print "$_\n" for glob "{@{[ join ',', @letters ]}}" x $len;

##</code><code>##

join ',', @letters

##</code><code>##

{A,B,C,D,E,F}{A,B,C,D,E,F}{A,B,C,D,E,F}{A,B,C,D,E,F}

##</code><code>##

print "$_\n" for glob (('{'. join( ',', @letters).'}') x $len);

##</code><code>##

print "$_\n" for glob +('{'. join( ',', @letters).'}') x $len;