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while语句

1.特点：条件为真就进入循环；条件为假就退出循环

2.语法结构:

while   表达式    do          command...    done

入门案例：

计算1-50偶数和

until语句 1.特点 : 和 while 刚好相反，只要不满足条件就一直循环 ( 屡败屡战 ) 2.语句结构：

until expression     do          command    done

入门案例：

计算1-50偶数和

实战脚本 练习1：编写一脚本，30秒同步一次系统时间。若同步失败，则进行邮件报警；若同步成功，每成功一百次发一封邮件进行通知。 练习2：写一个脚本自动搭建nfs服务

#!/bin/bashecho -e  "\033[32m######testing the network.......\033[0m"ping -c1 -w1 172.25.254.6 &>/dev/null	if [ $? -eq 0 ]	then		echo  -e "\033[32mthe network is ok !!\033[0m"	else		echo  -e "\033[31mthe network is not running!!\033[0m"		exit	fiecho -e "\033[32m########turnning down the selinux.......\033[0m"setenforce 0 &>/dev/null	if [$? -eq 0 ]	then		echo  -e "\033[32mselinux is turning down\033[0m"	fisystemctl stop firewalld &>/dev/null	if [ $? -eq 0 ]	then		echo -e "\033[32mfirewall is stoped"	fiecho -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	fiecho -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 $dirread -p "please input the subnet to share: " subnetread -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: " choiceif [ $choice -eq 1 ];then     > /etc/exportsficat >> /etc/exports << EOF$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/nullif [ $? -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-serverfi  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"

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