/INPUT=filespec

    Specifies an input file containing one or more DCL commands
    to be executed by the spawned subprocess. File type defaults
    to COM and no wildcards are allowed in the file specification.
    Once processing of the input file is complete, the subprocess
    is terminated. If both a command string and the /INPUT qualifier
    are specified, the specified command string executes before
    additional commands are obtained from the /INPUT qualifier. If neither is
    specified, SYS$INPUT is assumed (in which case a SPAWN/NOWAIT
    command is aborted if Ctrl/Y is pressed to abort something running
    in your parent process).

    You cannot explicitly specify non-record-oriented, process-
    permanent files (NRO PPFs) with the /INPUT qualifier. The
    system displays an error message when it encounters such a file as the
    value for the /INPUT qualifier.

    Note that when NRO PPFs are used as implicit input (that is,
    the /INPUT qualifier is not specified and SYS$INPUT is a NRO PPF),
    the SPAWN command can succeed, as shown in the following table:

    Process Type     SYS$INPUT  Implicit Input

    Interactive      NRO PPF    SYS$COMMAND

    Noninteractive   NRO PPF    Null device

    Any              Any other  SYS$INPUT

    If SYS$INPUT is a terminal, it cannot have an associated terminal
    mailbox.