use strict;
use warnings;

my @cache;
my $n_min=2;
my $n_max=6;


while (my $line =<DATA>) {
    chomp $line;
    push @cache, $line;
    for my $n ($n_min..$n_max) {
        print "$n: @cache[-$n .. -1]\n"   # last n of cache
            if @cache >= $n;
    }
    shift @cache if @cache == $n_max;     # keep cache at max size
} 


__DATA__
One
Two
Three
Four
Five
Six
Seven
Eight
Nine
Ten

##</code><code>##

2: One Two
2: Two Three
3: One Two Three
2: Three Four
3: Two Three Four
4: One Two Three Four
2: Four Five
3: Three Four Five
4: Two Three Four Five
5: One Two Three Four Five
2: Five Six
3: Four Five Six
4: Three Four Five Six
5: Two Three Four Five Six
6: One Two Three Four Five Six
2: Six Seven
3: Five Six Seven
4: Four Five Six Seven
5: Three Four Five Six Seven
6: Two Three Four Five Six Seven
2: Seven Eight
3: Six Seven Eight
4: Five Six Seven Eight
5: Four Five Six Seven Eight
6: Three Four Five Six Seven Eight
2: Eight Nine
3: Seven Eight Nine
4: Six Seven Eight Nine
5: Five Six Seven Eight Nine
6: Four Five Six Seven Eight Nine
2: Nine Ten
3: Eight Nine Ten
4: Seven Eight Nine Ten
5: Six Seven Eight Nine Ten
6: Five Six Seven Eight Nine Ten