How to change Org-mode babel tangle write to file way as append instead of override by default?

Question

By default, Org-mode will override current babel src block content on file original content (when the file already has content).

For example, I have an org-mode file content as the bellowing block:

#+BEGIN_SRC org
,* config file

,** config 1

,#+BEGIN_SRC clojure :tangle "data/code/tangle-append-test.clj"
(println "hello")
,#+END_SRC

,** config 2

,#+BEGIN_SRC clojure :tangle "data/code/tangle-append-test.clj"
(println "world")
,#+END_SRC

#+END_SRC

If you tangle the whole buffer file, then the result will looks like this:

The tangled file result content:

#+NAME: data/code/tangle-append-test.clj
#+BEGIN_SRC clojure
(println "hello")

(println "world")

#+END_SRC

This is fine. But here is my problem:

But if you tangle only current src block with [C-u C-c C-v t]. Then the current tangled src block will overwrite the whole destination file, like this:

 $ cat data/code/tangle-append-test.clj

(println "world")

UPDATED

My question: The single babel block override original file content, I hope to only append current tangled block without overwriting.

Answer 1

The following elisp code defines a new function org-babel-tangle-append appending the current source block to the tangle file. In org-mode 9.1.6 there is no user option to configure org-babel-tangle in that way.

If you copy-paste the full elisp code into your init file behind package-initialize the new function org-babel-tangle-append is bound to the key sequence C-c C-v + in org-mode after the next restart of emacs.

The code is tested with

• emacs-version 25.1.50.2
• org-version 9.1.6

In org-babel-tangle of that org version the old tangle file is deleted with delete-file before the new block(s) are collected there. The new function org-babel-tangle-append works by calling org-babel-tangle with delete-file temporarily overridden by ignore.

(defun org-babel-tangle-append ()
  "Append source code block at point to its tangle file.
The command works like `org-babel-tangle' with prefix arg
but `delete-file' is ignored."
  (interactive)
  (cl-letf (((symbol-function 'delete-file) #'ignore))
    (org-babel-tangle '(4))))

(defun org-babel-tangle-append-setup ()
  "Add key-binding C-c C-v C-t for `org-babel-tangle-append'."
  (org-defkey org-mode-map (kbd "C-c C-v +") 'org-babel-tangle-append))

(add-hook 'org-mode-hook #'org-babel-tangle-append-setup)

Answer 2

I recommend using the builtin org-mode :noweb-ref header to concatenate the code blocks because doing so will resolve the block tangling issue and will allow more flexibility in the future.

• Updated Code

    * config file
  
    #+BEGIN_SRC clojure :noweb yes :exports none :mkdirp yes :tangle data/code/tangle-append-test.clj 
      <<configs>>
    #+END_SRC
  
    ** config 1
  
    #+BEGIN_SRC clojure :noweb-ref configs
      (println "hello")
    #+END_SRC
  
    ** config 2
  
    #+BEGIN_SRC clojure :noweb-ref configs
      (println "world")
    #+END_SRC
  

• Tangling the code with C-c C-v C-t produces:

    (println "hello")
    (println "world")
  

As new sections are added, deleted, moved, or updated, tangling the code should always produce the code in the order expected:

• Future Code

    * config file
  
    #+BEGIN_SRC clojure :noweb yes :exports none :mkdirp yes :tangle data/code/tangle-append-test.clj 
      <<configs>>
    #+END_SRC
  
    ** config 1 - Added
  
    #+BEGIN_SRC clojure :noweb-ref configs
      (println "Howdy")
    #+END_SRC
  
    ** config 2 - Updated
  
    #+BEGIN_SRC clojure :noweb-ref configs
      (println "World")
    #+END_SRC
  
    ** config 1 - Moved
  
    #+BEGIN_SRC clojure :noweb-ref configs
      (println "hello")
    #+END_SRC
  
    ** config 4 - Added 
  
    #+BEGIN_SRC clojure :noweb-ref configs
      (println "earth")
    #+END_SRC
  

• Future Tangle

    (println "Howdy")
    (println "World")
    (println "hello")
    (println "earth")
  

Hope that helped.

---

This code was tested using:
GNU Emacs 25.2.1 (x86_64-unknown-cygwin, GTK+ Version 3.22.10)
Org mode version 9.1.2

Answer 3

What I do is I specify a single block per output file, and use noweb references to collect what goes into it:

Here are the blocks with the source you want:

#+name: hello-world
#+begin_src clojure
(println "hello")
#+end_src

#+name: hello-world
#+begin_src clojure
(println "world")
#+end_src

#+name: goodbye
#+begin_src clojure
(println "goodbye")
#+end_src

Here's the block that collects it all and tangles it:

#+begin_src clojure :noweb yes :tangle data/code/tangle-append-test.clj
<<hello-world>>
<<goodbye>>
#+end_src