ip_start=192.168
ip_end=.1.0
subnet=24
interval=`expr 60 \* 5` # 5 minutes
# run once
arp-scan $ip_start$ip_end/$subnet | tail -n +3 | ruby compare_wifi.rb;
# and stay updated
while sleep $interval; do
    arp-scan $ip_start$ip_end/$subnet | tail -n +3 | ruby compare_wifi.rb;
done