#!/bin/sh
if [ $# != 0 ]; then
	echo 'displaying: Heuristically prints the active X display.' >&2
	[ "$1" = -h ] || [ "$1" = --help ]; exit
fi
for p in $(pgrep -t $(cat /sys/class/tty/tty0/active)); do
	d="$(ps e $p | sed 's/.*DISPLAY=\([^ ]*\).*/\1/; t; d')"
	[ "$d" ] && printf %s\\n "$d" && exit
done
echo 'displaying: Could not determine the active X display' >&2
echo :0
exit 1