Shell pass parameters

We can execute Shell Script time , Pass parameters to script , The format of obtaining parameters in the script is ：$n.n Represents a number ,1 For executing the first parameter of the script ,2 For executing the second parameter of the script , And so on ……

example

In the following example, we pass three parameters to the script , And output respectively , among $0 For the filename of the execution （ Include file path ）：

1. #!/bin/bash
2. echo "Shell Pass parameter instance ！";
3. echo " File name of execution ：$0";
4. echo " The first parameter is zero ：$1";
5. echo " The second parameter is ：$2";
6. echo " The third parameter is zero ：$3";

Set executable permissions for scripts , And execute the script , The output is as follows ：

1. $ chmod +x test.sh
2. $ ./test.sh 123
3. Shell Pass parameter instance ！
4. File name of execution ：./test.sh
5. The first parameter is zero ：1
6. The second parameter is ：2
7. The third parameter is zero ：3

in addition , There are also a few special characters for processing parameters ：

Processing parameters	explain
$#	The number of parameters passed to the script
$*	Display all the parameters passed to the script in a single string . Such as ”$*” use 「”」 In a nutshell 、 With ”$1 $2 … $n” Output all parameters in the form of .
$$	The current process the script runs ID Number
$!	Of the last process running in the background ID Number
[email protected]	And $* identical , But use quotation marks , And return each parameter in quotation marks . Such as ”[email protected]” use 「”」 In a nutshell 、 With ”$1” “$2” … “$n” Output all parameters in the form of .
$-	Show Shell Current options used , And set Same command function .
$?	Display the exit status of the last command .0 No mistakes , Any other value indicates an error .

1. #!/bin/bash
2. echo "Shell Pass parameter instance ！";
3. echo " The first parameter is zero ：$1";
4. echo " The number of parameters is ：$#";
5. echo " The passed parameter is displayed as a string ：$*";

Execute the script , The output is as follows ：

1. $ chmod +x test.sh
2. $ ./test.sh 123
3. Shell Pass parameter instance ！
4. The first parameter is zero ：1
5. The number of parameters is ：3
6. The passed parameter is displayed as a string ：123

$* And [email protected] difference ：

1. The same thing ： All references to all parameters .
2. Difference ： Only in double quotes . Suppose you write three parameters when the script runs 1、2、3,, be " * " Equivalent to "1 2 3"（ Passed a parameter ）, and "@" Equivalent to "1""2""3"（ Three parameters are passed ）.
3. #!/bin/bash
4. echo "-- \$* demonstration ---"
5. for i in"$*";do
6. echo $i
7. done
8. echo "-- \[email protected] demonstration ---"
9. for i in"[email protected]";do
10. echo $i
11. done