tty -s < /dev/stdout} >@ stdout}]} {
    # stdout is a terminal
}
if {![catch {exec /bin/sh -c {/usr/bin/tty -s < /dev/stderr} 2>@ stderr}]} {
    # stderr is a terminal
}
======

Without the `-s` switch, the tty program not only checks if its stdin is a terminal, but it also prints the device name to its stdout, e.g. `/dev/pts/0`.




----
[MHo] 2021-09-17: How to test this on Windows? I found the following way if [twapi] is available:
======
package require twapi
twapi::import_commands
proc isStdinRedirected {} {
     catch {get_tcl_channel_handle stdin write}
}
puts [isStdinRedirected]
======
Examples:
======
c:\Users\matthiasu\usr\pgm\tcl\usr\Tst\isatty>echo test|tclkitsh test8.tcl
1

c:\Users\matthiasu\usr\pgm\tcl\usr\Tst\isatty>tclkitsh test8.tcl<nul
1

c:\Users\matthiasu\usr\pgm\tcl\usr\Tst\isatty>tclkitsh test8.tcl
0
======

----

Tcl internally uses `isatty()`.  Perhaps it could provide the following command:

======
chan isatty ...
======



** Page Authors **

   [amg]:   Provided the example of `[chan configure]` to check for a terminal.

   [pyk]:   

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