rappdirs is a port of appdirs to R. It lets you find the appropriate directory to save caches, logs, and data, on Linux, Mac, and Windows. It allows you to store files that need to shared across R sessions in a way that aligns with the CRAN policies.
What directory should your app use for storing user data? If running on Mac OS X, you should use:
If on Windows (at least English Win XP) that should be:
for roaming profiles but that is another story.
On Linux (and other Unices) the dir, according to the XDG spec (and subject to some interpretation), is either:
This kind of thing is what rappdirs is for. rappdirs will help you choose an appropriate:
For example, on Mac:
library(rappdirs) appname <- "SuperApp" appauthor <- "Acme" user_config_dir(appname, appauthor) #>  "~/Library/Application Support/SuperApp" user_data_dir(appname, appauthor) #>  "~/Library/Application Support/SuperApp" site_data_dir(appname, appauthor) #>  "/Library/Application Support/SuperApp" user_cache_dir(appname, appauthor) #>  "~/Library/Caches/SuperApp" user_log_dir(appname, appauthor) #>  "~/Library/Logs/SuperApp"