Ruby gsub to remove illegal characters in phone number

Question

I want to remove all characters in a string that do not belong in a phone number string. The first character may or may not be a "+" and all other characters must be digits.

I had gsub(/\D/, ''), but I want to keep the first character if it is a "+" (or a digit, of course). I then tried some negation, but this is not right, either: gsub(/^(\+?(\d))/, '').

How can I ignore the first character with regex iff it is a "+"?

Answer 1

How about using a negative lookahead at the beginning:

gsub(/(?!^\+)\D*/, '')

Basically, the above regex should remove any series of non-digits where the first character is not a single '+' character at the beginning of the string.

Hope it helps.