Great question. I learned them through osmosis over many years of looking at them in other people's code and tinkering myself. I don't remember ever going through a tutorial or reading a book. Probably not the best way to learn them as it definitely took a long time to have a good grip on them and I was missing important pieces for a long time. For example, it was only relatively recently that I learned that you can turn off "greedy" when using .* by adding a ? after it.