Ansible Check if a File Exists

Ansible is an automation tool that helps in configuring and managing servers, networking devices, and other infrastructure. It simplifies process of automation by providing a high-level language to describe infrastructure as code. In this article, we will discuss how to check if a file exists using Ansible.

Why Check if a File Exists in Ansible?

Checking if a file exists is an important task when automating infrastructure. It allows you to determine whether or not a file is present on a system, which can be useful when creating idempotent tasks. Idempotence means that a task can be run multiple times without changing result after first run. This ensures that task only makes changes when necessary, reducing risk of unintended consequences.

Methods For Checking if a File Exists in Ansible

There are several methods for checking if a file exists in Ansible, including using stat module, file module, and shell module. Let's discuss each of these methods in more detail.

Using stat module

The stat module is used to retrieve information about a file on a remote host. It returns a dictionary containing information about file, such as its size, permissions, and modification time. To use stat module to check if a file exists, you can use following task −

- name: Check if file exists using stat module
  stat:
    path: /path/to/file
  register: file_status

- name: Print file status
  debug:
    var: file_status.stat.exists

In this example, stat module is used to retrieve information about file at specified path. register keyword is used to save result of task to a variable called file_status. debug module is then used to print value of exists key in file_status.stat dictionary. If file exists, value of exists will be true, and if it does not exist, value will be false.

Using File Module

The file module is used to manage files and directories on a remote host. It can be used to create, delete, or modify files, as well as to set file permissions and ownership. To check if a file exists using file module, you can use following task −

- name: Check if file exists using file module
  file:
    path: /path/to/file
    state: file
  register: file_status

- name: Print file status
  debug:
    var: file_status.stat.exists

In this example, file module is used to ensure that file at specified path exists and is a regular file. register keyword is used to save result of task to a variable called file_status. debug module is then used to print value of exists key in file_status.stat dictionary. If file exists, value of exists will be true, and if it does not exist, value will be false.

Using Shell Module

The shell module is used to execute commands on a remote host using shell. It can be used to perform any task that can be done in a shell, including checking if a file exists. To check if a file exists using shell module, you can use following task −

- name: Check if file exists using shell module
  shell: test -f /path/to/file
  register: file_status
  ignore_errors: true

- name: Print file status
  debug:
    var: file_status.rc

In this example, shell module is used to execute test -f command, which tests if specified path exists and is a regular file. register keyword is used to save result of task to a variable called file_status. ignore_errors keyword is used to prevent task from failing if file does not exist. debug module is then used to print return code of command. If file exists, return code will be 0, and if it does not exist, return code will be 1.

Choosing Best Method

Each method for checking if a file exists in Ansible has its advantages and disadvantages. stat module is most reliable method, as it retrieves information directly from file system. However, it may be slower than other methods, as it requires a network round trip to remote host. file module is a good compromise between reliability and speed, as it uses same logic as stat module but is optimized for managing files. shell module is fastest method, as it uses a simple shell command to check if file exists. However, it may not work on all systems, as it depends on availability of test command.

Additional Tips and Tricks

Here are some additional tips and tricks for checking if a file exists in Ansible −

Use Conditional Statements

You can use conditional statements to execute tasks only if a file exists or does not exist. For example −

- name: Execute task only if file exists
  stat:
    path: /path/to/file
  register: file_status
  when: file_status.stat.exists

- name: Execute task only if file does not exist
  stat:
    path: /path/to/file
  register: file_status
  when: not file_status.stat.exists

In these examples, when keyword is used to execute task only if file exists or does not exist, depending on condition.

Use failed_when Keyword

You can use failed_when keyword to control behavior of a task if file does not exist. For example −

- name: Execute task and fail if file does not exist
  stat:
    path: /path/to/file
  register: file_status
  failed_when: not file_status.stat.exists

In this example, failed_when keyword is used to fail task if file does not exist.

Use Variables

You can use variables to make your playbooks more dynamic. For example −

- name: Check if file exists using variable
  stat:
    path: "{{ file_path }}"
  register: file_status

In this example, file_path variable is used to specify path to file. You can define this variable in your inventory or using command line arguments.

Use Loops

You can use loops to check multiple files at once. For example −

- name: Check if multiple files exist using loop
  stat:
    path: "{{ item }}"
  register: file_status
  loop:
    - /path/to/file1
    - /path/to/file2
    - /path/to/file3

In this example, loop keyword is used to iterate over a list of file paths. item variable is used to specify current file path in each iteration.

Use any_errors_fatal Keyword

You can use any_errors_fatal keyword to fail entire playbook if any file does not exist. For example −

- name: Check if multiple files exist and fail playbook if any file does not exist
  stat:
    path: "{{ item }}"
  register: file_status
  loop:
    - /path/to/file1
    - /path/to/file2
    - /path/to/file3
  any_errors_fatal: true

In this example, any_errors_fatal keyword is used to fail entire playbook if any file does not exist.

By using these tips and tricks, you can make your playbooks more robust and flexible when checking if a file exists in Ansible.

Conclusion

Checking if a file exists is an important task when automating infrastructure using Ansible. It allows you to create idempotent tasks that only make changes when necessary, reducing risk of unintended consequences. There are several methods for checking if a file exists in Ansible, including using stat module, file module, and shell module. Each method has its advantages and disadvantages, and best method depends on specific use case.