Need help to get correct regex format for usernames

I need help getting the regex format of my usernames correct. It suppose to require 3 letters in it and allow no spaces or _. I think I'm on the right track so far with this:

validates_format_of :username, :with => /([^a-zA-Z]*([a-zA-Z]+)[^a-zA-Z]*){3,}/ 

This allows spaces though and I'm not sure if this is correct in general. What corrections do I need for this regex to get rid of the ability to use spaces or _?


If you mean it has to be all letters, it's just:


Otherwise, use a lookahead:

/^(?=(.*[a-zA-Z]){3})[allowed characters here]+$/

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