zip command to create zip archives.
zip(zipfile, files, flags = "-r9X", extras = "", zip = Sys.getenv("R_ZIPCMD", "zip"))path.expand) will be performed.zip will by default use the
  value of R_ZIPCMD, which is set in etc/Renviron if an
  unzip command was found during configuration.  On Windows, the
  default relies on a zip program (for example that from
  Rtools) being in the path.  The default for flags is that appropriate for zipping up a
  directory tree in a portable way: see the system-specific help for the
  zip command for other possibilities.
  Argument extras can be used to specify -x or -i
  followed by a list of filepaths to exclude or include.
unzip, unz.