Find five letter words that are made up of letters {h, i, k, e, r, s} where each letter appears only once.

If we do

grep -i "^[hikers][hikers][hikers][hikers][hikers]$" /usr/share/dict/american-english
<code>
shows
<code>
Essie
Hesse
Irish
Kerri
Reese
Sheri
...

some of the words have the letters duplicated. For example, in 'Irish' the letter 'i' is repeated twice. Such words should be filtered out.

 % grep -i "^[hikers][hikers][hikers][hikers][hikers]$" /usr/share/dict/american-english | grep -viE '(.).*\1' 
Sheri
Shrek
heirs
hiker
hikes
hires
sheik
shire
shirk
skier