Are 'US/Eastern' and 'US/Central' and 'US/Pacific' deprecated for strftime or just PHP?

Question

I have a shell script (zsh, to be precise) which uses

strftime "%I:%M %p %Z (%a, %b %d)" "$EPOCHSECONDS"

to generate a "current time" such as

"02:45 PM CST (Thu, Mar 01)"

This needs to be able to display the time in several different USA timezones, and so I have been using 'US/Eastern', 'US/Central', and 'US/Pacific' like so:

export TZ='US/Eastern'
strftime "%I:%M %p %Z (%a, %b %d)" "$EPOCHSECONDS"

That seems to work just fine, and I prefer it to using TZ='America/CityName' because it doesn't require me to know which city is in which TZ, I just need to tell it which TZ I want.

However, I happened across http://www.php.net/manual/en/timezones.others.php and saw that it says

Please do not use any of the timezones listed here (besides UTC), they only exist for backward compatible reasons.

I don't know what the issues are with the US/Region names, but I'm curious to know if using them is likely to cause a problem in the foreseeable future, or are they still safe to use? Is it just PHP which doesn't like them, or is everyone moving away from them?

Answer 1

The standard format for naming timezones in the Olson database is Continent/City. The "old" names you mention like US/Eastern, US/Central, and many more, are listed as backward compatibility links in the tzdata source distribution (in the file "backward"). According to the comment at the top of the file, these names may have become backward compatibility links in late 1993.

I think I remember reading that this standard was adopted because it was felt to be more stable: geopolitical (country) boundaries change, cities never move around. Maybe also because names like "Eastern" and "Central" are thought to be more confusing because they mean different timezones in different parts of the world. However, I cannot find any references to the naming rationale at the moment, so don't quote me on this.

The Continent/City-style names are preferred. Notice that operating systems like Debian and Ubuntu ask you to select the system timezone using these names (unless they autodetect it at installation time), Using these names you wouldn't really be required to, as you say, "know which city is in which TZ" because the city name is, well, part of the timezone name! So if you happen to have learned the Continent/City names instead of or in addition to the Country/Region names, you're already OK.

That being said, I do not think that these names will ever disappear. On the timezone mailing list, they are definitely always called "backward compatibility", not "deprecated", and are intended to stay, notwithstanding what PHP recommends.