I think this link - https://swtch.com/~rsc/regexp/regexp1.html i- s the best place to start. Superb exposition on the background, theory, and implementation as well as a bit of history of how the industry lost its way with regular expressions. Regular expressions are beautiful, simple, and widely misunderstood. -rob On Sat, Aug 1, 2020 at 10:03 AM Bakul Shah wrote: > On Jul 31, 2020, at 3:57 PM, Will Senn wrote: > > > > I've always been intrigued with regexes. When I was first exposed to > them, I was mystified and lost in the greediness of matches. Now, I use > them regularly, but still have trouble using them. I think it is because I > don't really understand how they work. > > ... > > 1. What's the provenance of regex in unix (when did it appear, in what > form, etc)? > > 2. What are the 'best' implementations throughout unix (keep it pre > 1980s)? > > 3. What are some of the milestones along the way (major changes, forks, > disagreements)? > > 4. Where, in the source, or in a paper, would you point someone to > wanting to better understand the mechanics of regex? > > Start here: https://en.wikipedia.org/wiki/Thompson%27s_construction > > [I learned about regular expressions in an automata theory class, > before I knew anything about Unix. What helped me was learning > about finite state machines. You won't need more than paper and > pencil to construct one. Reading source code would make more > sense once you grasp how to construct a FSM corresponding to a RE.]