4.2BSD/usr/man/man1/tty.1

Compare this file to the similar file:
Show the results in this format: 

.TH TTY 1 "10 February 1983"
.SH NAME
tty \- get terminal name
.SH SYNOPSIS
.B tty
[ -s ]
.SH DESCRIPTION
.I Tty
prints the pathname of the user's terminal unless the \-s
(silent) is given. In either case, the exit value is zero if the
standard input is a terminal and one if it is not.
.SH DIAGNOSTICS
`not a tty' if the standard input file is not a terminal.