Loop judgment statements in Shell (2) while statement, until statement

while statement
1. Features: if the condition is true, enter the loop; if the condition is false, exit the loop

2. Grammatical structure:

   while   表达式
    do
          command...
    done

Getting started case:

Calculate 1-50 even numbers and


until statement
1. Features: It is the opposite of while, as long as the condition is not met, it will keep looping (failed repeatedly)
2. Statement structure:

   until expression 
    do
          command
    done

Getting started case:

Calculate 1-50 even number sum

Actual combat script
Exercise 1: Write a script to synchronize the system time every 30 seconds. If the synchronization fails, an email alarm will be sent; if the synchronization is successful, an email will be sent every 100 times for notification.

Exercise 2: Write a script to automatically build nfs service

#!/bin/bash
echo -e  "\033[32m######testing the network.......\033[0m"
ping -c1 -w1 172.25.254.6 &>/dev/null
	if [ $? -eq 0 ]
	then
		echo  -e "\033[32mthe network is ok !!\033[0m"
	else
		echo  -e "\033[31mthe network is not running!!\033[0m"
		exit
	fi

echo -e "\033[32m########turnning down the selinux.......\033[0m"
setenforce 0 &>/dev/null
	if [$? -eq 0 ]
	then
		echo  -e "\033[32mselinux is turning down\033[0m"
	fi
systemctl stop firewalld &>/dev/null
	if [ $? -eq 0 ]
	then
		echo -e "\033[32mfirewall is stoped"
	fi
echo -e "\033[32m########testing the software......\033[0m"
rpm -q rpcbind &>/dev/null
	if [ $? -eq 0 ]
	then
		echo "rpcbind is already installed"
     	else
		echo "rpcbind is not installed"
dnf install rpcbind -y
        if [ $? -eq 0 ];then
                         echo "rpcbind is now installed"
        else
                         echo "rpcbind install failed"   
                         exit 
                 fi
             exit
	fi
echo -e "\033[32m#######mkdir dir network chmod .......\033[0m"
read -p "Please input share dir:  " dir
[ -e $dir ] && {
        echo "the dir exists"
}||{
        mkdir -p $dir
        echo "$dir create success"
        exit
}
chmod 1777 $dir
read -p "please input the subnet to share: " subnet
read -p "please input share permission: " permission
 
echo -e "\033[32medit nfs configure file /etc/exports\033[0m"
read -p "input 1 -> clear config,default is add: " choice
if [ $choice -eq 1 ];then
     > /etc/exports
fi
cat >> /etc/exports << EOF
$dir $subnet($permission)
EOF
 
echo -e "\033[32msetting service start with poweron and start searvice......\033[0m "
 
echo -e "\033[31mcheck nfs-server is start?\033[0m"
systemctl status nfs-server.service | grep active &>/dev/null
if [ $? -eq 0 ];then
        systemctl restart nfs-server
        echo "Nfs server restart success"
else
        systemctl start rpcbind
        systemctl start nfs-server
        systemctl enable --now rpcbind
        systemctl enable --now nfs-server
fi
 
 
echo -e "\033[32m########testing wheather network could be use......."
showmount -e 172.25.254.6 | grep $dir &> /dev/null
[ $? -eq 0 ] && {
        echo -e "\033[32mshare success\033[0m" 
}||{
        echo -e "\033[32mshare failed\033[0m"
        exit 
}

echo -e "\033[32mnfs.service is created successfully!!!\033[0m"