Upgrade OS X operating system from the command line You can upgrade software with sudo softwareupdate --install --all. Is it possible to upgrade the OS itself from the command line?
Wouldn't appear to be, looking at the man page; unless it appears in the --list arg

https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man8/softwareupdate.8.html


     --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.