$OPEN

   The Open service makes an existing file available for processing
   by your program. The Open service specifies the type of record
   access to be used and determines whether the file can be shared.
   The Open service also performs an implicit Display service. The
   maximum number of files that can be open within an image at one
   time is 16383.

   Format

     SYS$OPEN  fab [,[err] [,suc]]
 

Additional information available:

Returns         Arguments       Condition_Values_Returned