this:

 my @nonempty_files = grep { ! -z $_ } @files;
[download]

looks not very trustworthy ;-). This might be wrong. Compare some test schenarios with this approach:

 ...
 my @nonempty_files = grep -e && !-z, @files;
 ...
[download]

(especially for non-accessible and non-existent files.)

Regards

mwa