$bef[$mid]    # is an entry out of the array @bef
$mid[$aft]    # is an entry out of the array @mid
$bef[$mid$aft # is a syntax error becuase there's no ] on the array en
+try
[$bef]        # works because they're no other way to look at the [
[download]

Look in the Perl docs about how to use arrays and this will make a lot more sense.
The immediate solution is to put a '\' in front of each '['

/\/\averick