#!/usr/bin/perl
use strict;
use warnings;
open my $fh, '<', 'list.txt' or die $!;
chomp(my @hosts = <$fh>);
close $fh;

while (my @five = splice @hosts, 0, 5) {
   print qq{command @five\n};
}

# prints:
command host1 host2 host3 host4 host5
command host6 host7 host8 host9 host10
command host11 host12
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