测试能否连通外网：

pingres=`ping -c 1 baidu.com | sed -n '/64 bytes from/p'`
if [ -z "$pingres" ]
then
        echo "network error" 
        exit 1
fi

查看局域网内不可达的ip，find_unreachable_ip_in_lan.sh：

#!/bin/sh

if [ "$1" != "" ]; then
	lan_prefix=$1
else
	lan_prefix="10.10.10"
fi

for ((i=2; i<255; i+=1))
do
	ip="$lan_prefix.$i"
	exists=`ping -c 2 $ip | grep -i Unreachable | wc -l`
	if [ "$exists" != "0" ]; then
		echo $ip
	fi
done

--end--