if ($card_map[$num]) {
    $card_map[$num]; # return value

 } else {
    $num; # return value

 } # end if

##</code><code>##

$ perl -wle 'my @card_map = qw(zero one two three); print $card_map[-2]'
two

##</code><code>##

my $return_value = '';
if ($num < 0) {
     $return_value = $negative;
     # continue with the positive value from here on
     $num = -$num;
}

# and append other results here:

$return_value .= $card_map[$num];
return $return_value;