This works for $n between 1 and the number of elements, inclusive.
It takes advantage of array slices when calling the subroutine.

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]);
}
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$n = 2 produces:

a b c
b c d
c d e
d e f
e f g
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$n = 4 produces:

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