process($data_ref, \@set_up, $template, $fd_out);

sub process
{
     my ($data, $set_up, $template, $fd_out) = @_;

     foreach my $record (@$data)
     {
          # ...
     }
}

##</code><code>##

my $fd_out;
open($fd_out, $what_file);

while (<$fd_out>) { # ... }

##</code><code>##

my $fd_out = IO::File->new($what_file, 'r');

while (<$fd_out>) { # ... }