[curiousgeorgio]

Since apparently this list allows decimals (bozo: 0.208), why does the regex need to exclude words ending in two o's? Words like "boo", "goo", and "igloo" can be made with the same rules, and it's a simpler grep -i '^[izehsglbo]\+$' /usr/share/dict/words

[cyclotron3k]

I was wondering the same thing too. And even if you wanted to keep this odd behaviour, it could be better written as

  /^[izehsglbo][izehsgl]o?$/