Just to keep everyone up to date, and so that I have a backup of this; here's some sloppy code.

#!/usr/bin/perl -w
use Net::Pcap;

my $err;
my $dev = $ARGV[0];
my $object;

$object = Net::Pcap::open_offline($dev, \$err);
unless (defined $object) {
    die 'Unable to create packet capture on device ', $dev, ' - ', $er
+r;
}

Net::Pcap::loop($object, -1, \&callback_function, '');
Net::Pcap::close($object);

sub callback_function {
  my ($user_data,$header,$packet) =@_;

  #the beacons have to be atleast 37 bytes
  if (length($packet)>36) {
    my $sourcemac = unpack ('H12',substr($packet,10,6));
    my $bs = unpack ('H12',substr($packet,16,6));
    my $o = unpack ('H2*',substr($packet,0,1));
    my $len = sprintf("%x",unpack ('H1',substr($packet,38,1)));
    my $ssid=0;
    if ($o eq "80") {
      $ssid=unpack ('A*',substr($packet,38,$len));
      if ($ssid eq " ") { #doesnt work yet
        $ssid=">no ssid<";
      }
      print "Beacon Frame: source mac:",$sourcemac," basestation id: $
+bs other: 
",$o," ssid: $ssid len: $len\n";
    }
  }
}
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