grep with regex for phone number

Question

I would like to get the phone numbers from a file. I know the numbers have different forms, I can handle for a single one, but don\'t know how to get a uniform regex. For ex

Answer 1

My first thought is that you may find it easier to see if your candidate number matches against one of four regular expressions. That will be easier to develop/debug, especially as/when you have to handle additional formats in the future.