Do you mean you want the data rate through each interface? Here's a really, truly brute-force solution, nearly fingers-to-keyboard so do make it your own.
Code:
IFACES="eth0 eth1 eth2 eth3"
start=`date +%s.%N`
for iface in $IFACES; do
let `ifconfig $iface | sed -nr 's/.*X bytes:([0-9]+).*X bytes:([0-9]+).*/'$iface'=\1+\2/gp'`
done
while true; do
sleep 5
now=`date +%s.%N`
statline=''
for iface in $IFACES; do
let new=`ifconfig $iface | sed -nr 's/.*X bytes:([0-9]+).*X bytes:([0-9]+).*/\1+\2/gp'`
statline="$statline `dc -e '4k['$iface':]n '$new' '$(($iface))'- '$now' '$start'-/n [b/s]p'`"
let $iface=$new
done
start=$now
echo $statline
done
