#! perl
use strict;
use warnings;

$allmac = "~/temp/allmac.txt";
print $allmac;
while (my $line = $allmac)
{
    if ($line =~ /C4:46:19:75:C1:55/)
    {
        $id = (split /\s+/, $line)[0];
		print "ID = $id\n";
    }
}