Shell Passing Arguments

When executing a Shell script, we can pass parameters to the script. The format for obtaining parameters within the script is:$n，nrepresents a number,1is the first parameter of the executed script,2is the second parameter of the executed script.

For example, you can use$1、$2etc. to reference the parameters passed to the script, where$1represents the first parameter,$2represents the second parameter, and so on.

Example

In the following example, we pass three parameters to the script and output them separately, where$0is the name of the executed file (including the file path):

Example

#!/bin/bash
# author: Example
# url:www.example.com

echo "Shell passing parameters example!";
echo "File name executed: $0";
echo "The first parameter is: $1";
echo "The second parameter is: $2";
echo "The third parameter is: $3";

Set executable permission for the script and execute it. The output is as follows:

$ chmod +x test.sh 
$ ./test.sh 1 2 3
Shell 传递参数实例！
执行的文件名：./test.sh
第一个参数为：1
第二个参数为：2
第三个参数为：3

In addition, there are several special characters used to handle parameters:

Parameter handling Description
$# Number of parameters passed to the script
$* Displays all parameters passed to the script as a single string.
For example, when "$*" is enclosed in double quotes, it outputs all parameters in the form "$1 $2 … $n".
$$ The current process ID of the script running
$! The ID of the last process running in the background
$@ Same as $*, but each parameter is quoted when used; it returns each parameter in quotes.
For example, when "$@" is enclosed in double quotes, it outputs all parameters in the form "$1" "$2" … "$n".
$- Displays the current options used by Shell, which is the same asthe set commandin function.
$? Displays the exit status of the last command. 0 means no error, any other value indicates an error.

Example

#!/bin/bash
# author: Example
# url:www.example.com

echo "Shell passing parameters example!";
echo "The first parameter is: $1";

echo "The number of parameters is: $#";
echo "The parameters passed are displayed as a string: $*";

Execute the script, and the output is as follows:

$ chmod +x test.sh 
$ ./test.sh 1 2 3
Shell 传递参数实例！
第一个参数为：1
参数个数为：3
传递的参数作为一个字符串显示：1 2 3

Difference between $* and $@:

  • Same: both reference all parameters.
  • Difference: it is only reflected when enclosed in double quotes. Suppose three parameters 1, 2, 3 are written when the script runs, then "$*" is equivalent to "1 2 3" (one parameter passed), while "$@" is equivalent to "1" "2" "3" (three parameters passed).

Example

#!/bin/bash
# author: Example
# url:www.example.com

echo "-- \$* Demo ---
for i in "$*"; do
    echo $i
done

echo "-- \$@ Demo ---
for i in "$@"; do
    echo $i
done

Execute the script, and the output is as follows:

$ chmod +x test.sh 
$ ./test.sh 1 2 3
-- $* 演示 ---
1 2 3
-- $@ 演示 ---
1
2
3
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