Hi diamondsandperls,
Just some thoughts:
With this: (From your OP),

my @patterns = ( qr/Record contentId\=\"\d+\"/ );
[download]

You are creating an array of just one element. Which of course would be a better if you just use a scalar variable, like so:

my $patterns = qr/Record contentId\=\"\d+\"/;
[download]

and then use the modified code print {$final_fh} /$pattern/, "\n"; by choroba.

Secondly, in your while loop, you are not using the data in the variable $_ at all, which are been read from your filehanle.
And ofcourse, you still have to "match" the pattern as showed by the previous answer.
Hope this helps.