/usr/bin/tty [-l] [-s]
The tty utility writes to the standard output the name of the terminal that is open as standard input. The name that is used is equivalent to the string that would be returned by the ttyname (3C) function.
The following options are supported:
Prints the synchronous line number to which the user's terminal is connected, if it is on an active synchronous line.
Inhibits printing of the terminal path name, allowing one to test just the exit status.
See environ(5) for descriptions of the following environment variables that affect the execution of tty: LANG, LC_ALL , LC_CTYPE, LC_MESSAGES, and NLSPATH.
The following exit values are returned:
Standard input is a terminal.
Standard input is not a terminal.
An error occurred.
See attributes(5) for descriptions of the following attributes:
The standard input is not a synchronous terminal and –l is specified.
The standard input is not a terminal and –s is not specified.
The –s option is useful only if the exit status is wanted. It does not rely on the ability to form a valid path name. Portable applications should use test –t.