With the upcoming release of ruby v2.5 scheduled (as per tradition) for 25th December, it’s good to know what’s changed in the language - so you can take advantage any new (or refined) features.
I recently published a powerful ruby gem on Github: regexp-examples. This library allows you to generate all (or one random) strings that match any regular expression! (With just a few limitations on what’s possible.) To install it yourself and have a quick play is dead easy: