$s1_cli->cmd(
	Command  => "/path/to/pre-loader.pl arg1 arg2 2>&1",
	Blocking => 0
);
do {
	Time::HiRes::sleep 0.2;
	($ok, $output) = $s1_cli->cmd_poll;
	print $output if length $output;
} until $ok;

##</code><code>##

$s1_cli->cmd(
	Command  => "/path/to/pre-loader.pl arg1 arg2 2>&1",
	Blocking => 0
);
$s1_cli->poll(
	Poll_code => sub {
		$output = ($s1_cli->cmd_poll)[1];
		print $output if length $output
	}
);