transform stream sent to a file by tee

Question

I want to redirect the stdout and stderr of a stream both to the screen and a file. For that I'm using the tool tee. However, before that stream goes to the file, I want to transform it using a pipe. So far, I have only managed to transform the stream that goes to stdout.

Example:

echo 'hello' | tee output.txt | tr 'h' 'e'

=> this will output eello to stdout and save hello to output.txt

However what I want is to print hello to stdout and save eello to output.txt.

Note: Changing the input stream is not an option for my problem.

Answer 1

With bash:

echo 'hello' | tee >(tr 'h' 'e' > output.txt)

With bash and Linux:

echo 'hello' | tee /proc/$$/fd/255 | tr 'h' 'e' > output.txt

See: What is the use of file descriptor 255 in bash process