my $data = "0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,".('c'x50).",16,17,18,19,20,21,22,23,24,25,26,27";

while ($data =~/[^\n]{16}/)
{
 $data =~s/([^\n]{16})/ch($1)/e;
}
print $data;
  
sub ch
{
 my $s = shift;
 my $p = rindex($s, ',', 14)+1;
 $p=15 unless($p);
 return substr($s, 0, $p)."\n".substr($s, $p)
};

##</code><code>##

$data =~s/([^\n]{16})/ch($1)/ge;

##</code><code>##

$data =~s/([^\n]{16})/pos($data)=0;ch($1)/ge;