How about:

@ar1 = split(';', $num1);
@ar2 = split(';', $num2);
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Update: if you want to know how to get

# given: @num = ("1;2;3", "4;5;6");
$array[0] = [1, 2, 3];
$array[1] = [4, 5, 6];
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then you want:

@array = map { [ split(';', $_) ] } (@num);
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The square brackets around split create an array reference out of what split returns.