IF=eth0

if [ ! -z $1 ]; then IF=$1; fi

D=$(grep $IF /proc/net/dev)
RX=$(echo $D | awk  '{print $2}')
TX=$(echo $D | awk  '{print $10}')

if [ "$2" != "" -a "$3" != "" ]; then
  RXD=$(($RX-$2))
  TXD=$(($TX-$3))
  RXDK=$(echo "scale=2;$RXD/1024" | bc )" Kb/s"
  TXDK=$(echo "scale=2;$TXD/1024" | bc )" Kb/s"
  echo -ne "D: $RXDK     | U: $TXDK      \r"
fi;
sleep 1;
$0 $IF $RX $TX