pwd

pwd命令是一个相当常用的命令，它告诉我们shell当前工作目录。
pwd是Print working directory的意思。
pwd是一个shell内置指令(shell builtin)。

$ type pwd
pwd is a shell builtin

详解

$ help pwd
pwd: pwd [-LP]
    Print the name of the current working directory.
    
    Options:
      -L    print the value of $PWD if it names the current working
        directory
      -P    print the physical directory, without any symbolic links
    
    By default, `pwd' behaves as if `-L' were specified.
    
    Exit Status:
    Returns 0 unless an invalid option is given or the current directory
    cannot be read.

可以看到，pwd命令实际上是打印出了shell环境变量$PWD的值。
-P选项打印出实际的路径，而非快捷链接（symbolic links）,该选项有时候会有用。