Example:

isql server:c:diremployee.gdb -x -user sysdba -password masterkey

generates the error:

Your user name and password are not defined. Ask your database administrator to set up an InterBase login.

If you have physical access to the database, or the ISC_USER and ISC_PASSWORD environmental variables are set then isql will not generate an error. For more information on the ISC_USER and ISC_PASSWORD environment variables see chapter 3 of the API Guide.