Loops — Ansible Documentation

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# Loops

Sometimes you want to repeat a task multiple times. In computer programming, this is called a loop. Common Ansible loops include changing ownership on several files and/or directories with the file module, creating multiple users with the user module, and repeating a polling step until a certain result is reached. Ansible offers two keywords for creating loops: `loop` and `with_<lookup>`.

Note

- We added `loop` in Ansible 2.5. It is not yet a full replacement for `with_<lookup>`, but we recommend it for most use cases.
- We have not deprecated the use of `with_<lookup>` - that syntax will still be valid for the foreseeable future.
- We are looking to improve `loop` syntax - watch this page and the changelog for updates.

- Comparing `loop` and `with_*`
- Standard loops
  - Iterating over a simple list
  - Iterating over a list of hashes
  - Iterating over a dictionary
- Registering variables with a loop
- Complex loops
  - Iterating over nested lists
  - Retrying a task until a condition is met
  - Looping over inventory
- Ensuring list input for `loop`: `query` vs. `lookup`
- Adding controls to loops
  - Limiting loop output with `label`
  - Pausing within a loop
  - Tracking progress through a loop with `index_var`
  - Defining inner and outer variable names with `loop_var`
  - Extended loop variables
  - Accessing the name of your loop_var
- Migrating from with_X to loop
  - with_list
  - with_items
  - with_indexed_items
  - with_flattened
  - with_together
  - with_dict
  - with_sequence
  - with_subelements
  - with_nested/with_cartesian
  - with_random_choice

## Comparing `loop` and `with_*`

- The `with_<lookup>` keywords rely on Lookup Plugins - even `items` is a lookup.
- The `loop` keyword is equivalent to `with_list`, and is the best choice for simple loops.
- The `loop` keyword will not accept a string as input, see Ensuring list input for loop: query vs. lookup.
- Generally speaking, any use of `with_*` covered in Migrating from with_X to loop can be updated to use `loop`.
- Be careful when changing `with_items` to `loop`, as `with_items` performed implicit single-level flattening. You may need to use `flatten(1)` with `loop` to match the exact outcome. For example, to get the same output as:

    with_items:
      - 1
      - [2,3]
      - 4

you would need:

    loop: "{{ [1, [2,3] ,4] | flatten(1) }}"

- Any `with_*` statement that requires using `lookup` within a loop should not be converted to use the `loop` keyword. For example, instead of doing:

    loop: "{{ lookup('fileglob', '*.txt', wantlist=True) }}"

it’s cleaner to keep:

    with_fileglob: '*.txt'

## Standard loops

### Iterating over a simple list

Repeated tasks can be written as standard loops over a simple list of strings. You can define the list directly in the task:

    - name: add several users
      user:
        name: "{{ item }}"
        state: present
        groups: "wheel"
      loop:
         - testuser1
         - testuser2

You can define the list in a variables file, or in the ‘vars’ section of your play, then refer to the name of the list in the task:

    loop: "{{ somelist }}"

Either of these examples would be the equivalent of:

    - name: add user testuser1
      user:
        name: "testuser1"
        state: present
        groups: "wheel"

    - name: add user testuser2
      user:
        name: "testuser2"
        state: present
        groups: "wheel"

You can pass a list directly to a parameter for some plugins. Most of the packaging modules, like yum_module and apt_module, have this capability. When available, passing the list to a parameter is better than looping over the task. For example:

    - name: optimal yum
      yum:
        name: "{{  list_of_packages  }}"
        state: present

    - name: non-optimal yum, slower and may cause issues with interdependencies
      yum:
        name: "{{  item  }}"
        state: present
      loop: "{{  list_of_packages  }}"

Check the module documentation to see if you can pass a list to any particular module’s parameter(s).

### Iterating over a list of hashes

If you have a list of hashes, you can reference subkeys in a loop. For example:

    - name: add several users
      user:
        name: "{{ item.name }}"
        state: present
        groups: "{{ item.groups }}"
      loop:
        - { name: 'testuser1', groups: 'wheel' }
        - { name: 'testuser2', groups: 'root' }

When combining Conditionals with a loop, the `when:` statement is processed separately for each item. See The When Statement for examples.

