View Available Software Updates in the Mac App Store
Disclaimer: This is an old post. Content may be out of date.
You can use the macappstore:// scheme to open the Mac App Store to view the currently available software updates:
/usr/bin/open macappstore://showUpdatesPageTo do this on behalf of the currently logged in user account:
su - `stat -f '%Su' /dev/console` -c "/usr/bin/open macappstore://showUpdatesPage"