function
Preface
In fact, the function of the shell is very simple. It is a breeze for students who have learned other programming languages.
What is a function
-
The shell allows a set of commands or statements to form a piece of usable code, these code blocks are called shell functions
-
Give this piece of code a name called the function name, and then you can directly call the function of this piece of code
-
Code modularization can be used to define functions in the shell to facilitate code reuse
-
Functions must be defined before they can be used
How to define a function
method one
函数名()
{
函数体（一堆命令的集合，来实现某个功能）
}
Method Two
function 函数名()
{
函数体（一堆命令的集合，来实现某个功能）
}
Familiar with function writing
- factorial
#!/bin/bash
factorial() {
factorial=1
for((i=1;i<=5;i++))
do
factorial=$[ $factorial * $i ]
echo "$factorial"
done
echo "5的阶乘是：$factorial"
}
factorial
#!/bin/bash
function factorial {
a=1
for ((i=1;i<=10;i++))
do
a=$[ $a * $i ]
echo "$a"
done
echo "10的阶乘是：$a"
}
factorial
- Transfer parameters
#!/bin/bash
factorial() {
factorial=1
for((i=1;i<=$1;i++))
do
factorial=$[ $factorial * $i ]
echo "$factorial"
done
echo "$1 的阶乘是：$factorial"
}
factorial $1
factorial $2
factorial $3
# 执行函数
bash factorial.sh 10 8 5
10 的阶乘是：3628800
8 的阶乘是：40320
5 的阶乘是：120
#!/bin/bash
factorial() {
a=1
for i in `seq $1`
do
let a*=$i
echo "$a"
done
echo "$1 的阶乘是：$a"
}
factorial $1
# 执行函数
[root@maomao ~]# bash cheng.sh 10
1
2
6
24
120
720
5040
40320
362880
3628800
10 的阶乘是：3628800
#!/bin/bash
fun () {
read -p "请输入一个数字计算他的阶乘：" num
fun=1
for((i=1;i<=$num;i++))
do
fun=$[ $fun * $i ]
echo "$fun"
done
}
fun $num
Function return value
- The function return value is a functionLast command
- The highest return value of the shell is255
#!/bin/bash
re() {
read -p "enter num：" num
return $[2*$num]
}
re
echo "re return value：$?"
#!/bin/bash
fun() {
read -p "enter num：" num
echo $[2*$num]
}
result=`fun`
echo "fun return value：$result"
#这个返回值不是真的返回值
FunctionreturnDescription:
- Return can end a function. Similar to the loop control statement break (end the current loop and execute the code behind the loop body).
- By default, return returns the status value of the last command in the function. The parameter value can also be given, and the range is between 0-256.
- If there is no return command, the function will return the exit status value of the last command.
return can end a function
#!/bin/bash
fun(){
echo 'maomao'
echo 'zhuzhu'
return
echo 'niuniu'
}
fun
# 执行脚本
[root@maomao ~]# bash test.sh
maomao
zhuzhu
return returns the status value of the last command in the function by default
#!/bin/bash
fun(){
echo 'zhuzhu'
echo 'maomao'
return 88
echo 'niuniu'
}
fun
# 执行脚本
[root@maomao ~]# bash test1.sh
zhuzhu
maomao
[root@maomao ~]# echo $?
88
Function parameter passing positional parameter
#!/bin/bash
if [ $# -ne 3 ];then
echo "useage：`basename $0` par1 par2 par3"
exit
fi
fun3() {
echo "$(($1 * $2 * $3 ))"
}
result=`fun3 $1 $2 $3` 这个$1 $2 $3是外面的参数赋给函数里的$1 $2 $3
echo "$result" 你传给程序 程序传给函数
# 执行脚本
[root@maomao ~]# bash parameter.sh 1 2 3
6
[root@maomao ~]# bash parameter.sh 2 3 4
24
如果result=`fun3 $3 $3 $3` 三个$3相乘 3*3*3
[root@maomao ~]# bash parameter.sh 1 2 3
27
Function parameter group variable
Calculate the multiplication of the values in the array
#!/bin/bash
num1=(1 2 3 4 5)
num2=(2 4 6 8 10)
array() {
local array=1
for i in $*
do
array=$[ array * $i ]
done
echo "$array"
}
array ${num1[*]}
array ${num2[@]}
# 执行脚本
[root@maomao ~]# bash array.sh
120
3840
Array passing parameters becomes a new array
#!/bin/bash
num=(1 2 3 4 5)
num2=(2 4 6 8 10)
array() {
local newarray=($*)
local i
for((i=0;i<$#;i++))
do
outarray[$i]=$(( ${newarray[$i]} * 5 ))
done
echo "${outarray[*]}"
}
result=`array ${
num[*]}`
echo ${result[*]}
result=`array ${
num2[@]}`
echo ${result[@]}
# 执行脚本
[root@maomao ~]# bash array1.sh
5 10 15 20 25
10 20 30 40 50
Change the value of the original array
#!/bin/bash
num=(2 4 6 8 10)
array() {
local newarray=()
local i
for i
do
newarray[i++]=$[ $i * 10 ]
done
