throughput of expdp

while true
do
prev=`ls -l *.dmp | awk '{a+=$5}END{printf("%.0f\n",a/1024/1024)}'`
sleep 60
next=`ls -l *.dmp | awk '{a+=$5}END{printf("%.0f\n",a/1024/1024)}'`
doorloop=`expr $next - $prev`
echo $next $prev $doorloop
done