Takes a string, such as a post title ("Rat Brains Fly Planes") and convets it into a ruby style variable name that can be used as an id or permalink url ("rat_brains_fly_planes")

Posted by Duane Johnson on rails list:
Here's the modified String class. This one
squeezes non-alphanumeric character sequences down to one underscore
and also makes sure it doesn't start or end with an underscore:

   1  
   2  class String
   3    def rubify
   4      downcase.gsub(/\W/, ' ').squeeze.strip.gsub(' ', '_')
   5    end
   6  
   7    def rubify!
   8      replace rubify
   9    end
  10  end

"!Hell93 o3#$@ the___re , dude".rubify
=> "hel93_o3_the_re_dude"

Luke Redpath suggested the following naming convention:
ID is short for identification the related verb of which is identify.

The appropriate verify_ macro would be verify_identity_of

A more conventional Ruby idiom would be to_id() (like to_s, to_i etc.).

   1  
   2  "My, what a beautiful day!".to_id
   3  
   4  => "my_what_a_beautiful_day"

If thats not clear enough or possibly confusing with the normal use of id in a Rails app, perhaps to_identifier() instead.