How to get the installed yum packages with Ansible?

Question

I am trying to get all the installed yum package on an RHEL machine. I can easily get it through using shell commands which is not idempotent and would like to use the yum command instead.

Shell command works fine:

- name: yum list packages
  shell: yum list installed > build_server_info.config

But when I try to use the yum command it just executes but do not give any results:

- name: yum_command 
  action: yum list=${pkg} list=available

Answer 1

I can easily get it through using shell commands which is not idempotent

You can't really talk about idempotence, when you are querying the current state of a machine.

"Idempontent" means that the task will ensure the machine is in the desired state no matter how many times you run a certain task.

When you query current state, you don't describe the desired state. No matter what you do, what method you use, the term "idempotent" is just not applicable.

---

Regarding your example, which does not give you results - you have repeated twice the same argument list and the task should fail (it doesn't, which looks like an Ansible quirk).

To get a list of installed packages, you should use:

- name: yum_command 
  yum:
    list=installed
  register: yum_packages

- debug:
    var: yum_packages

It saves a list of dictionaries describing each package to a variable yum_packages.

You can then use a JSON Query Filter to get a single package (tar):

- debug: var=item
  with_items: "{{yum_packages|json_query(jsonquery)}}"
  vars:
    jsonquery: "results[?name=='tar']"

to get a result like this:

"item": {
    "arch": "x86_64",
    "epoch": "2",
    "name": "tar",
    "nevra": "2:tar-1.26-31.el7.x86_64",
    "release": "31.el7",
    "repo": "installed",
    "version": "1.26",
    "yumstate": "installed"
}

Or only its version:

- debug: var=item
  with_items: "{{yum_packages|json_query(jsonquery)}}"
  vars:
    jsonquery: "results[?name=='tar'].version"

"item": "1.26"