Actually, the title is a bit misleading; mas allows you to download anything from the Mac App Store that you’ve purchased or previously downloaded for free – so if you’ve legitimately acquired every macOS release since the beginning of recorded time (like I have) then it’s a simple matter to go and grab those installers and download them to your Mac for your archiving/amusement/future use needs.
So, how to do it. First, you’ll need to go and download and install a package manager like homebrew. You can get the latest version by copying and pasting this into your browser of choice:
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
You’ll also need the current version of the Xcode command-line tools (if you don’t already have the current version of Xcode downloaded and installed). There are pre-built packages kicking around Apple’s site, but the easiest way to get the current version is to put this into the Terminal:
xcode-select --install
…and then sitting back and clicking the appropriate buttons to say that yes, you want to install this and you haven’t just decided to start slapping a bunch of additional tools into place on your system just for the hell of it.
Once both homebrew and the Xcode tools are in place, you can start downloading mas by typing the following:
brew install mas
Simple enough, right? The next part is a tiny bit trickier.
Typing mas into a new Terminal window will helpfully default to giving you the options that you have to play with, thus:
Now, provided you’re already signed into the App Store on your Mac you shouldn’t have to tinker around with the account option, but blindly typing in mas install isn’t going to do you any good unless you know what ID the App Store has assigned to the package that you’re looking for. The easiest, simplest way of locating the information you need is to go to the App Store via the built-in app and search from there. Let’s use macOS Catalina as an example, thus:
Click on the share icon and choose “Copy Link”:
…and then paste that into the text editor of your choice to get the full URL of the application you’re targeting:
The ID that we’re looking for is the number to the right of the “id” – in this case 1466841314.
Finally, feed that number to mas like so:
mas install 1466841314
Your application should start downloading once you hit return.
There are some gotchas with this, and it’s not universally reliable. If you share purchases with someone via Family Sharing then the App Store will occasionally decide that irrespective of whether you’re the person who purchased the app or not the app belongs to the other person, and that you’re not allowed to download it. Additionally, you might also run into the odd “HTTP 500 Internal Server” error, although I’ve found that waiting a few minutes and trying again seems effective.
Still, the good thing about using mas to download packages is that it can be an enormous time-saver if your company has a standard suite of applications that it owns through the App Store and wants to deploy to new machines that don’t use/aren’t enrolled in some kind of Mobile Management or Deployment scheme. After all, if you can get homebrew onto a machine then it’s possible to script mas to download specific items to specific machines.