Library /sys$common/syshlp/mailhelp.hlb SPAWN, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 command

    Specifies the DCL command string that executes in the context
    of the created subprocess. When the command completes, the
    subprocess terminates and control is returned to the parent
    process. If this parameter is not specified, a subprocess is
    created that transfers control to DCL command level.