When you call Connection::execute() you are returned an ExecutionStream object, this object allows you to receive
the command output in various ways. This is a single-use object, you cannot run additions commands on this object,
you must call Connection::execute() again.
$exec = $command->execute("...");
echo $exec->getOutput(); // will echo everything except stderr
$exec = $command->execute("...");
$out = $exec->getSegmentedOutput();
echo $out['stdout']; // the good
echo $out['stderr']; // the bad
This can only be achieved by piping stderr to stdout -
$exec = $command->execute("... 2>&1");
echo $exec->getOutput(); // stderr inline with stdout