You need to keep track of two things: where to start, and how many to show.

First set $start to one unless we're getting a param.

unless(param('start')){ $start = 1 }
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Then use two counters to track where to start and how many to process.

for(@array){
    $c++; # count all items
    if($c >= $start){ # if $c count is = or greater than where to star
+t
        $d++; # count items that match first test
        unless($d > $show){ # unless $d count is greater than how many
+ to show
            print # or whatever
            }
        }
    }
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Then calculate the 'previous n' and 'next n' links.

$previous = ($start-$show);
unless($previous < 1){ # unless we're already at the beginning
    print qq~<a href="$url?start=$previous&show=$show">
    Previous $show</a>~;
    }
    
$next = ($start+$show);
unless($next > $c){ # unless we're already at the end
    print qq~<a href="$url?start=$next&show=$show">
    Next $show</a>~;
    }
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