It seems to me that the author did not initially read the documentation they linked to (https://www.gnu.org/software/libc/manual/html_node/TZ-Variab...) and is now complaining in an annoying and entitled manner.
It truncated the name because of the underscores, but you can do `TZ=somerandomthing date` to see it just reports what you say it is.
If `TZ=EST date` adjusts the offset to EST, then a reasonable person would expect `TZ=EDT date` to either adjust the offset to EDT, or fail noisily if it's not aware of that offset code.
At a skim through the documentation I don't see anything warning about it's current behaviour.
But it is aware of it! You just told it, using the TZ variable, what EDT is. It's a timezone called EDT, with no offset from UTC!
If you wanted an offset, you should have written `TZ=EDT+4 date`
> But it is aware of it! You just told it
The user didn't intend to. Defining a new offset code should be explicit, not a silent fall-back when it's unable to find EDT.
Well, they should have read the docs. They clearly show examples of how to define a timezone right there. It isn't a fallback, it's what TZ is for.
Edit: perhaps `date` should have a `-z --zoneinfo` option, in which you could specify a timezone by file and it would fail if the file did not exist. This would fix the issue and avoid breaking existing scripts.
You can say that about any bad design choice, and in this case I'd argue that the linked docs don't even agree with the behaviour. The syntax given by the docs for creating a new timezone requires explicitly specifying an offset (then optional stuff like daylight savings).
The quirk may be documented elsewhere, but before getting caught out by it the average user has no reason to be searching through multiple sources of documentation for an oddity they don't yet know exists.
> It isn't a fallback, it's what TZ is for.
If I'm understanding, `TZ=EDT` will search for an "EDT" timezone in its database, fail, then instead silently default to creating a new timezone with 0:00 offset. That's pretty much how I'd define a fall-back.
But you can still define a brand new timezone with the TZ variable. Perhaps you want to argue that you shouldn't be able to, but that's what it's for, as the document linked above clearly states.
sane: report an error in some hard to ignore form
less sane: ignore the provided timezone, display the time in UTC and properly mark it with "UTC"
insane: ignore the provided timezone, display the time in UTC, but then mark it with the prefix of the provided timezone anyway.
I don't care how well documented the insane behavior is, it's still insane.
If you set your machine to something weird, then expect the utility that reports on those settings to report the weird settings you set.
In this specific case though, even those docs do not explain what happens if the value is "invalid"!
By the documentation "EST", "EDT" and "America/Los_Angeles" are not valid TZ environment variable values, as none of them matches any of the formats. offset doesn't seem to be optional, and within offset hours are not optional.
Ok, maybe it is too pedantic, a permissive implementation can interpret no offset as 0, right? But that's not what happens here. The implementation looks up the timezone by the provided name somewhere, and only when it doesn't find it it falls back to 0 as an offset.
This lookup behavior doesn't seem to be documented on that page. It's not described in the GNU date man page either even though it uses TZ='America/Los_Angeles' as an example.
If the file specification filespec is omitted, or its value cannot be interpreted, then Coordi‐
nated Universal Time (UTC) is used. If filespec is given, it specifies another tzfile(5)-format
file to read the timezone information from. If filespec does not begin with a '/', the file
specification is relative to the system timezone directory. If the colon is omitted each of the
above TZ formats will be tried.So even if someone finds this sentence somehow this is still underspecified. The full logic seems to be for a TZ that doesn't start with ':' :
1. First format tried, if it fails...
2. ...interpret TZ as filespec, if it fails...
3. ...interpret TZ as std with offset 0.
Note that there is fallback parsing of TZ that is not described at all (essentially 3rd and 4th formats), and two fallbacks, not one.