SCHedule allows SCHED to be started interactively to specify options that might vary from run to run (such as PLOT, DEBUG etc.) and still get most of it's input from an external file. That external file is specified with SCHedule.
Under unix, environment variables may be used. For example, if SCHED is defined to mean /users/cwalker/sched, the base area under which all sched stuff is kept (substitute your local directory), then one can specify one of the example schedules with SCHEDULE = $SCHED/examples/manual_1.key. Use the setenv (c or t shell) or export (korn shell) to set environment variables.