while (<XCH0S>) {
    chomp;
    tr/A-Z/a-z/;
    $xch0{(split",")[2]}++;    
}
while (<XCH3S>) {
    chomp;
    tr/A-Z/a-z/;
    my $dn = (split",")[2];    
    print "DN of extra record is: $dn\n" if !defined $xch0{$dn};
}