As Raffzahn says, you can’t redirect standard error under DOS, at least not with the standard
COMMAND.COM. With 4DOS, both output streams can be redirected with
>&. That would allow you to redirect to a file as well as a device.
Instead of trying to redirect the input and output streams to use a serial connection, under DOS you’d change the TTY:
This will work with any character device (with varying results if the character device isn’t appropriate).
Note that many DOS programs don’t use the standard input and output streams, but read from the keyboard and write to the screen without using DOS services; such programs won’t honour redirection or
CTTY and won’t work over a serial connection.
(Amusingly enough, DOS has five standard device handles: standard input, standard output, standard error, standard auxiliary and standard list. The first three are attached to
CON by default; the fourth to
AUX, and the fifth to