On Jul 17, 2006, at 12:35 PM, Steve Throckmorton wrote:

> file_ext.sub!(/\A\.(?=.)/, ".")
>
> I understand all except (?=.)

That's a look-ahead assertion, ensuring there is at least one  
character following the period.  Observe:

 >> test = ".hidden_file"
=> ".hidden_file"
 >> test.sub!(/\A\.(?=.)/, ".")
=> ".hidden_file"
 >> test = "."
=> "."
 >> test.sub!(/\A\.(?=.)/, ".")
=> nil

Hope that helps.

James Edward Gray II