run a "who -m" command in a logon trigger

Hello,

On my Linux environment, my dba users first connect with their personal id account and then run a su - oracle command, so I'd want to use the result of the "who -m" command in a dbms_session.set_identifier() procedure used inside an after logon trigger in order to identify initial user in audit files.

Is there an easier solution than using dbms_scheduler, dbms_pipe or external procedure to retrieve the result of the shell command?

Thank's

Dan