Ansible Truth Table

• Rules
• Truth Table
• Test Playbook

Everything in an Ansible playbook is first YAML, then it's Ansible.

Rules

Values specified in YAML go through the following stages:

1. Parse as YAML as specified by YAML syntax;

   • true, True, TRUE, false, False, FALSE -> boolean
   • tRUE, TrUe, fALSE, FaLsE, … -> string

   • "true", "True", "TRUE", "false", "False", "FALSE", … -> string

   • yes, Yes, YES, no, No, NO -> boolean
   • yES, YeS, nO, … -> string

   • "yes", "Yes", "YES", "no", "No", "NO", … -> string

   • on, On, ON, off, Off, OFF -> boolean
   • oN, oFF, oFf, … -> string

   • "on", "On", "ON", "off", "Off", "OFF", … -> string

   • y, Y, n, N -> string

   • "y", "Y", "n", "N" -> string

   • 0, 1 -> number
   • "0", "1" -> string

2. Parse as Ansible syntax.

   This step converts the following string (case insensitively) to boolean:

   • "true"
   • "false"
   • "yes"
   • "no"

3. 1. If variable goes through bool filter, it additionaly converts the following string (case-insensitively) and numbers to boolean:

      • "on" -> boolean True

      • "off" -> boolean False

      • "1" -> boolean True
      • "0" -> boolean False

      • Any other string -> boolean False

      • 1 -> boolean True
      • 0 -> boolean False
      • Any other number -> boolean False

   2. If variable is prefixed with not operator:

      • all non empty string is treated as True, with not operator, the result becomes False;

      • 0 treated as False, 1 and any other number as True; with not operator, they become True and False respectively.

Truth Table

The following is a truth table for the rules above:

Test Playbook

Test it yourself with the following ansible playbook:

- hosts: localhost
  gather_facts: no
  tasks:
  - set_fact:
      t0: 1
      t1: "1"
      t2: true
      t3: "true"
      t4: yes
      t5: "yes"
      t6: on
      t7: "on"
      t8: y
      t9: "y"

      f0: 0
      f1: "0"
      f2: false
      f3: "false"
      f4: no
      f5: "no"
      f6: off
      f7: "off"
      f8: n
      f9: "n"

  - name: "var"
    debug: var=item
    loop: "{{ [t0, t1, t2, t3, t4, t5, t6, t7, t8, t9, f0, f1, f2, f3, f4, f5, f6, f7, f8, f9] }}"

  - name: "{{ var|bool }}"
    debug: msg={{ item|bool }}
    loop: "{{ [t0, t1, t2, t3, t4, t5, t6, t7, t8, t9, f0, f1, f2, f3, f4, f5, f6, f7, f8, f9] }}"

  - name: "{{ not var }}"
    debug: msg={{ not item }}
    loop: "{{ [t0, t1, t2, t3, t4, t5, t6, t7, t8, t9, f0, f1, f2, f3, f4, f5, f6, f7, f8, f9] }}"