shell 监控局域网的主机是否up

#!/bin/bash
for ((i=30;i<60;i++)) ;do                        
ping -c 3 172.31.0.$i>/dev/null 
#ping -c 172.31.0.30 ~172.31.0.59
if [[ $? -eq 0 ]]                  #if up $?==0
then echo "172.31.0.$i is alive"
else 
echo "172.31.0.$i isn't up"
fi
done

#!/bin/bash
for ((i=30;i<60;i++)) ;do                        
if ping -c 3 172.31.0.$i>/dev/null ;  then 
echo "172.31.0.$i is alive"
else 
echo "172.31.0.$i isn't up"
fi
done

监控局域网的主机是否up，可以使用ping命令，如果ping 通$?等于0，ping不通 返回非0