Ansible - variable to select artifact

[David Nadelson]

Hi All, 

I'm a DBA learning to use ansible to automate.  I'm wondering if anyone can point me to docs on how to use ansible to select a file based on the value of a variable.   i.e.  if variable=x than choose 1.txt  if variable=y then choose 2.txt.  

Thanks, 

David 

[Abhijeet Kasurde]

Hi David,

Here is the basic of getting input from the user and reading the file -

```

# ls
1.txt    2.txt    main.yml

# cat main.yml

---
- hosts: localhost
  gather_facts: no
  tasks:
    - debug:
        msg: "{{ lookup('file', filenumber + '.txt') }}"

# ansible-playbook main.yml -e "filenumber=1"

...

TASK [debug] *****************************************************************************
ok: [localhost] => {
    "msg": "one"
}

...

# ansible-playbook main.yml -e "filenumber=2"

...

TASK [debug] *****************************************************************************
ok: [localhost] => {
    "msg": "two"
}

...

```

You can read more about -

1. https://docs.ansible.com/ansible/latest/collections/ansible/builtin/debug_module.html

2. https://docs.ansible.com/ansible/latest/collections/ansible/builtin/file_lookup.html

3. https://docs.ansible.com/ansible/latest/reference_appendices/general_precedence.html#using-e-extra-variables-at-the-command-line

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--

Thanks,

Abhijeet Kasurde

[Todd Lewis]

Hello, David.

You could use a lookup table implemented as a simple dict. If you only need it in one task, you can define it in that task's vars section as I've done below, or farther "up" in host_vars, group_vars, etc., as long as it's defined somewhere. Here's a simple demo. I'm mapping colors to veggies, but you could map to file names or whatever. Be sure to handle the "missing" case.

[utoddl@tango ansible]$ cat select-artifact.yml
---
- name: Select artifact based on value
  hosts: localhost
  gather_facts: false
  tasks:
    - name: Match an artifact based on a value
      ansible.builtin.debug:
        msg: "Value {{ item }} matches artifact {{ artifacts[item] | default('!missing!') }}."
      vars:
        artifacts:
          green: cucumbers
          red: tomatoes
          purple: cabage
          yellow: squash
      loop:
        - red
        - orange
        - yellow
        - green
        - blue
        - indigo
        - violet
[utoddl@tango ansible]$ ansible-playbook select-artifact.yml

PLAY [Select artifact based on value] *********************************************************

TASK [Match an artifact based on a value] *****************************************************
ok: [localhost] => (item=red) => {
    "msg": "Value red matches artifact tomatoes."
}
ok: [localhost] => (item=orange) => {
    "msg": "Value orange matches artifact !missing!."
}
ok: [localhost] => (item=yellow) => {
    "msg": "Value yellow matches artifact squash."
}
ok: [localhost] => (item=green) => {
    "msg": "Value green matches artifact cucumbers."
}
ok: [localhost] => (item=blue) => {
    "msg": "Value blue matches artifact !missing!."
}
ok: [localhost] => (item=indigo) => {
    "msg": "Value indigo matches artifact !missing!."
}
ok: [localhost] => (item=violet) => {
    "msg": "Value violet matches artifact !missing!."
}

PLAY RECAP ************************************************************************************
localhost                  : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

Cheers,
--
Todd

[Rowe, Walter P. (Fed)]

Todd's dictionary lookup is elegant and flexible. I'd go with that model.

It supports any number of choices and gracefully gives a default value.

Walter
--
Walter Rowe, Division Chief
Infrastructure Services, OISM
Mobile: 202.355.4123

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[Rowe, Walter P. (Fed)]

If you didn't want a default value and instead wanted to gracefully handle an invalid value you could do something like this:

- name: validate filename lookup value

  assert:

    that:

      - my_var in file_table.keys()

    fail_msg: "File lookup key '{{ my_var }}' is not valid"

    success_msg: "File lookup key '{{ my_var }}' is valid"

- name: do my file-based task

  debug:

    msg: "File name is {{ artifacts[my_var] }}"

The "assert" task will fail the playbook if any of the tests fail (you can list more than one test).

If all the tests pass then the playbook continues to the next task.

Walter
--
Walter Rowe, Division Chief
Infrastructure Services, OISM
Mobile: 202.355.4123

To view this discussion on the web visit https://groups.google.com/d/msgid/ansible-project/9B6013A3-11F0-4D69-B9E6-56BAEC15EA40%40nist.gov.

[Rowe, Walter P. (Fed)]

Silly me .. I should re-read my own code before pressing 'send'!

- name: validate filename lookup value

  assert:

    that:

      - my_var in file_table.keys()

    fail_msg: "File lookup key '{{ my_var }}' is not valid"

    success_msg: "File lookup key '{{ my_var }}' is valid"

- name: do my file-based task

  debug:

    msg: "File name is {{file_table[my_var] }}"

An added footnote .. keys() provides the dictionary keys in the lookup table as a list.

vars:

  file_table:

    oracle: /apps/oracle/some/file/path

    mysql: /apps/mysql/other/path

    postgres: /apps/postgres/different/path

With this dictionary, file_table.keys() returns a list of [ mysql, oracle, postgres ].The assert task tests my_var against that list. If my_var isn't one of those values, the assert task fails. If my_var is one of those values, the debug task prints the corresponding value associated with the key that my_var provides. If my_var is oracle, the debug prints /apps/oracle/some/file/path.

Walter
--
Walter Rowe, Division Chief
Infrastructure Services, OISM
Mobile: 202.355.4123

To view this discussion on the web visit https://groups.google.com/d/msgid/ansible-project/8EAC318D-AF10-40AE-8787-0710A5BD552F%40nist.gov.

[David Nadelson]

Thank you all so much for the responses.