流程控制之case语句

一、语法

case 变·量 in
模式一）
	命令序列1
	；；
模式二）
	命令序列2
	；；
...
*)
	无匹配后命令序列
esac

二、案例

1）案例一

#判断用户的类型

[root@db04 /scripts/day05]# vim user.sh 
#!/bin/bash

read -p "please input user name:" name
[ -z "$name" ] && echo "The user name must exist" && exit

case $name in
"root")
    echo "admin"
    ;;
"jh")
    echo "com user"
    ;;
*)
    echo "other user"
esac

[root@db04 /scripts/day05]#  chmod +x user.sh

2）案例二

#编写nginx启动脚本

[root@db04 /scripts/day05]# vim nginx.sh 
#!/bin/bash


[ $# -ne 1 ] && echo "Usage: $0 {start|stop|restart|reload|status}" && exit

function start() {
    ps aux |grep [n]ginx |grep -q master
    if [ $? -eq 0 ];then
        echo "nignx is started"
    else
        /usr/local/nginx/sbin/nginx &>/dev/null
        if [ $? -eq 0 ];then
            echo "nginx start success..."
        else
            echo "nginx start failed"
        fi
    fi
}

function stop(){
   ps aux |grep [n]ginx |grep -q master
    if [ $? -eq 0];then
       /usr/local/nginx/sbin/nginx -s stop
       sleep 3
       ps aux |grep [n]ginx |grep -q  master      
       if [ $? -ne 0 ];then
           echo "nginx stop success..."
           sleep 3
       else
           echo "nginx stop failed"
       fi
    else
        echo "nginx is stopped"
    fi
}

case $1 in
"start")
    start
    ;;
"stop")
    stop
    ;;

"restart")
    stop
    start
    ;;

"reload")
    stop
    start
    ;;

"status")
    ps aux |grep [n]ginx |grep -q  master
    if [ $? -eq 0 ];then
        echo "nginx is up"
    else
        echo "ngins is down"
    fi
    ;;
*)
    echo "Usage: $0 {start|stop|restart|reload|status}"
esac

[root@db04 /scripts/day05]#  chmod +x nginx.sh

3）案列三

[root@jh shell]# vim nginx_stat.sh
#!/bin/bash
. /etc/init.d/functions
if [ $# -ne 1 ]
then
echo "USAGE $0 {start|stop|restart}"
exit 1
fi
if [ "$1" == "start" ]
then
action "start nginx" /bin/true
elif [ "$1" == "stop" ]
then
action "stop nginx" /bin/true
elif [ "$1" == "restart" ]
then
action "restart nginx" /bin/true
else
echo "USAGE $0 {start|stop|restart}"
exit 1
fi
[root@jh shell]# chmod +x nginx_stat.sh
[root@jh shell]# ./nginx_stat.sh start
start nginx 						[ 确定 ]
[root@jh shell]# ./nginx_stat.sh restart
restart nginx 						[ 确定 ]
[root@jh shell]# ./nginx_stat.sh
USAGE ./nginx_stat.sh {start|stop|restart}

4）案列四

# 储备知识1
netstat -lntup|grep  ":80\b"  # \b锚定单词的结尾
# 储备知识2
action:打印一段信息并执行给定的命令，然后根据给定命令的执行的结果来调用 success,failure方
法，确定最终显示的内容
[root@jh shell]# action "nginx start is" :
nginx start is                       [  确定 ]
[root@jh shell]# action "nginx start is" /bin/true
nginx start is                       [  确定 ]
[root@jh shell]# action "nginx start is" /bin/false
nginx start is                       [失败]


# 代码
[root@jh shell]# vim nginx_stat.sh
#!/bin/bash
. /etc/init.d/functions
args=$1
fun(){
[ $? -eq 0 ] && action "Nginx $args is " /bin/true  || echo "Nginx $args is
" /bin/false
}
case $1 in
 start)
   netstat -lntup|grep  ":80\b" &>/dev/null
   if [ $? -eq 0 ]
   then
     echo "Nginx is runing..."
   else
     /usr/sbin/nginx
     fun
   fi
   ;;
 stop)
   /usr/sbin/nginx -s stop
   fun
   ;;
 reload)
   /usr/sbin/nginx -s reload
   fun
   ;;
 restart)
   netstat -lntup|grep  ":80\b" &>/dev/null
   if [ $? -ne 0 ]
   then
     /usr/sbin/nginx
    [ $? -eq 0 ] && echo "Nginx start is ok" || echo "Nginx start is
failed"
   else
     /usr/sbin/nginx -s stop              
    [ $? -eq 0 ] && echo "Nginx stop is ok" || echo "Nginx stop is failed"
     sleep 2
     /usr/sbin/nginx
     fun
   fi
   ;;
 status)
   netstat -lntup|grep  ":80\b" &>/dev/null
   if [ $? -eq 0 ]
   then
     echo "Nginx is runing ..."
   else
     echo "Nginx is not runing ..."
   fi
   ;;
  *)
    echo "Usage: $0 {start|stop|status|restart|reload}"
    exit 2
esac

5）案例五

#编写一个简易跳板机脚本

# 储备知识
Linux中断信号区别为：键入不同、对应操作不同、启用不同。
1、HUP中断信号：HUP中断信号的对应操作为让进程挂起，睡眠。同<Ctrl+X>
2、INT中断信号：INT中断信号的对应操作为正常关闭所有进程。同<Ctrl+C>
3、TERM中断信号 15：TERM中断信号的对应操作为正常的退出进程。
4、KILL中断信号 9：KILL中断信号的对应操作为强制关闭进程。
5、STOP 19暂停（同 Ctrl + Z）
6、CONT 18继续（与STOP相反， fg/bg命令）
7、TSTP中断信号：TSTP中断信号的对应操作为暂时停用进程。

# 代码
[root@jh shell]# cat jumpserver.sh
#!/bin/bash
 
cat<<EOF
1. BACKUP 10.0.0.41
2. WEB02  192.168.12.21
3. WEB03  10.0.0.9
EOF
trap "echo 不要乱按键盘,否则服务器将会爆炸" HUP INT TSTP
while true
do
  read -p "请输入连接主机编号信息: " num
  read -p "请输入账号: " user
  case $num in
   1)
     ssh [email protected]
     [ $? -ne 0 ] && echo "connect faild"
     ;;
   2)
     ssh [email protected]
     [ $? -ne 0 ] && echo "connect faild"
     ;;
   *)
     echo "请输入连接主机信息"
  esac
done