[R] Sys.glob() doesn't handle a UNC windows path beginning with backslashes

[Keith Jewell]

Hi,

Back in 2010 I had a problem with 'update.packages()', which I worked around 
by mapping a drive letter to a UNC path [described in 
<http://finzi.psych.upenn.edu/Rhelp10/2010-February/229820.html> but my 
current workaround is
assign(".lib.loc", sub("\\\\\\\\Server02/stats", "L:", .libPaths(), 
ignore.case = TRUE), env=environment(.libPaths))].

More recently a colleague had problems using the 'FactoMineR' plug in for 
the Rcmdr package;
a) directly loading 'RcmdrPlugin.FactoMineR' opened and "crashed" R 
Commander;
b) opening R Commander without FactoMiner, the Tools option 'Load Rcmdr 
plug-in(s)...' was greyed out.

It transpired that in .libPaths() the path to the library holding 
'RcmdrPlugin.FactoMineR' was specified as a UNC address: 
\\\\Server02/stats/R/library/2.13>. Mapping a virtual drive letter (e.g. L:) 
and specifying the path in .libPaths() as a 'local file system' (LFS) 
address <L:/R/library/2.13> fixed the problem.

I contacted Professor Fox (maintainer of Rcmdr) who told me that Rcmdr finds 
plug-in packages via the command
  plugins <- unlist(lapply(.libPaths(), function(x) Sys.glob(file.path(x, 
"*/etc/menus.txt"))))
Because file.path and Sys.glob are both vectorised I think (but am not 
certain) that this could be simplified to:
  plugins <- Sys.glob(file.path(.libPaths(), "*/etc/menus.txt"))
but that's by the way, the problem seems to lie in Sys.glob under Windows 
operating systems.

I note that 'help(Sys.glob)' on my Windows system  differs from 
<http://finzi.psych.upenn.edu/R/library/base/html/Sys.glob.html>.
The latter says "For precise details, see your system's documentation on the 
glob system call.  There is a POSIX 1003.2 standard  <snip> The rest of 
these details are indicative (and based on the POSIX standard)".
On Windows "The glob system call is not part of Windows, and we supply a 
partial emulation. <snip> An attempt is made to handle UNC paths starting 
with a double backslash" which doesn't really inspire confidence.

This was discussed in a 2009 R-devel thread starting here 
<https://stat.ethz.ch/pipermail/r-devel/2009-June/053879.html>, but the 
patch proposed in that thread seems not to have been implemented (??).

Trying to avoid Sys.glob in the Rcmdr application I came up with this:
      list.files(path=file.path(list.files(path=.libPaths(), 
full.names=TRUE), "etc"), pattern="^menus\\.txt$", full.names=TRUE)
It seems to give identical results to Sys.glob for mapped drives, works with 
UNC paths in Windows, and seems quite fast.

So my questions relate to diagnosis, prognosis, and prescription (cure?).

1) Diagnosis: Am I correct that my problem(s) originate in the "partial 
emulation" of glob in Windows.

2) Prognosis: If so, is there any likelihood that the emulation will improve 
in the near future?

3) Prescription: If not:

a) is assign(".lib.loc", sub("\\\\\\\\Server02/stats", "L:", .libPaths(), 
ignore.case = TRUE), env=environment(.libPaths))
a reasonable workaround in a specific case?

b) is list.files(path=file.path(list.files(path=.libPaths(), 
full.names=TRUE), "etc"), pattern="^menus\\.txt$", full.names=TRUE)
a reasonable replacement for the Sys.glob() construction in Rcmdr? I don't 
want to suggest to Prof. Fox an amendment which fixes my problem but 
'breaks' it for others!

Thanks in advance,

Keith Jewell

R version 2.13.0 (2011-04-13)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=English_United Kingdom.1252
[2] LC_CTYPE=English_United Kingdom.1252
[3] LC_MONETARY=English_United Kingdom.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United Kingdom.1252

attached base packages:
[1] datasets  grDevices splines   graphics  stats     utils     tcltk
 [8] tools     methods   base