Another way would be to grab five lines at a time from your input. The &groupsOf subroutine runs the code block given as the first argument on however many items at a time, second argument, of the third and subsequent arguments which in the code below are the lines of the input file. Given this tool:-

$ cat spw1081756tool.pl
#!/usr/bin/perl
#
use strict;
use warnings;

use 5.014;

say qq{$0 \@ARGV ->@ARGV<-};
$
[download]

Running this code:-

use strict;
use warnings;

use 5.014;

sub groupsOf (&$@);

open my $hostsFH, q{<}, \ <<EOD or die $!;
host1
host2
host3
host4
host5
host6
host7
host8
host9
host10
host11
host12
EOD

groupsOf {
    system q{spw1081756tool.pl}, map { chomp; $_ } @_;
    } 5, <$hostsFH>;

close $hostsFH or die $!;

sub groupsOf (&$@)
{
    my $rcToRun  = shift;
    my $groupsOf = shift;

    my $rcDoIt;
    $rcDoIt = sub
       {
           return $rcToRun->(
              map shift,
                 1 .. do {
                     my $elems = scalar( @_ );
                     $groupsOf < $elems ? $groupsOf : $elems
                     } ),
           @_ ? &$rcDoIt : ();
       };
    return &$rcDoIt;
}
[download]

Gives this output:-

./spw1081756tool.pl @ARGV ->host1 host2 host3 host4 host5<-
./spw1081756tool.pl @ARGV ->host6 host7 host8 host9 host10<-
./spw1081756tool.pl @ARGV ->host11 host12<-
[download]

I hope this is helpful.