Awk is a great and oft-forgotten tool. Not only is it useful, the awk way of thinking about stream processing generalizes nicely to a bunch of other areas. You have a block that runs before anything else happens, a block run just before the program exits, and a block run for every piece of input. In awk, the input is a line of text, but nothing stops you from generalizing this to say a frame from a video (split into channels in various colorspaces, fed through a processing pipeline, returning another, processed image), a sound frame, a sensor measurement...