Pipe and watch piped output?

Question

I want to make a shell-pipe like this:

producer | analyser > report.txt

and watch the output of producer while it is generating data (a big log-file) for analysis.

How can I do that?

Answer 1

In /bin/sh and compatibles:

producer | tee /dev/fd/3 | (analyser > report.txt) 3>&1

I've tested this only on Linux and Cygwin. On some Unix-likes you may have to change /dev/fd/3 to whatever their equivalent is.