How to set Linux environment variables with Ansible

Question

There are multiple ways to do this and from your question it's nor clear what you need.

1. If you need environment variable to be defined PER TASK ONLY, you do this:

- hosts: dev
  tasks:
    - name: Echo my_env_var
      shell: "echo $MY_ENV_VARIABLE"
      environment:
        MY_ENV_VARIABLE: whatever_value

    - name: Echo my_env_var again
      shell: "echo $MY_ENV_VARIABLE"

Note that MY_ENV_VARIABLE is available ONLY for the first task, environment does not set it permanently on your system.

TASK: [Echo my_env_var] ******************************************************* 
changed: [192.168.111.222] => {"changed": true, "cmd": "echo $MY_ENV_VARIABLE", ... "stdout": "whatever_value"}

TASK: [Echo my_env_var again] ************************************************* 
changed: [192.168.111.222] => {"changed": true, "cmd": "echo $MY_ENV_VARIABLE", ... "stdout": ""}

Hopefully soon using environment will also be possible on play level, not only task level as above. There's currently a pull request open for this feature on Ansible's GitHub: https://github.com/ansible/ansible/pull/8651

UPDATE: It's now merged as of Jan 2, 2015.

2. If you want permanent environment variable + system wide / only for certain user

You should look into how you do it in your Linux distribution / shell, there are multiple places for that. For example in Ubuntu you define that in files like for example:

• ~/.profile
• /etc/environment
• /etc/profile.d directory
• ...

You will find Ubuntu docs about it here: https://help.ubuntu.com/community/EnvironmentVariables

After all for setting environment variable in ex. Ubuntu you can just use lineinfile module from Ansible and add desired line to certain file. Consult your OS docs to know where to add it to make it permanent.

I did not have enough reputation to comment and hence am adding a new answer.
Gasek answer is quite correct. Just one thing: if you are updating the .bash_profile file or the /etc/profile, those changes would be reflected only after you do a new login. In case you want to set the env variable and then use it in subsequent tasks in the same playbook, consider adding those environment variables in the .bashrc file.
I guess the reason behind this is the login and the non-login shells.
Ansible, while executing different tasks, reads the parameters from a .bashrc file instead of the .bash_profile or the /etc/profile.

As an example, if I updated my path variable to include the custom binary in the .bash_profile file of the respective user and then did a source of the file. The next subsequent tasks won't recognize my command. However if you update in the .bashrc file, the command would work.

 - name: Adding the path in the bashrc files
   lineinfile: dest=/root/.bashrc line='export PATH=$PATH:path-to-mysql/bin' insertafter='EOF' regexp='export PATH=\$PATH:path-to-mysql/bin' state=present
 
-  - name: Source the bashrc file
   shell: source /root/.bashrc

 - name: Start the mysql client
   shell: mysql -e "show databases";

This would work, but had I done it using profile files the mysql -e "show databases" would have given an error.

- name: Adding the path in the Profile files
   lineinfile: dest=/root/.bash_profile line='export PATH=$PATH:{{install_path}}/{{mysql_folder_name}}/bin' insertafter='EOF' regexp='export PATH=\$PATH:{{install_path}}/{{mysql_folder_name}}/bin' state=present

 - name: Source the bash_profile file
   shell: source /root/.bash_profile

 - name: Start the mysql client
   shell: mysql -e "show databases";

This one won't work, if we have all these tasks in the same playbook.

Here's a quick local task to permanently set key/values on /etc/environment (which is system-wide, all users):

- name: populate /etc/environment
  lineinfile:
    dest: "/etc/environment"
    state: present
    regexp: "^{{ item.key }}="
    line: "{{ item.key }}={{ item.value}}"
  with_items: "{{ os_environment }}"

and the vars for it:

os_environment:
  - key: DJANGO_SETTINGS_MODULE 
    value : websec.prod_settings  
  - key: DJANGO_SUPER_USER 
    value : admin

and, yes, if you ssh out and back in, env shows the new environment variables.

For persistently setting environment variables, you can use one of the existing roles over at Ansible Galaxy. I recommend weareinteractive.environment.

Using ansible-galaxy:

$ ansible-galaxy install weareinteractive.environment

Using requirements.yml:

- src: franklinkim.environment

Then in your playbook:

- hosts: all
  sudo: yes
  roles:
    - role: franklinkim.environment
      environment_config:
        NODE_ENV: staging
        DATABASE_NAME: staging

This is the best option. As said Michal Gasek (first answer), since the pull request was merged (https://github.com/ansible/ansible/pull/8651), we are able to set permanent environment variables easily by play level.

- hosts: all
  roles:
     - php
     - nginx
  environment:
    MY_ENV_VARIABLE: whatever_value