#!/usr/bin/perl 

use strict;
use warnings;
use Net::Pcap;
use NetPacket::Ethernet;
use NetPacket::IP;
use NetPacket::TCP;

my $err;
my $type = 'DLT_IEEE802_11';
my $dev  = Net::Pcap::lookupdev( \$err );
if ( defined $err ) {
    die "Unable to determine network device for monitoring - ", $err;
}

my ( $addr, $net, $mask );
if ( Net::Pcap::lookupnet( $dev, \$net, \$mask, \$err ) ) {
    die "Unable to look up device information for ", $dev, " - ", $err
+;
}
print STDOUT "${dev}: addr/mask -> $addr/$mask\n";

my $WiFiobject = Net::Pcap::open_live( $dev, 2048, 1, -1, \$err );
my $w802 = Net::Pcap::datalink($type);
Net::Pcap::set_datalink( $WiFiobject, $w802 );
unless ( defined $WiFiobject ) {
    die 'Unable to create packet capture on device ', $dev, ' - ', $er
+r;
}
die 'Unable to perform packet capture'
  unless Net::Pcap::loop( $WiFiobject, -1, \&syn_packets, '' );
Net::Pcap::close($WiFiobject);

sub syn_packets {
    my ( $user_data, $header, $packet ) = @_;
    my $macaddr = NetPacket::Ethernet->decode($packet);
    print "$macaddr->{'src_mac'},  $macaddr->{'dest_mac'}\n";

}
[download]

Update: Making some progress. This is better still. I added Net::Pcap::FindDevice

#!/usr/bin/perl 

use strict;
use warnings;
use Data::Dumper;
use Net::Pcap;
use Net::Pcap::FindDevice;
use NetPacket::Ethernet;
use NetPacket::IP;
use NetPacket::TCP;

my $err;
my $type = 'DLT_IEEE802_11';
my $dev  = find_device($ARGV[0]);
my ( $addr, $net, $mask );
if ( Net::Pcap::lookupnet( $dev, \$net, \$mask, \$err ) ) {
    die "Unable to look up device information for ", $dev, " - ", $err
+;
}
print STDOUT "${dev}: addr/mask -> $addr/$mask\n";

my $WiFiobject = Net::Pcap::open_live( $dev, 128000, -1, 500, \$err );
my $w802 = Net::Pcap::datalink_name_to_val($type);
Net::Pcap::set_datalink( $WiFiobject, $w802 );
unless ( defined $WiFiobject ) {
    die 'Unable to create packet capture on device ', $dev, ' - ', $er
+r;
}
die 'Unable to perform packet capture'
  unless Net::Pcap::loop( $WiFiobject, -1, \&syn_packets, '' );
print Dumper ($WiFiobject);

Net::Pcap::close($WiFiobject);

sub syn_packets {
    my ( $user_data, $header, $packet ) = @_;
    my $macaddr = NetPacket::Ethernet->decode($packet);
    print "$macaddr->{'src_mac'},  $macaddr->{'dest_mac'}\n";

}
[download]

works perfectly with wired ethernet. I can do that with the first version i posted, but when i use wireless i get errors

Unable to look up device information for wifi - wifi: no IPv4 address 
+assigned at catchme-ng.pl line 17.
[download]

so i comment that part out and it sniffs! But it thinks all source MAC addresses are elite:

wifi: addr/mask -> /
000031333337,  440000009000
000031333337,  440000009000
^C
[download]

:( I feel like i am so close. I just need to sniff MAC addresses from wireless packets (ALL). like Airodump-ng does.

in khen1950fx's code my $dev  = find_device($ARGV[0]); says that the name "wifi" printed in the error message is retrieved from $ARGV[0]. You call your device wlan0 not wifi. Maybe try wlan0 as the argument?