### Iterating over a dictionary

To loop over a dict, use the `dict2items` Dict Filter:

    - name: create a tag dictionary of non-empty tags
      set_fact:
        tags_dict: "{{ (tags_dict|default({}))|combine({item.key: item.value}) }}"
      loop: "{{ tags|dict2items }}"
      vars:
        tags:
          Environment: dev
          Application: payment
          Another: "{{ doesnotexist|default() }}"
      when: item.value != ""

Here, we don’t want to set empty tags, so we create a dictionary containing only non-empty tags.

## Registering variables with a loop

You can register the output of a loop as a variable. For example:

    - shell: "echo {{ item }}"
      loop:
        - "one"
        - "two"
      register: echo

When you use `register` with a loop, the data structure placed in the variable will contain a `results` attribute that is a list of all responses from the module. This differs from the data structure returned when using `register` without a loop:

    {
        "changed": true,
        "msg": "All items completed",
        "results": [
            {
                "changed": true,
                "cmd": "echo \"one\" ",
                "delta": "0:00:00.003110",
                "end": "2013-12-19 12:00:05.187153",
                "invocation": {
                    "module_args": "echo \"one\"",
                    "module_name": "shell"
                },
                "item": "one",
                "rc": 0,
                "start": "2013-12-19 12:00:05.184043",
                "stderr": "",
                "stdout": "one"
            },
            {
                "changed": true,
                "cmd": "echo \"two\" ",
                "delta": "0:00:00.002920",
                "end": "2013-12-19 12:00:05.245502",
                "invocation": {
                    "module_args": "echo \"two\"",
                    "module_name": "shell"
                },
                "item": "two",
                "rc": 0,
                "start": "2013-12-19 12:00:05.242582",
                "stderr": "",
                "stdout": "two"
            }
        ]
    }

Subsequent loops over the registered variable to inspect the results may look like:

    - name: Fail if return code is not 0
      fail:
        msg: "The command ({{ item.cmd }}) did not have a 0 return code"
      when: item.rc != 0
      loop: "{{ echo.results }}"

During iteration, the result of the current item will be placed in the variable:

    - shell: echo "{{ item }}"
      loop:
        - one
        - two
      register: echo
      changed_when: echo.stdout != "one"

## Complex loops

### Iterating over nested lists

You can use Jinja2 expressions to iterate over complex lists. For example, a loop can combine nested lists:

    - name: give users access to multiple databases
      mysql_user:
        name: "{{ item[0] }}"
        priv: "{{ item[1] }}.*:ALL"
        append_privs: yes
        password: "foo"
      loop: "{{ ['alice', 'bob'] |product(['clientdb', 'employeedb', 'providerdb'])|list }}"

### Retrying a task until a condition is met

New in version 1.4.

You can use the `until` keyword to retry a task until a certain condition is met. Here’s an example:

    - shell: /usr/bin/foo
      register: result
      until: result.stdout.find("all systems go") != -1
      retries: 5
      delay: 10

This task runs up to 5 times with a delay of 10 seconds between each attempt. If the result of any attempt has “all systems go” in its stdout, the task succeeds. The default value for “retries” is 3 and “delay” is 5.

To see the results of individual retries, run the play with `-vv`.

When you run a task with `until` and register the result as a variable, the registered variable will include a key called “attempts”, which records the number of the retries for the task.

Note

You must set the `until` parameter if you want a task to retry. If `until` is not defined, the value for the `retries` parameter is forced to 1.

### Looping over inventory

To loop over your inventory, or just a subset of it, you can use a regular `loop` with the `ansible_play_batch` or `groups` variables:

    # show all the hosts in the inventory
    - debug:
        msg: "{{ item }}"
      loop: "{{ groups['all'] }}"

    # show all the hosts in the current play
    - debug:
        msg: "{{ item }}"
      loop: "{{ ansible_play_batch }}"

There is also a specific lookup plugin `inventory_hostnames` that can be used like this:

    # show all the hosts in the inventory
    - debug:
        msg: "{{ item }}"
      loop: "{{ query('inventory_hostnames', 'all') }}"

    # show all the hosts matching the pattern, ie all but the group www
    - debug:
        msg: "{{ item }}"
      loop: "{{ query('inventory_hostnames', 'all:!www') }}"

More information on the patterns can be found on Working with Patterns

## Ensuring list input for `loop`: `query` vs. `lookup`

The `loop` keyword requires a list as input, but the `lookup` keyword returns a string of comma-separated values by default. Ansible 2.5 introduced a new Jinja2 function named Invoking lookup plugins with query that always returns a list, offering a simpler interface and more predictable output from lookup plugins when using the `loop` keyword.

You can force `lookup` to return a list to `loop` by using `wantlist=True`, or you can use `query` instead.

These examples do the same thing:

    loop: "{{ query('inventory_hostnames', 'all') }}"

    loop: "{{ lookup('inventory_hostnames', 'all', wantlist=True) }}"

## Adding controls to loops

New in version 2.1.

The `loop_control` keyword lets you manage your loops in useful ways.

### Limiting loop output with `label`

New in version 2.2.

When looping over complex data structures, the console output of your task can be enormous. To limit the displayed output, use the `label` directive with `loop_control`:

    - name: create servers
      digital_ocean:
        name: "{{ item.name }}"
        state: present
      loop:
        - name: server1
          disks: 3gb
          ram: 15Gb
          network:
            nic01: 100Gb
            nic02: 10Gb
            ...
      loop_control:
        label: "{{ item.name }}"

The output of this task will display just the `name` field for each `item` instead of the entire contents of the multi-line `{{ item }}` variable.

### Pausing within a loop

New in version 2.2.

To control the time (in seconds) between the execution of each item in a task loop, use the `pause` directive with `loop_control`:

    # main.yml
    - name: create servers, pause 3s before creating next
      digital_ocean:
        name: "{{ item }}"
        state: present
      loop:
        - server1
        - server2
      loop_control:
        pause: 3

### Tracking progress through a loop with `index_var`

New in version 2.5.

To keep track of where you are in a loop, use the `index_var` directive with `loop_control`. This directive specifies a variable name to contain the current loop index:

    - name: count our fruit
      debug:
        msg: "{{ item }} with index {{ my_idx }}"
      loop:
        - apple
        - banana
        - pear
      loop_control:
        index_var: my_idx

### Defining inner and outer variable names with `loop_var`

New in version 2.1.

You can nest two looping tasks using `include_tasks`. However, by default Ansible sets the loop variable `item` for each loop. This means the inner, nested loop will overwrite the value of `item` from the outer loop. You can specify the name of the variable for each loop using `loop_var` with `loop_control`:

    # main.yml
    - include_tasks: inner.yml
      loop:
        - 1
        - 2
        - 3
      loop_control:
        loop_var: outer_item

    # inner.yml
    - debug:
        msg: "outer item={{ outer_item }} inner item={{ item }}"
      loop:
        - a
        - b
        - c

Note

If Ansible detects that the current loop is using a variable which has already been defined, it will raise an error to fail the task.

### Extended loop variables

New in version 2.8.

As of Ansible 2.8 you can get extended loop information using the `extended` option to loop control. This option will expose the following information.

Variable | Description
`ansible_loop.allitems` | The list of all items in the loop
`ansible_loop.index` | The current iteration of the loop. (1 indexed)
`ansible_loop.index0` | The current iteration of the loop. (0 indexed)
`ansible_loop.revindex` | The number of iterations from the end of the loop (1 indexed)
`ansible_loop.revindex0` | The number of iterations from the end of the loop (0 indexed)
`ansible_loop.first` | `True` if first iteration
`ansible_loop.last` | `True` if last iteration
`ansible_loop.length` | The number of items in the loop
`ansible_loop.previtem` | The item from the previous iteration of the loop. Undefined during the first iteration.
`ansible_loop.nextitem` | The item from the following iteration of the loop. Undefined during the last iteration.

    loop_control:
      extended: yes

### Accessing the name of your loop_var

New in version 2.8.

As of Ansible 2.8 you can get the name of the value provided to `loop_control.loop_var` using the `ansible_loop_var` variable

For role authors, writing roles that allow loops, instead of dictating the required `loop_var` value, you can gather the value via:

    "{{ lookup('vars', ansible_loop_var) }}"

## Migrating from with_X to loop

With the release of Ansible 2.5, the recommended way to perform loops is the use the new `loop` keyword instead of `with_X` style loops.

In many cases, `loop` syntax is better expressed using filters instead of more complex use of `query` or `lookup`.

The following examples will show how to convert many common `with_` style loops to `loop` and filters.

### with_list

`with_list` is directly replaced by `loop`.

    - name: with_list
      debug:
        msg: "{{ item }}"
      with_list:
        - one
        - two

    - name: with_list -> loop
      debug:
        msg: "{{ item }}"
      loop:
        - one
        - two

### with_items

`with_items` is replaced by `loop` and the `flatten` filter.

    - name: with_items
      debug:
        msg: "{{ item }}"
      with_items: "{{ items }}"

    - name: with_items -> loop
      debug:
        msg: "{{ item }}"
      loop: "{{ items|flatten(levels=1) }}"

### with_indexed_items

`with_indexed_items` is replaced by `loop`, the `flatten` filter and `loop_control.index_var`.

    - name: with_indexed_items
      debug:
        msg: "{{ item.0 }} - {{ item.1 }}"
      with_indexed_items: "{{ items }}"

    - name: with_indexed_items -> loop
      debug:
        msg: "{{ index }} - {{ item }}"
      loop: "{{ items|flatten(levels=1) }}"
      loop_control:
        index_var: index

### with_flattened

`with_flattened` is replaced by `loop` and the `flatten` filter.

    - name: with_flattened
      debug:
        msg: "{{ item }}"
      with_flattened: "{{ items }}"

    - name: with_flattened -> loop
      debug:
        msg: "{{ item }}"
      loop: "{{ items|flatten }}"

### with_together

`with_together` is replaced by `loop` and the `zip` filter.

    - name: with_together
      debug:
        msg: "{{ item.0 }} - {{ item.1 }}"
      with_together:
        - "{{ list_one }}"
        - "{{ list_two }}"

    - name: with_together -> loop
      debug:
        msg: "{{ item.0 }} - {{ item.1 }}"
      loop: "{{ list_one|zip(list_two)|list }}"

### with_dict

`with_dict` can be substituted by `loop` and either the `dictsort` or `dict2items` filters.

    - name: with_dict
      debug:
        msg: "{{ item.key }} - {{ item.value }}"
      with_dict: "{{ dictionary }}"

    - name: with_dict -> loop (option 1)
      debug:
        msg: "{{ item.key }} - {{ item.value }}"
      loop: "{{ dictionary|dict2items }}"

    - name: with_dict -> loop (option 2)
      debug:
        msg: "{{ item.0 }} - {{ item.1 }}"
      loop: "{{ dictionary|dictsort }}"

### with_sequence

`with_sequence` is replaced by `loop` and the `range` function, and potentially the `format` filter.

    - name: with_sequence
      debug:
        msg: "{{ item }}"
      with_sequence: start=0 end=4 stride=2 format=testuser%02x

    - name: with_sequence -> loop
      debug:
        msg: "{{ 'testuser%02x' | format(item) }}"
      # range is exclusive of the end point
      loop: "{{ range(0, 4 + 1, 2)|list }}"

### with_subelements

`with_subelements` is replaced by `loop` and the `subelements` filter.

    - name: with_subelements
      debug:
        msg: "{{ item.0.name }} - {{ item.1 }}"
      with_subelements:
        - "{{ users }}"
        - mysql.hosts

    - name: with_subelements -> loop
      debug:
        msg: "{{ item.0.name }} - {{ item.1 }}"
      loop: "{{ users|subelements('mysql.hosts') }}"

### with_nested/with_cartesian

`with_nested` and `with_cartesian` are replaced by loop and the `product` filter.

    - name: with_nested
      debug:
        msg: "{{ item.0 }} - {{ item.1 }}"
      with_nested:
        - "{{ list_one }}"
        - "{{ list_two }}"

    - name: with_nested -> loop
      debug:
        msg: "{{ item.0 }} - {{ item.1 }}"
      loop: "{{ list_one|product(list_two)|list }}"

### with_random_choice

`with_random_choice` is replaced by just use of the `random` filter, without need of `loop`.

    - name: with_random_choice
      debug:
        msg: "{{ item }}"
      with_random_choice: "{{ my_list }}"

    - name: with_random_choice -> loop (No loop is needed here)
      debug:
        msg: "{{ my_list|random }}"
      tags: random

See also

About Playbooks
  An introduction to playbooks
Roles
  Playbook organization by roles
Best Practices
  Best practices in playbooks
Conditionals
  Conditional statements in playbooks
Using Variables
  All about variables
User Mailing List
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