georg-mayer / prenv

Environment variables preprocessor e.g. for docker-compose, docker, python and php.

prenv v0.1

Environment variables preprocessor e.g. for docker-compose, docker, python and php.

Keep your .env file the single source of environment variable defintion!

prenv keeps variable names and values aligned in any kind of project and any kind of programming langugae or configuration file!

prenv solves the "no includes" problem for docker/docker-compose files!

 

Background

DockerFiles and docker-compose files currently don't allow include statements. Bigger projects end up in large numbers of environment variables which all need to be kept in-sync over many different files, which cause massive waste of time when e.g. a newly introduced environment variable was forgotten to be added to a pythong modul.

Prenv resolvs these issues by reading all variables from the local .env file and put them into any type and number of files based on a user-defined template. The whole mechanism is very simple but effective.

This works not only for docker, but also in any programming language that accepts either ## or // as single line comments.

 

Functionality So Far

• reads all variables and their values from the .env file in the local directory

• finds all files in the local directory which have the tag prenv- in the filename

• in any of these files include tags of the form

  • ##PRENV##<template> (e.g. for docker, docker-compose, python); or
  • //PRENV//<template> (e.g. for php)

  and prenv will:

  1. add below the template for each environment variable add a new line, based on the template:

  2. use the same indent as the template used;

  3. will replace any occurence of $VAR in the template with the name of the environment variable;

  4. will replace any occurence of ${VAR} with ${NAME_OF_ENVIRONMET_VAR};

  5. will replace any occurence of $VAL with the value of the environment variable;

  6. will store the changes in a new file (in the same directory) with the same name as the original file, only with the tage prenv- removed from the filename.

 

Example

This is the example .env file:

PROJECTNAME=prenv_is_so_cooool
LOGLEVEL=INFO
BASEURL=127.0.0.1:8001
CONTEXT=./../../..
LOCALBASEDIR=${CONTEXT}/${PROJECTNAME}

The prenv-test.yml file looks like this:

variables:
    ##PRENV##- $VAR=$VAL

project:
    args:
        //PRENV//- $VAR=${VAR}

After running prenv with /usr/bin/python3 prenv.py a new test.yml file is created with the following content:

variables:
    ##PRENV##- $VAR=$VAL
    - PROJECTNAME=prenv_is_so_cooool
    - LOGLEVEL=INFO
    - BASEURL=127.0.0.1:8001
    - CONTEXT=./../../..
    - LOCALBASEDIR=${CONTEXT}/${PROJECTNAME}

project:
    args:
        //PRENV//ENV $VAR=${VAR}
        ENV PROJECTNAME=${PROJECTNAME}
        ENV LOGLEVEL=${LOGLEVEL}
        ENV BASEURL=${BASEURL}
        ENV CONTEXT=${CONTEXT}
        ENV LOCALBASEDIR=${LOCALBASEDIR}

Note that you can re-use the same variable names in e.g. python to read all these variables e.g. into a dictionary. So the prenv-env_var.py file:

import os

def read_envs() -> dict:
    """
    reads all gloable variables into a dict
    """
    env_dict: dict = dict()

    ##PRENV##env_dict['$VAR'] = os.getenv('$VAR')

    return env_dict

after running prenv becomes the env_var.py file:

import os

def read_envs() -> dict:
    """
    reads all gloable variables into a dict
    """
    env_dict: dict = dict()

    ##PRENV##env_dict['$VAR'] = os.getenv('$VAR')
    env_dict['PROJECTNAME'] = os.getenv('PROJECTNAME')
    env_dict['LOGLEVEL'] = os.getenv('LOGLEVEL')
    env_dict['BASEURL'] = os.getenv('BASEURL')
    env_dict['CONTEXT'] = os.getenv('CONTEXT')
    env_dict['LOCALBASEDIR'] = os.getenv('LOCALBASEDIR')

    return env_dict

 

Planned for upcoming versions

• should work also with python - needs testing;
• needs additional comment tags to work also with php;
• include an additional tag which allows to change a specifc variable at a specific location, e.g. name: ###PRENV###$_PROJECTNAME### should result in name: prenv_is_so_cooool in the above example;
• allow different input and output directories;
• regulate verbosity with a -v CLI flag;
• add a restriction tag in variable names, which will then only applied when converting specific files, skipped for others, e.g. the .env variable names could be trailed by something like "SEC_".

 

Limitations

• only works on files in a single directory;
• variables cannot be skipped, i.e. it is not possible to have only a subset of variables put into a file.