module Puppet::Parser::Functions
        newfunction(:interface_alias, :type => :rvalue) do |args|
                interface_alias = args[0]
                $stderr = File.open("/tmp/plugin.output","w")
                 interface_data = `/sbin/ip address show label #{interface_alias}`.split
                 if interface_data[1].nil?
                     "_default_"
                 else
                     interface_data[1].gsub(/\/\d+/, '') 
                 end
        end
end

--- manifest usage ---

$foo = interface_alias("eth0:0")