Is there anything that can't be done with Terminal?
Not a lot 🙂
I typed in the command, was asked for a password and was put back at my machine and user name prompt.
That's correct. The password prompt was from
sudo - checking that you have authorization to make this kind of change.
Is there a command to put this back to the default and how do you know if it's working?
You'll know if it's working when you run
softwareupdate -l from the command line. If you're using a custom Software Update Server, you'll get a line like:
2009-04-01 14:06:53.718 softwareupdate[9102] Loading CatalogURL
http://server.net:8088/index.sucatalog
If you're using the standard Apple service the above line won't be printed.
From memory, if you using Software Update in the GUI, the window title is set to the name of the custom server, but it's been a while since I've done it that way.
As for undoing this and reverting to the standard Apple server, just:
sudo defaults delete com.apple.SoftwareUpdate CatalogURL
and you're set.