@output = $timestamp .'.sql';
open(my $fh, '>', @output) or die "Could not create file '@output': $!";

##</code><code>##

$output = $timestamp .'.sql';
open(my $fh, '>', $output) or die "Could not create file '$output': $!";

##</code><code>##

open(my $fn, '<', $filename) ...

##</code><code>##

open(my $fn, '<', "$directory/$filename") ...