How do I interpolate elisp variables in org-mode option headers?

Question

I want to achieve something like this:

#+latex_header: \input{${PUT_SOME_ELISP_VALUE_HERE}night_beamer_common1.tex}

Answer 1

You can do it with a macro:

#+MACRO: foo (eval (concat "#+latex_header: \\input{" my-var "/night-beamer-common1.tex}"))

{{{foo}}}

* Intro

This is a test.

AFAICT, macros are not expanded in the value position of an option header, so you cannot say:

#+MACRO: foo (eval (concat "\\input{" my-var "/night_beamer_common1.tex}"))

#+LATEX_HEADER: {{{foo}}}

You can define the variable with #+BIND in the Org mode file itself or use a global value:

#+BIND: my-var "/foo/bar/baz"

...

If you decide to use #BIND, remember to enable it by customizing org-export-allow-bind-keywords or setting it to t in your init file.

You cannot use a file-local variable however. This does not work:

#+MACRO: foo (eval (concat "#+latex_header: \\input{" my-var "/night-beamer-common1.tex}"))

{{{foo}}}

* Intro

This is a test.

* COMMENT Local variables

# Local variables:
# my-var: "/foo/bar/baz"
# End:

I suspect it has something to do with lexical scoping - I get this backtrace:

Debugger entered--Lisp error: (void-variable my-var)
  (concat "#+latex_header: \\input{" my-var "/night-beamer-common1.tex}")
  (closure (t) (&rest _) (concat "#+latex_header: \\input{" my-var "/night-beamer-common1.tex}"))()
  apply((closure (t) (&rest _) (concat "#+latex_header: \\input{" my-var "/night-beamer-common1.tex}")) nil)
  (if (functionp template) (apply template (org-element--property :args macro nil nil)) (replace-regexp-in-string "\\$[0-9]+" #'(lambda (m) (or (nth (1- (string-to-number ...)) (org-element--property :args macro nil nil)) "")) template nil 'literal))
  (let* ((value (if (functionp template) (apply template (org-element--property :args macro nil nil)) (replace-regexp-in-string "\\$[0-9]+" #'(lambda (m) (or ... "")) template nil 'literal)))) (format "%s" (or value "")))
  (progn (let* ((value (if (functionp template) (apply template (org-element--property :args macro nil nil)) (replace-regexp-in-string "\\$[0-9]+" #'(lambda ... ...) template nil 'literal)))) (format "%s" (or value ""))))
  (if template (progn (let* ((value (if (functionp template) (apply template (org-element--property :args macro nil nil)) (replace-regexp-in-string "\\$[0-9]+" #'... template nil 'literal)))) (format "%s" (or value "")))))
  (let ((template (cdr (assoc-string (org-element--property :key macro nil nil) templates t)))) (if template (progn (let* ((value (if (functionp template) (apply template ...) (replace-regexp-in-string "\\$[0-9]+" ... template nil ...)))) (format "%s" (or value ""))))))
  org-macro-expand((macro (:standard-properties [94 103 nil nil 0 nil nil nil nil nil nil nil nil nil nil nil nil #<buffer foo.org<2>>] :key "foo" :value "{{{foo}}}" :args nil)) (("date" . "") ("title" . "") ("email" . "") ("author" . "") ("foo" closure (t) (&rest _) (concat "#+latex_header: \\input{" my-var "/night-beamer-common1.tex}")) ("input-file" . "foo.org") ("modification-time" closure ((modtime 25838 660 285864 51000) (visited-file . "/tmp/foo.org")) (arg1 &optional arg2 &rest _) (format-time-string arg1 (or (and (org-string-nw-p arg2) (org-macro--vc-modified-time visited-file)) modtime))) ("keyword" lambda (arg1 &rest _) (org-macro--find-keyword-value arg1 t)) ("n" lambda (&optional arg1 arg2 &rest _) (org-macro--counter-increment arg1 arg2)) ("property" lambda (arg1 &optional arg2 &rest _) (org-macro--get-property arg1 arg2)) ("time" lambda (arg1 &rest _) (format-time-string arg1))))
...

but I have not dug any further.