And have him sue me? HA!! Lesson #1 when having to shoot someone, never, and I mean NEVER shoot to wound. If it's serious enough... and a guy running at you with a knife is as serious as it gets... to pull a gun, you had better shoot him dead!!
I used to get news emails from some site that had to do with gun owners and stuff, it was pretty cool, you got the latest news on handguns, rifles and ammo. It would have little news stories, which were documented in court.
To make a long story short, a guy was walking to his car, and a man came out with a large knife told the man to get in the car, and drive him somewhere. The man pulled his snubnose hammerless .357 revolver (Yeah I know... a ladies gun. Pshhh.) and shot the man in the leg 2 times. Then he called the police.
The man was arrested, but a while later was taken to court, and sued for shooting the man in the leg. The guy with the knife argued that he only asked for a ride, and the guy with the gun shot him before he drew the knife. After he was shot, he took the knife out for self defence...
Well this might sound really stupid, but it held up in court and the man had to pay this guy a lot of money. Moral of the story? Shoot to kill. If it's bad enough to have to pull your gun, you Kill the attacker.