use strict;
use Algorithm::Loops qw( NextPermute );

##</code><code>##

my @list= sort ('A'..'B'); # Find unique permutations for AB?
my $cnt;
my @list1;

##</code><code>##

# $l represents one blank tile cycling thru all letter values
for my $l ('A'..'Z') {

##</code><code>##

  @list1 = sort(@list,$l); # Very important to sort
  print"@list1\n"; # Show what's happening

##</code><code>##

  printf"%5d. ", ++$cnt;
  print"@list1\n"; # Display permutations

  } while( NextPermute( @list1 ) );

}

##</code><code>##

print"Counted $cnt unique permutations";
print $/;

##</code><code>##

A A B
 1. A A B
 2. A B A
 3. B A A
A B B
 4. A B B
 5. B A B
 6. B B A
A B C
 7. A B C
 8. A C B
 9. B A C
10. B C A
11. C A B
12. C B A
A B D
13. A B D
14. A D B
15. B A D
16. B D A
17. D A B
18. D B A
...
...
...
Counted 150 unique permutations