Given that you're adding an else clause, it'd be nice to flip the conditional, so that it's <code> if (MINUSF) { new code } else { modified old code } </code> instead of <code> if (!MINUSF) { what to do if -f wasn't passed } else { what to do if -f wasn't not passed } </code>
Positive conditionals are more intelligible: humans have easily-triggered cognitive defects around double-negation.