Duplicate command output, print un-post-treated copy to stdout and store post-treated copy into a file

Question

I'm trying to duplicate a command's output so I apply a post-treatment to one stream, then store it to a file while printing the original one on stdout.

Closest I could come with is:

command | tee /dev/stdout | sed 's/foo/bar/g' > out.txt

which does not work as the > captures both outputs.

I'd like to avoid using a temporary file if possible. Any clue?

Answer 1

Try

command | tee >(sed 's/foo/bar/g' > out.txt)

See ProcessSubstitution - Greg's Wiki for an explanation of >(...). In short, it causes tee to write to a path that pipes the written data as input to the sed 's/foo/bar/g' > out.txt command.