You are getting the real length of the array. Appending additional commas doesn't extend the length of the array. You would have to write this as: 
my @array_2 = (1,2,3,4,5,6,7,8,9,undef,undef,undef,undef,undef,undef);

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or 
my @array_2 = (1,2,3,4,5,6,7,8,9);
$array_2[14] = undef;

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The reason that trailing commas are not a syntax error is so that you can write code like this: 
my %hash = (
    a => 1,
    b => 2,
);

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If the comma added another "undef" to the list then you would get a warning: 
Odd number of elements in hash assignment.
Use of uninitialized value in list assignment.

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In reply to Re: find real length of an array by jand
in thread find real length of an array by Anonymous Monk

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