if [ -z "$1" ]
then
	echo "Usage: $0 <interface>"
	exit 1
fi

if ! /sbin/ifconfig $1 >/dev/null 2>&1
then
	echo "interface inexistante"
	exit 2
fi
			
while /bin/true;
do
	eval `/sbin/ifconfig $1 | grep 'RX bytes' | sed 's/^.*bytes:\([^ ]*\) .*bytes:\([^ ]*\) .*$/newrx=\1; newtx=\2/'`
	if [ -n "$oldrx" ]
	then
		echo -ne 'Réception (ko/s): '$((($newrx-$oldrx)/1024))' Emission (ko/s): '$((($newtx-$oldtx)/1024))'                 \r'
	fi
	oldrx=$newrx; oldtx=$newtx; sleep 1;
done