Someone

#!/bin/bash
# Almost everything of this is shamelessly copied from
# http://www.lugmen.org.ar/~conan/tmp/wmii/status
INTERFACE="eth0"

while true; do
    RX0=`grep $INTERFACE /proc/net/dev | tr ':' ' ' | awk {'print $2'}`
    TX0=`grep $INTERFACE /proc/net/dev | tr ':' ' ' | awk {'print $10'}`
    sleep 2
    RX1=`grep $INTERFACE /proc/net/dev | tr ':' ' ' | awk {'print $2'}`
    TX1=`grep $INTERFACE /proc/net/dev | tr ':' ' ' | awk {'print $10'}`
    RX="$(((RX1-RX0)/2048))"
    TX="$(((TX1-TX0)/2048))"

    RX="RX `printf %3d $RX`KB/s"
    TX="TX `printf %3d $TX`KB/s"
    

    echo "$INTERFACE: $RX $TX"
done