shell学习二十七--循环控制命令

Dear 丶 2022-06-04 04:53 284阅读 0赞

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。