So if I type "man sleep," this is going to give me the user's manual for a program called sleep, but there's a gotcha and the problem set it makes clear, sleep notice that it says at top left sleep one.

所以如果我键入“man，sleep“，它将,给我一个叫做sleep程序的用户手册，但是这里有个参考信息，它使问题更清晰，请注意它指明在左上角。

哈佛公开课 - 计算机科学课程节选