Execute on file change

You have all been there – wanting to execute something whenever a file or a set of files changes. There are several tools that will help you, but so far entr is the simplest, most no-nonsense solution I have found.
I’ve been using it the past few days when creating a dynamic nginx reverse proxy config with consul-template, and it works like a charm.
Go check it out – it is available through apt on ubuntu and brew on OSX.