The unix command tty displays the name of the terminal type.tty is the controling terminal interface.
The file /dev/tty is, in each process a synonym for the control terminal assosciated with the process group of that process. It can be used for programs that demand the name of a file for output, when typed output is desired .
The tty command prints the path name of the user terminal.
-l prints the synchronous line number to which the user's terminal is connected, if it is on an active
-s inhibits the printing of the terminal path name, allowing one to just test the exit code.
The exit codes are as follows:
2 if invalid options were specified
0 if standard input is a terminal.
The error message not an active synchronous line, appears if the standard input is not a synchronous terminal and -1 is specified.
The error message not a tty, appears if the standard input is not a terminal and -s is not specified.