Article Directory
One, Shell function
- The function of the function is to list the part of the code that needs to be used multiple times in the program, and then give this part of the code a name. All other repeated calls of this part of the code can only be called by this name (similar to an alias). When you need to modify this part of the repeated code, you only need to change a piece of code in the function body to implement the call modification.
- Advantages of functions
Defining the same program segment as a function can reduce the amount of code in the entire program.
Increase the readability of the program and ease of management.
When modifying, you only need to modify the function, and you don’t need to find the places that need to be modified in the program.
Two, Shell function format
Function format one:
function name() { #function是shell中的关键字，专门用来定义函数 name是函数名
statements #statements是函数要执行的代码，也就是一组语句；
[return value] #return value表示函数的返回值，其中return是shell关键字，专门用在函数中返回一个值；这一部分可以写也可以不写。
} #由{ }包围的部分称为函数体，调用一个函数，实际上就是执行函数体中的代码。
Function format two:
name() {
statements
[return value]
}
Three, function return value
- return means to exit the function and return an exit value, which can be displayed by the $? variable in the script
Usage principles:
1. Take the return value as soon as the function ends, because the $? variable only returns the exit status code of the last command executed.
2. The exit status code must be 0~255, and the value will be divided by 256 if it exceeds
function double {
read -p "请输入：" data
return $[$data* 2]
}
double
echo $?
operation result:
- Echo
echo can return any string result
is usually used to return data, for example: string value or list value
double ( ) {
read -p "请输入：" data
echo $[$data * 2]
}
double
Four, function parameter transfer
#!/bin/bash
sum() {
s=$[$1 + $2]
echo $s
}
sum $1 $2
~
#!/bin/bash
#!/bin/bash
sum() {
s=$[$1 + $2]
echo $s
}
read -p "请输入第一个参数：" first
read -p "请输入第二个参数：" second
sum $first $second
Five, 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
#!/bin/bash
ak () {
local i #设置局部变量
i=8
echo $i
}
i=9 #全局环境
ak
echo $i
Six, recursion
- Function calls its own function
#!/bin/bash
factorial() {
if [ $1 -eq 1 ]
then
echo 1
else
local temp=$[$1 - 1]
local result=$(factorial $temp)
echo $[$1 * $result]
fi
}
read -p "请输入：" data
result=$(factorial $data)
echo $result
Seven, recursive directory
function list_files () {
for f in 'ls $1'
do
if [-d "$1/$f" ] ；then
echo "$2$f" #如果是目录就输出这个目录，$2为空格是用于区分父子目录
list_files "$1/$f" " $2"
else
echo "$2$f" #不是目录则输出$f结果
fi
done
}
list_files "/var/log" ""
Eight, create a library
- Create multiple functions in one script and use them in other scripts to call the functions in the library
#!/bin/bash
jiafa() {
echo $[$1 + $2]
}
jianfa() {
echo $[$1 - $2]
}
chengfa() {
echo $[$1 * $2]
}
chufa() {
if [ $2 -ne 0 ];then
echo $[$1 / $2]
else
echo "$2不能为0"
fi
}
#!/bin/bash
. /root/ku.sh
read -p "输入第一个参数值：" first
read -p "输入第二个参数值：" second
result1=`jiafa $first $second`
result2=`jianfa $first $second`
result3=$(chengfa $first $second)
result4=$(chufa $first $second)
echo "相加结果：$result1"
echo "相减结果：$result2"
echo "相成结果：$result3"
echo "相除结果：$result4"
~
