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

       /OUTPUT=file-spec

    Identifies the output file to which the results of the SPAWN
    operation are written. Whenever you use the /NOWAIT qualifier,
    you should also use the /OUTPUT qualifier to specify a new
    output destination. Doing so prevents output from being displayed
    while you are specifying new commands. If you omit the /OUTPUT
    qualifier, output is written by default to the current SYS$OUTPUT
    device.