Regex that does not allow consecutive dots

Question

I have a Regex to allow alphanumeric, underscore and dots but not consecutive dots:

^(?!.*?[.]{2})[a-zA-Z0-9_.]+$

I also need to now allow

Answer 1

Re-write the regex as

^[a-zA-Z0-9_]+(?:\.[a-zA-Z0-9_]+)*$

or (in case your regex flavor is ECMAScript compliant where \w = [a-zA-Z0-9_]):

^\w+(?:\.\w+)*$

See the regex demo

Details:

• ^ - start of string
• [a-zA-Z0-9_]+ - 1 or more word chars
• (?:\.[a-zA-Z0-9_]+)* - zero or more sequences of:
  • \. - a dot
  • [a-zA-Z0-9_]+ - 1 or more word chars
• $ - end of string