The regex you've got already has several problems:
Firstly, it contains dots. In regex, a dot means "match any character", where you need to match just an actual dot. For this, you need to escape it, so put a back-slash in front of the dots.
Secondly, but you're matching any three digits in each section. This means you'll match any number between 0 and 999, which obviously contains a lot of invalid IP address numbers.
This can be solved by making the number matching more complex; there are other answers on this site which explain how to do that, but frankly it's not worth the effort -- in my opinion, you'd be much better off splitting the string by the dots, and then just validating the four blocks as numeric integer ranges -- ie:
^ start of string
(?!0) Assume IP cannot start with 0
(?!.*\.$) Make sure string does not end with a dot
(
(
1?\d?\d| A single digit, two digits, or 100-199
25[0-5]| The numbers 250-255
2[0-4]\d The numbers 200-249
)
\.|$ the number must be followed by either a dot or end-of-string - to match the last number
){4} Expect exactly four of these
$ end of string
Unit test for a browser's console:
var rx=/^(?!0)(?!.*\.$)((1?\d?\d|25[0-5]|2[0-4]\d)(\.|$)){4}$/;
var valid=['1.2.3.4','11.11.11.11','123.123.123.123','255.250.249.0','1.12.123.255','127.0.0.1','1.0.0.0'];
var invalid=['0.1.1.1','01.1.1.1','012.1.1.1','1.2.3.4.','1.2.3\n4','1.2.3.4\n','259.0.0.1','123.','1.2.3.4.5','.1.2.3.4','1,2,3,4','1.2.333.4','1.299.3.4'];
valid.forEach(function(s){if (!rx.test(s))console.log('bad valid: '+s);});
invalid.forEach(function(s){if (rx.test(s)) console.log('bad invalid: '+s);});
210.110 – must have 4 octets
255 – must have 4 octets
y.y.y.y – only digits are allowed
255.0.0.y – only digits are allowed
666.10.10.20 – octet number must be between [0-255]
4444.11.11.11 – octet number must be between [0-255]
33.3333.33.3 – octet number must be between [0-255]
JavaScript code to validate an IP address
function ValidateIPaddress(ipaddress) {
if (/^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/.test(ipaddress)) {
return (true)
}
alert("You have entered an invalid IP address!")
return (false)
}
Full credit to oriadam. I would have commented below his/her answer to suggest the double zero change I made, but I do not have enough reputation here yet...
change:
-(?!0) Because IPv4 addresses starting with zeros ('0.248.42.223') are valid (but not usable)
If you wrtie the proper code you need only this very simple regular expression: /\d{1,3}/
function isIP(ip) {
let arrIp = ip.split(".");
if (arrIp.length !== 4) return "Invalid IP";
let re = /\d{1,3}/;
for (let oct of arrIp) {
if (oct.match(re) === null) return "Invalid IP"
if (Number(oct) < 0 || Number(oct) > 255)
return "Invalid IP";
}
return "Valid IP";
}
But actually you get even simpler code by not using any regular expression at all:
function isIp(ip) {
var arrIp = ip.split(".");
if (arrIp.length !== 4) return "Invalid IP";
for (let oct of arrIp) {
if ( isNaN(oct) || Number(oct) < 0 || Number(oct) > 255)
return "Invalid IP";
}
return "Valid IP";
}
Always looking for variations, seemed to be a repetitive task so how about using forEach!
function checkIP(ip) {
//assume IP is valid to start, once false is found, always false
var test = true;
//uses forEach method to test each block of IPv4 address
ip.split('.').forEach(validateIP4);
if (!test)
alert("Invalid IP4 format\n"+ip)
else
alert("IP4 format correct\n"+ip);
function validateIP4(num, index, arr) {
//returns NaN if not an Int
item = parseInt(num, 10);
//test validates Int, 0-255 range and 4 bytes of address
// && test; at end required because this function called for each block
test = !isNaN(item) && !isNaN(num) && item >=0 && item < 256 && arr.length==4 && test;
}
}
Of the answers I checked, they're either longer or incomplete in their verification. Longer, in my experience, means harder to overlook and therefore more prone to be erroneous. And I like to avoid repeating similar patters, for the same reason.
The main part is, of course, the test for a number - 0 to 255, but also making sure it doesn't allow initial zeroes (except for when it's a single one):
[1-9]?\d|1\d\d|2(5[0-5]|[0-4]\d)
Three alternations - one for sub 100: [1-9]?\d, one for 100-199: 1\d\d and finally 200-255: 2(5[0-5]|[0-4]\d).
This is preceded by a test for start of lineor a dot ., and this whole expression is tested for 4 times by the appended {4}.
This complete test for four byte representations is started by testing for start of line followed by a negative look ahead to avoid addresses starting with a .: ^(?!\.), and ended with a test for end of line ($).
This is what I did and it's fast and works perfectly:
function isIPv4Address(inputString) {
let regex = new RegExp(/^(([0-9]{1,3}\.){3}[0-9]{1,3})$/);
if(regex.test(inputString)){
let arInput = inputString.split(".")
for(let i of arInput){
if(i.length > 1 && i.charAt(0) === '0')
return false;
else{
if(parseInt(i) < 0 || parseInt(i) >=256)
return false;
}
}
}
else
return false;
return true;
}
Explanation: First, with the regex check that the IP format is correct. Although, the regex won't check any value ranges.
I mean, if you can use Javascript to manage regex, why not use it?. So, instead of using a crazy regex, use Regex only for checking that the format is fine and then check that each value in the octet is in the correct value range (0 to 255). Hope this helps anybody else. Peace.
well I try this, I considered cases and how the entries had to be:
function isValidIP(str) {
let cong= /^(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]|[0-9])\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]|[0-9])\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]|[0-9])\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]|[0-9])$/
return cong.test(str);}