Shell jump loop shift parameter left use of function

1. shift The command is used to move parameters ( Move left ), It is usually used to traverse each parameter in turn without knowing the number of incoming parameters
   And then carry out corresponding treatment （ Common in Linux Start scripts for various programs in ）
2. When scanning the parameters of the processing script program , Often used shift command , If your script needs to 10 Or 10 More than one
   Parameters , You need to use shift Command to access the second 10 And the parameters after that
3. Use return Command to exit the function and return a specific exit code . notes ： The determination of the status code must be run at the end of the function return Return value ; The value range of the status code （0~255）

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[[email protected] ~]# cat fun-4.sh 
#!/bin/bash
fun1(){
 read -p "Input a value: " va
 echo $[$va*5] }
num=$(fun1)
echo current num is $num
[[email protected] ~]# sh fun-4.sh 
Input a value: 22
current num is 110

     

      
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notes ： The return value of the function here is different from that of other programming languages . If there is in the function return sentence , Then through the “ Variable =$( Function name )” Can't get the return value of the function . Only the function has written echo Before returning . Want to get return Return value , Only after a function call , adopt “ Variable name =$?” In the form of .
4. use function When defining a function, add a space between the left brace and the preceding function name , No mistake will be reported . If function name is used () There is no need to add a space in the form of

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function fun1 {
    num=$[var1*2]
}
fun1(){
    num=$[var1*2]
}

     

      
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5. Global variables , By default , The variables you define in the script are global variables , The variables you define outside the function can also be used inside the function