Depends on how deep the scratch is...
If it's not that deep, then a judicious buffing will probably work.
3M makes a liquid rubbing compound that's really great for light/medium scratches in the clear coat. Comes in a small grey bottle, costing about $5-$7. I've used it many times with much success.
I'd try this, rubbing it out by hand, before actually attacking with a buffer. Once the scratch is out, I'd then go back over the general area with either a polish like Nu Finish or even a light application of the liquid compound using the buffer to blend the freshly compounded area with the surrounding clear coat. Using the buffer will require much care, though. Too much in one spot will take the clear-coat off rather quickly.
If it's a heavier scratch down to the base coat, but not the metal, the scratch would likely only need to be lightly sanded out, have the clear coat re-applied, and then wet-sanded and buffed/polished. A bit more labor intensive, but still a relatively simple DIY project.
If it's down to the bare metal, I'd opt for a body shop repair.
Good luck!