As the AM pointed out, $fileb is a filehandle ... one that's only opened for writing but still, a filehandle. Maybe you need the filehandle to be open for reading and writing? In that case, just do so. I always find it useful to take the code in the docs and modify them to meet my conditions *before* I try to jam the new code into a legacy system:

...
my $response_body;

#
# open the file for reading and writing
#
open( my $fileb, "+>", \$response_body );
$curl->setopt( CURLOPT_WRITEDATA, $fileb );

...

# rewind the file handle
seek $fileb, 0, 0;
while( <$fileb> ) {
  print $_;
}
[download]