How to change desktop background from command line in Unity?

Question

I have a script that updates my desktop background every day with the NASA APOD. Since upgrading to 11.10, that script stopped working, presumably because I'm using gconftool-2 to actually update the desktop background. Is there a new way to do this under Unity?

Answer 1

Both Unity and Gnome Shell (Gnome 3) use GSettings now instead of GConf. So in Unity and Gnome Shell you can use the command-line tool gsettings for that. Like gconftool, it lets you get or set an individual key.

You can get the current URI of the background image as follows:

gsettings get org.gnome.desktop.background picture-uri
'file:///home/serrano/Pictures/x.jpg'

And set the background URI as follows (which will immediately update your desktop background):

gsettings set org.gnome.desktop.background picture-uri file:///home/serrano/Pictures/y.jpg

Notice that you must prepend the URI with "file://" for this to work (unlike with gconftool).

In order to make your script work with both Gnome 2 and Shell/Unity, you can let it do a Gnome version check first:

gnome-session --version

That will return the version of Gnome. If the version number starts with 3, then gsettings can be used. If it returns a version starting with 2, let your script use gconftool instead.