Hi,
maybe i'm simplifying your requirements too much or it's a matter of performance, but you could solve this by splitting the numbers.

#!/usr/bin/perl

use strict;
use warnings;

my $numbers = '222,345,222,678,222,222,543,111,222';
my @numbers = split(',', $numbers);
my $i       = 1;

for my $number (@numbers) {
    if ( '222' eq $number && $i < scalar(@numbers) ) {
        print "AFTER $number-$numbers[$i]\n";
    }
    $i++;
}
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