prints a number at the same location in a line until 0 (countdown)

countdown.sh

#!/bin/sh -x          
# -x prints every command before it executes it

# prints 3, 2, 1, 0 in the same location
echo -n " "
let i=3
while [ ${i} -ge 0 ]
do
    printf "\b${i}"
    let i-=1
    sleep 1
done
echo ""