Global Shell Options

  [Errors]         nounset -u      errexit -e   inherit_errexit   pipefail
  [Globbing]       noglob -f       nullglob     failglob        X dotglob
                   dashglob (true)
  [Other Option]   noclobber -C
  [Debugging]      errtrace -E     extdebug   X verbose           xtrace -x     
  [Interactive]    emacs           vi
  [Compat]         eval_unsafe_arith            ignore_flags_not_impl
                   ignore_shopt_not_impl
  [Optimize]       rewrite_extern
