Start pppd if ethernet connection has no network, kill it if ethernet comes up

ppp.sh

#!/bin/sh

CONNECTION=1

while [ 1 ]
do
    if ping -q -c 1 -w 1 -I eth0 google.com > /dev/null ; then
        if [ $CONNECTION -eq 0 ] ; then
            echo "Ethernet connection is up, killing pppd"
            killall pppd
            CONNECTION=1
        fi
    else
        if [ $CONNECTION -eq 1 ] ; then
            echo "No ethernet connection, dialing pppd"
            pppd call gsm
            CONNECTION=0
        fi
    fi

    sleep 60
done