Shell script - special variables: shell $, $*, [email protected], $$$

Variable	meaning
$0	File name of the current script .
$n（n≥1）	Parameters passed to a script or function .n It's a number , Indicates the number of parameters . for example , The first parameter is $1, The second parameter is $2.
$#	Number of arguments passed to script or function .
$*	All parameters passed to a script or function .
[email protected]	All parameters passed to a script or function . When double quotes " " Inclusion time ,[email protected] And $* not quite the same
$?	Exit status of last command , Or the return value of the function
$$	At present Shell process ID. about Shell Script , It's the process of these scripts ID.

$* And [email protected] Difference ： When wrapped in double quotation marks ,[email protected] There is no change when it is not wrapped in double quotation marks ,[email protected] It's still an array , Each parameter is still separate ; But when $* When wrapped in double quotation marks ,SHELL All parameters will be integrated into one string .

Pass parameters to the script file

The script is as follows ：

#!/bin/bash
echo "Process ID: $$"
echo "File Name: $0"
echo "First Parameter : $1"
echo "Second Parameter : $2"
echo "All parameters 1: [email protected]"
echo "All parameters 2: $*"
echo "Total: $#"

Output ：

Process ID: 5943
File Name: bash
First Parameter : Shell
Second Parameter : Linux
All parameters 1: Shell Linux
All parameters 2: Shell Linux
Total: 2