Ansible select & selectattr Filters: Filter Lists by Condition (Guide)

By Luca Berton · Published 2024-01-01 · Category: troubleshooting

How to filter lists in Ansible with select, selectattr, and map filters. Filter by attribute, test conditions, chain filters.

🎯 Filtering Data in Ansible: `selectattr` and `map(attribute)`

selectattr in Ansible is a Jinja2 filter that filters a list of dictionaries down to only the items whose attribute matches a test, such as equalto, defined, match, or search.

When working with lists of dictionaries in Ansible, filtering and extracting specific values is a common requirement. Jinja2 provides two powerful filters to accomplish this:

selectattr → Filters the list based on a condition.
map(attribute) → Extracts a specific field from the filtered result.

In this article, you'll learn:

✅ How to filter lists of dictionaries in Ansible using selectattr
✅ How to extract specific values using map(attribute)
✅ How to handle missing values safely using default()

---

📌 Understanding `selectattr` and `map(attribute)`

Before jumping into Ansible playbooks, let's break down these Jinja2 filters.

✅ `selectattr('name', 'equalto', search_name')`

Filters a list of dictionaries to select only the ones where name == search_name.

✅ `map(attribute='folder')`

Extracts the folder field from the filtered result.

✅ Example Syntax

{{ variable | selectattr('name', 'equalto', search_name) | map(attribute='folder') | list }}

selectattr filters the list where name equals search_name.
map(attribute='folder') extracts only the folder values.
list ensures the result is returned as a list.

---

🔥 Example Use Case

Scenario

You have a list of users and their home directories (folder). You want to search for a specific user and get their folder path.

Example Data

variable:
  - name: alice
    folder: /home/alice
  - name: bob
    folder: /home/bob
  - name: charlie
    folder: /home/charlie

Using `selectattr` and `map(attribute)` in Ansible

- name: Search for a name and get its folder
  hosts: localhost
  gather_facts: no
  vars:
    variable:
      - name: alice
        folder: /home/alice
      - name: bob
        folder: /home/bob
      - name: charlie
        folder: /home/charlie
    search_name: alice
  tasks:
    - name: Get folder for a specific user
      debug:
        msg: "{{ variable | selectattr('name', 'equalto', search_name) | map(attribute='folder') | list }}"

---

🎯 Expected Output

selectattr returns a filtered list containing only the dictionaries that match the condition; piping that result through map(attribute='folder') reduces it to a plain YAML list of the matched folder values, as shown below. When the Ansible playbook executes the selectattr filter successfully, it extracts the matching folder path and displays it in the task result. Here's what you'll see for each scenario:

When `search_name: alice`:

TASK [Get folder for a specific user] *********************************************
ok: [localhost] => {
    "msg": [
        "/home/alice"
    ]
}

When `search_name: bob`:

TASK [Get folder for a specific user] *********************************************
ok: [localhost] => {
    "msg": [
        "/home/bob"
    ]
}

---

🔹 Getting a Single Value Instead of a List

By default, the output is a list with one value. If you need only the string value, add .0:

- name: Get a single folder for a user
  debug:
    msg: "{{ (variable | selectattr('name', 'equalto', search_name) | map(attribute='folder') | list).0 }}"

📌 Expected Output

TASK [Get a single folder for a user] *********************************************
ok: [localhost] => {
    "msg": "/home/alice"
}

---

🚨 Handling Missing Values Gracefully

If the search_name does not exist in the list, you may encounter an error. To prevent this, use default():

- name: Get folder safely
  debug:
    msg: "{{ (variable | selectattr('name', 'equalto', search_name) | map(attribute='folder') | list | default(['/not-found'])).0 }}"

📌 Expected Output When `search_name` is Missing

TASK [Get folder safely] *********************************************
ok: [localhost] => {
    "msg": "/not-found"
}

---

✅ Summary Table

Method	Output
	list	`["/home/alice"]`
`.0`	`"/home/alice"`
`default(['/not-found'])`	`"/not-found"` if no match

---

🚀 Why Use This Approach?

✔ Filters data dynamically ✔ Extracts only necessary values ✔ Handles missing values safely ✔ Works efficiently with lists of dictionaries

These Jinja2 filters are invaluable when working with structured data in Ansible playbooks!

Category: troubleshooting

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About Luca Berton

Ansible select & selectattr Filters: Filter Lists by Condition (Guide)

🎯 Filtering Data in Ansible: selectattr and map(attribute)

📌 Understanding selectattr and map(attribute)

✅ selectattr('name', 'equalto', search_name')

✅ map(attribute='folder')