sub write_vars {
    my $filename = shift(@_);
    my $vars = shift(@_);
   
    open(FILE, ">$filename");
    
    foreach my $key (keys %{$vars}) {
    # this one is just for convienence
    my $i = \( $vars->{$key} );
        # this is a switch statement
        # make a reference to $vars->{$key} and pass it to ref
        for (ref $i) {
            # if it is scalar, ref will return SCALAR...
            if (/SCALAR/) {
                print FILE "s:$key:" . $vars->{$key} . ";\n";
            }
            # ...otherwise it returns an empty string
            # which means it is a hash or an array
            else {
                $j = $vars->{$key};
                $type = ref $j;
                # if it is an array, print out each element
                if ($type eq "ARRAY") {
                    print FILE "a:$key";
                    for my $element ( @{$j} ) {
                        print FILE ":$element";
                    }
                    print FILE ";\n";
                }
                # likewise for a hash, print out the key/value pairs
                elsif ($type eq "HASH") {
                    print FILE "h:$key";
                    for my $k ( keys %{$j} ) {
                        print FILE ":$k," . $j->{$k};
                    }
                    print FILE ";\n";
                }
            }
        }
    }
   
    close(FILE);
        
    return;
}

%a = qw(One 1 Three 3);
@b = qw(Foo Bar Baz Blah);
%foo = ('a', \%a, 'b', \@b, 'c', 'C');

write_vars("test.txt", \%foo);