my @bar = undef;
print("There are ", scalar(@bar), " elements in \@bar\n");
print("\@bar is empty\n")    if !@bar;
print("\@bar isn't empty\n") if @bar;

my @foo;
print("There are ", scalar(@foo), " elements in \@foo\n");
print("\@foo is empty\n")    if !@foo;
print("\@foo isn't empty\n") if @foo;