From hb at biostat.ucsf.edu  Tue May 22 21:05:31 2012
From: hb at biostat.ucsf.edu (Henrik Bengtsson)
Date: Tue, 22 May 2012 12:05:31 -0700
Subject: [Rd] Best way to locate R executable from within R?
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On Tue, May 22, 2012 at 11:39 AM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
> On Tue, May 22, 2012 at 1:34 PM, Henrik Bengtsson <hb at biostat.ucsf.edu> wrote:
>> Hi,
>>
>> I'd like to spawn of a new R process from within R using system(),
>> e.g. system("R -f myScript.R"). ?However, just specifying "R" as in
>> that example is not guaranteed to work, because "R" may not be on the
>> OS's search path.
>>
>> ?What is the best way, from within a running R, to infer the command
>> (basename or full path) for launching R in way that it works on any
>> OS? ?I came up with the following alternatives, but I'm not sure if
>> they'll work everywhere or not:
>>
>> 1. Rbin <- commandArgs()[1];
>>
>> 2. Rbin <- file.path(R.home(), "bin", "R");
>>
>> Other suggestions that are better?
>>
>
> At least on Windows one could run R via R.exe, Rterm.exe or Rgui.exe
> amd #2 would not pick up the differences. ?On the other hand if I do
> this on the Windows command line on my Vista system with R 2.15.0
> patched:
>
> cd \program files\R\R-2.15.x\bin\i386
> Rterm.exe
>
> and then enter commandArgs() into R, the output is "Rterm.exe" with no path.

Thanks, I overlooked this need.  For my particular use case, I'm
interested in launching R in "batch" mode, so "R" will do (but not
"Rgui").

>
> The fact that one can have 32 bit and 64 bit R executables on the same
> system complicates things too.
>
> Thus, on Windows something like this might work:
>
> ? file.path(R.home("bin"), R.version$arch, basename(commandArgs()[[1]]))
>
> If there are cases that I missed then this might pick up those too:
>
> ? R <- commandArgs()[[1]]
> ? if (R == basename(R)) R <- file.path(R.home("bin"), R.version$arch, R)

FYI, R.home("bin") is not the same as file.path(R.home(), "bin"), cf.
help("R.home").  R.home("bin") will pick up the current architecture
directory (by using .Platform$r_arch), e.g.

> R.home("bin")
[1] "C:/PROGRA~1/R/R-2.15.0patched/bin/x64"

/Henrik

>
> --
> Statistics & Software Consulting
> GKX Group, GKX Associates Inc.
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> email: ggrothendieck at gmail.com
>
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[Rd] Best way to locate R executable from within R?
Henrik Bengtsson