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}++
    }
};