VMS Help RTL Routines, LIB$, LIB$DO_COMMAND, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 command-string

    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor

    Text of the command that LIB$DO_COMMAND executes. The command-
    string argument is the address of a descriptor pointing to
    the command text. The maximum length of the command is 255
    characters.