#!/usr/bin/env perl

use strict;
use warnings;
use autodie qw{:all};

my $hosts = 2;
my $tool = 'echo';

my @cmd = ($tool);

while (<DATA>) {
    chomp;
    push @cmd, $_; 

    if ($. % $hosts == 0) { 
        system @cmd;
        @cmd = ($tool);
    }
}

system @cmd if @cmd > 1;

__DATA__
host1
host2
host3
host4
host5

##</code><code>##

host1 host2
host3 host4
host5