#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11121442
use warnings;

my $data = '1,2,3,4,5,6,7,8,9,8,7,6,5,4,3,2,1,';
my $target = 5;

print $data =~ /\b$target,((?:\d+,){3})/g, "\n";