File.binary? method for Ruby

gistfile1.txt

# Mostly works, but is returning true on jpg images.
class File  
  def self.binary?(file)
    s = (File.read(file, File.stat(file).blksize) || "")
    s = s.encode('US-ASCII', :undef => :replace).split(//)
    ((s.size - s.grep(" ".."~").size) / s.size.to_f) > 0.30
  end
end