I'm quite a fan of Regex Crossword (for both learning and practicing). As the name implies, crosswords but with regex! Quite fun, at least for me.

To make things even more fun, regex differs in subtly different ways, the regex that works in perl might not work in sed. There are two main dialects, BRE and ERE, and lots of tool specific additions. So I find myself wondering if grep is using extended regular expressions, or is that in egrep, or is egrep the standard grep nowadays? One time I saw Russ Cox use Acme, and I saw the real power of regex when used by someone intuitively. But I am no Russ Cox.

I'd learn regex, but it looks like the kind of tool that programmers would shove into every single search function hole and expect everyone to know it even though it makes no sense for it to be there.