Работа с сетевыми интерфейсами (Debian, Ubuntu)

#!/bin/sh
set -e
export LANG=C
iface="$1"
mac=$(/sbin/ifconfig "$iface" | sed -n -e '/^.*HWaddr \([:[:xdigit:]]*\).*/{s//\1/;y/ABCDEF/abcdef/;p;q;}')
which=""
while read testmac scheme; do
	if [ "$which" ]; then continue; fi
	if [ "$mac" = "$(echo "$testmac" | sed -e 'y/ABCDEF/abcdef/')" ]; then which="$scheme"; fi
done
if [ "$which" ]; then echo $which; exit 0; fi
exit 1

auto dsl-provider
iface dsl-provider inet ppp
      pre-up /sbin/ifconfig eth0 up 
      provider dsl-provider