Regex to validate domain name with port

Question

I am new developer and don't have much exposure on Regular Expression. Today I assigned to fix a bug using regex but after lots of effort I am unable to find the error.

Here is my requirement.

My code is:

string regex = "^([A-Za-z0-9\\-]+|[A-Za-z0-9]{1,3}\\.[A-Za-z0-9]{1,3}\\.[A-Za-z0-9]    {1,3}\\.[A-Za-z0-9]{1,3}):([0-9]{1,5}|\\*)$";

Regex _hostEndPointRegex = new Regex(regex);

bool isTrue = _hostEndPointRegex.IsMatch(textBox1.Text);

It's throwing an error for the domain name like "nikhil-dev.in.abc.ni:8080".

I am not sure where the problem is.

I think your problem is that - hasn't been allowed... that said, my RegEx isn't great. — Danny Beckett
– Danny Beckett, Commented Apr 17, 2013 at 11:26
Why reinvent the wheel, poorly? There's a few functions like Uri.CheckHostName() (as supposed here) and a hideous regex is shown here. — CodeCaster
– CodeCaster, Commented Apr 17, 2013 at 11:30

John Sobolewski · Accepted Answer · 2013-04-17 12:08:58Z

Your regex is a bit redundant in that you or in some stuff that is already included in the other or block.

I just simplified what you had to

(?:[A-Za-z0-9-]+\.)+[A-Za-z0-9]{1,3}:\d{1,5}

and it works just fine...

I'm not sure why you had \ in the allowed characters as I am pretty sure \ is not allowed in a host name.

Your problem is that your or | breaks things up like this...

[A-Za-z0-9\\-]+

or

[A-Za-z0-9]{1,3}\\.[A-Za-z0-9]{1,3}\\.[A-Za-z0-9]{1,3}\\.[A-Za-z0-9]{1,3}

or

\*

Which as the commentor said was not including "-" in the 2nd block.

So perhaps you intended

^((?:[A-Za-z0-9\\-]+|[A-Za-z0-9]{1,3})\.[A-Za-z0-9]{1,3}\.[A-Za-z0-9]{1,3}\.[A-Za-z0-9]{1,3}):([0-9]{1,5}|\*)$

However the first to two or'ed items would be redundant as + includes {1-3}.

ie. [A-Za-z0-9\-]+ would also match anything that this matches [A-Za-z0-9]{1,3}

You can use this tool to help test your Regex: http://regexpal.com/

Personally I think every developer should have regexbuddy

The regex above although it works will allow non-valid host names.

it should be modified to not allow punctuation in the first character.

So it should be modified to look like this.

(?:[A-Za-z0-9][A-Za-z0-9-]+\.)(?:[A-Za-z0-9-]+\.)+[A-Za-z0-9]{1,3}:\d{1,5}

Also in theory the host isn't allowed to end in a hyphen.

it is all so complicated I would use the regex only to capture the parts and then use Uri.CheckHostName to actually check the Uri is valid.

Or you can just use the regex suggested by CodeCaster

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