{
 local @ARGV = 'not_a_file';
 local $SIG{__WARN__} = sub { die shift };
 # SIG{__WARN__} is now set INSIDE the while loop
 # also, so you might want to unset it locally there
 while (<>) {
  print "This won't print\n";
 }
 print "This won't print either\n";
}