If you try to run a

php ezpublish/console --env=prod ezpublish:legacy:script  

on a script that doesn't start by calling the ob_end_flush(); method, the first $cli->output won't appear.

Steps:

Add a test.php file inside ezpublish_legacy folder with the following content

#!/usr/bin/env php
<?php
ob_end_flush();
require_once 'autoload.php';

$cli = eZCLI::instance();

$cli->output( "First test" );
$cli->output( "Second test" );

The resulting