#!/usr/bin/perl

use strict;
use warnings;

my @record = ();	# record accumulator
my $row = 1;		# record counter

while (<DATA>) {
  chomp;
  s/,,,$//;
  if (m/^$/) {
    print join(',', $row++, @record), ",,\n";
    @record = ();	# reset for next record
  } else {
    push @record, $_;
  }
}

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