my %onedir = map { $_ => undef } grep /^\w/, readdir(DIR1);
my %twodir = map { $_ => undef } grep /^\w/, readdir(DIR2);

for my $file ( sort keys %onedir ) {
    next unless ( exists( %twodir{$file} ));
    Calc( "$dir1/$file", "$dir2/$file", $testfile );
}