require 'tk'

TkRoot.new{ title 'cget' }
c = TkCanvas.new.pack

message = <<END
width = #{c.cget('width').inspect}
height = #{c.cget('height').inspect}
bg = #{c.cget('bg').inspect}
END

msg = TkMessage.new(nil, 'relief'=>'ridge').pack('fill'=>'x', 'padx'=>20)
TkButton.new(nil, 'text'=>'canvas.cget', 'command'=>proc{
  msg.text( message.chop )
}).pack

Tk.mainloop