my $response_data;
my $response_header;
open(my $RD, ">", \$response_data);
open(my $RH, ">", \$response_header);
...
$curl->setopt(CURLOPT_WRITEDATA, $RD);
$curl->setopt(CURLOPT_HEADERDATA, $RH);
...
$curl->perform;
print "Response header: $response_header\n";
print "Response body: $response_body\n";