Side note: in the *nix world piping few common tools together is hardly ever considered coding, even if it includes (simple) code for
sed, awk or sh. It's a standard way of creating solutions that fit your needs, instead of hoping that some programmer has anticipated them and implemented inside a single tool. E.g. your "I won't be searching for doubles" can be implemented by additional s/\(.\)\1//g in sed. I'm not saying you should change your requirements, I'm just noticing it is an example of how solving problems in the gist of the Unix philosophy works.