敲门砖

qiāoménzhuān

[a brick picked up to knock on the door and thrown away when it has served its purpose-a stepping-stone to success] 拣砖头敲门, 门开后即弃砖。 比喻谋求名利的手段

这是敲门砖, 敲开便丢下他。 我们既作了官, 做诗何用。 --明·西湖居士《春游》