[xertopertha]

This produces 35 items. The grep version gives 93

[adrianmonk]

Yeah, I failed to make the pattern case insensitive.

Here's a fixed version that also handles S/5:

    sed -E -e '/^[A-FIOSa-fios]{6}$/!d; y/abcdefiosIOS/ABCDEF105105/; s/^/#/' /usr/share/dict/words