Question

I want to match either foo bar baz or bar baz foo. foo can be in either position, but it must be present. I’m not too familiar with lookaheads, and look behinds, but I feel like that’s got to be the way to do it. Any tips?

Answer 1

There may be a cleaner way to do this, but the following should work:

/^(?=.*foo)(foo )?bar baz( foo)?$/

http://www.rubular.com/r/7wEVNi5G1Q

Alternatively, you can just use | to match one option or the other:

/foo bar baz|bar baz foo/