reverse filter in ansible

reverse filter in ansible

reverse filter is also available in ansible to reverse the list of values like sort filter.

Lets see the example using reverse filter,

- hosts: localhost
  connection: local
  gather_facts: no

  tasks:

	- name: initialize list of values
  	set_fact:
    	list_values: [2, 4, 1, 9, 3]

	- name: sort defined list
  	set_fact:
    	sorted_desc_list_values: "{{ list_values | reverse }}"

	- name: Print the var
  	debug:
    	var: sorted_desc_list_values

Output:

$ ansible-playbook sort_list.yml
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'

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

TASK [initialize list of values] ********************************************************************************************************************************************
ok: [localhost]

TASK [sort defined list] ****************************************************************************************************************************************************
ok: [localhost]

TASK [Print the var] ********************************************************************************************************************************************************
ok: [localhost] => {
	"sorted_desc_list_values": ""
}

PLAY RECAP ******************************************************************************************************************************************************************
localhost              	: ok=3	changed=0	unreachable=0	failed=0	skipped=0	rescued=0	ignored=0   

when we use reverse filter, getting "" instead of list values.

So we need use list filter to get the list of values in reverse order.

- hosts: localhost
  connection: local
  gather_facts: no

  tasks:

	- name: initialize list of values
  	set_fact:
    	list_values: [2, 4, 1, 9, 3]

	- name: sort defined list
  	set_fact:
    	sorted_desc_list_values: "{{ list_values | reverse | list }}"

	- name: Print the var
  	debug:
    	var: sorted_desc_list_values

Output:

$ ansible-playbook sort_list.yml
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'

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

TASK [initialize list of values] ********************************************************************************************************************************************
ok: [localhost]

TASK [sort defined list] ****************************************************************************************************************************************************
ok: [localhost]

TASK [Print the var] ********************************************************************************************************************************************************
ok: [localhost] => {
	"sorted_desc_list_values": [
    	3,
    	9,
    	1,
    	4,
    	2
	]
}

PLAY RECAP ******************************************************************************************************************************************************************
localhost              	: ok=3	changed=0	unreachable=0	failed=0	skipped=0	rescued=0	ignored=0  

Looks like result of list values are not sorted in descending order correctly.

- hosts: localhost
  connection: local
  gather_facts: no

  tasks:

	- name: initialize list of strings
  	set_fact:
    	list_values: ['text2', 'text1', 'data3','data1', 'info']

	- name: sort defined list
  	set_fact:
    	sorted_list_strings: "{{ list_values | reverse | list }}"

	- name: Print the var
  	debug:
    	var: sorted_list_strings

Output:

$ ansible-playbook sort_list_strings.yml
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'

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

TASK [initialize list of strings] *******************************************************************************************************************************************
ok: [localhost]

TASK [sort defined list] ****************************************************************************************************************************************************
ok: [localhost]

TASK [Print the var] ********************************************************************************************************************************************************
ok: [localhost] => {
	"sorted_list_strings": [
    	"info",
    	"data1",
    	"data3",
    	"text1",
    	"text2"
	]
}

PLAY RECAP ******************************************************************************************************************************************************************
localhost              	: ok=3	changed=0	unreachable=0	failed=0	skipped=0	rescued=0	ignored=0   

Looks like result of list strings are also not sorted in descending order correctly.

« Previous Next »