bash内部命令变量

有些内部命令在目录列表时是看不见的，它们由shell本身提供，常用的内部命令有echo eval exec export readonly read shift wait exit和点(.)

其中加了底纹是常用的变量

shift这个比较特殊，应用这个参数之后，你用$#会发现，如果你定义的是3个参数，可是显示出来的却是2个参数，而且，每个参数对应的参数值都会少1，如图：

[[email protected] zhouyu]# set -- i am zhouyu

[[email protected] zhouyu]# echo $1 $2 $3

i am zhouyu

[[email protected] zhouyu]# echo $1

i

[[email protected] zhouyu]# echo $2

am

[[email protected] zhouyu]# echo $3

zhouyu

[[email protected] zhouyu]# shift

[[email protected] zhouyu]# echo $1

am

[[email protected] zhouyu]# echo $2

zhouyu

[[email protected] zhouyu]# echo $3

[[email protected] zhouyu]#

[[email protected] zhouyu]# echo $#

2

[[email protected] zhouyu]# shift

[[email protected] zhouyu]# echo $1

zhouyu

[[email protected] zhouyu]# echo $2

[[email protected] zhouyu]# echo $3

[[email protected] zhouyu]# echo $#

1

[[email protected] zhouyu]#

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