How to a save register variable to a file in Ansible

Ansible is an open-source automation tool that allows you to manage and configure IT infrastructure using a declarative approach. It simplifies the process of automating tasks such as software installations, configuration management, and application deployments across multiple servers or devices.

Saving a register variable

One of the key features of Ansible is its ability to execute tasks on remote hosts and collect data from those tasks. When Ansible runs a task, it can capture the output or result of that task and store it in a variable. This is known as registering a variable. Register variables can hold data like the output of a command, the content of a file, or any other information generated during the playbook execution.

A common use case in Ansible is to save the data stored in a registered variable to a file. Storing the output in a file is useful for documentation, reporting, or simply for future reference.

Using the copy module

The copy module in Ansible is used to copy files from the control node (the machine running Ansible) to remote hosts. You can use this module to save the content of the registered variable to a file on the remote host:

Code explanation

• Line 1: The three dashes (---) indicate the beginning of a YAML file. This Ansible playbook is starting, and it's written in YAML format.

• Line 2: The hosts section specifies the target hosts for the playbook. In this case, it targets the localhost, which means the playbook will run on the local host.

• Line 3: The connection option is set to local, which tells Ansible to execute tasks locally on the control node (the machine where Ansible is running) instead of using SSH to connect to remote hosts.

• Line 4: The tasks section starts here, where you define a list of tasks to be executed.

• Line 5: This task is named Get system uptime. The name parameter provides a description of what the task does for better readability in the output.

• Line 6: Ansible is using the ansible.builtin.shell module to run a shell command on the local host. The command being run is uptime. The uptime is a common Unix/Linux command that displays the system's current uptime. It shows the time since the system was last booted and additional information, such as the current time, the number of logged-in users, and the system load average.

• Line 7: The register parameter is used to store the output of the uptime command in a variable named my_register_var for later use.

• Line 9: This task is named Save system uptime to a file.

• Line 10: The copy module is used to copy files from the control node to the target host. In this case, we are using it to save the system uptime to a file on the local host.

• Line 11: The content parameter specifies the content that should be saved to the file. We are using "{{ my_register_var.stdout }}" to access the output of the uptime command that we previously stored in the my_register_var variable.

• Line 12: The dest parameter specifies the destination path where the file will be created. "{{ lookup('env', 'PWD') }}/uptime.txt" will save the file in the current working directory of the control node (local host) with the name uptime.txt.

Conclusion

The playbook above essentially executes the uptime command locally on the control node (localhost), captures its output, stores in register variable and then saves it to a file named uptime.txt in the current working directory of the control node.