my $filepath = "<path here>";
my $filename = $ENV{'QUERY_STRING'};
my $filesize = -s "$filepath/$filename";

print "Content-disposition: attachment; filename=$filename\n";
print "Content-Length: $filesize\n";
print "Content-Type: application/octet-stream\n\n";
my $buffer;
open FILE, "$filepath/$filename" or die "Oops $!";
binmode FILE;
binmode STDOUT;
print $buffer while (read(FILE, $buffer, 4096));
close FILE;