my %hosts = map{
  split /\s+/, $_, 2
}<DATA>; # Or substitute your favourite filehandle here.
__DATA__
host1 1.1.1.1
host2 1.2.3.5
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Note, however, that the format you give is not the standard format for hosts files. The usual format is more like...

# IP Masq gateway:
192.168.0.80    pedestrian
# Primary desktop:
192.168.0.82    raptor1
# Family PC upstairs:
192.168.0.84    trex tyrannosaur family
# Domain servers:
205.212.123.10  dns1 brutus
208.140.2.15    dns2
156.63.130.100  dns3 cherokee
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This is easy enough to read too...

open HOSTS, "</etc/hosts"; # Or "<C:\\WINDOWS\\hosts";
my %hosts = map{
  my $ip, $hn, @hn;
  if (not /^\s*#/) {
    chomp; s/\s*#.*$//;
    ($ip, @hn) = split /\s+/, $_;
  }
  map { $_ => $ip }, @hn;
}<HOSTS>;
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$;=sub{$/};@;=map{my($a,$b)=($_,$;);$;=sub{$a.$b->()}}
split//,".rekcah lreP rehtona tsuJ";$\=$ ;->();print$/
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