--- IO.read(path,[length,[offset]])  ruby 1.7 feature

    path ǻꤵ줿ե offset ֤ 
    length Хʬɤ߹֤ޤ礦ɰʲΤ褦Ư
    򤷤ޤ

      port = open(path)
      port.pos = offset if offset
      begin
        port.read length
      ensure
        port.close
      end

    length  nil Ǥ뤫άˤϡEOF ޤɤ߹
    ߤޤ

    IO  EOF ãƤ nil ֤ޤ

    path Υץoffset ֤ؤꡢեɤ߹
    ߤ˼Ԥ㳰 Errno::EXXX ȯޤ
    length ξ硢㳰 ArgumentError ȯޤ

