gistfile1.rb

filename = "some file name.with dots.html.markdown"
parts = f.split(".")
last_index_of_spc = parts.index(parts.select{|s| s =~ / /}.last)
suffix = parts[last_index_of_spc + 1..-1]
prefix = parts[0..last_index_of_spc].join(".")
p [prefix, suffix]