There's no fixed dimensions for perl's array : they are dynamicly extensible.
You can pre-allocate an amount of elements by playing with the $#array value ( see camel's book for more details ).

You can get the number of elements in an array by invoke it in a scalar context. exemple :

$count = @array;
or
$count = scalar @array;
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Update

Too late ... there's already many responses more sharp ... So scuse me ( and my poor english :) and forget this node.

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Hope this helps