The Desired Results Suppose that we want a regex to match a sum of two variables. x + y length + width // no underscores in this example rectan_width + rectan_height // spaces around `+` rectan_width+rectan_height // no spaces around `+` Attempt at a Functioning Regular Expression Here is what I have so far… (?<=s|^|b)(?:[_/]b|b[_/]|d*.?d+|[A-Za-z0-9]|([A-Za-z0-9]+))+(?=s|$|b) […]