`tty': Print file name of terminal on standard input
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`tty' prints the file name of the terminal connected to its standard
input. It prints `not a tty' if standard input is not a terminal.
Synopsis:
tty [OPTION]...
The program accepts the following option. Also see Note:Common
options.
`-s'
`--silent'
`--quiet'
Print nothing; only return an exit status.
Exit status:
0 if standard input is a terminal
1 if standard input is not a terminal
2 if given incorrect arguments
3 if a write error occurs