sub process_file {
    my $filename = shift or die "Missing filename!";
    open (FILE, $filename) or die "Unable to open $filename because $!\n";

    while ($line = <FILE2>) {
        chomp ($line);
        ($chrX, $chrpos, $value11, $value22) = split (/\t/, $line);
        $key2 = join ("_", $chrX, $chrpos);
        if (exists $hash{$key2} > 0) {
            $hash{key2} = $value11 + $value1;
            $hash{key2} = $value22 + $value2;
            $hash{key2}++
        }
    }
    close FILE;
}