I didn't even know about the Pullman, but now I've found my new religion!
EDIT: Nvm, I guess it's the common sandwich shape. I just found some images that were incredibly perfectly square and thought Pullman were these particular perfect shapes that required some forbidden technique.
Pullman loaves are indeed square. There's a special pan used that gives a pullman loaf flat sides all around.
There are variations with angled sides, but the standard is for the loaf to be square as well as flat topped. You can even find some that are cube shaped rather than the longer, more typical version.
Without the lid, you do get the more usual store loaf shape, with flat sides and bottom, but a rounded top.
Now, depending on the dough recipe, you may not get visually ideal squares shapes, since it has to rise enough to push into the corners enough to look square. And some pans have rounded corners to begin with, so that only the top side corners are going to be able to be fully square with right angle corners if things go perfectly.
But the pans to get 90° angles do exist, and an experienced baker can tweak a recipe to be relatively reliable at getting the bread to fill those corners so that the end loaf is visually square, if not perfectly square by measuring.
Some of that may seem like semantics, but your standard sandwich loaf is baked in either a flat sided loaf pan with an open top, or a pullman pan without the lid on. Some will use a slightly angled pan with an open top.