Program in UNIX which checks after every one-minute whether user has logged in or not

A friend of yours has promised to log in at a particular time. However, he has not kept the promise. You want to contact him as soon as he logs in. Write a shell script which checks after every one-minute whether your friend has logged in or not. The logname should be supplied to the shell script at command prompt.

echo "Enter User number :"

read un

x=`who | grep $un |wc -l`

if [ $x -ne 0 ]

then

        echo "User $un logged in "

else

        while [ $x -eq 0 ]

        do

                sleep 2

                x=`who|grep $un|wc -l`

                if [ $x -ge 1 ]

                then

                        echo "now user logged in "

                        write $un >hi

                        exit

                fi

        done

fi