In computing, tty is a command in Unix and Unix-like operating systems to print the file name of the terminal connected to standard input.

[3] The tty command is commonly used to check if the output medium is a terminal.

The command prints the file name of the terminal connected to standard input.

If no file is detected (in case, it's being run as part of a script or the command is being piped) "not a tty" is printed to stdout and the command exits with an exit status of 1.

The command also can be run in silent mode (tty -s) where no output is produced, and the command exits with an appropriate exit status.