To expand on injunjoel's reply, try:

use CGI;

my $query = new CGI;

if ($query->param("item") eq "select")
 {
  &retrieve_data;
 }
elsif ($query->param("item") eq "update")
 {
  &update_data;
 }
sub retrieve_data
{
[download]

That should do it. It's one of those crazy bugs that we have all stared at for hours and simply not seen the obvious. Take heart, we've all been there.