We allow both mode strings ("r" etc.) and keyword arguments (read=true) in open for both commands and files. Generally the mode strings correspond to equivalent keyword arguments. However they behave differently for processes:

julia> open(`ls foo`, read=true) do f
       end

julia> ls: cannot access foo: No such file or directory

julia> open(`ls foo`, "r") do f
       end
ls: cannot access foo: No such file or directory
ERROR: failed process: Process(`ls foo`, ProcessExited(2)) [2]

This is because there is a special method for opening a process with a function and mode string (which adds the ProcessFailedException), but the keyword arg form is caught by the fallback that just calls close when the function returns. I assume we want them both to give the ProcessFailedException?