方法1：

#!/bin/bash
# blog: http://lizhenliang.blog.51cto.com
 
function check_ip() {
    IP=$1
    VALID_CHECK=$(echo $IP|awk -F. '$1<=255&&$2<=255&&$3<=255&&$4<=255{print "yes"}')
    if echo $IP|grep -E "^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$">/dev/null; then
        if [ ${VALID_CHECK:-no} == "yes" ]; then
            echo "IP $IP available."
        else
            echo "IP $IP not available!"
        fi
    else
        echo "IP format error!"
    fi
}

Example

check_ip 192.168.1.1
check_ip 256.1.1.1

方法2：

#!/bin/bash
# blog: http://lizhenliang.blog.51cto.com
 
function check_ip() {
    IP=$1
    if [[ $IP =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
        FIELD1=$(echo $IP|cut -d. -f1)
        FIELD2=$(echo $IP|cut -d. -f2)
        FIELD3=$(echo $IP|cut -d. -f3)
        FIELD4=$(echo $IP|cut -d. -f4)
        if [ $FIELD1 -le 255 -a $FIELD2 -le 255 -a $FIELD3 -le 255 -a $FIELD4 -le 255 ]; then
            echo "IP $IP available."
        else
            echo "IP $IP not available!"
        fi
    else
        echo "IP format error!"
    fi
}

Example

check_ip 192.168.1.1
check_ip 256.1.1.1

加个循环，如果错误则重新输入，直到正确：

#!/bin/bash
# blog: http://lizhenliang.blog.51cto.com
 
function check_ip() {
    local IP=$1
    VALID_CHECK=$(echo $IP|awk -F. '$1<=255&&$2<=255&&$3<=255&&$4<=255{print "yes"}')
    if echo $IP|grep -E "^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$" >/dev/null; then
        if [ $VALID_CHECK == "yes" ]; then
         echo "IP $IP  available!"
            return 0
        else
            echo "IP $IP not available!"
            return 1
        fi
    else
        echo "IP format error!"
        return 1
    fi
}
while true; do
    read -p "Please enter IP: " IP
    check_ip $IP
    [ $? -eq 0 ] && break
done