Match all email addresses belonging to a specific domain and its subdomains - ruby

Question

I am looking to match all email addresses from a specific domain.
Any email coming from example.com or foo.example.com should match, everything else should be rejected. To do this, I could do some basic string matching to check if the given string ends with, or contains, example.com which would work fine but it also means that something like fooexample.com will pass.
Hence, based on the above requirements, I started working on a pattern that would pass the domain and its sub-domain. I was able to come up with the following regex pattern:
`/\b[A-Z0-9._%+-]+#[A-Z0-9.-]+\.example.com\b/i`
This only matched subdomains, but I have seen the pattern at "How to match all email addresses at a specific domain using regex?" which handles the main domain.
Is there a way to combine these two into something that works for any address from example.com.

Answer 1

How about
/\b(?:(?![_.-])(?!.*[_.-]{2})[a-z0-9_.-]+(?<![_.-]))#(?:(?!-)(?!.*--)[a-z0-9-]+(?<!-)\.)*example\.com\b/i

Answer 2

This one would also match 'tagged' and 'tagged-subdomain' mails like a+b#example.com and a+b#i.example.com
(([A-Za-z0-9]+_+)|([A-Za-z0-9]+\-+)|([A-Za-z0-9]+\.+)|([A-Za-z0-9]+\++))*[A-Za-z0-9]+#(?:(?!-)(?!.*--)[a-z0-9-]+(?<!-)\.)*example\.com\b
Hope it helps you

Answer 3

I'd recommend reading "Stop Validating Email Addresses With Your Complex Regex".
From that point, I'd look for:
/#.*\bexample\.com/
For instance:
%w[foo#example.com foo#barexample.com foo#subdomain.example.com].grep(/#.*\bexample\.com/)
=> ["foo#example.com", "foo#subdomain.example.com"]
It's too easy to end up with a regex that is a maintenance nightmare, and that doesn't accomplish what you need. I highly recommend keeping it simple.