I don't really understand your code ...

here a variation which avoids reading the whole file in once, but instead line by line

use strict;
use warnings;

my @cache;
my $n=4;

while (my $line =<DATA>) {
    chomp $line;
    push @cache, $line;
    if (@cache >= $n) {
        print "@cache\n";
        shift @cache;
    }
} 


__DATA__
One
Two
Three
Four
Five
Six
Seven
Eight
Nine
Ten
[download]

(Marshall++ was faster)