foo(\%bar);

sub bar {
	my $bar_ref = $_[0]; #I know what is at index 0 and that's what I want
	my ($bar_ref) = @_; #same as above but I can not process anything else from the list
	my $bar_ref = shift; # same as #1 but I want to continue processing @_ and am unsure about indexes and/or presence
}