[Rd] Fwd: Using existing envars in Renviron on friendly Windows

[Henrik Bengtsson]

Two comments/suggestions:

1. What about recommending to always quote the value in Renviron
files, e.g. ABC="Hello world" and DEF="${APPDATA}/R-library"?  This
should a practice that works on all platforms.

2. What about having readRenviron() escapes strings it imports via
environment variables?  See example below.  Is there ever a use case
where someone wants/needs, or even rely on, the current behavior? (I
would even like to argue the current behavior is a design bug that
should be fixed.)  As an analogue from the shell world, Bash escapes
its input.

To illustrate the latter, with:

A=C:\\ABC
B=${A}
C="${A}"

or equivalently:

A="C:\ABC"
B=${A}
C="${A}"

we currently get:

$ Rscript -e "Sys.getenv(c('A', 'B', 'C'))"
        A         B         C
"C:\\ABC"   "C:ABC" "C:\\ABC"

If base::readRenviron() would escape "input" environment variables, we
would get identical values for both 'B' and 'C', which I think is what
most people would expect.

To be clear, this is a problem that occur on all platforms, but it's
more likely to be revealed on MS Windows since paths uses backslashes,
but you could image a Linux user using something like
A="Hello\nworld\n" and would also be surprised about the above
behavior, when they end up with B="Hellonworldn".

/Henrik

On Wed, Oct 20, 2021 at 7:31 AM Michał Bojanowski <michal2992 using gmail.com> wrote:
>
> Hello Tomas,
>
> Yes, that's accurate although rather terse, which is perhaps the
> reason why I did not realize it applies to my case.
>
> How about adding something in the direction of:
>
> 1. Continuing the cited paragraph with:
> In particular, on Windows it may be necessary to quote references to
> existing environment variables, especially those containing file paths
> (which include backslashes). For example: `"${WINVAR}"`.
>
> 2. Add an example (not run):
>
> # On Windows do quote references to variables containing paths, e.g.:
> # If APPDATA=C:\Users\foobar\AppData\Roaming
> # to point to a library tree inside APPDATA in .Renviron use
> R_LIBS_USER="${APPDATA}"/R-library
>
> Incidentally the last example is on backslashes too.
>
> What do you think?
>
> On Mon, Oct 18, 2021 at 5:02 PM Tomas Kalibera <tomas.kalibera using gmail.com> wrote:
> >
> >
> > On 10/15/21 6:44 PM, Michał Bojanowski wrote:
> > > Perhaps a small update to ?.Renviron would be in order to mention that...
> >
> > Would you have a more specific suggestion how to update the
> > documentation? Please note that it already says
> >
> > "‘value’ is then processed in a similar way to a Unix shell: in
> > particular the outermost level of (single or double) quotes is stripped,
> > and backslashes are removed except inside quotes."
> >
> > Thanks,
> > Tomas
> >
> > > On Fri, Oct 15, 2021 at 6:43 PM Michał Bojanowski <michal2992 using gmail.com> wrote:
> > >> Indeed quoting works! Kevin suggested the same, but he didnt reply to the list.
> > >> Thank you all!
> > >> Michal
> > >>
> > >> On Fri, Oct 15, 2021 at 6:40 PM Ivan Krylov <krylov.r00t using gmail.com> wrote:
> > >>> Sorry for the noise! I wasn't supposed to send my previous message.
> > >>>
> > >>> On Fri, 15 Oct 2021 16:44:28 +0200
> > >>> Michał Bojanowski <michal2992 using gmail.com> wrote:
> > >>>
> > >>>> AVAR=${APPDATA}/foo/bar
> > >>>>
> > >>>> Which is a documented way of referring to existing environment
> > >>>> variables. Now, with that in R I'm getting:
> > >>>>
> > >>>> Sys.getenv("APPDATA")    # That works OK
> > >>>> [1] "C:\\Users\\mbojanowski\\AppData\\Roaming"
> > >>>>
> > >>>> so OK, but:
> > >>>>
> > >>>> Sys.getenv("AVAR")
> > >>>> [1] "C:UsersmbojanowskiAppDataRoaming/foo/bar"
> > >>> Hmm, a function called by readRenviron does seem to remove backslashes,
> > >>> but not if they are encountered inside quotes:
> > >>>
> > >>> https://github.com/r-devel/r-svn/blob/3f8b75857fb1397f9f3ceab6c75554e1a5386adc/src/main/Renviron.c#L149
> > >>>
> > >>> Would AVAR="${APPDATA}"/foo/bar work?
> > >>>
> > >>> --
> > >>> Best regards,
> > >>> Ivan
> > > ______________________________________________
> > > R-devel using r-project.org mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-devel
>
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