def var(name)
    res = send_cmd("print #{name}").join("").chomp
    if /undefined variable:/ =~ res
      kernel_raise GnuplotError,res.strip
    end
    res
  end
def var(name)
    res = send_cmd("print #{name}").join("").chomp
    if /undefined variable:/ =~ res
      kernel_raise GnuplotError,res.strip
    end
    res
  end
`var` returns Gnuplot variable (not Gnuplot command)