Combine 3 strings into one
===

I've been trying to combine 3 strings into one and having trouble doing so.

the strings are below.

    $from="/2/3/4/5/6/";
    $to="/30/31/32/33/34/";
    $sub="/2/3/4/5/6/7/8/9/10/11/12/";#this is dynamic, ever changing past > (/2/3/4/5/6/)

the output must look like this below.

    $output="/30/31/32/33/34/6/7/8/9/10/11/12/";

else if `$sub` changes like below then.

    $from="/2/3/4/5/6/";
    $to="/30/31/32/33/34/";
    $sub="/2/3/4/5/6/7/8/";
    $output="/30/31/32/33/34/6/7/8/";

and else if `$to` changes then this.

    $from="/2/3/4/5/6/";
    $to="/30/31/";
    $sub="/2/3/4/5/6/7/8/";
    $output="/30/31/6/7/8/";

the `$to` needs to be first, then the `$sub` at the end, minus the `$from` before the end `/*/(eg./6/)` to be combined into 1 string.

how is this possible?