#! /bin/bash

export MAIN_DIALOG='
  <vbox>
    <list selection-mode="3">
      <variable>LIST</variable>
      <item>First item</item>
      <item>Second item</item>
      <item>Third item</item>
    </list>
    <hbox>
     <button ok></button>
     <button cancel></button>
    </hbox>
  </vbox>
'

gtkdialog --program=MAIN_DIALOG