$ cat -vet pm_11118005_data
Eli Stern,,, $
10-Nov-19,,, $
1 subscriber,,, $
,,, $
Abdessamed Ham,,, $
15-Nov-19,,, $
0 subscribers,,, $
,,, $
Arne Martinson,,, $
22-Nov-19,,, $
0 subscribers,,, $
,,, $

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

{
    open my $fh, '<', 'pm_11118005_data';
    local $/ = "\n,,, \n";
    while (<$fh>) {
        chomp;
        print join(',', $., split(/,,, \n?/)), ",, \n";
    }
}

##</code><code>##

1,Eli Stern,10-Nov-19,1 subscriber,, 
2,Abdessamed Ham,15-Nov-19,0 subscribers,, 
3,Arne Martinson,22-Nov-19,0 subscribers,,