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 controling terminals

   [handling of ANSI terminals using Expect]:   

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

   [terminal control sequence]:   


** Reference **

   [http://vt100.net/%|%VT100.net]:   This site is 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 **

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

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

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