use Encode qw(encode decode);
   my $regexp_source = "... regexp string ...";
   my $regexp_utf8   = encode('utf8', decode('euc-jp', $regexp_source));
   my $regexp        = qr($regexp_utf8);

   my $ua = LWP::UserAgent->new();
   my $response = $ua->get('http://foo.bar.com');

   my $encoding = guess_encoding($response);
   my $normalized = encode('utf8', decode($encoding, $response->content));

   if ($normalized =~ /$regexp/) {
      store_data($response);
   }