Skip to main content

Render jinja2 templates on the command line using shell environment variables

Project description

envtpl
======

_Render jinja2 templates on the command line with shell environment variables_

Installation
------------

pip install envtpl

How-to
------

Say you have a configuration file called whatever.conf that looks like this

foo = 123
bar = "abc"

You can use envtpl to set `foo` and `bar` from the command line by creating a file called whatever.conf.tpl

foo = {{ FOO }}
bar = "{{ BAR }}"

If you run

FOO=123 BAR=abc envtpl < whatever.conf.tpl > whatever.conf

you'll get back the original whatever.conf.

You can also specify default values

foo = {{ FOO | default(123) }}
bar = "{{ BAR | default("abc") }}"

Running

FOO=456 envtpl < whatever.conf.tpl > whatever.conf

will generate

foo = 456
bar = "abc"

This is all standard [Jinja2 syntax](http://jinja.pocoo.org/docs/templates/), so you can do things like

{% if BAZ is defined %}
foo = 123
{% else %}
foo = 456
{% endif %}
bar = "abc"

If an environment variable is missing, envtpl will throw an error

$ echo '{{ FOO }} {{ BAR }}' | FOO=123 envtpl
Error: 'BAR' is undefined

You can change this behaviour to insert empty strings instead by passing the `--allow-missing` flag.

Instead of reading from stdin and writing to stdout, you can pass the input filename as an optional positional argument,
and set the output filename with the `--output-file` (`-o`) argument.

envtpl -o whatever.conf whatever.conf.tpl

As a convenience, if you don't specify an output filename and the input filename ends with `.tpl`, the output filename will be the input filename without the `.tpl` extension, i.e.

envtpl whatever.conf.tpl
# is equivalent to
envtpl -o whatever.conf whatever.conf.tpl

By default, envtpl will **delete** the input template file. You can keep it by passing the `--keep-template` flag.

There's a special `environment(prefix='')` function that you can use as a kind of wildcard variable. If you have `hello.tpl`

hello = {{ FOO }}
{% for key, value in environment('MY_') %}{{ key }} = {{ value }}
{% endfor %}

and compile it using

FOO=world MY_baz=qux MY_foo=bar envtpl hello.tpl

You end up with

hello = world
baz = qux
foo = bar

What's the point?
-----------------

I use this script quite a lot in Docker images. Usually I'll have the CMD execute some file, like /bin/start_container, that sets up the runtime configuration for the container by inserting environment variables into config files before starting the main process. A redis example could look like this

#!/bin/bash
# start_container

envtpl /etc/redis.conf.tpl

redis-server

This is the use case I've optimised for, so that's why envtpl by default will delete the original template file.

Project details


Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distribution

envtpl-0.3.tar.gz (4.1 kB view hashes)

Uploaded Source

Supported by

AWS AWS Cloud computing and Security Sponsor Datadog Datadog Monitoring Fastly Fastly CDN Google Google Download Analytics Microsoft Microsoft PSF Sponsor Pingdom Pingdom Monitoring Sentry Sentry Error logging StatusPage StatusPage Status page