@almatic - I hate to be real picky, but would you really use:
Code:
let "sum = sum + $(df | grep area | awk '{print $4}' | sed -n ''$i'p')"
Both awk and sed have all that you need to do any of the other steps, it seems pointless to include all 3.
Maybe this example will help:
Code:
df | awk '/area/{sum+=$4}END{print sum}'