I'm writting a shell script and at the begining I login to sqlplus by
sqlplus -l user_name/password@instance
what I would like is to check if the database is down or not , and if the database has started moved to the next step else sleep for a certain time and then check again .
I know how to do the sleep part, but I don't know how to check if the database is not down. can some one help me please.

Thanks,