list-sub.yml

# test performing substitution in strings of a list

- name: Test substitution in list of strings
  hosts: localhost
  gather_facts: false
  tasks:

  - name: Before substitution
    debug:
      var: files1

  # This was my first attempt and it worked but the list had to have exactly two elements
  #
  # - name: Replace
  #   set_fact:
  #     files1:
  #       - "{{ files1[0] | regex_replace('^/etc/pam.d/', root + '/') }}"
  #       - "{{ files1[1] | regex_replace('^/etc/pam.d/', root + '/') }}"

  - name: Replace
    set_fact:
      files2: "{{ files2 + [ item | regex_replace('^/etc/pam.d/', root + '/') ] }}"
    loop: "{{ files1 }}"

  - name: After substitution
    debug:
      var: files2

  vars:
    root: "/usr/share/authselect/default/sssd/password-auth"

    files1:
      - "/etc/pam.d/password-auth"
      - "/etc/pam.d/system-auth"

    files2: []