Never use a shutdown abort unless you absolutely have to, if you do yuo will be caught doing instance recovery everytime you open the database. I assume you shutting down to do a cold backup or something so here is the best method to follow. In your script do the following:

Shutdown immediate followed by a startup restrict then shutdown normal

The shutdown immediate ensures the database closes even if users are still connected. Start up restrict starts the database up but only allows people with restricted session (i.e. DBA's) to start a session then the shutdwon normal ensures that the database is shutdown clean and all transactions have been rolled back and the redo logs are clean.

Cheers