test]# cat check_ip.sh
#!/bin/bash    
function check_ip() {   
    IP=$1   
    VALID_CHECK=$(echo $IP|awk -F. '$1<=255&&$2<=255&&$3<=255&&$4<=255{print "yes"}')   # 检查每个数字是否小于等于255
    if echo $IP|grep -E "^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$">/dev/null; then   # 检查格式是否为数字组成的三位数并且中间是点
        if [ ${VALID_CHECK:-no} == "yes" ]; then   
            echo "IP $IP available."   
        else   
            echo "IP $IP not available!"   
        fi   
    else   
        echo "IP $IP format error!"   
    fi   }   
# Example   
check_ip 192.168.1.1   
check_ip 256.1.1.1
check_ip 2444.1.1.1

test]# sh check_ip.sh
IP 192.168.1.1 available.
IP 256.1.1.1 not available!
IP 2444.1.1.1 format error!
test]#