# line mode
...

{
   # paragraph mode
   local $/ = '';
   ...
}

# line mode
...

##</code><code>##

sub process_csv {
   ...

   open(my $fh, '<', ...)
      or die(...);

   while (<$fh>) {
      ...
      process_file(...);
      ...
   }

   ...
}

sub process_file {
   ...

   local $/ = '';

   open(my $fh, '<', ...)
      or die(...);

   while (<$fh>) {
      ...
   }

   ...
}