How to write regex for domain validation that will trigger pattern error in Angular form

Question

I am validating a domain field in the form. I am using Validators.pattern(this.domainPattern) for doing that. I am using below pattern:

public domainPattern: string = "^(?:[a-z0-9][a-z0-9-]{0,61}[a-z0-9]\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]$";

It works fine for many cases. But when there is a white space in domain it is not triggering pattern error. What I am missing?

Quick help will be highly appreciated.

Thanks.

Add sample strings that should pass validation, show us what should pass and does not pass, explain your logic for regex. — Michał Turczyn
– Michał Turczyn, Commented Mar 26, 2019 at 5:06
google.com abc.co.in should pass. But goo gle.com should not pass — Ashish Bisht
– Ashish Bisht, Commented Mar 26, 2019 at 5:13
This is impossible to answer without knowing what you really want. I can type this-s.asjfjff.validdddd-cddddd for example and tihs is valid. Is this supposed to be valid? — JackPRead
– JackPRead, Commented Mar 26, 2019 at 8:11
By the way, your pattern doesn't accept whitespace so if you are matching whitespace there is a problem elsewhere, not in the regex pattern. — JackPRead
– JackPRead, Commented Mar 26, 2019 at 8:12

Michał Turczyn · Accepted Answer · 2019-03-26 05:56:29Z

4

Try this pattern:

(?(?<= )(?=[^ ])|^)(?:[a-z0-9][a-z0-9-]{0,61}[a-z0-9]\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]

I just added (?(?<= )(?=[^ ])|^), conditional which checks:

first it checks condition (?<= ) if what is preceeding is space, if it is, then check if what's after is not a space with (?=[^ ]), if the condition fails, then check if we are at the beginning of a string with ^.

Demo

UPDATE

OP said:

I want user to enter just one valid domain name. If user enters "google.com google.com" it should be treated as invalid

Then you could use this pattern

^(?!.* .*)(?:[a-z0-9][a-z0-9-]{0,61}[a-z0-9]\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]$

Just added (?!.* .*) which checks if there's sapce in following line, if it is, then it won't match anything, as space indicated multiple domain names.

Another demo

edited Mar 26, 2019 at 5:56

answered Mar 26, 2019 at 5:48

Michał Turczyn

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2 Comments

Ashish Bisht Over a year ago

Thanks for that @Michal. But in my case, I want user to enter just one valid domain name. If user enters "google.com google.com" it should be treated as invalid.

Ashish Bisht Over a year ago

Thanks @MichalTurczyn. It works as expected. I was struggling for this since yesterday.

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