>perl -wMstrict -le
"my $data = 'A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z';
 ;;
 my @ra = split m{ (?: , [^,]+){5} \K , }xms, $data;
 ;;
 printf qq{'$_'  } for @ra;
"
'A,B,C,D,E,F'  'G,H,I,J,K,L'  'M,N,O,P,Q,R'  'S,T,U,V,W,X'  'Y,Z'

##</code><code>##

>perl -wMstrict -le
"my $data = 'A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z';
 ;;
 my @ra = split m{ (?: , [^,]+){4} \K , }xms, $data;
 ;;
 printf qq{'$_'  } for @ra;
"
'A,B,C,D,E'  'F,G,H,I,J'  'K,L,M,N,O'  'P,Q,R,S,T'  'U,V,W,X,Y'  'Z'