follow chromatic's advice if you simply want to match 'NOT cr{digit}'.

but your regex already matches entries that don't end in cr{digit}. i fiddled with the string a bit, and your regex returns whatever the last field is (like 'myrouter1-cr2').

so if you're parsing a text file and looking for instances of 'confederation-as-router' and want to return all the aliases ( or whatever the last field is ) you're already there.

otherwise, a bit more info might help all concerned to help 'append to the regex'