The shell function

The shell function

Linux shells can be user-defined functions, which can then be called at will in shell scripts.

The definition format of the function in the shell is as follows:

[ function ] funname [()]

{

    action;

    [return int;]

}

Description:

• 1, can be with the fun () definition, can also be directly fun() definition, without any parameters.
• 2, parameter return, you can show plus: return return, if not, will be the last command to run the result, as a return value. R eturn followed by the value n (0-255).

The following example defines a function and calls it:

#!/bin/bash
demoFun(){
    echo "这是我的第一个 shell 函数!"
}
echo "-----函数开始执行-----"
demoFun
echo "-----函数执行完毕-----"

Output:

-----函数开始执行-----
这是我的第一个 shell 函数!
-----函数执行完毕-----

Here's a function with a return statement:

#!/bin/bash
funWithReturn(){
    echo "这个函数会对输入的两个数字进行相加运算..."
    echo "输入第一个数字: "
    read aNum
    echo "输入第二个数字: "
    read anotherNum
    echo "两个数字分别为 $aNum 和 $anotherNum !"
    return $(($aNum+$anotherNum))
}
funWithReturn
echo "输入的两个数字之和为 $? !"

The output is similar to the following:

这个函数会对输入的两个数字进行相加运算...
输入第一个数字: 
1
输入第二个数字: 
2
两个数字分别为 1 和 2 !
输入的两个数字之和为 3 !

The function returns a value that passes $after the function is called? t o get.

Note: All functions must be defined before they can be used. T his means that the function must be placed at the beginning of the script until the shell interpreter first discovers it. C all a function using only its function name.

Function arguments

In Shell, you can pass arguments to a function when it is called. I nside the function body, the value of the argument is obtained in the form of $n, for example, $1 represents the first argument and $2 represents the second argument...

Examples of functions with parameters:

#!/bin/bash
funWithParam(){
    echo "第一个参数为 $1 !"
    echo "第二个参数为 $2 !"
    echo "第十个参数为 $10 !"
    echo "第十个参数为 ${10} !"
    echo "第十一个参数为 ${11} !"
    echo "参数总数有 $# 个!"
    echo "作为一个字符串输出所有参数 $* !"
}
funWithParam 1 2 3 4 5 6 7 8 9 34 73

Output:

第一个参数为 1 !
第二个参数为 2 !
第十个参数为 10 !
第十个参数为 34 !
第十一个参数为 73 !
参数总数有 11 个!
作为一个字符串输出所有参数 1 2 3 4 5 6 7 8 9 34 73 !

Note that $10 does not get the 10th argument, and $10 is required to get the {10}. W hen n is 10, you need to use ${n to get the parameters.

In addition, there are several special characters for handling parameters: