#!/bin/sh
# may need to become a C program someday.
xdpyinfo -display $DISPLAY | \
    grep dimensions | \
    head -1 | \
    sed -n 's/^.*dimensions[^0-9]*\([0-9]*\)x\([0-9]*\) pixels.*$/\1 \2/p'
#dimensions:    1152x900 pixels (325x254 millimeters)