To clarify what nardo said above, when you write:

@ARGV[0]
#instead of...
$ARGV[0]
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You are confusing scalar and array contexts. The first line (the way you did it) is actually an array slice, and perl interprets it as a one element array. The second line tells perl to treat it as a scalar value, that value being the first element of the array. This is a common beginners mistake (i used to do it) because it seems intuitive that arrays are always preceeded by a @, whether you are indexing them or not. However, once you understand what @, $, and % *really* do, it will make sense. They tell perl what kind of value you are talking about, and they also serve to select the namespace (scalars, arrays, and hashes all have seperate namespaces). If something is supposed to be a number, string, or other scalar value, it has to have a $ in front of it. So, when you index an array, you are selecting a scalar value out of the array, so of course the expression must be preceeded by a $.

Hope this helps,
Mark