#!/usr/bin/perl
use strict;
use warnings;

open my $hostsIn, '<', "/etc/hosts" or die "Cannot open hosts file! \n";
my @hosts = <$hostsIn>;
close $hostsIn;

foreach my $line (@hosts) {
    next if $line !~ /($ARGV[0])/;

    print $line;
    $line = undef;
}