判断输入的IP地址是否合法
#!/bin/bash
IP=$1
[[ $IP =~ ^(([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]).){3})([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$ ]] && echo $IP is valid || echo $IP is invalid
#!/bin/bash
IP=$1
[[ $IP =~ ^(([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]).){3})([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$ ]] && echo $IP is valid || echo $IP is invalid