Is this a regex bug?

[rank1seeker at gmail.com]

Or am I crazy?

echo '-m' | egrep '^\-[[:alnum:]]+$'
echo '-n' | egrep '^\-[[:alnum:]]+$'
echo '-o' | egrep '^\-[[:alnum:]]+$'

Guess what?
Only middle one, '-n' doesn't match it.
Is this an RE bug or I clearly ain't seeing obvious?!

echo '-n' | egrep '^\-[0-9A-Za-z]+$'
    Doesn't work either

9.2-RELEASE-p3  i386


Domagoj Smolčić