To attach input files, typically containing [B/D] program macros, data, and so forth, via the command line we could start the program as follows:
bd [i1=file1] [i2=file2] ...
There are 6 input channels, i1 ...i6, which can be associated with an external file in this way. Input files may be located in any directory that will be searched according to the search path (which may also be amended at start-up: see below). The current directory is always searched first, and then the path given in the environment variable BDMACROS (if any). The BDMACROS environment variable is set as described above. It can be set to contain a string of paths which are to be searched for input files. The CHANNEL: command can also be used to associate input files with [B/D] channels.
If input channel i1 is assigned on the command line, it acts as a log-in channel: [B/D] obeys all commands therein in the usual way, including macro switches, and the end of file marker causes control to be returned to the screen channel. Otherwise channels can be assigned using the CHANNEL: command.