When the program is run, input and output files and additions to the search path may be included on the command line, and it is possible to set up a file to act as a log-in file, so that [B/D] obeys the commands on the log-in file first. Input and output files can be attached, and additions to the search path made, interactively as well. We discuss each possibility in turn below; the various possibilities can be mixed on the eventual command line.