Is there a gnu/unix command to both save a file without consuming stream?

Question

I seem to faintly remember some unix command that allows you to save out put while piping to the next program.

Eg.

echo "hello world!"  \
| mystery_command hello.txt \
| sed -E "s/hello/goodbye/g" \
> goodbye.txt

Would both create a file called hello.txt with "hello world!" as contents. and a file called goodbye.txt with "goodbye world!" as contents.

Answer 1

I believe you are thinking of tee(1).