@files = qw(model4run1 model2run1 model4run2 model1run1);

my $first = shift(@files);
my $combined = $first;
foreach (@files) {
	$combined &= $_;
}

$combined ^= $first;
$combined =~ s/[^\x00].*//;

my $prefix = substr($first, 0, length($combined));
print qq{Prefix is "$prefix"\n};