use strict;
my @subjects=("camel, flea, humbug, hubris", "Camel, Flea, Humbug & Hubris","CAMEL, FLEA, HUMBUG and HUBRIS");
for (@subjects) {  
  my @elements=split /\s*,\s*/;
  push @elements, split /\s+&\s+/, pop(@elements);
  push @elements, split /\s+and\s+/, pop(@elements);
  print join "\n", @elements;
  }