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I am trying to execute an external program on a string. This code works, but it saves the string to a temporary file in order to run call-process. This seems quite roundabout. I'd rather not use a shell command either.

Is there a way to call an external program on a string without writing to a temporary file?

(defun my/execute-program-on-string (program string &optional args)
  "Call PROGRAM with ARGS on STRING."
  (let  (input-file input-buffer output-buffer exit-code result)
    (unwind-protect
    (setq input-file (make-temp-file "/tmp/emacs-execute-"))
      (write-region string nil input-file nil)
      (setq input-buffer (create-file-buffer input-file)
        output-buffer (generate-new-buffer (format "*%s*" program))
        exit-code (call-process program input-file output-buffer nil args))
      (if (zerop exit-code)
      (setq result
        (with-current-buffer output-buffer (buffer-string)))
    (throw 'external-program-error exit-code))
      (progn
    (kill-buffer input-buffer)
    (kill-buffer output-buffer)))
    result))


(my/execute-program-on-string "cat" "Hello, World!" "-n")
  • My version of Emacs does not have f-write-text ... Your minimal working example requires using undisclosed third-party libraries ... Many other forum participants might be able to help if we didn't have to familiarize ourselves with that library and install it ... – lawlist Jun 17 '18 at 2:16
  • @lawlist Good point. I've replaced that function call with an equivalent line for better reproducibility. – Hatshepsut Jun 17 '18 at 2:56
  • Does the function buffer-substring, with optional arguments START END help any with this situation? This would turn the buffer contents (or the portion between START/END) into a string without writing it to a file, if that is what is being sought here. – lawlist Jun 17 '18 at 4:36
4

You can use call-process-region to send string to a program as standard input, for example,

(with-temp-buffer
  (call-process-region "Hello, World!" nil "cat" nil t nil "-n")
  (buffer-string))
;; => "     1   Hello, World!"

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