获取命令帮助：man 0 个改进

几乎任何命令之前输入 man，来显示该命令的帮助手册（用q退出man）：

LS(1)                            User Commands                           LS(1)

NAME
        ls - list directory contents

SYNOPSIS
        ls [OPTION]... [FILE]...

DESCRIPTION
        List  information  about  the FILEs (the current directory by default).
        Sort entries alphabetically if none of -cftuvSUX nor --sort  is  speci-
        fied.

        Mandatory  arguments  to  long options are mandatory for short options
        too.
...