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Number   :  3107
Date     :  2002-11-14
Author   :  CBFalconer
Subject  :  Re: Change to Standard Time: identical files withdifferent
Size(KB) :  2


Kan Yabumoto wrote:
> 
> XXCOPY has a little obscure set of switches to make fine
> adjustments to time-comparison operations.
> 
> I assume most of you are aware that XXCOPY allows you to
> control the degree of match in timestamp comparison, FF
> and its fine-tune variations:
> 
> /FF // same as /FF2
> /FFn // same as /FF+n/FF-n
> /FF+n // add a positive slack value up to n
> /FF-n // add a negative slack value up to n
> 
> (n is in seconds but can be H (hours), M (minutes) with
> the suffix letter).
> 
> You may add /FF+1H or /FF-1H to handle the time matching
> problem. But anything more than a few seconds (the
> 2 second default should be sufficient in almost all cases)
> seems too much.
> 
> But, there is another mechanism (which could be combined
> with the /FF if you want) that is originally designed
> for inter-timezone timestamp comparison.
> 
> /TS+n // add n hours to the source timestamp
> /TS-n // subtract n hours to the source timestamp
> 
> When you copy a file using /TS, the overwriting (new) file
> created in the destination directory will receive the
> adjusted time stamp (the source timestamp is adjusted
> by the value before comparison and will therefore be
> copied to the destination when the operation is complete).
> 
> Then, we have another switch that modifies the destination
> timestamp before the comparison.
> 
> /TD+n // add n hours to the destination timestamp
> /TD-n // subtract n hours from the dest timestamp.
> 
> Remember, the adjustment will be made just once prior to
> the file comparison. If the operation is not for copy
> (e.g., list-only, delete, etc.), then /TS+n and /TD-n
> will have identical behavior (/TS-n and /TD+n is also
> an equivalent pair). But, when the file is copied, the
> /TS version and /TD version has the difference. Usually,
> /TS version probably is the right one to use.
> 
> Note, /TS and /TD uses the unit of hours by default
> which can be changed to M (minutes), or S (seconds) just
> like the /FF cases.
> 
> While /FF has a similar effect to /TD or /TS, I believe
> /TS and /TD are the superior choice because the compensation
> is exact whereas /FF adds fuzziness in the comparison
> which adds undesirable fuzziness. /TD and /TS are to
> adjust the comparison operation without increasing
> the uncertainty.

The reason is that more intelligent OSs than W98 etc. maintain
time stamps in UTC, and convert for display. However backwards
compatibility requires the use of local time stamps, and there is
no simple cure. Of course you *could* have your machine keep time
in GMT, and then results would be self-consistent. 

A useful set of switches, though. Probably the best solution. 
Maybe one should run XXCOPY through an alias (or a batch file)
which is altered at daylight/standard changeover time. You still
have to be aware. :-[

-- 
Chuck F (cbfalconer@y...) (cbfalconer@w...)
Available for consulting/temporary embedded and systems.
 USE worldnet address!



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