In this image of the truck used in the attack in Nice, France, you can easily count the bullet holes.
I count 29 bullet holes in the windshield. The driver's position on this truck is on the right side of the picture. In France, people drive on the right side of the road, as in most of the rest of the world.
The bullet holes are decidedly biased to the left hand side. The shooter was probably in front of the truck on the passenger side, aiming his shots toward the drivers position.
I suspect that the shooter used a rifle. The shots seem reasonable well spaced, as if attempting to reach the driver as he might take cover within the cab, or as the angle of the line of fire changed as the truck moved. The event happened quickly. The number of shots on the windsheild are well within the standard 30 shot capacity of a current French FAMAS G2. It is also within the 30 round capacity of Mini-14 variants used by some French police, though they are often seen with 20 round magazines.
There are five bullet holes on the drivers side door. The placement suggests that those were done with a pistol.
The placement of the shots on the windshield implies a rifle shooter taking aimed shots.
The NYTimes reports that the driver was found shot to death in the passenger seat of the truck.
Link to Gun Watch