Have you ever been faced with a situation where you need to encode a string with all sorts of problem characters into a URL-safe string, but, for whatever reason, urlencode() just won't do the job? 

What you need is a function that will give you nothing but numbers and letters-- no %'s or &'s, spaces, or any other non-alphanumeric character.

Well, look no further that PHP's bin2hex() function, and its pack() function.

It can convert this tricky string:

(!X>4Ob=h/&hN\'

Into this much nicer string, which can easily pass through a URL, MySQL query, XML tags, etc, since it is guaranteed to only ever be letters and numbers:

2821583e344f623d682f26684e5c27

And then decoding is a snap.  Here are the functions you need:

function hex_encode($input) {
  return bin2hex($input);
}

function hex_decode($input) {
  return pack("H*", $input);
}

Enoy!