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;

##</code><code>##

There are 1 elements in @bar
@bar isn't empty
There are 0 elements in @foo
@foo is empty

##</code><code>##

my @bar = (undef, 'a');
print(defined($bar[0])?1:0, "\n");  # 0
print(defined($bar[1])?1:0, "\n");  # 1
print(defined($bar[2])?1:0, "\n");  # 0 (doesn't exist)