Downloads a random image from Unsplash and sets the wallpaper every so often (currently only works with Gnome/Unity/Cinnamon/etc)

unsplash_wallpaper.sh

#!/bin/sh

while :
do
	wget -q -O unsplash_wallpaper.jpg https://unsplash.it/1920/1080/?random
	gsettings set org.gnome.desktop.background picture-uri file://$PWD/unsplash_wallpaper.jpg
	sleep 1h   # Change this if you want a different update frequency (e.g. 30m, 12h, 24h, etc...).
done

#!/bin/sh

while :
do
	wget -q -O unsplash_wallpaper.jpg https://unsplash.it/1920/1080/?random
        osascript -e 'tell application "Finder" to set desktop picture to POSIX file "$PWD/unsplash_wallpaper.jpg"'	
	sleep 1h
done

If you want curl instead just replace the wget line.

curl -o unsplash_wallpaper.jpg https://unsplash.it/1920/1080/?random