Can somebody help me out with an algo?

I'm trying to get a six-character string *in stepped sequence* from the array of
possible unique six-character strings for the character class of [a-zA-Z0-9_].

I need to make sure that I don't skip over any possiblilities in the array of
possibilities, so I think that once the stepped sequence of the algo has reached
the last possible index before @#possibilities (<-- Perl syntax meaning the last
array element in my list of possible strings) it needs to recognize that the
next element to be retrieved from the array is the value of its incremented step
plus one. (Maybe the shift isn't necessary if the array length is a uneven
number?)

Obviously this means that the algo must keep track of its its current position
in the array, and make sure not to use any previously retrieved elements by
noting its current index, the length of the array, and the value of its
incremented step.  At this point that shift over the array elements of (step+1)
must occur.

I can't just start popping or splicing elements out of the array to do this with
a simple process of elimination (unless I keep track of the indicies of all the
elements that got spliced out of the array, I guess).  Keep in mind that this
retrieval of unique 6-char strings must occur between non-persistant
cgi-sessions in order to assign website visitors one of these unique numbers as
a product serial number.

The way I've been planning to track the current position of the algorithm in the
array between sessions is to use a simple flat-file database containing only the
integer representative of the array index where the algo left off after the
previous cgi-session ended.

Any ideas?  I thought it would be a fun brain buster to toss out for
everyone :o)

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