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I have data that is timestamped with UNIX time, which is the number of seconds since January 1, 1970 UTC. Unfortunately, it seems that most of the date and time functions in Mathematica are based on the system's local time zone. How can I convert a UNIX timestamp to a DateList in UTC?

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DateList[] takes an absolute time as input. But M absolute time start in 1900 and not 1970. Hence take your Unix time, and add to it AbsoluteTime[{1970, 1, 1, 0, 0, 0}], which is 2208988800 seconds. Now your Unix list become M absolute time, then you can use DateList on it. Will this work for you? If you show some input will help. –  Nasser Aug 26 '13 at 0:17
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The number of seconds between January 1, 1900 and January 1, 1970 can be given by AbsoluteTime[{1970, 1, 1, 2, 0, 0}]. There is also DateList which, if given a number, will calculate what the date would be if that was the number of seconds given by AbsoluteTime.

DateList[AbsoluteTime[], TimeZone -> 2]

{2013, 8, 26, 2, 28, 7.97767}

DateList[AbsoluteTime[{1970, 1, 1, 2, 0, 0}] + First@ReadList["!date +%s"]]

{2013, 8, 26, 2, 28, 7.}

The slight difference seems to be because the UNIX timestamp rounds downwards.

(First@ReadList["!date +%s"] only gives the current timestamp on UNIX systems. Everyone else will have to paste in their own timestamps to try it out. Also, I'm using my own time zone which is +2.)

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