The Oracle 10g Database offers several new features for SQL*Plus. The two main new features introduced with 10g are the new DEFINE variables and the enhanced SPOOL command.
Starting with Oracle 10g, the DEFINE command has three new predefined variables:
_USER. This Contains the user name that is supplied by the user to make the current connection. The result here is the same as the output from the SHOW USER command.
_DATE. This contains the current date or a user-defined fixed string. By default, _DATE displays the current date and is dynamic. _DATE uses the date format as shown with NLS_DATE_FORMAT.
_PRIVILEGE. This contains the privilege level of the current connection. The value for _PRIVILEGE ...