open my $fh, '<', $data_file or die "failed to open '$data_file' $!";  
while( <$fh> ) {  
    my ($mac, $ip) = (split(/ /, $_))[3,5];  
    $uniq{ $mac } = $ip; 
}  
close $fh;  
  
foreach my $mac ( sort keys %uniq ) { # sorts by mac addresses lexically 
 
# if you need to sort numerically, do this instead 
# foreach my $mac ( sort {$a <=> $b} keys %uniq ) 
 
    print "$mac \t $uniq{$mac}\n";  
}