I wrote a simple command line tool which can read and set the desktop picture. Neil Martin had the brilliant idea to call it desktoppr.

$ desktoppr
/Library/Desktop Pictures/Sierra.jpg

$ desktoppr "/Library/Desktop Pictures/BoringBlueDesktop.png"

When you have multiple displays, desktoppr will list all desktop pictures:

$ desktoppr
/Library/Desktop Pictures/HotStepper.jpg
/Library/Desktop Pictures/LyricalGangster.jpg
/Library/Desktop Pictures/MrOfficer.jpg

When you pass a file desktoppr will set it as the desktop picture for all screens:

$ desktoppr /Library/Desktop Pictures/NaahNananah.jpg
$ desktoppr
/Library/Desktop Pictures/NaahNananah.jpg
/Library/Desktop Pictures/NaahNananah.jpg
/Library/Desktop Pictures/NaahNananah.jpg

You can also set the desktop for a specific screen: (index starts at zero)

$ desktoppr 0 /Library/Desktop Pictures/HotStepper.jpg
$ desktoppr 1 /Library/Desktop Pictures/LyricalGangster.jpg
$ desktoppr 2 /Library/Desktop Pictures/MrOfficer.jpg

Use the scale verb to control how the desktops are scaled. It can have the values fill (default), stretch, center, and fit.

desktoppr scale center

This will set the scale for all screens.

USe the color verb to set the background color. You can pass a hex string for the background color:

desktoppr color 000000      # black background
desktoppr color FFFFFF      # white background
desktoppr color FF0000      # red background

This will set the background color for all screens.

You can get the code for desktoppr on my Github page and an installer here. The installer pkg will install the tool in /usr/local/bin. Alternatively, a brew casks exists, so you could install it using brew install --cask desktoppr if you have Homebrew installed.

When you want to run it from a management script it is safest to include the entire path:

/usr/local/bin/desktoppr "/Library/Desktop Pictures/BoringBlueDesktop.png"

Since the desktoppr tool also sets user preferences, you still need to pay attention that it runs as the user. A LaunchAgent or a solution like outset is a good choice to manage this. Alternatively, you can run the command as the current user from a root script.

The tool requires the Swift 5 Runtime support for command line tools when you install it on versions of macOS older than 10.14.4.

I have written a few blog posts that describe different use strategies for setting a desktop picture:

• Strategies to using desktoppr
• Random Desktop Background with desktoppr