sub nextPermute(\@)
{
    my( $vals )= @_;
    my $last= $#{$vals};
    return ""   if  $last < 1;
    # Find last item not in reverse-sorted order:
    my $i= $last-1;
    $i--   until  $i < 0  ||  $vals->[$i] lt $vals->[$i+1];
    # If complete reverse sort, we are done!
    return ""   if  -1 == $i;
    # Re-sort the reversely-sorted tail of the list:
    @{$vals}[$i+1..$last]= reverse @{$vals}[$i+1..$last]
      if  $vals->[$i+1] gt $vals->[$last];
    # Find next item that will make us "greater":
    my $j= $i+1;
    $j++  until  $vals->[$i] lt $vals->[$j];
    # Swap:
    @{$vals}[$i,$j]= @{$vals}[$j,$i];
    return 1;
}

#Code to make the sample use below friendly:
if(  0 == @ARGV  ) {
    die "Usage: $0 word\n",
        "   or: $0 t o k e n s\n",
        "Prints all unique permutations of the letters or words given.\n";
} elsif(  1 == @ARGV  ) {
    @ARGV= $ARGV[0] =~ /(.)/gs;
    $"= "";
}

#Sample use:
@ARGV= sort @ARGV;
do {
    print "@ARGV\n";
} while( nextPermute(@ARGV) );