use Data::Dumper;

open(DATA, "<", "test.dat");
my $data = {};
while (<DATA>) {
	chomp;
	/(.*)::=(.*)/;
	if (!exists($data->{$1})) {
		$data->{$1} = [];
	}
	$data->{$1}[$#{$data->{$1}} + 1] = $2;
}
print Dumper($data);