Print and Output with Elisp

Its signature is

  (message FORMAT_STRING &rest ARGS)

  ;; for example:
  (message "Name is %s" "Joe") ; => Name is Joe

It displays a message at the bottom of the screen, as well as into the *Messages* buffer.

insert function inserts string to current buffer at cursor position.

It has signature

  (insert &rest ARGS)

  ;; for example
  (insert "something")

The print function has signature

  (print OBJECT &optional TARGET)

The print function will print the Lisp object in Lisp syntax with a newline.

Tips. When writing a Elisp script that does batch processing, it’s recommended to print to own buffer, because the *Messages* buffer scrolls off.

  ;; EXAMPLE:

  (setq xbuff (generate-new-buffer "*my output*"))
  (print "something" xbuff) ; print to our custom buffer
  (switch-to-buffer xbuff)

It also has sibling functions: prin1 function acts like print function but without newline; princ function outputs in more human-readable format, and without newline.

Use the warn function, print messages to *Warnings* buffer.

  (warn FORMAT_STRING &rest ARGS)

  ;; EXAMPLE:
  (warn "You got a problem: %s" "Incorrect input.")

This feature is akin to with ... as ... feature in Python. It binds standard output to a specified buffer, evaluates the body, and then show that buffer. The buffer is cleared before getting printed to; print functions print to this buffer by default.

  ;; SYNTAX:
  (with-output-to-temp-buffer BUFFER_NAME &rest BODY)

  ;; EXAMPLE:
  (let ((xbuff (generate-new-buffer "*MY OUTPUT*")))
    (with-output-to-temp-buffer xbuff
      (print "ABC") ; This string is printed to xbuff
      ))