Found through a Twitter tweet by Stefano Di Paola, Russ Cox explains how Google Search code worked before the company shut it down. Cox worked at Google as an intern in 2006. He tells us that at the time "Google had an internal tool called gsearch that acted as if it ran grep over all the files in the Google source tree and printed the results." Cox explains the detailed and complicated code, summarizing its use.
Unfortunately, but his work is well done