循环判断ping网段

#!/bin/bash
for i in `seq 1 254`
do
    ping -c 1 192.168.191.$i > /dev/null
    if [ $? -eq 0 ]
    then
          echo "192.168.191.$i 存活"
    else
          echo "192.168.191.$i 不存活" >> /root/ip.txt
    fi   
done