TTY(1) General Commands Manual TTY(1)
tty - display the name of the terminal
tty [ -s ]
tty prints the pathname of the user's terminal unless the -s (silent)
option is given. In either case, the exit value is zero if the standard
input is a terminal, and one if it is not.
-s Silent. Does not print the pathname of the user's terminal.
9 September 1987 TTY(1)