Question

I want to check the range of ip address in a regular expression ,
I was using this way and it’s working so successfully

function validate_ip(ip)
{
       // See if x looks like an IP address using our "almost IP regex".
    var regex = /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/;
    var match = regex.exec(ip);
    if (!match) return false;
    // Additional code to check that the octets aren't greater than 255:
    for (var i = 1; i <= 4; ++i) {
        if (parseInt(match[i]) > 255) 
            return false;
    }
    return true;
}

now i want to perform checking of the range and the syntax in just regular expression
can this be done ?

Answer 1

The most straightforward approach is to look at the different cases:

25[0-5]|2[0-4]\d|1?\d\d?

This will match numbers between 0 and 255, disallowing prefixed zeroes such as: 055.

If you want to exclude zero:

25[0-5]|2[0-4]\d|1\d\d|[1-9]\d?