use strict;
use warnings;
my $fname = shift or die "usage: $0 fname\n";
open(my $fh, '<', $fname) or die "error: open '$fname': $!";
my $chunksize = 2;
my $chunk = "";
while ( my $line = <$fh> ) {
$chunk .= $line;
next if $. % $chunksize;
print "---chunk---\n$chunk";
$chunk = "";
}
close $fh;
if (length $chunk) {
print "---chunk (leftover)---\n$chunk";
}
####
---chunk---
one
two
---chunk---
three
four
##
##
---chunk---
one
two
---chunk---
three
four
---chunk (leftover)---
five