--- File.extname(filename)      ruby 1.7 feature

    ե̾ filename γĥʬ(Ǹ "." ³ʸ)
    ֤ޤǥ쥯ȥ̾˴ޤޤ "." 䡢ե̾Ƭ "." 
    ϳĥҤΰȤƤϸʤޤfilename ˳ĥҤ
    ޤʤ϶ʸ֤ޤ

      p File.extname("foo/foo.txt")     # => ".txt"
      p File.extname("foo/foo.tar.gz")  # => ".gz"
      p File.extname("foo/bar")         # => ""
      p File.extname("foo/.bar")        # => ""
      p File.extname("foo.txt/bar")     # => ""
      p File.extname(".foo")            # => ""


    File.basename, File.dirname ⻲ȡ

