p "2007-06-07".gsub("-", "/")
#=> "2007/06/07"
p "2007-06-07".gsub(/\d+/, "*")
#=> "*-*-*"
p "2007-06-07".gsub(/\d+/) {|m| m.to_i.to_s(16) }
#=> "7d7-6-7"