Question

My problem is that I need to match if a string contains any words besides the one(s) I list.

For example, I may have this approved list:

User1
User2

Here are two examples of what should match and what shouldn’t.

Should match (because User3 is not approved):

User1
User2
User3

Shouldn’t match (because every string listed is in the approved list):

User1

I have tried lookaround assertions, but they do not actually consume the letters as they try to match, so with a string like "User1\r\nUser2", I get matches like "ser1\r\n". I want to know if there are any other words besides what I deem allowable.

I cannot use a programming language to do this; I am only allowed to hand a regular expression to the program. The language will be Perl.

Answer 1

Does /\b((?!(User1\b|User2\b)).+?)\b/ do what you’re looking for?

\b means word break, i.e. the gap between a word and non-word character (zero-width).

?! signifies a negative lookahead assertion (also zero-width).

.+? is being used to catch anything not matching the excluded words.

Hope this helps.