Well it depends on how they are stored in the file. If there is only one IP per line, this code will do:

my @ip_array = ();
if(open(F_IP,"<$filename"))
{
  my %ip_hash = ();
  foreach my $ip (<F_IP>)
  {
    chomp($ip);
    #No duplicates!
    $ip_hash{$ip} = 1;
  } 
  close(F_IP);
  @ip_array = keys(%ip_hash);
}
else
{
  die "AHHHHH! Error Error go away!!";
}

#Just keep doing your thing man...
[download]

Note that I wrote this on the fly and have not tested it. It should give you a good start though. =)

--habit