shell学习二十七--循环控制命令

循环控制命令

break continue exit
对比：
break continue exit一般用于循环结构中控制循环（for，while，if）的走向。
命令       说明
break n    n 表示跳出循环的层数，如果省略n表示跳出整个循环。
continue n n 表示退到第n层继续循环，如果省略n表示跳出本次循环，忽略本次循环的剩余代码，进入循环的下一次循环。
exit n     n 退出当前shell程序，n为返回值，n也可以省略，再下一个shell里通过$?接收这个n值。
return n   n 用于在函数里，作为函数的返回值，用于判断函数执行是否正常。

实例1：
[root@node01 day13]# vi break01.sh 
#!/bin/sh
for ((i=0; i<=5; i++))
do
   if [ $i -eq 3 ] ;then
     #continue;
     break;
     #exit
   fi
    echo $i
done
echo "ok"
[root@node01 day13]# sh break01.sh 
0
1
2
ok
[root@node01 day13]# vi break01.sh 
#!/bin/sh
for ((i=0; i<=5; i++))
do
   if [ $i -eq 3 ] ;then
     #continue;
     #break;
   exit
   fi
    echo $i
done
echo "ok"
[root@node01 day13]# sh break01.sh 
0
1
2
[root@node01 day13]# vi break01.sh 
#!/bin/sh
for ((i=0; i<=5; i++))
do
   if [ $i -eq 3 ] ;then
     continue;
     #break;
     #exit
   fi
    echo $i
done
echo "ok"
[root@node01 day13]# sh break01.sh 
0
1
2
4
5
ok

实例2：
开发shell脚本实现给服务器临时配置多个别名ip，并可以随时撤销配置的所有ip。
ip地址为：192.168.145.120--192.168.145.150，其中192.168.145.130不能设置。
配置ip命令（ifconfig/ip)提示：ifconfig eth0:0 192.168.145.130/24 up

#!/bin/sh
for ((i=130;i<=150;i++))
do
   if [ $i -eq 130 ];then
    continue
   fi
    ifconfig eth0:$i 192.168.145.$i/24 up
done

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:0c:29:a7:4c:37 brd ff:ff:ff:ff:ff:ff
    inet 192.168.145.130/24 brd 192.168.145.255 scope global eth0
    inet 192.168.145.131/24 brd 192.168.145.255 scope global secondary eth0:131
    inet 192.168.145.132/24 brd 192.168.145.255 scope global secondary eth0:132
    inet 192.168.145.133/24 brd 192.168.145.255 scope global secondary eth0:133
    inet 192.168.145.134/24 brd 192.168.145.255 scope global secondary eth0:134
    inet 192.168.145.135/24 brd 192.168.145.255 scope global secondary eth0:135
    inet 192.168.145.136/24 brd 192.168.145.255 scope global secondary eth0:136
    inet 192.168.145.137/24 brd 192.168.145.255 scope global secondary eth0:137
    inet 192.168.145.138/24 brd 192.168.145.255 scope global secondary eth0:138
    inet 192.168.145.139/24 brd 192.168.145.255 scope global secondary eth0:139
    inet 192.168.145.140/24 brd 192.168.145.255 scope global secondary eth0:140
    inet 192.168.145.141/24 brd 192.168.145.255 scope global secondary eth0:141
    inet 192.168.145.142/24 brd 192.168.145.255 scope global secondary eth0:142
    inet 192.168.145.143/24 brd 192.168.145.255 scope global secondary eth0:143
    inet 192.168.145.144/24 brd 192.168.145.255 scope global secondary eth0:144
    inet 192.168.145.145/24 brd 192.168.145.255 scope global secondary eth0:145
    inet 192.168.145.146/24 brd 192.168.145.255 scope global secondary eth0:146
    inet 192.168.145.147/24 brd 192.168.145.255 scope global secondary eth0:147
    inet 192.168.145.148/24 brd 192.168.145.255 scope global secondary eth0:148
    inet 192.168.145.149/24 brd 192.168.145.255 scope global secondary eth0:149
    inet 192.168.145.150/24 brd 192.168.145.255 scope global secondary eth0:150
    inet6 fe80::20c:29ff:fea7:4c37/64 scope link 
       valid_lft forever preferred_lft forever
3: pan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN 
    link/ether 42:17:c7:b3:af:ed brd ff:ff:ff:ff:ff:ff
[root@node01 day13]# /etc/init.d/network  restart
Shutting down interface eth0:  Device state: 3 (disconnected)
                                                           [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:  Active connection state: activating
Active connection path: /org/freedesktop/NetworkManager/ActiveConnection/72
state: activated
Connection activated
                                                           [  OK  ]
[root@node01 day13]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:0c:29:a7:4c:37 brd ff:ff:ff:ff:ff:ff
    inet 192.168.145.130/24 brd 192.168.145.255 scope global eth0
    inet6 fe80::20c:29ff:fea7:4c37/64 scope link 
       valid_lft forever preferred_lft forever
3: pan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN 
    link/ether 42:17:c7:b3:af:ed brd ff:ff:ff:ff:ff:f

实例3：
写一个脚本，实现判断192.168.145.0/24网络里，当前在线用户的ip有那些
判断在线：ping通
ping通后，返回值为0
[root@node01 day13]# vi ping.sh 
#!/bin/sh
for i in `seq 254`
do
   ping -c2 -i 1 -w 1 192.168.145.$i >/dev/null 2>&1
   if [ $? -eq 0 ]; then
      echo "192.168.145.$i is up">>/data/wolf/uplist.log
   else
     echo "192.168.145.$i is down">>/data/wolf/downlist.log
   fi
done
[root@node01 ~]# tail -f /data/wolf/uplist.log 
192.168.145.1 is up
192.168.145.2 is up
192.168.145.130 is up
192.168.145.131 is up
192.168.145.132 is up
192.168.145.133 is up
192.168.145.135 is up
192.168.145.136 is up
192.168.145.137 is up
192.168.145.138 is up
192.168.145.139 is up
192.168.145.141 is up
192.168.145.142 is up
192.168.145.144 is up
192.168.145.146 is up
192.168.145.149 is up
192.168.145.150 is up
[root@node01 ~]# tail -f /data/wolf/downlist.log 
192.168.145.29 is down
192.168.145.30 is down
192.168.145.31 is down
192.168.145.32 is down

实例4：
写一个脚本解决dos攻击产生案例
提示：根据web log或者网络连接数，监控当一个ip并发连接数或者短时内pv达到100，
就调用命令封掉对应的ip，监控频率每隔3分钟。防火墙命令为
iptables -A INPUT -s 192.168.145.130 -j DROP
web也可以分析log，把单ip pv数高的疯掉。按天定义PV=1000封掉。
#!/bin/sh
do
   awk '{print $1}' access.log|grep -v "^$"|sort|uniq -c /data/wolf/tmp.log
   exec </tmp/tmp.log
   while read line
   do
      ip=`echo $line|awk 'print $2'`
      count=`echo $line|awk 'print $1'`
         if [ $count -gt 3 ] && [ `iptables -L -n|grep "$ip"`|wc -l -lt 1 ]
            then
                iptables -A INPUT -s $ip -j DROP
                echo "$line is dropped" >>/data/wolf/droplist.log
         fi
   done
   sleep 5
done

或者通过网络连接数来判断
netstat -an|grep EST|awk -F '[ :]+' '{print $6}'|sort|uniq -c>/tmp/tmp.log
上面的脚本里的awk命令换成上面的netstat命令即可。