You can check whether a key in a hash exists with the exists() function, and you can check if an array has anything it by comparing it's length to 0. If you want to check whether a given value in a hash is an array you could use ref(), and if so, just dereference it to check it's length.

my %hash    = qw(foo bar baz quux);
my $key     = "baz";
my @array   = qw(x y z);
$hash{$key} = \@array;

print "$key exists in %hash\n" if exists $hash{$key};
print "\@array has contents\n" if @array > 0;
print "\$hash{\$key} is an array\n" if ref($hash{$key}) eq 'ARRAY';
print "\$hash{\$key} is an array with contents\n"
    if @{$hash{$key}} > 0;

__output__

baz exists in %hash
@array has contents
$hash{$key} is an array
$hash{$key} is an array with contents
[download]

HTH

broquaint