[jeff-hykin]

For context, AFAIK, I maintain the largest Textmate (read as "regex document") grammar in the world; the C++ textmate grammar for VS Code. (Don't mistake that as bragging, its a literally-unfixable dumpster fire) It has pretty much forced me to regularly use every regex feature, from recursive named backreferences to atomics and time complexity of lookahead's combinatorial explosions.

https://regexr.com/ is one of the most amazing interactive resources, I can't recommend enough. Back in the day I used it to go from beginer to intermediate. And while I never used this next site to learn, https://regex-vis.com/ is a great place to check out. From intermediate to master I've pretty much relied on rexegg.com/ for discovering the advanced stuff and engine differences. After that https://regex101.com/ was helpful for performance analysis. I first learned regex just mucking around in the CLI with some guidance from a programmer friend. Pure trial and error learning.

While I am inclined to say "the only way to learn regex is to use it", after reading the comments I must agree it would've been nice to have examples of pitfalls and misconceptions. There's a lot of them that can take a very very long time to learn without direct examples. I've never even heard of Jeff Fried (not till this post at least). So props to people who can actually read those kinds of books.

[cdaringe]

Im also inclined to say just use it, based on pareto principle. regexr.com is the best, and has a cheatsheet section. Further, hover tooltips explaining expression behavior. Our team has an informal policy of “link to regexr demo” in comments at callsites for anything absolutely nontrivial.