Here's another, using regex. Frankly I'm a little shaky on why it actually works:

my $a = "1,2,3,4,5,6,7,8";
my @even = ($a =~ /(.+?),.+?,?/g); #prints 1,3,5,7
my @old = ($a =~ /.+?,(.+?),?/g); # prints 2,4,6,8
[download]