# Validate a data set
ITEM: foreach my $item (@data) {
    foreach my $key (qw(foo bar baz)) {
        if (!exists $item->{$key}) {
            warn "Couldn't grok item. $key missing. Skipping.\n", Dumper($item);
            next ITEM;
        }
    }
    # Do something useful with this item.
}

##</code><code>##

if (3 != grep {exists $item->{$_}} qw(foo bar baz)) {
    warn ....; # but your warning can't be as specific.
    next;
}