use strict;
use warnings;

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

for my $line (0..$#hosts) {
    if ($hosts[$line] =~ /($ARGV[0])/) {
        print "$hosts[$line]";
        delete $hosts[$line]
    }
}