use strict; 
use warnings;

open my $fh, '<', 'notexistant.txt' or die qq(File open failed);   #OK:     File open failed at

open (my $fh, '<', 'notexistant.txt') || die qq(File open failed); #OK too: File open failed at..

open my $fh, '<', 'notexistant.txt' || die qq(File open failed);   #WRONG 
print  <$fh>;                                                      # readline() on closed filehandle $fh at..