envdir 0.7

This is a Python port of daemontools’ tool envdir. It works on Windows and other systems which can run Python. It’s well tested and doesn’t need a compiler to be installed.

envdir runs another program with a modified environment according to files in a specified directory.

So for example, imagine a software you want to run on a server but don’t want to leave certain configuration variables embedded in the program’s source code. A common pattern to solve this problem is to use environment variables to separate configuration from code.

envdir allows you to set a series of environment variables at once to simplify maintaining complicated environments, for example in which you have multiple sets of those configuration variables depending on the infrastructure you run your program on (e.g. Windows vs. Linux, Staging vs. Production, Old system vs. New system etc).

Let’s have a look at a typical envdir:

$ tree envs/prod/
envs/prod/
├── DJANGO_SETTINGS_MODULE
├── MYSITE_DEBUG
├── MYSITE_DEPLOY_DIR
├── MYSITE_SECRET_KEY
└── PYTHONSTARTUP

0 directories, 3 files
$ cat envs/prod/DJANGO_SETTINGS_MODULE
mysite.settings
$

As you can see each file has a capitalized name and contains the value of the environment variable to set when running your program. To use it, simply prefix the call to your program with envdir:

$ envdir envs/prod/ python manage.py runserver

That’s it, nothing more and nothing less. The way you structure your envdir is left to you but can easily match your configuration requirements and integrate with other configuration systems. envdirs contain just files after all.

An interesting summary about why it’s good to store configuration values in environment variables can be found on the 12factor site.