How can I include variable values in tangled files?

Question

I have a variable defined in my heading that I would like to use in one text source block that I tangle to a file.

Example:

* Test
:PROPERTIES:
:header-args:  :var foo=222
:END:

... use foo in some shell scripts ...

#+BEGIN_SRC text :tangle config-file
I want to include value of FOO here
#+END_SRC

Answer 1

Use built-in :noweb functionality

1. Add named elisp src block to return the variable value.

   #+NAME: foo-value
   #+BEGIN_SRC elisp :exports none 
     foo
   #+END_SRC
   
   #+RESULTS: foo-value
   : 222
   

   Note: I choose elisp for this example because elisp code is enabled by default. This trick will also work with other languages, e.g.ruby and python.

2. Add :noweb yes header to the src block that will be tangled.

   #+BEGIN_SRC text :noweb yes :tangle config-file 
     I want to include value of <<foo-value()>> here.
   #+END_SRC
   

   When the file is tangled, the <<foo-value()>> will be replaced with 222.

---

Below is the updated version of your example code:

* Test
:PROPERTIES:
:header-args:  :var foo=222
:END:

#+NAME: foo-value
#+BEGIN_SRC elisp :exports none 
  foo
#+END_SRC

#+RESULTS: foo-value
: 222

#+BEGIN_SRC text :noweb yes :tangle config-file 
  I want to include value of <<foo-value()>> here.
#+END_SRC

---

The code in this answer was tested using
emacs version: GNU Emacs 26.1
org-mode version: 9.1.14

---

Thanks for asking a great question! Hope that helped!

Answer 2

If I understand your question, the following does what you want:

* Test  
:PROPERTIES:
:header-args:  :var foo=222
:END:

#+BEGIN_SRC bash :tangle tangle.txt
echo $foo
#+END_SRC

I can tangle this with C-c C-v t, which produces the file tangle.txt:

foo='222'
echo $foo

You have to specify what kind of code your code block is. In my example, a bash script. If you just specify text as you did, org won't know what syntax to use to define your variable.