for $i(0..$length2){
    push @array2, $array[$i];
    $i+=2;
}
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Don't modify the loop variable in the loop. This is bad programming practice. If you want to do something like this, make the loop do it for you:

for ($i=0;$i<=@array-2;$i+=2) {
    push @array2, $array[$i];
}
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For the next section:

for $i(1..$length){
    push @array2, $array[$i];
    $i+=2;
}
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Careful you don't step off the array. While this works, it's fragile and easy to break.

You should use strict; and use warnings;, and then use the debugger to find out where it goes horribly wrong ;)

I'd do it for you now, but I have to run for the carpool!