Question

How do you determine if all hash keys have some value ?

Answer 1

From perldoc -f exists:

               print "Exists\n"    if exists $hash{$key};
               print "Defined\n"   if defined $hash{$key};
               print "True\n"      if $hash{$key};

               print "Exists\n"    if exists $array[$index];
               print "Defined\n"   if defined $array[$index];
               print "True\n"      if $array[$index];

A hash or array element can be true
only if it’s defined, and defined if
it exists, but the reverse doesn’t
necessarily hold true.