sha1 (LineCache)

    # File lib/linecache.rb, line 240
      def sha1(filename)
        filename = unmap_file(filename)
        return nil unless @@file_cache.member?(filename)
        return @@file_cache[filename].sha1.hexdigest if
          @@file_cache[filename].sha1
        sha1 = Digest::SHA1.new
        @@file_cache[filename].lines.each do |line|
          sha1 << line
        end
        @@file_cache[filename].sha1 = sha1
        sha1.hexdigest
      end