urlmonitor - print out the URLs requested system wide on the main network interface

urlmonitor

# urlmonitor - print out the URLs requested system wide on the main network interface

# Accept a network interface name as an optional argument
  iface = ARGV.first

# No interface specified? Try to guess which one is king..
  unless iface
    `ifconfig -l`.split.each do |iface|
      next if iface =~ /^lo/
      break if `ifconfig #{iface}` =~ /inet (0|1|2)/
    end
  end

# Get tcpdump running, grep out relevant HTTP headers and build them
# in to URLs
  STDOUT.sync = true
  IO.popen(%{sudo tcpdump -i en1 -n -s 0 -w - | grep -a --line-buffered -E "Host\: .*|GET \/.*"}, 'r') do |pipe|
    pipe.sync = true
    while line = pipe.gets
      path = $1.chomp and host = nil if line =~ /GET (.*?)\s/
      host = $1.chomp if line =~ /Host: (.*)/
      if path && host
        puts "http://#{host}#{path}"
        path = host = nil
      end
    end
  end

You hardcoded en1.
It doesn't output a thing for me, what could be the problem (I'd really like to have this one in my toolbox)?