shell-command-default-error-buffer

shell-command-default-error-buffer is a variable defined in `simple.el'.
Its value is

nil

Documentation:
Buffer name for `shell-command' and `shell-command-on-region' error output.
This buffer is used when `shell-command' or `shell-command-on-region'
is run interactively. A value of nil means that output to stderr and
stdout will be intermixed in the output stream.