用法
for 变量名 in 值列表
do
命令序列
done

for i in seq 1 5; do
echo $i
done

ping 20网段所有主机是否ping通

!/bin/bash

for ip in 192.168.20.{1..254}
do
ping -c 1 -i 0.01 -w 1 $ip &>/dev/null
if [ $? -eq 0 ]
then
echo $ip up
else
echo $ip down
fi
done