# syntax: <c>keys HASH</c>
my $rgb = { red => 0x00f, green => 0xf00, blue => 0x0f0 }; # from perldata
my @keys = keys $rgb; # fatal: Type of arg 1 to keys must be hash
my @keys = keys %$rgb; # correct
my @keys = keys %ENV; # correct

# syntax: <c>push ARRAY,LIST</c>
# first example
my @names = original_member();
my @new_members = get_new_members('20071001');
push @names, @new_members;

# second example
my $another_members = [qw(ray tom dave)];
push $another_members, @names; # fatal: Type of arg 1 to push must be array
push @$another_members, @names; # correct