johngg@shiraz:~/perl/Monks$ perl -Mstrict -Mwarnings -E '
my @arr1 = qw{ 1 2 3 };
my @arr2 = q{a} .. q{g};
my @arr3 = qw{ I II III };

my $globStr
   = qq{{@{ [ join q{,}, @arr3 ] }}}
   .  q{__}
   . qq{{@{ [ join q{,}, @arr2 ] }}}
   .  q{__}
   . qq{{@{ [ join q{,}, @arr1 ] }}};
say $globStr;

say for
   map { join q{,}, reverse split m{__} }
   glob $globStr;'
{I,II,III}__{a,b,c,d,e,f,g}__{1,2,3}
1,a,I
2,a,I
3,a,I
1,b,I
2,b,I
3,b,I
1,c,I
2,c,I
3,c,I
1,d,I
2,d,I
3,d,I
1,e,I
2,e,I
3,e,I
1,f,I
2,f,I
3,f,I
1,g,I
2,g,I
3,g,I
1,a,II
2,a,II
3,a,II
1,b,II
2,b,II
3,b,II
1,c,II
2,c,II
3,c,II
1,d,II
2,d,II
3,d,II
1,e,II
2,e,II
3,e,II
1,f,II
2,f,II
3,f,II
1,g,II
2,g,II
3,g,II
1,a,III
2,a,III
3,a,III
1,b,III
2,b,III
3,b,III
1,c,III
2,c,III
3,c,III
1,d,III
2,d,III
3,d,III
1,e,III
2,e,III
3,e,III
1,f,III
2,f,III
3,f,III
1,g,III
2,g,III
3,g,III