my @key   = qw( chr fivep threep strand );
my @files = qw( file1.tab file2.tab );

my %c7;
foreach my $file (@files) {
    csv (
	in      => $file,
	out     => undef,
	sep     => "\t",
	on_in   => sub { $c7{pack "A10l>l>l>", @{$_[1]}[0..3]}{$file} = $_[1][6] }
	);
    }

say join "\t" => @key, @files;
foreach my $key (sort keys %c7) {
    say join "\t" => (unpack "A10l>l>l>" => $key), map { $c7{$key}{$_} // 0 } @files;
    }