in reply to 'prev' in for loop

prev simply isn't Perl. next and last are though.

You can always rewrite a for-loop from:

foreach my $item (@list) { something($item); }
for (my $i = 0; $i < @list; $i++) { something($list[$i]); }
By modifying $i you can get to the "previous" iteration (something like $i--. However, be careful not to create an infinite loop.

Hope this helps, -gjb-