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formatC(mode = "character") was documented to work, but did not. (PR#13474)
dir() does a better job when dir is of rhe form "d:", the currrent directory is not the root on that drive, and either 'full' or 'recursive' is true.
Sys.setenv() and Sys.getenv() now use the Windows API functions rather than the buggy C runtime functions, allowing longer settings, e.g. for a long PATH.