>perl -wMstrict -le
"my @ra = (0, 1, 42, 3, 4, 5, 6, 7, 8, 42, 10, 42, 12, 42);
 ;;
 for my $i (0 .. $#ra) {
   look_back_5_for_42(\@ra, $i);
   }
 ;;
 sub look_back_5_for_42 {
   my ($ar, $current_i) = @_;
   ;;
   my $back = $current_i - 5 + 1;
   $back = 0 if $back < 0;
   ;;
   printf qq{at index $current_i: };
   for my $i ($back .. $current_i) {
     printf qq{42 at index $i, } if $ar->[$i] == 42;
     }
   print '';
   }
"
at index 0:
at index 1:
at index 2: 42 at index 2,
at index 3: 42 at index 2,
at index 4: 42 at index 2,
at index 5: 42 at index 2,
at index 6: 42 at index 2,
at index 7:
at index 8:
at index 9: 42 at index 9,
at index 10: 42 at index 9,
at index 11: 42 at index 9, 42 at index 11,
at index 12: 42 at index 9, 42 at index 11,
at index 13: 42 at index 9, 42 at index 11, 42 at index 13,