Dumpfile Database after Logout ?

I'm still studying, but even with the help, I can't make it.

I would like to create a backup of the database after logging out.

I managed to delete entries older than 30 days:

$sql = DB::PrepareSQL("DELETE FROM Kontaktliste WHERE DATEDIFF(NOW(), Datum) > 30");
DB::Exec( $sql );

But how can I have a backup created after the lougout?

Data:
$ db_name = "kd73296_tvk";
$ sql_file = "dump_". $ db_name. "_". date ('Ymd_Hi'). ".sql";

Unfortunately, it doesn't work that way.
I now sit here all Sunday and read through every manual, but I can't find anything about backing up the database.

Please help again

thanks
Andreas
German translated with Google