Martin Maechler <maechler at stat.math.ethz.ch>
on Mon, 16 Oct 2017 19:13:31 +0200 writes:
Stephen Berman <stephen.berman at gmx.net>
on Sun, 15 Oct 2017 01:53:12 +0200 writes:
> (I reported the test failure mentioned below to R-help but was advised
> that this list is the right one to address the issue; in the meantime I
> investigated the matter somewhat more closely, including searching
> recent R-devel postings, since I haven't been following this list.)
> Last May there were two reports here of problems with Sys.timezone, one
> where the zoneinfo directory is in a nonstandard location
> (https://stat.ethz.ch/pipermail/r-devel/2017-May/074267.html) and the
> other where the system lacks the file /etc/localtime
> (https://stat.ethz.ch/pipermail/r-devel/2017-May/074275.html). My
> system exhibits a third case: it lacks /etc/timezone and does not set TZ
> systemwide, but it does have /etc/localtime, which is a copy of, rather
> than a symlink to, a file under zoneinfo. On this system Sys.timezone()
> returns NA and the Sys.timezone test in reg-tests-1d fails. However, on
> my system I can get the (abbreviated) timezone in R by using as.POSIXlt,
> e.g. as.POSIXlt(Sys.time())$zone. If Sys.timezone took advantage of
> this, e.g. as below, it would be useful on such systems as mine and the
> regression test would pass.
> my.Sys.timezone <-
> function (location = TRUE)
> {
> tz <- Sys.getenv("TZ", names = FALSE)
> if (!location || nzchar(tz))
> return(Sys.getenv("TZ", unset = NA_character_))
> lt <- normalizePath("/etc/localtime")
> if (grepl(pat <- "^/usr/share/zoneinfo/", lt) ||
> grepl(pat <- "^/usr/share/zoneinfo.default/", lt))
> sub(pat, "", lt)
> else if (lt == "/etc/localtime")
> if (!file.exists("/etc/timezone"))
> return(as.POSIXlt(Sys.time())$zone)
> else if (dir.exists("/usr/share/zoneinfo") && {
> info <- file.info(normalizePath("/etc/timezone"), extra_cols = FALSE)
> (!info$isdir && info$size <= 200L)
> } && {
> tz1 <- tryCatch(readBin("/etc/timezone", "raw", 200L),
> error = function(e) raw(0L))
> length(tz1) > 0L && all(tz1 %in% as.raw(c(9:10, 13L, 32:126)))
> } && {
> tz2 <- gsub("^[[:space:]]+|[[:space:]]+$", "", rawToChar(tz1))
> tzp <- file.path("/usr/share/zoneinfo", tz2)
> file.exists(tzp) && !dir.exists(tzp) &&
> identical(file.size(normalizePath(tzp)), file.size(lt))
> })
> tz2
> else NA_character_
> }
> One problem with this is that the zone component of as.POSIXlt only
> holds the abbreviated timezone, not the Olson name.
Yes, indeed. So, really only for Sys.timezone(location = FALSE) this
should be given, for the default location = TRUE it should
still give NA (i.e. NA_character_) in your setup.
Interestingly, the Windows versions of Sys.timezone(location =
FALSE) uses something like your proposal, and I tend to think that
-- again only for location=FALSE -- this should be used on
on-Windows as well, at least instead of returning NA then.
Also for me on 3 different Linuxen (Fedora 24, F. 26, and ubuntu
14.04 LTS), I get
whereas on Windows I get Europe/Berlin for the first (why on
earth - I'm really in Zurich) and get "CEST" ("Central European Summer Time")
for the 2nd one instead of NA ... simply using a smarter version
of your proposal. The windows source is
in R's source at src/library/base/R/windows/system.R :
Sys.timezone <- function(location = TRUE)
{
tz <- Sys.getenv("TZ", names = FALSE)
if(nzchar(tz)) return(tz)
if(location) return(.Internal(tzone_name()))
z <- as.POSIXlt(Sys.time())
zz <- attr(z, "tzone")
if(length(zz) == 3L) zz[2L + z$isdst] else zz[1L]
}
From what I read, the last three lines also work in your setup
where it seems zz would be of length 1, right ?
I'd really propose to use these 3 lines in the non-Windows
version of Sys.timezone .. at the end *instead* of NA_character_
(or a slightly safer version which gives NA_character_ if zz is
of length 0 {e.g. if there is no "tzone" attribute}.
> i don't know how to
> get the Olson name using only R functions, but maybe it would be good
> enough to return the abbreviated timezone where possible, e.g. as above.
> (On my system I can get the Olson name of the timezone in R with a shell
> pipeline, e.g.: system("find /usr/share/zoneinfo/ -type f | xargs md5sum
> | grep $(md5sum /etc/localtime | cut -d ' ' -f 1) | head -n 1 | cut -d
> '/' -f 5,6"), but the last part of this is tailored to my configuration
> and the whole thing is not OS-neutral, so it isn't suitable for
> Sys.timezone.)
Definitely not. I still recommend you think of a more portable
solution for the `location = TRUE` (default) case in Sys.timezone().
Returning the non-location form (e.g "CEST") when something like
"Europe/Zurich" is expected is really not a good idea,
and you are lucky that the regression test passes "accidentally" ...
Martin