For example, call sqlldr:
sqlldr SYSTEM/PA$$WORD control=loader.ctl > output.txt
And we get in the answer:
SQL*Loader: Release 10.2.0.1.0 - Production on Wed Nov 21 17:00:14 2012 Copyright (c) 1982, 2005, Oracle. All rights reserved. SQL*Loader-128: unable to begin a session ORA-01017: invalid username/password; logon denied
And if you just call sqlldr control=loader.ctl
and then enter username and password from the keyboard, then everything is fine.