Username Prompt in SQLLoader

Has anyone determined how to get rid of or bypass the annoying username prompt from Sqlplus, export, import, or sqlloader??. The accounts which execute these are defined as OS authentication in the database so that we do not have to put the username/password in the command files, but the processes HAVE to run in a "batch" or unattended mode: ie, cron starts a job to load a new file into the database at 4:00 am, and it stalls then dies at the USERNAME prompt. Also, if the database authentication is at the OS level, why does the prompt even come up??. Any help would be GREATLY appreciated. Thanks,

                         Tom
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|           /\       |Tom Pennington tompenn_at_info.census.gov|
|      /\  /  \  /\  |======================================|
| /\  /  \/    \/  \ |"Of all the things I have lost in my  |
|/  \/   /      \   \| life, I miss my mind the most"       |