n=0

while true
do
    # If 'n' is even, print 'Tick'
    if (( $n % 2 == 0 ))
    then
        echo "Tick"
    # Else print 'Tock'
    else
        echo "Tock"
    fi

    # Increment 'n'
    (( n++ ))

    # Pause program for a second before printing next message
    sleep 1
done