It displays the output in the minibuffer, right? I'm not sure there's a
very easy solution. Documented behaviour of `shell-command' is that
,----
| The output appears in the buffer `*Shell Command Output*'. If the
| output is short enough to display in the echo area (which is determined
| by the variables `resize-mini-windows' and `max-mini-window-height'), it
| is shown there, but it is nonetheless available in buffer `*Shell
| Command Output*' even though that buffer is not automatically displayed.
`----
so it seems rather hard-wired to me (i.e. you'd have to write your own
function or use defadvice).