How do I walk up at a T-junction?
Press "g" and then the direction to stop at intersections. Not SHIFT-direction.
More generally, use the "?" command to read the documentation for various nethack commands, including the differences between SHIFT, "g", "G"/CTRL, and "m" as movement modifiers.
See also http://strategywiki.org/wiki/NetHack/Controls#Advanced_movement
I strongly disagree with the first sentence, but the answer is to use _ to run to where you want to go.