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Ansible select elements that are blanks from a list

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I need a variable with all the blank elements present in the _names list. I tried this :

blanks: "{{ _names|select('search', '') | list }}"

But it dosent seem to work

here is the list:

    "_names":
    [
        "",
        "ABC",
        "",
        ""
    ]

To give some context, I need this variable to count the blank elements and compare it.

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Zeitounator avatar Server
fr flag
Zeitounator

The easy intuitive way is to select the elements equal to an empty string. An other one a bit counter intuitive but more compact to write is to simply reject elements (which by default will reject all non empty values). The following playbook demonstrate both solutions which give the same result.

Note: the reject method here will only work as long as other non-empty elements in the list do not evaluate to false. If you ever false boolean values, they will be retained as well

- hosts: localhost
  gather_facts: false

  vars:
      _names:  ["","ABC","",""]
      blanks_select: "{{ _names | select('==', '') | list }}"
      blanks_reject: "{{ _names | reject | list }}"

  tasks:
    - debug:
        var: "{{ item }}"
      loop:
        - blanks_select
        - blanks_reject

Which gives:

PLAY [localhost] *********************************************************************

TASK [debug] *********************************************************************
ok: [localhost] => (item=blanks_select) => {
    "ansible_loop_var": "item",
    "blanks_select": [
        "",
        "",
        ""
    ],
    "item": "blanks_select"
}
ok: [localhost] => (item=blanks_reject) => {
    "ansible_loop_var": "item",
    "blanks_reject": [
        "",
        "",
        ""
    ],
    "item": "blanks_reject"
}

PLAY RECAP *********************************************************************
localhost : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
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br flag
Vladimir Botka
The *reject* variant works if there is no item in the list that evaluates to *False*. You can convert the items to strings first if you want to, e.g. ``blanks: "{{ _names|map('string')|reject|length }}"``.
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Zeitounator avatar
fr flag
Zeitounator
@VladimirBotka absolutely correct, hence why I gave the two approach in case the current input example evolves. I added that precision in the answer though. Thanks.
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