sub uid_lastname {
    my( $uid, $firstname ) = @_;
    my @lastnames;
    keys %$uid;
    while( my( $key, $val ) = each %$uid ){
        if( $val->{firstname} eq $firstname ){
            push @lastnames, $val->{lastname};
        }
    }
    return @lastnames if wantarray;
    return $lastnames[0] if @lastnames;
    die "firstname not found";
}