I have seen the command line to pop open system preferences and go to the update window. For previous macOS versions, often the upgrade to the newest macOS is all that shows up unless you click the blue more info... in the description. Clicking on that would show the security update and safari update for the current macOS version. Is there a command line to open that link as well?
+8I ran into the same situation, it is no problem to open the main Software Update Preferences window with the following command, but I am still looking for a way to open the "more info" option:
open /System/Library/PreferencePanes/SoftwareUpdate.prefPane
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