ansible lineinfile module to match variable_value

Question

how can one possibly match value of a variable through regex parameter in lineinfile module?

- name: emptyline before search
  lineinfile:
    dest: ~/file
    insertbefore: '^{{ search_text }}$'
    line: ''

I tried above with both single/double quotes around, it doesn't seem to work

Answer 1

For a file test.txt

hello
something
test
hello
something

a run of a test playbook like

---
- hosts: localhost
  become: false
  gather_facts: false

  vars:

    BEFORE: "test"

  tasks:

  - name: Add line before
    lineinfile:
      path: test.txt
      insertbefore: '^{{ BEFORE }}$'
      line: ''

results into an output of

hello
something

test
hello
something

the expected one.