war story: parallel(1) command

[Lennart Sorensen]

On Tue, Jul 30, 2013 at 06:33:44PM -0400, Eric B wrote:
> Your "likely the same" is context dependent.
> I agree with what you say above in the context of random file
> corruption or in the case of files containing random bits.
> 
> For Hugh's case, he wants to hash all the files in a real filesystem
> to find real differences.
> 
> If one calculates the SHA-N hash for each file, that would
> answer the question ("Are these files the same or different?")
> with virtual certainty.  There is NO need for an additional
> compare if the same hash is found.

Of course there is.  If you don't, you simply indicate you have no
understanding of what a hash is.

> When probabilities are too astronomically unlikely,
> they never happen in reality.

That's not good enough for file comparison.

Of course you are unlikely to find two different files with the same
hash, so must likely the extra comparison won't happen on files that
are not the same, but you still need to do it.

-- 
Len Sorensen
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