On 02/20/2018 09:46 AM, John Hawkinson wrote:
in general, for most locations, the US/* ("backward") form seemed the better choice.
It depends on how portable you want to be. Some implementations do not use the 'backward' file, so TZ='US/Eastern' does not work for them. FreeBSD is one such, or at least it was the last time I recall checking; see Garrett Wollman's email <https://mm.icann.org/pipermail/tz/2008-May/014941.html>. So, in practice I would say TZ='America/New_York' is more portable than TZ='US/Eastern'. If New York ever switches to Atlantic time (unlikely but conceivable given the current state of US politics), we'll link some other location to US/Eastern in the 'backward' file. Although it's not now clear what that other location would be (it'd depend on what part of the US switches), one candidate would be America/Indiana/Indianapolis. This is because if Jacksonville, Philadelphia and New York all switch to Atlantic time, then Indianapolis could well be the largest remaining city observing US Eastern time. This should amuse those of us who recall the history of UT offsets in Indiana.