Hi Dave, you need to use = and single quotes.
To restrict the results to files that only contains the exact string in the variable, use the = (equal) character in the search criteria. For example the search criteria '123' will return '123' or '1234' whereas the search criteria '=123' will only return '123'. To exclude a string use the ! (exclamation) character. For example '!123' will return anything not including the string '123'.
So, perhaps create a list that has those criteria in the search card.