If the logical name  DBG$INIT  is  defined  at  the  start  of  a
     debugging session, then the file that it translates to is used as
     an initialization file.  DEBUG commands in the file are  executed
     as if the file had been called with @.  This feature is useful if
     there is a particular set of commands  that  you  always  execute
     when  you  start  up  the  debugger,  such as commands that set a
     directory search list or set certain modules.

     Example:

     $ CREATE DEBUG.COM
     SET SOURCE [],SRC$
     SET MODE SCREEN
     SET STEP SILENT
     $ DEFINE DBG$INIT DEBUG.COM