Send notification to a user via notify-send

notify-user.sh

#! /usr/bin/env bash
# Usage: notify-user.sh username notify-send-args

uid=$(id -u $1)
displays=($(who | grep -E "$1 .+\(:[0-9](\.[0-9])*\)" | awk '{print $NF}' | sort -u))

for display in $displays; do
    sudo -u $1 DISPLAY=${display:1:-1} \
               DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/$uid/bus \
               notify-send "${@:2}"
done