Adapting my reply to Reading files n lines a time illustrates another approach: 

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";
}

[download]

Sample output with two simple test files, one with four lines: 

---chunk---
one
two
---chunk---
three
four

[download]

and one with five lines: 

---chunk---
one
two
---chunk---
three
four
---chunk (leftover)---
five

[download]

For your use-case you would obviously do something different to my crude printing of chunks above.

Some Similar PM Nodes

In reply to Re: Dealing with nextline of a file by eyepopslikeamosquito
in thread Dealing with nextline of a file by jnarayan81

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