shell 按行读取并保存成数组

从ip.txt里读取IP.然后把IP地址赋值到一个数组里.
IP文件如下：
Address:  220.181.26.163
Address:  220.181.26.174
Address:  220.181.26.175
Address:  220.181.26.176
Address:  220.181.19.228
Address:  220.181.19.229
Address:  220.181.26.161
Address:  220.181.26.162

方法一：
for x in ` awk '{print $2}' ip.txt `
{
echo $x
}
方法二：
ARRAY=($(awk '{print $2}' ip.txt))
方法三：
n=0;while read a b;do array[$n]=$b;((n++));done<ip.txt

方法四：
n=1
while ((n<=$(cat ip.txt|wc -l)))
do
    ipaddr[$n]=$(cat ip.txt|sed -n "${n}p"|awk '{print $2}')
    ((n+=1))
done
n=`expr $n - 1`