my $hostfile = '/tmp/jn/hosts';
open my $hostFH, '<', $hostfile
   or die "open: < $hostfile: $!\n";

##</code><code>##

$ perl -le '
> @IPs = qw{ 22.32.87.12 56.67.38.61 101.12.34.54 };
> print for sort @IPs;'
101.12.34.54
22.32.87.12
56.67.38.61
$

##</code><code>##

use strict;
use warnings;

my %seen;
my @sortedUniques =
   map  { ( split m{\s+}, $_->[ 0 ] )[ 0 ] }
   sort { $a->[ 1 ] cmp $b->[ 1 ] }
   grep { ! $seen{ $_->[ 1 ] } ++ }
   map  {
            m{^(\d+)\.(\d+)\.(\d+)\.(\d+)\t}
            ? [ $_, sprintf q{%03d%03d%03d%03d}, $1, $2, $3, $4 ]
            : ()
        }
   <DATA>;

print qq{$_\n} for @sortedUniques;

__END__
# hosts file

10.31.17.65	fw2
192.168.1.78	hosta
192.168.1.21	hostb
10.31.17.65	fw2dup
10.23.212.6	hostc
192.168.100.254	fw1
192.168.1.21	hostbdup

##</code><code>##

10.23.212.6
10.31.17.65
192.168.1.21
192.168.1.78
192.168.100.254