If you have Perl version 5.10 or later, this also works:

c:\@Work\Perl\monks>perl -wMstrict -le
"use 5.010;
 ;;
 for my $s ('21112,/vol/voly,blx',  '21113,/vol/eng,blz',  '21114,/vol
+/eng,file') {
   my $t = $s;
   $t =~ s{ .* \K , }{}xms;
   print qq{'$s' -> '$t'};
   }
"
'21112,/vol/voly,blx' -> '21112,/vol/volyblx'
'21113,/vol/eng,blz' -> '21113,/vol/engblz'
'21114,/vol/eng,file' -> '21114,/vol/engfile'
[download]

Update: Slightly changed code example to enhance clarity.