Accessing Os Environment Variables From Jinja2 Template

Is it possible to access a OS environment variable directly from a Jinja2 template?

Solution 1:

Following @Renier's pointer about custom filters in the comments, I figured out a possible solution.

Define a custom filter:

def env_override(value, key):
  returnos.getenv(key, value)

Install the filter in the environment:

env.filters['env_override'] = env_override

Use the filter as follows:

"test" : {{ "default" | env_override('CUSTOM') }}

Where the appropriate environment variable can be set as:

export CUSTOM=some_value

If the environment variable is set the output will be:

"test" : some_value

Otherwise:

"test" : default

Solution 2:

I believe you can access environment variables like so:

{{ env['XMPP_DOMAIN'] or "localhost" }}

This is from an example in a config file that I saw recently for a Docker deployment of ejabberd.

hosts:
  - "{{ env['XMPP_DOMAIN'] or "localhost" }}"

NOTE: You can see the rest of the example in the run file from the Github repo.

As I understand things the heavy lifting is done by this bit of code:

readonly PYTHON_JINJA2="import os;
import sys;
import jinja2;
sys.stdout.write(
    jinja2.Template
        (sys.stdin.read()
    ).render(env=os.environ))
"""

And this code is what is used to generate a template file:

cat${CONFIGTEMPLATE} \
      | python -c "${PYTHON_JINJA2}" \
      > ${CONFIGFILE}

References

• rroemhild/docker-ejabberd docker image via github

Solution 3:

The answer here works beautifully but you can still get rid of the useless use of cat and compress it to a single statement:

python -c 'import os
import sys
import jinja2
sys.stdout.write(
    jinja2.Template(sys.stdin.read()
).render(env=os.environ))' <$CONFIGTEMPLATE >$CONFIGFILE

P.S.: Stack Overflow does not allow formatted code in comments. Therefore I had to post this as a separate answer instead of commenting on https://stackoverflow.com/a/27984610/1070890.

Solution 4:

In bash let's setup our example

export MYENVVAR=foo

$ nano example.py

from jinja2 import Template
import os
template = Template("Hello {{ env['MYENVVAR'] or 'DefaultVal' }}")
r = template.render(env=os.environ, name='somethingelse')
print(r)

Run template

    $ python3 example.py

https://jinja.palletsprojects.com/en/2.11.x/intro/

Solution 5:

Here is a list of variables that you can access from your template. I was trying to access some app.config variables and I managed to do it by calling config:

{% if current_user.id == config['ADMIN_ID'] %}
 ######## SOME HTML ########
{% endif %}

Flask-Login adds the current_user variable to your templates