...
 my $input = $mw->getOpenFile();
 open FILE, ">$input" or die $!;
 FILE->autoflush(1);
 ...
 tie @lines, 'Tie::File', $input or die $!;
 ...

##</code><code>##

 ...
 open FILE, ">$input" or die $!;
 tie @array, 'Tie::File', \*FILE, ...;
 ...