isValidIP

As promised, more regular expression fun. This week we're going to validate IP addresses. An IP address consists of four octets separated by periods. A lazy person might be inclined to use a regular expression of \d{1,3} for each octet, but that would allow numbers larger than 255. A more complex expression is needed: ([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1}).

This expression consists of three parts separated by the pipe character "|". The first part, [1]?\d{1,2}, matches numbers between 0 and 199. The second part, 2[0-4]{1}\d{1}, matches numbers between 200 and 249. The third part, 25[0-5]{1}, matches numbers between 250 and 255. We will repeat this pattern four times, once for each octet, and separate with periods.

ASP

1. function isValidIP(ip)
2.     dim regEx
4.     set regEx = new RegExp
6.     with regEx
7.         .IgnoreCase = True
8.         .Global = True
9.         .Pattern = "^([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})(\.([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})){3}$"
10.     end with
12.     if regEx.Test(trim(CStr(ip))) then
13.         isValidIP = true
14.     else
15.         isValidIP = false
16.     end if
18.     set regEx = nothing
19. end function

PHP

1. function isValidIP($ip)
2. {
3.     $pattern = "/^([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})(\.([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})){3}$/";
4.     return (preg_match($pattern, $ip) > 0) ? true : false;
5. }

Next week we're going to build on this pattern to validate something else. I wonder what that could be?

• View ASP implementation on Snipplr
• View PHP implementation on Snipplr