Select Code to Download

$ perl -wnle 'push @x, $_; if(@x>=2) {print "@x"; shift @x}' input.txt
Hello I
...
$ perl -wnle 'push @x, $_; if(@x>=3) {print "@x"; shift @x}' input.txt
Hello I am
I am happy

#!/usr/bin/env perl
use warnings;
...
for my $i (0..@array-$WINSIZE) {
    print @array[$i..$i+$WINSIZE-1];
}

$ perl window.pl input.txt 2
Hello I
I am
am happy