How to make Ansible execute a shell script if a package is not installed

Question

How can I make Ansible execute a shell script if a (rpm) package is not installed? Is it somehow possible to leverage the yum module?

Answer 1

Since Ansible 2.5, you can use the package_facts module:

- name: Gather package facts
  package_facts:
    manager: auto

- name: Debug if package is present
  debug:
    msg: 'yes, mypackage is present'
  when: '"mypackage" in ansible_facts.packages'

- name: Debug if package is absent
  debug:
    msg: 'no, mypackage is absent'
  when: '"mypackage" not in ansible_facts.packages'

Note: you need the python bindings for apt/rpm installed on the target, e.g. python-apt for Debian.