interfaceup() {
# interface exists?
if [ ! -f /sys/class/net/$1/flags ]; then return 1; fi
let "IFUP = `cat /sys/class/net/$1/flags` & 1"
IFUP="$(($(cat /sys/class/net/$1/flags) & 1))"
# interface has UP flag?
if [ $IFUP -eq 0 ]; then return 1; fi
if [ "$IFUP" -eq 0 ]; then return 1; fi
return 0
}