How does {m}{n} (“exactly n times” twice) work?

Question

So, some way or another (playing around), I found myself with a regex like \\d{1}{2}.

Logically, to me, it should mean:

(A digit exac

Answer 1

I have never seen the {m}{n} syntax anywhere. It seems that the regex engine on this Rubular page applies the {2} quantifier to the smallest possible token before that - which is \\d{1}. To mimick this in Java (or most other regex engines, it would seem), you need to group the \\d{1} like so:

^(\\d{1}){2}$

See it in action here.