hroptatyr/dateutils

What is datediff's expected behavior w.r.t. Daylight Saving Time changes?

Closed this issue · 3 comments

mattdm commented

I grew up in Indiana, long enough ago that we didn't have to deal with this nonsense. But alas, madness seems to be almost universal. So:

$ date -d "2021-03-14 1:59"
Sun Mar 14 01:59:00 AM EST 2021

$ date -d "2021-03-14 2:00"
date: invalid date ‘2021-03-14 2:00’

$ date -d "2021-03-14 3:00"
Sun Mar 14 03:00:00 AM EDT 2021

... but:

$ datediff "2021-03-14 1:59" "2021-03-14 3:00"
3660s

I guess an alternate way of asking this is: what timezone does datediff assume when one isn't explicitly given? My naïve expectation was that it'd follow the timezone set in my environment, including handling DST transitions.

hroptatyr commented

Hi Matt,
the timezone that's used by default is UTC. And you're right you'd have to specify it explicitly

$ datediff --from-zone America/New_York "2021-03-14 1:59" "2021-03-14 3:00"
60s

The opposite is more interesting

$ datediff --from-zone America/New_York "2021-11-07 1:59" "2021-11-07 2:00"
3660s

and there is no way (as per ISO 8601 and hence dateutils) to specify which one of the two 2 o'clocks you're referring to.

  • ❤️1
mattdm commented

Thanks! I guess probably the concrete thing here is that it'd be nice to have this information (UTC) in the man page, and perhaps also the example.

hroptatyr commented

I followed your suggestion and mentioned the special treatment of some zones, and UTC in particular. I'm ready to roll a new release, if not by this week then by the next.

  • 👍1