REGEX match unlimited of one character but only two of another

Question

I would like to capture a string with the longest possible amount of one character followed by no more than two of another character. Example:

aaaaabbbbbbbb

Would capture:

aaaaabb, bb and b

I have tried:

(a*)(b)(?!\2{2})

but this is only grabbing the two b's like so:

bb

https://regex101.com/r/g6vuUZ/5 – Eraklon Feb 11 '20 at 22:42 — Eraklon, Feb 11 '20 at 22:42
Why does it only capture `b`, not all the other `bb` pairs? – Barmar Feb 11 '20 at 22:42 — Barmar, Feb 11 '20 at 22:42

score 1 · Accepted Answer · answered Feb 11 '20 at 22:46

a*b{0,2}

This matches any number of a followed by up to 2 b.

When using your input, it matches

aaaaabb
bb
bb
bb

Since {0,2} is greedy, it always matches pairs of b, not just a single one. It matches all the remaining bb because they're preceded by zero a, which is matched by a*.

DEMO

REGEX match unlimited of one character but only two of another

1 Answers1