unlink deletes the file(s) or directories specified by x.unlink(x, recursive = FALSE, force = FALSE)* and ?) are allowed.0 for success, 1 for failure, invisibly.
  Not deleting a non-existent file is not a failure, nor is being unable
  to delete a directory if recursive = FALSE.  However, missing
  values in x are regarded as failures.path.expand) is done on x. If recursive = FALSE directories are not deleted,
  not even empty ones. On most platforms ‘file’ includes symbolic links, fifos and
  sockets.  unlink(x, recursive = TRUE)
  deletes the just symbolic link if the target of such a link is a directory. Wildcard expansion is done by the internal code of
  Sys.glob.  Wildcards never match a leading . in
  the filename, and files . and .. will never be
  considered for deletion.
  Wildcards will only be expanded if the system supports it.  Most
  systems will support not only * and ? but also character
  classes such as [a-z] (see the man pages for the system
  call glob on your OS).  The metacharacters * ? [ can
  occur in Unix filenames, and this makes it difficult to use
  unlink to delete such files (see file.remove),
  although escaping the metacharacters by backslashes usually works.  If
  a metacharacter matches nothing it is considered as a literal
  character. recursive = TRUE might not be supported on all platforms, when it
  will be ignored, with a warning: however there are no known current
  examples.
  Character classes such as [a-z] are supported.  The
  metacharacter [ can occur in Windows filenames, and this makes
  it difficult to use unlink to delete such files (see
  file.remove).  If a wildcard matches
  nothing it is considered as a literal character. Windows cannot remove the current working directory, nor any file
  which is open nor any directory containing such a file. UTF-8-encoded paths not valid in the current locale can be used.file.remove.