Regex to match specific strings without a given prefix

Question

I need to match all of its lines that contains a value and that don\'t have a given prefix.

Example: I want all lines that contains word when it\'s not pref

Answer 1

You may need

(?<!prefix )word

(and maybe take care of the spaces).

(?!) is a negative lookahead but in your case you need a negative lookbehind (i.e. (?<!)).