You have all probably seen my post on my favorite regex of all time. But here's my second favorite regex of all time:
[,-.]
Any idea what this regexp matches? Scroll down for the answer.
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It matches a comma, dash, and dot. But why is that interesting? Because when you have a regex with a dash in the middle, it means a range, and it also means a range here. However, a comma, dash, and dot are one after another in the ASCII table, so it matches a range from the comma to the dot, which includes the dash itself! In a way it's a self-matching regex!
Take a look at the ASCII table for a quicker visual understanding. See the comma, dash, and dot characters with blue background, they come one after another.
[,-.] matches itself.
See you next time!