if (!$line || $!) {

##</code><code>##

if (open(FH, $filename)) {
    # Here $! is meaningless.
    ...
} else {
    # ONLY here is $! meaningful.
    ...
    # Already here $! might be meaningless.
}
# Since here we might have either success or failure,
# here $! is meaningless.

##</code><code>##

my $isOpen = open($handle, $templateLocation) or die "foo: $!";