Echo to both stdout and stderr

Question

I have a probably pretty easy beginner question: How do I echo from a shell script into both stdout and stderr? I know that I can echo to stderr echo "foo" 1>&2 but I need the output in both. I tried some Googling but nothing worked.

user_7084863 · Answer

echo foo | tee >(cat >&2)

This will work even if stderr is not supported.

Note: Soren's answer will not work if you have su'ed to another account that does have write permissions to the tty; but mine will.

Echo to both stdout and stderr

2 Answers