Shortcode, Concatenating & Parse error: syntax error, unexpected T_FOREACH

instead:

$out .=  foreach ($greeting as $greet){ .'<td>' . echo $greet->id . '</td>' . } .'</table>';

try:

foreach ($greeting as $greet){ $out .=  '<td>' . $greet->id . '</td>'; } 
$out .=  '</table>';