Shell script functions

One 、Shell function

The function lists the parts of the program that need to be used many times , Then give this part a name , All other repeated calls to this part of the code can only call this name （ Similar to alias ）. When you need to modify this part of the duplicate code , You only need to change a copy of the code in the function body to realize the call modification .

The advantages of functions
Define the same program segment as a function , It can reduce the amount of code in the whole program .
Increase the readability of the program , And easy to manage .
When modifying, you only need to modify the function , There is no need to look everywhere in the program for changes

Two 、Shell Function format

3、 ... and 、 Function return value

1、return

return Represents the exit function and returns an exit value , You can use $ ? The variable displays the value
Usage principle
Take the return value as soon as the function ends , because $? Variable returns only the exit status code of the last command executed
Exit status code must be 0~255, When exceeded, the value will be divided by 256 Remainder

2、echo

echo You can return any string result
Usually used to return data , for example ： String value or list value

Four 、 Function arguments

Parameter passing is to pass the parameters in the body code to the function body , Position parameters are generally used $n($1、$2、$3…)

#!/bin/bash
sum() {
s=$[$1 + $2]
echo $s
}
read -p “ Please enter the first parameter ：” first
read -p “ Please enter the second parameter ：” second
sum $first $second

5、 ... and 、 The scope of function variable

Function in Shell In the script, only in the current Shell Effective in the environment
Shell Variables in scripts are globally valid by default
Restrict variables to functions and use local command

#!/bin/bash
Part() {
echo “ This is the first one inside i Value ：$i"i=10echo"thisyesInsideMinistryThe\; firstTwoindividualiOfvalue：$i”
local i=15
echo “ This is the third one inside i Value : $i”
}

i=5
echo " This is the outside i Value ：$i"Partecho"thisyesLetterCountOf\; boardThat\text{'}s\; okEndiOfvalue$i

6、 ... and 、 recursive

1、 Factorial

The factorial of a positive integer is the product of all positive integers less than or equal to the number

fact() {
if [ $1-eq1]thenecho1elselocaltemp=$[$1-1]localresult=$(fact $temp)
echo $[$1 * KaTeX parse error: Expected 'EOF', got '}' at position 12: result] fi }̲ read -p " Please enter …(fact $n)
echo $result

2、 Recursive directory

Display all directories and files in this directory （ Include directories and files under subdirectories ）

#!/bin/bash
list_files () {
for f in ls $1
do
if [ -d “$1/$f” ]
then
echo “+$2$f”
list_files “$1/$f” " $2"
else
echo “-$2$f”
fi
done
}
list_files “/var/log” “”