VMS Help TCPIP Services, FTP, Appending Files  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The FTP APPEND command allows you to concatenate a local file to
    a file on a connected remote host. The following command appends
    local file JUL_DEC.DAT to file YEAR.DAT on remote host KALI. (A
    connection has already been established to the remote host.)

    FTP> APPEND JUL_DEC.DAT YEAR.DAT
    200 PORT command successful
    150 Opening data connection for year.dat. (130.180.4.8,1108)
    226 Append transfer complete
    local:large.txt   remote:remote.dat
    15596 bytes sent in 00:00:00.10 seconds (152.30 Kbytes/s)