Shell programming-shell function establishment function library script call work efficiency doubled

shell function

Functions can be defined by the user, and then can be called casually in the shell script

Function format

method 1

function 函数名 {
   命令序列
}

Method 2

函数名 () {
   命令序列
}

Function return value return

• return means to exit the function and return an exit value, which can be displayed by the $? variable in the script
  • The return value is taken as soon as the function ends, because the $? variable only returns the exit status code of the last command executed
  • The exit status code must be 0-255, the excess value will be divided by 256 to take the remainder
    
    
    

Function parameters

• In the Shell, that can be passed when calling the function parameters in $1, $2, $3, $4... $#, $*indicating the call back function parameters with
  an outer and function $1, $2... keyboard input value after the call to the script file
• As shown
  
  
• Example: The value accumulated from 1 to 10 is calculated by passing parameters

• Multiply the added value by 2
  by assigning a function
  

The scope of function variables

• Functions in Shell scripts are only valid in the current Shell environment
• Variables in Shell scripts are globally effective by default
• Use the local command to limit the variable to the function
  
  

Recursion

• Function calls its own function
• Factorial example
  

#分析思路比如输入5时
fact 5
$1=5     temp=4     result=fact 4     echo 5 * (4 * (3 * (2 * (1))))
fact4
$1=4     temp=3     result=fact 3     echo 4 * (fact 3)
fact3
$1=3     temp=2     result=fact 2     echo 3 * (fact 2)
fact2
$1=2     temp=1     result=fact 1     echo 2 * (fact 1)
fact1
1

Recursive directory

Recursively view the directories and files in the /var/log directory

Function library

• The function of the function library: write the functions that implement the same type of function in the same script file for easy classification, and you can call it directly when you use the function

• Define a simple algorithm function library. The functions in the library are as follows

• Addition function add

• Subtraction function

• Multiplication function

• Divide function divider
  

• Call the function in the function library