Find five letter words that are made up of letters {h, i, k, e, r, s} where each letter appears only once.
grep -Ei "^[hikers]{5}$" /usr/share/dict/american-english
gives
Essie Hesse Irish Kerri Reese Sheri ...
where some letters are duplicated in some of the words. For example, the letter 'i' appears twice in the word 'Irish'. We need to filter out all such words.
Pipe the output to grep -viE '(.).*\1'
. For example
% grep -Ei "^[hikers]{5}$" /usr/share/dict/american-english | grep -viE "(.).*\1" Sheri Shrek heirs hiker hikes hires sheik shire shirk skier