echo "${newarray[*]}"
}
result=`array ${
num[*]}`
echo "${result[*]}"
# 执行脚本
[root@maomao ~]# bash array2.sh
20 40 60 80 100
- The function accepts positional parameters $1 $2 $3… $n
- The function accepts array variables $@ $*
- The function will receive all the parameters assigned to the array newarry=($*)
Applications
- Write a script to collect the basic information (name, gender, age) entered by the user, if you do not enter it, you will always be prompted to enter
- Finally, output the corresponding content according to the user's information
#!/bin/bash
#该函数实现用户如果不输入内容则一直循环直到用户输入为止，并且将用户输入的内容打印出来
input_fun()
{
input_var=""
output_var=$1
while [ -z $input_var ]
do
read -p "$output_var" input_var
done
echo $input_var
}
input_fun 请输入你的姓名:
或者
#!/bin/bash
fun()
{
read -p "$1" var
if [ -z $var ];then
fun $1
else
echo $var
fi
}
#调用函数并且获取用户的姓名、性别、年龄分别赋值给name、sex、age变量
name=$(input_fun 请输入你的姓名:)
sex=$(input_fun 请输入你的性别:)
age=$(input_fun 请输入你的年龄:)
#根据用户输入的性别进行匹配判断
case $sex in
man)
if [ $age -gt 18 -a $age -le 35 ];then
echo "中年大叔你油腻了吗？加油"
elif [ $age -gt 35 ];then
echo "保温杯里泡枸杞"
else
echo "年轻有为。。。"
fi
;;
woman)
xxx
;;
*)
xxx
;;
esac
Comprehensive case
Task background
Although the existing springboard has realized a unified entrance to access the production server, the yunwei user has too much authority to operate all the directory files on the springboard, and there is a security risk of accidental deletion of data, so I hope you make some security strategies to ensure the springboard The normal use of the machine.
Specific requirements
- Only allow yunwei users to remotely connect to the background application server through the springboard to do some maintenance operations
- When the company's operation and maintenance personnel remotely connect to the springboard through a yunwei user, the following menu will pop up for selection:
欢迎使用Jumper-server，请选择你要操作的主机：
3. DB1-Master
4. DB2-Slave
5. Web1
6. Web2
h. help
q. exit
- When the user selects the corresponding host, the direct login without password is successful
- If the user does not input, the user will be prompted for input until the user chooses to log out
Comprehensive analysis
- Put the script in the .bashrc file in the yunwei user's home directory (/shell05/jumper-server.sh)
- Define the menu as a function [Print Menu], which is convenient for later calling
- Use the case statement to realize the user's choice [define variables interactively]
- When the user selects a certain server, further ask the user what needs to be done case...esac interactively define variables
- Use loops to realize that users don't choose to keep choosing
- Restrict users to directly close the terminal exit after exiting
#!/bin/bash
# jumper-server
# 定义菜单打印功能的函数
menu()
{
cat <<-EOF
欢迎使用Jumper-server，请选择你要操作的主机：
1. DB1-Master
2. DB2-Slave
3. Web1
4. Web2
h. help
q. exit
EOF
}
# 屏蔽以下信号
trap '' 1 2 3 19
# 调用函数来打印菜单
menu
#循环等待用户选择
while true
do
# 菜单选择，case...esac语句
read -p "请选择你要访问的主机:" host
case $host in
1)
ssh [email protected]
;;
2)
ssh [email protected]
;;
3)
ssh [email protected]
;;
h)
clear;menu
;;
q)
exit
;;
esac
done
将脚本放到yunwei用户家目录里的.bashrc里执行：
bash ~/jumper-server.sh
exit
Further improve the demand
In order to further enhance the safety of the springboard, the staff visit the production environment through the springboard, but cannot stay on the springboard.
#!/bin/bash
#公钥推送成功
trap '' 1 2 3 19
#打印菜单用户选择
menu(){
cat <<-EOF
欢迎使用Jumper-server，请选择你要操作的主机：
1. DB1-Master
2. DB2-Slave
3. Web1
4. Web2
h. help
q. exit
EOF
}
#调用函数来打印菜单
menu
while true
do
read -p "请输入你要选择的主机[h for help]：" host
#通过case语句来匹配用户所输入的主机
case $host in
1|DB1)
ssh [email protected]
;;
2|DB2)
ssh [email protected]
;;
3|web1)
ssh [email protected]
;;
h|help)
clear;menu
;;
q|quit)
exit
;;
esac
done
自己完善功能：
1. 用户选择主机后，需要事先推送公钥；如何判断公钥是否已推
2. 比如选择web1时，再次提示需要做的操作，比如：
clean log
重启服务
kill某个进程
supplement
1) SIGHUP 重新加载配置
2) SIGINT 键盘中断^C
3) SIGQUIT 键盘退出
9) SIGKILL 强制终止
15) SIGTERM 终止（正常结束），缺省信号
18) SIGCONT 继续
19) SIGSTOP 停止
20) SIGTSTP 暂停^Z