Ansible selectattr Filter: Filter Lists by Attributes (Guide)

By Luca Berton · Published 2022-05-09 · Category: installation

How to use Ansible selectattr filter to filter lists by attributes. Select items matching conditions, combine with map and reject filters with examples.

Ansible selectattr Filter: Filter Lists by Attributes (Guide)

How to Filter A List By Its Attributes in an Ansible Playbook?

selectattr filter in Ansible Playbook?

{{ users|selectattr("is_active") }}
{{ users|selectattr("email", "none") }}

Today we're talking about Ansible selectattr Jinja filter. Filters a sequence of objects by applying a test to the specified attribute of each object, and only selecting the objects with the test succeeding. If no test is specified, the attribute's value will be evaluated as a boolean. The two examples explain how-to for a specific attribute or value using a users list example.

Links

Data manipulation

Jinja selectattr

## Playbook

How to filter a list by its attributes in an Ansible Playbook. I'm going to use the selectattr filter to select only one information from Ansible System Information (Facts). Specifically, I'm going to filter only for enabled features in a network interface (eth1).

code

---
- name: selectattr Playbook
  hosts: all
  gather_facts: true
  tasks:
    - name: all features
      ansible.builtin.debug:
        var: 'ansible_facts.eth1.features'
    - name: filter enabled
      ansible.builtin.debug:
        msg: "{{ (ansible_facts.eth1.features | dict2items | selectattr('value', 'match', 'on') ) }}"

execution

ansible-pilot $ ansible-playbook -i virtualmachines/demo/inventory variables/selectattr.yml
PLAY [selectattr Playbook] ****************************************************************************
TASK [Gathering Facts] ****************************************************************************
ok: [demo.example.com]
TASK [all features] *******************************************************************************
ok: [demo.example.com] => {
    "ansible_facts.eth1.features": {
        "esp_hw_offload": "off [fixed]",
        "esp_tx_csum_hw_offload": "off [fixed]",
        "fcoe_mtu": "off [fixed]",
        "generic_receive_offload": "on",
        "generic_segmentation_offload": "on",
        "highdma": "off [fixed]",
        "hw_tc_offload": "off [fixed]",
        "l2_fwd_offload": "off [fixed]",
        "large_receive_offload": "off [fixed]",
        "loopback": "off [fixed]",
        "netns_local": "off [fixed]",
        "ntuple_filters": "off [fixed]",
        "receive_hashing": "off [fixed]",
        "rx_all": "off",
        "rx_checksumming": "off",
        "rx_fcs": "off",
        "rx_gro_hw": "off [fixed]",
        "rx_gro_list": "off",
        "rx_udp_gro_forwarding": "off",
        "rx_udp_tunnel_port_offload": "off [fixed]",
        "rx_vlan_filter": "on [fixed]",
        "rx_vlan_offload": "on",
        "rx_vlan_stag_filter": "off [fixed]",
        "rx_vlan_stag_hw_parse": "off [fixed]",
        "scatter_gather": "on",
        "tcp_segmentation_offload": "on",
        "tls_hw_record": "off [fixed]",
        "tls_hw_rx_offload": "off [fixed]",
        "tls_hw_tx_offload": "off [fixed]",
        "tx_checksum_fcoe_crc": "off [fixed]",
        "tx_checksum_ip_generic": "on",
        "tx_checksum_ipv4": "off [fixed]",
        "tx_checksum_ipv6": "off [fixed]",
        "tx_checksum_sctp": "off [fixed]",
        "tx_checksumming": "on",
        "tx_esp_segmentation": "off [fixed]",
        "tx_fcoe_segmentation": "off [fixed]",
        "tx_gre_csum_segmentation": "off [fixed]",
        "tx_gre_segmentation": "off [fixed]",
        "tx_gso_list": "off [fixed]",
        "tx_gso_partial": "off [fixed]",
        "tx_gso_robust": "off [fixed]",
        "tx_ipxip4_segmentation": "off [fixed]",
        "tx_ipxip6_segmentation": "off [fixed]",
        "tx_lockless": "off [fixed]",
        "tx_nocache_copy": "off",
        "tx_scatter_gather": "on",
        "tx_scatter_gather_fraglist": "off [fixed]",
        "tx_sctp_segmentation": "off [fixed]",
        "tx_tcp6_segmentation": "off [fixed]",
        "tx_tcp_ecn_segmentation": "off [fixed]",
        "tx_tcp_mangleid_segmentation": "off",
        "tx_tcp_segmentation": "on",
        "tx_tunnel_remcsum_segmentation": "off [fixed]",
        "tx_udp_segmentation": "off [fixed]",
        "tx_udp_tnl_csum_segmentation": "off [fixed]",
        "tx_udp_tnl_segmentation": "off [fixed]",
        "tx_vlan_offload": "on [fixed]",
        "tx_vlan_stag_hw_insert": "off [fixed]",
        "vlan_challenged": "off [fixed]"
    }
}
TASK [filter enabled] *****************************************************************************
ok: [demo.example.com] => {
    "msg": [
        {
            "key": "tx_checksumming",
            "value": "on"
        },
        {
            "key": "tx_checksum_ip_generic",
            "value": "on"
        },
        {
            "key": "scatter_gather",
            "value": "on"
        },
        {
            "key": "tx_scatter_gather",
            "value": "on"
        },
        {
            "key": "tcp_segmentation_offload",
            "value": "on"
        },
        {
            "key": "tx_tcp_segmentation",
            "value": "on"
        },
        {
            "key": "generic_segmentation_offload",
            "value": "on"
        },
        {
            "key": "generic_receive_offload",
            "value": "on"
        },
        {
            "key": "rx_vlan_offload",
            "value": "on"
        },
        {
            "key": "tx_vlan_offload",
            "value": "on [fixed]"
        },
        {
            "key": "rx_vlan_filter",
            "value": "on [fixed]"
        }
    ]
}
PLAY RECAP ****************************************************************************************
demo.example.com           : ok=3    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
ansible-pilot $

code with ❤️ in GitHub

Conclusion

Now you know how to Filter A List By Its Attributes in an Ansible Playbook.

Basic selectattr

- vars:
    users:
      - { name: alice, role: admin, active: true }
      - { name: bob, role: user, active: true }
      - { name: charlie, role: admin, active: false }
  debug:
    msg:
      - "Admins: {{ users | selectattr('role', 'eq', 'admin') | list }}"
      - "Active: {{ users | selectattr('active') | list }}"
      - "Admin names: {{ users | selectattr('role', 'eq', 'admin') | map(attribute='name') | list }}"
      # ['alice', 'charlie']
      # [alice_dict, bob_dict]
      # ['alice', 'charlie']

Test Operators

Operator	Example	Description
`eq` / `equalto`	`selectattr('role', 'eq', 'admin')`	Equals
`ne`	`selectattr('status', 'ne', 'disabled')`	Not equals
`match`	`selectattr('name', 'match', '^web')`	Regex match
`search`	`selectattr('desc', 'search', 'important')`	Regex search
`in`	`selectattr('env', 'in', ['prod', 'staging'])`	In list
`defined`	`selectattr('email', 'defined')`	Attribute exists
`undefined`	`selectattr('phone', 'undefined')`	Attribute missing
`truthy`	`selectattr('active')`	Truthy value

rejectattr (Inverse)

# Exclude inactive users
- debug:
    msg: "{{ users | rejectattr('active', 'eq', false) | list }}"

# Exclude admins
- debug:
    msg: "{{ users | rejectattr('role', 'eq', 'admin') | map(attribute='name') | list }}"

Chain with map

- vars:
    servers:
      - { name: web1, env: prod, ip: 10.0.1.10 }
      - { name: web2, env: prod, ip: 10.0.1.11 }
      - { name: dev1, env: dev, ip: 10.0.2.10 }
  set_fact:
    prod_ips: "{{ servers | selectattr('env', 'eq', 'prod') | map(attribute='ip') | list }}"
    # ['10.0.1.10', '10.0.1.11']

Complex Filtering

# Multiple conditions (chain selectattr)
- set_fact:
    target: "{{ servers | selectattr('env', 'eq', 'prod') | selectattr('role', 'eq', 'web') | list }}"

# Select + sort
- set_fact:
    sorted_prod: "{{ servers | selectattr('env', 'eq', 'prod') | sort(attribute='name') | list }}"

Practical Examples

Find hosts needing updates

- set_fact:
    needs_update: "{{ host_info | selectattr('update_available', 'eq', true) | map(attribute='hostname') | list }}"

Filter packages by state

- set_fact:
    installed: "{{ packages | selectattr('state', 'eq', 'installed') | map(attribute='name') | list }}"
    missing: "{{ packages | rejectattr('state', 'eq', 'installed') | map(attribute='name') | list }}"

Find matching strings in list

# select (not selectattr) for simple lists
- set_fact:
    python_packages: "{{ all_packages | select('match', '^python.*') | list }}"

FAQ

selectattr vs select?

selectattr: Filter list of dicts by attribute
select: Filter simple list by test

Why do I need `| list` at the end?

selectattr returns a generator. Pipe to list to materialize it, especially when using length or accessing by index.

Can I use selectattr in when conditions?

when: (users | selectattr('name', 'eq', 'admin') | list | length) > 0

Basic selectattr

- vars:
    users:
      - { name: alice, role: admin, active: true }
      - { name: bob, role: user, active: true }
      - { name: charlie, role: admin, active: false }
      - { name: dave, role: user, active: false }
  debug:
    msg: "{{ users | selectattr('role', 'eq', 'admin') | list }}"
# [{"name": "alice", ...}, {"name": "charlie", ...}]

Common Tests

# Equal
"{{ users | selectattr('role', 'eq', 'admin') | list }}"

# Not equal
"{{ users | rejectattr('role', 'eq', 'admin') | list }}"

# Truthy (boolean true)
"{{ users | selectattr('active') | list }}"

# Defined
"{{ users | selectattr('email', 'defined') | list }}"

# Contains (string)
"{{ users | selectattr('name', 'contains', 'li') | list }}"

# Match (regex)
"{{ users | selectattr('name', 'match', '^a.*') | list }}"

# Greater than
"{{ servers | selectattr('cpu', 'gt', 4) | list }}"

# In list
"{{ users | selectattr('role', 'in', ['admin', 'superadmin']) | list }}"

selectattr + map

# Get names of active admin users
- debug:
    msg: >-
      {{ users
         | selectattr('role', 'eq', 'admin')
         | selectattr('active')
         | map(attribute='name')
         | list }}
# ["alice"]

rejectattr (Inverse)

# Users who are NOT admins
"{{ users | rejectattr('role', 'eq', 'admin') | list }}"

# Inactive users
"{{ users | rejectattr('active') | list }}"

Practical: Filter Services

- service_facts:

- set_fact:
    running_services: >-
      {{ ansible_facts.services.values()
         | selectattr('state', 'eq', 'running')
         | map(attribute='name')
         | list }}

- debug:
    msg: "Running: {{ running_services | length }} services"

Practical: Filter Inventory

# Hosts with enough memory
- set_fact:
    big_hosts: >-
      {{ groups['all']
         | map('extract', hostvars)
         | selectattr('ansible_memtotal_mb', 'defined')
         | selectattr('ansible_memtotal_mb', 'gt', 4096)
         | map(attribute='inventory_hostname')
         | list }}

Chain Multiple Filters

- vars:
    packages:
      - { name: nginx, version: "1.24", installed: true, critical: true }
      - { name: redis, version: "7.0", installed: true, critical: false }
      - { name: postgres, version: "15", installed: false, critical: true }
  set_fact:
    missing_critical: >-
      {{ packages
         | selectattr('critical')
         | rejectattr('installed')
         | map(attribute='name')
         | list }}
# ["postgres"]

With Loops

- user:
    name: "{{ item.name }}"
    state: present
  loop: "{{ users | selectattr('active') | list }}"
  become: true

FAQ

selectattr vs json_query?

selectattr is simpler — use for single-attribute filtering. json_query (JMESPath) handles complex nested queries. Start with selectattr, use json_query when needed.

How to filter by nested attribute?

selectattr doesn't support dot notation. Flatten the data first or use json_query:

"{{ data | json_query('[?server.status==`running`]') }}"

selectattr returns a generator?

Yes — always add | list at the end to materialize the result.

Category: installation

Watch the video: Ansible selectattr Filter: Filter Lists by Attributes (Guide) — Video Tutorial

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About Luca Berton

Ansible selectattr Filter: Filter Lists by Attributes (Guide)

How to Filter A List By Its Attributes in an Ansible Playbook?

selectattr filter in Ansible Playbook?

Links

code

execution

Conclusion

Basic selectattr

Test Operators

rejectattr (Inverse)

Chain with map

Complex Filtering

Practical Examples

Find hosts needing updates

Filter packages by state

Find matching strings in list

FAQ

selectattr vs select?

Why do I need | list at the end?

Can I use selectattr in when conditions?

Basic selectattr

Common Tests

selectattr + map

rejectattr (Inverse)

Practical: Filter Services

Practical: Filter Inventory

Chain Multiple Filters

With Loops

FAQ

selectattr vs json_query?

How to filter by nested attribute?

selectattr returns a generator?

Related Articles

Why do I need `| list` at the end?