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I'm using .org files to keep track of my system configuration across different machines and I want certain code blocks to be tangled only if certain conditions are met.

Let's say I have something like this in my .init.el

(defvar is-desktop (equal (system-name) "desktop"))
(defvar is-laptop (equal (system-name) "laptop"))

How would I set a specific src block to be tangled only (when is-desktop)?

Something like this:

#+begin_src shell :tangle ~/.shells/exports.sh

export EDITOR="emacsclient"

#+end_src

#+begin_src conf :tangle (when is-desktop)"~/.gnupg/gpg-agent.conf")

  default-cache-ttl 172800
  max-cache-ttl 282800
  pinentry-program /home/user/.stumpwm.d/modules/util/pinentry/stumpwm-pinentry

#+end_src

When org-babel-tangle the first block will be 'tangled' but the second will not.

Is there a way to do that?

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  • 1
    According to the answer here, you can just use elisp directly in the source block its header. So, adapting from that answer, you would get :tangle (when is-desktop ~/.shells/exports.sh) Aug 23, 2023 at 10:26
  • What happens if is-desktop is nil?
    – NickD
    Aug 23, 2023 at 12:05
  • 1
    Assuming that is-desktop is defined, then :tangle (if is-desktop "~/.shells/exports.sh" "no") should work: the expression has to return a string in all cases (in this case, either the pathname or "no").
    – NickD
    Aug 23, 2023 at 12:06
  • The answer under the link mentions that if the expression returns nil, then the block does not get tangled. As the answer got 12 upvotes, I assumed it was correct. I did not test it, therefore I wrote 'according to the answer...'. Aug 24, 2023 at 7:56
  • Using :tangle (when (string= (system-name) "desktop") "yes) works when t, but when nil it will fail to tangle all blocks. Is there a way to just not tangle a single block? Aug 27, 2023 at 4:56

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