Fast forward-backward (write-read)

[Virgil Stokes]

On 23-Oct-2012 19:56, Tim Chase wrote:
> On 10/23/12 12:17, Virgil Stokes wrote:
>> On 23-Oct-2012 18:09, Tim Chase wrote:
>>>> Finally, to my question --- What is a fast way to write these
>>>> variables to an external file and then read them in
>>>> backwards?
>>> Am I missing something, or would the fairly-standard "tac"
>>> utility do the reversal you want?  It should[*] be optimized to
>>> handle on-disk files in a smart manner.
>> Not sure about "tac" --- could you provide more details on this
>> and/or a simple example of how it could be used for fast reversed
>> "reading" of a data file?
> Well, if you're reading input.txt (and assuming it's one record per
> line, separated by newlines), you can just use
>
>    tac < input.txt > backwards.txt
>
> which will create a secondary file that is the first file in reverse
> order.  Your program can then process this secondary file in-order
> (which would be backwards from your source).
>
> I might have misunderstood your difficulty, but it _sounded_ like
> you just want to inverse the order of a file.
Yes, I do wish to inverse the order,  but the "forward in time" file will be in 
binary.

--V