You can upgrade software with
sudo softwareupdate --install --all. Is it possible to upgrade the OS itself from the command line?
Since the OS X installer is an app, you would need a scripting framework to automate clicking of the buttons. Far easier to set up a MDM solution where the installer is turned into a netboot resource than to hack apart the UI and script the installation.
You can integrate these with most MDM like Casper/Munki or roll an imaging solution like DeployStudio - but all of these require external computers to manage/supply the computer being updated. There isn't a simple extension to the Apple provided
Wouldn't appear to be, looking at the man page; unless it appears in the --list arg
--l | --list List all available updates. -i | --install Each update specified by args is downloaded and installed. args can be one of the follow-ing: following: ing: -r | --recommended All updates that are recommended for your system. These are prefixed with a * character in the --list output. -a | --all All updates that are applicable to your system, including those non-recommended ones, which are prefixed with a - character in the --list output. (Non-recom-mended (Non-recommended mended updates are uncommon in any case.) item ... One or more specified updates. The --list output shows the item names you can specify here, prefixed by the * or - characters.