I have this

(defun insert-dateutc ()
  (shell-command "printf %s $(date +\"%Y-%m-%dT%H:%M:%S\")" t))

which I want to use in this

(defun foo1 ()
  (format "this is the date-time %s" (insert-dateutc)))

but the output is the elisp id number of the function call (yes?)

==> "this is the date-time 1185"
2015-11-18T20:31:30 ; <-- inserted

with the actual desired return left outside. I need to suppress that number and get the actual date-time output. Gosh, I know it's something simple...

  • 1
    Is your question really about getting something from the shell process, to use in Emacs, or is it just about being able to display or return or insert a timestamp string in Emacs? If the latter, just use current-time-string or use current-time with format-time-string.
    – Drew
    Commented Nov 18, 2015 at 20:54
  • I want to use the output of that shell-command in the first function, i.e., not just any timestamp. Obviously I could just put the (shell-command ...) part in foo1, but it does the same thing AFAIK.
    – 147pm
    Commented Nov 18, 2015 at 20:57
  • You can use call-process or start-process, to get more control. Otherwise, the shell-command call you are using puts the output of the printf command in the current buffer, at point. You could wrap the call in with-current-buffer-window or similar (in which case you don't need the second arg), to recuperate the output.
    – Drew
    Commented Nov 18, 2015 at 21:01
  • (defun foo1 () (format "this is the date-time %S" (shell-command "date +\"%Y-%m-%dT%H:%M:%S\"" t))) is without the printf, but with the same bad results. The printf was only to avoid a newline. What exactly should I do with call-process?
    – 147pm
    Commented Nov 18, 2015 at 21:08
  • . . . of course if I can get ISO 8601 format of UTC out of format-time-string I'm home free. . .
    – 147pm
    Commented Nov 18, 2015 at 21:14

1 Answer 1


If what you want is just a timestamp, you can use

(defvar user-time-format
  (eval-when-compile (or (getenv "STRFTIME") "%Y-%m-%d %a %H:%M:%S %Z"))
  "The time format for the user to set.")
(defun user-time-format (&optional insert)
  "Return or insert the time string according to `user-time-format'."
  (interactive "P")
  (let ((str (format-time-string user-time-format)))
    (if insert (insert str)
        (if (called-interactively-p 'interactive) (message "%s" str) str))))

except you would set user-time-format to "%Y-%m-%dT%H-%M-%S".

However, your question raises an interesting issue, so let us discuss it too.

Your insert-dateutc is fine (but see below), but it inserts the date instead of returning it, so foo has to correct that:

(defun foo ()

(format "timestamp = [%s]" (foo))
==> "timestamp = [2015-11-18T16:37:12]"

Finally, take a look at C-h f shell-command RET. It says discourages the use of this function in lisp code, recommending call-process instead:

  (call-process "date" nil t nil "+%Y-%m-%dT%H:%M:%S")
  (buffer-substring-no-properties 1 (line-end-position 0)))
==> "2015-11-18T16:47:27"
  • Your foo (with the format bundled inside a cl-flet) works fine -- in my scratch, but when I call it in my org buffer . . . nothing appears. Apparently the format form doesn't "print"?
    – 147pm
    Commented Nov 19, 2015 at 1:10
  • format converts its arguments to a string. you might want to pass it to insert which will insert the string into the buffer or use message instead of format to report the text in the echo area.
    – sds
    Commented Nov 19, 2015 at 2:30

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