How to run a task when variable is undefined in ansible

Question

I am looking for a way to perform a task when ansible variable is not registers  undefined e g   -- name  some task    command   sed -n  5p     app dirs includes   BUILD info    awk   print   2      when     deployed revision  AND    deployed revision stdout      register  deployed revision

User · Answer

Strictly stated you must check all of the following: defined, not empty AND not None.

For "normal" variables it makes a difference if defined and set or not set. See foo and bar in the example below. Both are defined but only foo is set.

On the other side registered variables are set to the result of the running command and vary from module to module. They are mostly json structures. You probably must check the subelement you're interested in. See xyz and xyz.msg in the example below:

cat > test.yml <<EOF
- hosts: 127.0.0.1

  vars:
    foo: ""          # foo is defined and foo == '' and foo != None
    bar:             # bar is defined and bar != '' and bar == None

  tasks:

  - debug:
      msg : ""
    register: xyz    # xyz is defined and xyz != '' and xyz != None
                     # xyz.msg is defined and xyz.msg == '' and xyz.msg != None

  - debug:
      msg: "foo is defined and foo == '' and foo != None"
    when: foo is defined and foo == '' and foo != None

  - debug:
      msg: "bar is defined and bar != '' and bar == None"
    when: bar is defined and bar != '' and bar == None

  - debug:
      msg: "xyz is defined and xyz != '' and xyz != None"
    when: xyz is defined and xyz != '' and xyz != None
  - debug:
      msg: "{{ xyz }}"

  - debug:
      msg: "xyz.msg is defined and xyz.msg == '' and xyz.msg != None"
    when: xyz.msg is defined and xyz.msg == '' and xyz.msg != None
  - debug:
      msg: "{{ xyz.msg }}"
EOF
ansible-playbook -v test.yml

User · Answer

From the ansible docs  If a required variable has not been set  you can skip or fail using Jinja2   s defined test  For example   tasks   - shell  echo  I ve got     foo     and am not afraid to use it     when  foo is defined  - fail  msg  Bailing out  this play requires  bar     when  bar is not defined   So in your case  when  deployed revision is not defined should work

User · Answer

As per latest Ansible Version 2 5  to check if a variable is defined and depending upon this if you want to run any task  use undefined keyword   tasks      - shell  echo  I ve got     foo     and am not afraid to use it         when  foo is defined      - fail  msg  Bailing out  this play requires  bar         when  bar is undefined   Ansible Documentation

[ansible] How to run a task when variable is undefined in ansible?

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