I checked the errata pages at O'Reilly but saw no mention of what I think might be an error on page 224 of "Programming Perl, 3rd Edition". More specifically, I'm talking about the following code: 
@common = inter ( \%foo, \%bar, \%joe );
sub inter {
    my %seen;
    for my $href (@_) {
        while (my $k  = each %$href ) {
            $seen{$k}++;
        }
    }
    return grep { $seen{$_} == @_ } keys %seen;
}
=======================================================

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When I tried printing @common using the following data: 
__DATA__
my %foo = (
    'one' => 1,
    'two' => 2,
    'three' => 3,
);

my %bar = (
    'two' => 5,
    'four' => 6,
);

my %joe = (
    'three' => 7,
    'four' => 8,
    'five' => 89,
);

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@common came back null for me. However, when I changed this line:

return grep { $seen{$_} == @ } keys %seen;
to this:
return grep { $seen{$_} } keys %seen;

@common returned: 

three five one two four

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which judging by the description in the book, appears to be what the code is supposed to yield. I find it hard to believe I would catch an error like this. Can someone please back me up on this?

$PM = "Perl Monk's";
$MCF = "Most Clueless Friar Abbot";
$nysus = $PM . $MCF;

Edit by tye

In reply to Code mistake in Camel book? by nysus

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