$ printf '%s\n' {a..f}{a..f}{a..f}{a..f}|head aaaa aaab aaac aaad aaae aaaf aaba aabb aabc aabd $ printf '%s\n' {a

$ printf '%s\n' {a..f}{a..f}{a..f}{a..f}|head aaaa aaab aaac aaad aaae aaaf aaba aabb aabc aabd $ printf '%s\n' {a..f}{a..f}{a..f}{a..f}|wc -l 1296 So say you've guessed acab and gotten two black pins, then you know nothing is in the right position, so you can `grep -v acab` but also that two of your pins should be used somewhere `grep -E 'a.*[cab]|c.*[ab]|b.*[ca]'` (hope I got that right?) $ printf '%s\n' {a..f}{a..f}{a..f}{a..f}|grep -v acab | grep -E 'a.*[cab]|c.*[ab]|b.*[ca]'|wc -l 756 That filters your options down. However, I don't understand how/whether grepping can give you the optimal next guesses – some of these will give you less information than others. (Of course, you could run some simulations with grep, argmaxing over all the possible responses like the article says, but then you're not just doing simple grepping.)