envdir (Python port)

This is a Python port of daemontools' tool envdir.

What?

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 maintaing 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.

Why?

Because envdir is small enough that it shouldn't be tied to a bigger software distribution like daemontools that requires a compiler.

Also, this Python port can easily be used on Windows, not only UNIX systems.

Installation

pip install envdir

or:

easy_install envdir

Usage

Command line

Quoting the envdir documentation:

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

Interface:

envdir d child

d is a single argument. child consists of one or more arguments.

envdir sets various environment variables as specified by files in the directory named d. It then runs child.

If d contains a file named s whose first line is t, envdir removes an environment variable named s if one exists, and then adds an environment variable named s with value t. The name s must not contain =. Spaces and tabs at the end of t are removed. Nulls in t are changed to newlines in the environment variable.

If the file s is completely empty (0 bytes long), envdir removes an environment variable named s if one exists, without adding a new variable.

envdir exits 111 if it has trouble reading d, if it runs out of memory for environment variables, or if it cannot run child. Otherwise its exit code is the same as that of child.

Note

This Python port behaves different for multi line environment variables. It will not only read the first line of the file but the whole file. Take care with big files!

Alternatively you can also use the python -m envdir form to call envdir.

Python

To use envdir in a Python file (e.g. Django's manage.py) you can use:

import envdir
envdir.read()

envdir will try to find an envdir directory next to the file you modified.

It's also possible to explicitly pass the path to the envdir:

import os
import envdir

envdir.read('/home/jezdez/mysite/envs/prod')

Shell

envdir also includes an optional CLI tool called envshell which launches a subshell using the given directory. It basically allows you to make a set of environment variable stick to your current shell session if you happen to use envdir a lot outside of simple script use.

For example:

$ envshell ~/mysite/envs/prod/
Launching envshell for /home/jezdez/mysite/envs/prod. Type 'exit' or 'Ctrl+D' to return.
$ python manage.py runserver
..

To leave the subshell, simply use the exit command or press Ctrl+D.

Feedback

Feel free to open tickets at https://github.com/jezdez/envdir/issues. Say thanks at https://www.gittip.com/jezdez/.