open IN_FILE, "<my_in_file" or die "Cannot open my_in_file\n";
LINE:
whle (<IN_FILE) {
    # This is a big block
    if (/^\S/) {
    } elsif (/^\s{2}\S/) {
        # Do what you want to do for middle hash
    } elsif (/^\s{4}\S/) {
        # Do what you want to do for inner hash
    } else {
        die "Bad line in datafile\n";
    }
}
close IN_FILE;