spgrass6, initGRASS() on MacOSX

Hello,

I want to use spgrass6 in an R session outside GRASS on Mac OSX. 
Therefore I want to use initGRASS to set some needed environmental 
variables etc. initGRASS() needs gisBase as one parameter which is the 
direcotry path to the GRASS binaries. What is the standard path on Mac 
OS X? My GRASS.app is in / /Applications/GRASS-6.5.app...

so I tried following two approaches so far without success:

initGRASS("/Applications/GRASS-6.5", home=tempdir())

Fehler in initGRASS("/Applications/GRASS-6.5", home = tempdir()) :
 /Applications/GRASS-6.5 not found

initGRASS("/Applications/GRASS-6.5.app", home=tempdir())

Fehler in system(paste("g.version", get("addEXE", envir = .GRASS_CACHE),  :
 Fehler bei der Ausf"uhrung des Kommandos

I don't know what is causing the problem in the second approach?
Does anyone know how to use initGRASS on Mac OS X in an R session outside GRASS correctly?

Best regards,
Johannes
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