Shell to Ansible Conversion

Overview

Shell scripts execute commands imperatively; Ansible declares desired state. Conversion means rethinking operations as state declarations, not translating commands line-by-line. The goal is idempotency: running twice produces identical results.

When to Use

• Converting existing shell scripts to playbooks
• Migrating manual server setup procedures
• Replacing bash automation with Ansible
• Converting Dockerfile RUN commands

Core Principle

Don't wrap shell commands in Ansible's shell module. Find the module that achieves the same end state declaratively.

# Shell: imperative
mkdir -p /opt/app
chown app:app /opt/app

# Ansible: declarative
- ansible.builtin.file:
    path: /opt/app
    state: directory
    owner: app
    group: app
    mode: '0755'

Conversion Table

Shell Command	Ansible Module	Notes
mkdir -p	ansible.builtin.file	state: directory
cp	ansible.builtin.copy	Static files
cp with variables	ansible.builtin.template	Use .j2 templates
rm -rf	ansible.builtin.file	state: absent
ln -s	ansible.builtin.file	state: link
chmod, chown	Include in file/copy/template	mode, owner, group params
apt-get install	ansible.builtin.apt	update_cache: yes
yum install	ansible.builtin.yum	Or use package for cross-platform
pip install	ansible.builtin.pip	Specify executable if needed
useradd	ansible.builtin.user	Handles home, shell, groups
systemctl start	ansible.builtin.service	state: started
systemctl enable	ansible.builtin.service	enabled: yes
curl -O	ansible.builtin.get_url	Use checksum for verification
tar -xzf	ansible.builtin.unarchive	remote_src: yes if already on target
echo >> file	ansible.builtin.lineinfile	Ensures line exists
cat > file	ansible.builtin.copy	content: parameter

Control Flow Conversion

Conditionals

# Shell
if [ -f /etc/debian_version ]; then
    apt-get install nginx
fi

# Ansible
- ansible.builtin.apt:
    name: nginx
  when: ansible_os_family == "Debian"

Loops

# Shell
for user in alice bob; do
    useradd $user
done

# Ansible
- ansible.builtin.user:
    name: "{{ item }}"
  loop:
    - alice
    - bob

When Shell Module is Necessary

Use command or shell only when no module exists. Always add proper change detection:

- name: Run custom installer
  ansible.builtin.shell: /opt/app/install.sh
  args:
    creates: /opt/app/.installed  # Skip if file exists
  register: install_result
  changed_when: "'Installed' in install_result.stdout"
  failed_when: install_result.rc != 0 and 'already installed' not in install_result.stderr

Variable Extraction

Identify values to parameterize:

• Version numbers → app_version: "1.2.3"
• Paths → app_dir: "/opt/app"
• Usernames → app_user: "appuser"
• Ports → app_port: 8080

Place in defaults/main.yml for easy override.

Conversion Workflow

1. Read entire script, identify major phases
2. Map each command to Ansible module
3. Extract hardcoded values as variables
4. Order tasks for dependencies (dirs before files)
5. Add handlers for service restarts
6. Test with --check --diff
7. Verify idempotency: second run shows no changes