Regex match for a URL input

Question

I am trying to write a regex expression for a URL that matches if you include the protocol (https://), and host name (name and extension e.g youtube.com). i have included a regex 101 link below.

Where im struggling is trying to not match simply 'youtube' and also writing the syntax for matching https:// as a group. I cant escape properly for the double forward slash or colon.

https://regex101.com/r/0KUyxu/5

/^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9]|[https:\//])$/gm

It should not match:

youtube
https://youtube
www.youtube

It should however match:

https://youtube.com
youtube.com
www.youtube.com
https://www.youtube.com

Any help would be greatly appreciated, thanks!

This is a character class notation [https:\//] But why not specify youtube in the pattern? — The fourth bird
– The fourth bird, Commented Nov 17, 2020 at 11:19
i cant specify 'youtube' directly as the url will be different everytime depending on the users input. — twt333
– twt333, Commented Nov 17, 2020 at 11:20

ST Selvam · Accepted Answer · 2020-11-17 11:42:37Z

[Tested in the chrome console.]

I Can't completely do what you asked for did something relative to that (I think so!)

function urlRegexTest(testUrl) {
var expression = /(https?:\/\/(?:www\.|(?!www))[a-zA-Z0-9][a-zA-Z0-9-]+[a-zA-Z0-9]\.[^\s]{2,}|www\.[a-zA-Z0-9][a-zA-Z0-9-]+[a-zA-Z0-9]\.[^\s]{2,}|https?:\/\/(?:www\.|(?!www))[a-zA-Z0-9]+\.[^\s]{2,}|www\.[a-zA-Z0-9]+\.[^\s]{2,})/gi;
var regex = new RegExp(expression);
var url = testUrl;
console.log("URL ="+url);
var res = "";
if (url.match(regex)) {
    res = "Valid URL";
} else {
    res = "Invalid URL";
}
console.log(res);
}

Test inputs & outputs

urlRegexTest("godaddy.in") URL =godaddy.in Invalid URL

urlRegexTest("godaddy.com") URL =godaddy.com Invalid URL

urlRegexTest("www.godaddy.com") URL =www.godaddy.com Valid URL

urlRegexTest("https://godaddy.com") URL =https://godaddy.com Valid URL

urlRegexTest("http://godaddy.com") URL =http://godaddy.com Valid URL

urlRegexTest("http://godaddy.in") URL =http://godaddy.in Valid URL

urlRegexTest("http://sts.in") URL =http://sts.in Valid URL

urlRegexTest("godaddy.in") URL =godaddy.in Invalid URL

urlRegexTest("https://godaddy.in") URL =https://godaddy.in Valid URL

urlRegexTest("www.godaddy.in") URL =www.godaddy.in Valid URL

You can refer for more info about this question:- https://www.geeksforgeeks.org/how-to-validate-url-using-regular-expression-in-javascript/

The fourth bird · Accepted Answer · 2020-11-17 13:12:47Z

Perhaps for your example data it would suffice to check that the string does not start with www. and does not contain a dot anymore.

^(?!www\.[^.\r\n]*$)\S+\.[a-z]{2,}$

Regex demo

Or a bit more specific, where you can specify the allowed characters using character classes and

^(?!www\.[^.\r\n]*$)(?:https?://)?[a-zA-Z0-9]+(?:[.-][a-zA-Z0-9]+)*\.[a-z]{2,}$

Explanation

^ Start of string
(?!www\.[^.\r\n]*$) Negative lookahead, assert the start does not start with www. without anymore dots
(?:https?://)? Optionally match http, optional s and ://
[a-zA-Z0-9]+ Match 1+ any of the listed chars in the character class
(?:[.-][a-zA-Z0-9]+)* Optionally repeat matching either a . or - (to prevent matching consecutive dots and hyphens if that should not be possible) and 1+ times any of the listed chars in the character class
\.[a-z]{2,} Match . and 2 or more times a char a-z
$ End of string.

Regex demo

Carlo Moretti · Accepted Answer · 2020-11-17 16:11:08Z

1

Your regex seems quite complex, this should work fine:

^(https?:\/\/)?([0-z\-\.]+)\.([a-z]{2,})$

and you'll also have:

group 1 → protocol
group 2 → domain name
group 3 → domain extension

Edit

To handle the case where it shouldn't match the www.domainname, you can use negative lookbehind like this:

^(https?:\/\/)?([0-z\-\.]+)(?<!www)\.([a-z]{2,})$

here the tester: https://regex101.com/r/0KUyxu/8

edited Nov 17, 2020 at 16:11

answered Nov 17, 2020 at 11:30

Carlo Moretti

2,2602 gold badges28 silver badges43 bronze badges

2 Comments

twt333 Over a year ago

This is an elegant solution and makes a lot more sense, thank you, however what about the instance where it should not match www.youtube? regex101.com/r/0KUyxu/7

Carlo Moretti Over a year ago

yeah sorry I added a version with negative lookbehind to handle the www before the .

Orkun Berk Yuzbasioglu · Accepted Answer · 2020-11-17 11:40:26Z

0

For this case, try: [a-zA-Z.://]+.com$

This expression matches a string of length one or more containing letters in the alphabet plus . , : , / before the .com. However, if the domain name contains any special characters, then this would fail.

edited Nov 17, 2020 at 11:40

answered Nov 17, 2020 at 11:34

Orkun Berk Yuzbasioglu

1651 silver badge10 bronze badges

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