Rotates a wallpaper on either Gnome or OS X

rotate-wallpaper.sh

#!/bin/bash
# Rotate wallpapers on GNOME or OSX
# (OSX users need to install coreutils)
set -e

WALLPAPERS="$HOME/wallpaper"

if [[ -n "$(command -v gsettings)" ]]; then
    paper=`find $WALLPAPERS -type f | shuf -n 1`
    PID=$(pgrep gnome-session)
    export DBUS_SESSION_BUS_ADDRESS=$(grep -z DBUS_SESSION_BUS_ADDRESS /proc/$PID/environ|cut -d= -f2-)
    gsettings set org.gnome.desktop.background picture-uri "file:///$paper"
elif [[ -n "$(command -v osascript)" ]]; then
    paper=`find $WALLPAPERS -type f | gshuf -n 1`
    osascript -e "tell application \"Finder\" to set desktop picture to POSIX file \"$paper\""
fi

I also have a cron entry:

0 *     * * *      /home/doublecompile/bin/rotate-wallpaper