说明：  本文将较为详细地介绍 Linux 下最常用的 shell，bash。bash(Bourne Again Shell) 是 Linux 的缺省 shell，并被大多数用户所使用，在本文中你将学会：
(This article will introduce Linux in more detail under the most commonly used shell, bash. bash (Bourne Again Shell) is a Linux default shell, and the majority of users, in this article you will learn:)