open FILE, $filename ||
        die "Cannot open $filename for reading: $!\n";
#due to precedence rules, if you use the ||
#parens are needed
open (FILE, '<', $filename) ||
        die "Cannot open $filename for reading: $!\n";
#or use the lower precedence "or"
open FILE, '<', $filename or
        die "Cannot open $filename for reading: $!\n";