use warnings;
use strict;

my $l = 'abc,2,3,4,5,6 abc,7,5,2,1,6,2,3 abc,8,2,1,3,1,4 ....... def,8,9,4,5,6 def,5,6,2,1 ';
my %hash;
    my $k;
    for (split/[,. ]+/ => $l){
      if(/\D+?/){
       $k = $_
      }else{
      push @{$hash{$k}},$_
      }
    }

 print $_,',',join (',' => @{$hash{$_}}),$/ for sort keys %hash;