We want two stdout streams - one for data another for metadata - instead of sending metadata to stderr - we could send it a 4th fd (3).
How would we do that? Here is a bad start:
my_progam > <( exec<> 3 ) 3> file1 2> file2
so in the echo process, how can it write to 3? I am trying to open up a file descriptor using process substitution instead of a "real" file.