shell脚本变量的参数

https://stackoverflow.com/questions/5163144/what-are-the-special-dollar-sign-shell-variables

mkdir folder && cd $_ （创建一个目录，并且立马切换到这个目录里面去。）

$1

,

$2

,

$3

, ... are the positional parameters.

"$@"

is an array-like construct of all positional parameters,

{$1, $2, $3 ...}

.

"$*"

is the IFS expansion of all positional parameters,

$1 $2 $3 ...

.

$#

is the number of positional parameters.

$-

current options set for the shell.

$$

pid of the current shell (not subshell).

$_

most recent parameter (or the abs path of the command to start the current shell immediately after startup).

$IFS

is the (input) field separator.

$?

is the most recent foreground pipeline exit status.

$!

is the PID of the most recent background command.

$0

is the name of the shell or shell script.