These are some shelf brackets I designed to fit a 1"x8" (actual board size of these from hardware stores is actually .75"x7.25") to make a clean looking shelf with only one cut to a pine or other wooden board. There is a left, center, and right bracket along with a template to help you place your screws. I used 8x1" screws and they fit perfectly.

For short shelves, there is no reason to use the center shelve STL, but for longer ones, you may want to print one or several. I recommend tree supports just for the screw bracket. I printed in PLA .2 Strength setting on a .4 nozzle with a 25% gyroid infill also I increased the walls to 6 each for top and bottom and wall loops to 7 to make it stronger.