How to execute shell commands?

Executing Shell Commands in Ansible

Ansible is a powerful automation tool that allows you to execute a wide range of tasks on remote hosts, including running shell commands. In this guide, we'll explore the different ways to execute shell commands using Ansible.

Using the command Module

The command module is one of the most commonly used modules in Ansible for executing shell commands. It allows you to run a single command on a remote host without the need for a shell. Here's an example:

- name: Execute a command
  command: echo "Hello, Ansible!"
  register: command_output

In this example, the command module is used to execute the echo "Hello, Ansible!" command on the remote host. The register keyword is used to store the output of the command in the command_output variable, which can be used later in the playbook.

Using the shell Module

The shell module is similar to the command module, but it allows you to execute more complex shell commands that require a shell environment. This can be useful when you need to use shell-specific features, such as pipes, redirects, or environment variables. Here's an example:

- name: Execute a shell command
  shell: |
    echo "Hello, Ansible!"
    echo "This is a multi-line command."
  register: shell_output

In this example, the shell module is used to execute a multi-line command on the remote host. The output of the command is stored in the shell_output variable.

Using the script Module

The script module allows you to execute a local script on the remote host. This can be useful when you have a complex script that you want to run on multiple hosts. Here's an example:

- name: Execute a local script
  script: /path/to/script.sh
  register: script_output

In this example, the script module is used to execute the script.sh script on the remote host. The output of the script is stored in the script_output variable.

Handling Command Errors

By default, Ansible will fail the task if the command or script returns a non-zero exit code. You can use the ignore_errors keyword to ignore the exit code and continue the playbook execution. Here's an example:

- name: Execute a command that might fail
  command: /path/to/command.sh
  ignore_errors: true
  register: command_output

In this example, the ignore_errors keyword is used to continue the playbook execution even if the command.sh script returns a non-zero exit code.

Conclusion

Executing shell commands is a fundamental task in Ansible, and the command, shell, and script modules provide a flexible and powerful way to do so. By understanding these modules and how to handle command errors, you can effectively automate a wide range of tasks on your remote hosts.