use Scalar::Util qw[ looks_like_number ];

sub special_compare {
   my ($x, $y) = @_;

   if(&looks_like_number($x) and &looks_like_number($y)) {
      return ($x <=> $y);
   } else {
      return (lc $x cmp lc $y);
   }
}

my @argA = ('hallo', 3, 'Hallo', "", 22, "das war's" );
@argA = sort { special_compare($a, $b) } @argA;

print join("\n", @argA);