Suppose I have a function that is 'noisy' and prints to standard output rudely.

(defun not-my-noisy-function ()
  "A function outside my control"
  (print "Haha! Butts!"))

I would like to be able to make calls to that function without corresponding messages in stdout. I was hoping that there was an elisp construct which would evaluate the form discarding standard-output from its body. A little bit like ignore-errors, but applicable to an output stream instead of thrown exceptions. I haven't been about to find anything in the vein of "suppress"/"silent"/"discard"/"redirect" for output streams.

(evaluate-silently ;; macro I wish existed

My first thought of setting standard-output to nil doesn't seem to do the trick.

(let ((standard-output nil))
  (print "Nope; doesn't work.  You can still hear me."))

Interestingly the elisp manual says it must not be nil and doesn't say anything about values other than t, a buffer, or a marker. I can't seem to find documentation about an "real" streams in the elisp manual; only optional parameters to output functions which only seem to duplicate captured standard output rather redirecting it. with-output-to-string and with-output-to-temp-buffer also only seem to duplicate output to a buffer.

As a last recourse I could manually examine problematic functions and use cl-flet (to override print,message, etc), but I would rather not take that approach. Unfortunately this is the only technique that I've identified to accomplish this.

(cl-flet ((print (&rest body) nil))
  (print "I am being ignored!?!!"))

Is there a better way? I hope I just haven't divined the correct apropos incantation.


You were following a good line of enquiry regarding standard-output, but just didn't manage to find the right information.

The value of standard-output has to be a valid value for the PRINTCHARFUN argument, which C-hf print describes nicely:

Optional argument PRINTCHARFUN is the output stream, which can be one
of these:

   - a buffer, in which case output is inserted into that buffer at point;
   - a marker, in which case output is inserted at marker's position;
   - a function, in which case that function is called once for each
     character of OBJECT's printed representation;
   - a symbol, in which case that symbol's function definition is called; or
   - t, in which case the output is displayed in the echo area.

If PRINTCHARFUN is omitted, the value of `standard-output' (which see)
is used instead.

Hence you can simply bind standard-output to the canonical function for doing nothing:

(let ((standard-output 'ignore))
  (print "hello"))
| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.