linux - tty (1)

       tty  -  print  the  file name of the terminal connected to
       standard input

       tty [-s] [--silent] [--quiet] [--help] [--version]

       This manual page documents the GNU version  of  tty.   tty
       prints  the file name of the tty connected to its standard
       input.  It prints `not a tty' if the standard input is not
       a tty. Its exit status is:
       0 if the standard input is a tty
       1 if the standard input is not a tty
       2 if given incorrect arguments
       3 if a write error occurs

   OPTIONS
       --help Print  a  usage message on standard output and exit
              successfully.

       -s, --silent, --quiet
              Print nothing; only return an exit status.

       --version
              Print version information on standard  output  then
              exit successfully.