Split is your friend:

my @chapters = split /\./, $chapter;
pop @chapters;
my $prev_chapter = join '.' @chapters;
[download]

(I'm sure this can be golfed, but this is for clarity now :D)

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Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain