activemonitor

#!/bin/bash

# This script requires xdotool.
# You can install it with:
# sudo apt-get install xdotool
# or
# sudo pacman -S xdotool
# etc.

# Get the geometry of the focused window.
read -r window_x window_y < <(xdotool getactivewindow getwindowgeometry --shell | grep -E 'X=|Y=' | cut -d= -f2 | tr '\n' ' ')

# Get the list of connected monitors and their geometries from xrandr.
while read -r name status primary geometry rest; do
	if [[ "$status" == "connected" ]]; then
		# from "1920x1080+0+1080" get "1920 1080 0 1080"
		read -r width height x_offset y_offset < <(echo "$geometry" | sed -e 's/x/ /' -e 's/+/ /')

		# Check if the focused window is within this monitor's bounds.
		if ((window_x >= x_offset && window_x < x_offset + width && window_y >= y_offset && window_y < y_offset + height)); then
			echo "$name"
			exit 0
		fi
	fi
done < <(xrandr)

exit 1