sub do_something_with { print "@_\n"; }
my @elements = qw( a b c d e f g );
my $n = 2;

for my $i ($n-1 .. $#elements) {
  do_something_with(@elements[($i-($n-1))..$i]);
}

##</code><code>##

a b c
b c d
c d e
d e f
e f g

##</code><code>##

a b c d
b c d e
c d e f
d e f g