Message count

My problem is not directly related to procmail, but maybe someone help.
I'd like to get number of messages saved to given mail folder using just simple
unix command (like grep, wc etc.) from script. Is there some non-redundant (one
per message) text token to use? I've tried "^Messge-ID: " but doesn't seem to
work O.K. Maybe  some special program exists just to display folder statistic.
                                                        Maciej