PHP generate all possible String -

I want to set "a **" for example and now I have all the probabilias with "Sir" and two other characters. I want to create an array with stars. So aaa, aab, aac, aad, ..., aba, abb, abc, abd, ... axx

Is it possible with PHP? Any ideas how?

foreach (category ('a', 'z') $ a) foreign currency Range ('A', 'Z') as $ B) "A $ a $ b \ n" echo;