How to negate specific word in regex?

A great way to do this is to use negative lookahead:

^(?!.*bar).*$

The negative lookahead construct is the pair of parentheses, with the opening parenthesis followed by a question mark and an exclamation point. Inside the lookahead [is any regex pattern].

Solution:

^(?!.*STRING1|.*STRING2|.*STRING3).*$

xxxxxx OK

xxxSTRING1xxx KO (is whether it is desired)

xxxSTRING2xxx KO (is whether it is desired)

xxxSTRING3xxx KO (is whether it is desired)

Unless performance is of utmost concern, it's often easier just to run your results through a second pass, skipping those that match the words you want to negate.

Regular expressions usually mean you're doing scripting or some sort of low-performance task anyway, so find a solution that is easy to read, easy to understand and easy to maintain.

You could either use a negative look-ahead or look-behind:

^(?!.*?bar).*
^(.(?<!bar))*?$

Or use just basics:

^(?:[^b]+|b(?:$|[^a]|a(?:$|[^r])))*$

These all match anything that does not contain bar.