let error_to_string = function
| `Process (`Exec (bin, cmd), how) ->
fmt "Executing %S[%s]: %s"
bin (String.concat ~sep:", " (List.map cmd ~f:(fmt "%S")))
(match how with
| `Exn e -> fmt "Exn %s" @@ Printexc.to_string e
| `Non_zero s -> fmt "Non-zero: %s" s)