Regex match no groups, 1st group OR 2nd group but not both. Something like 'NAND'

Question

I can't figure out how to write regex that matches these:

• everyone hi
• hi everyone
• hi

But not this:

• everyone hi everyone

The regex (?:everyone )?hi(?: everyone)? will match the latter as well (which is not what I want). How to make such a regex? Or is it just not possible? I couldn't do enough research because I couldn't express the problem in correct words. Sorry if I posted a duplicate

Answer 1

Here is a brute force alternation way to get this done:

^(?:everyone +hi|hi(?: +everyone)?)$

RegEx Demo

RegEx Details:

• ^: Start
• (?:: Start a non-capture group
  • everyone: Match everyone:
  • +hi: Match 1+ spaces followed by hi
  • |: OR
  • hi: Match hi:
• (?: +everyone)?: Optionally match 1+ spaces followed by everyone
• ): End non-capture group
• $: End

Answer 2

You could explicitly make a regex for each case (the first will capture two), utilizing beginning and end of line tokens

(^hi( everyone)?$) (^everyone hi$)