$num1 = "1;2;3";
$num2 = "4;5;6";

(@ar1, @ar2) = map { split(';', $_) } ($num1, $num2);

print "ar1 size  = " . scalar(@ar1) . "\n";
print "ar2 size  = " . scalar(@ar2) . "\n";

output:
ar1 size = 6;
ar2 size = 0;