It looks like you're expecting a reference to, say, $nam to stringify to nam. It doesn't, because the names are there for your convenience, not Perl's. I'd write something like this:

my $password = {};

while (<F>)
{
    my ($name, @attributes) = split(/:/, $_);
    my %attributes;
    @attributes{qw( pwd uid gid dsc hom shl )} = @attributes;  
    $password->{$name} = \%attributes;
}
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