Re-reading original post, this seems to be a dirt floor, with concrete wall(s) which were added to keep snakes out.
My suggestion to not leave the ends of the french drain pipe open is because the original post stated that the purpose of the concrete wall was to keep snakes out. The holes in the "french drain" pipe will allow flow of water to the gravel below the drain pipe. The gravel/rocks/?whatever? beneath the pipe is where the water eventually ends up.
Of course, the pipe itself should be installed at an incline, so that the part outside is lower than the portion inside. The pipe for the french drain is not solid, but has fairly large holes all around it, which is why it needs to be wrapped in some type of water-permeable fabric to allow water to pass through, but not clog the holes with dirt. The length of pipe needed would depend on the quantity of water involved, as well as how well the soil drains.