helpful one-liner examples for testing STDOUT and STDERR:
Print only stdout: ruby -e 'i=$stderr.puts("err"); $stderr.flush; $stdout.puts("out"); $stdout.flush; exit' 2>/dev/null
Print only stderr: ruby -e 'i=$stderr.puts("err"); $stderr.flush; $stdout.puts("out"); $stdout.flush; exit' 1>/dev/null