Trap 1 - some solutions 

• Use a lower precedence 'or' operator:

open my $fh, '<', $filename or die "open($filename): $!";

• Use parens around function args:

open(my $fh, '<', $filename) || die "open($filename): $!";

• Make the check implicit:

use Fatal qw(open);

open my $fh, '<', $filename;