I'd like to write a URL shortener that doesn't have to use a database. Instead, to have as few moving parts as possible, the script would just create a unique hash for my URL based on an algorithm (like md5, except an md5 would be too long). I'm not really sure how I'd go about doing this. Any advice?
If it matters, I'd prefer to write this in Ruby.
Ultimately if you're after a short link, you simply need to generate a suitably legible unique code (try to omit similar letters/numbers such as zero and 'o', in case some poor bugger actually has to type it in) and associate that code with the original URL in some form of store.
Whilst I can understand why you don't want to use a database, in many ways it's the perfect form of storage, especially if you look at one of the dedicated key/value stores such as Cassandra, Redis, MongoDB, etc. (That said, a simple "traditional" SQL database may be an easy first step if you're in unfamiliar territory.)