envproc

Easy environment variable preprocessor for configuration files

Why

When building docker containers you usually rely on environment variables as a source for configuration setting and exposing single settings to the user of the ready made containers. Unfortunately not all softwares allow the substitution of environment variables in their config files.

Here envproc comes in handy. Ultra lightweight (apart from needing python 2.7 to run) and easy to use while setting up your containers during build or even on startup time.

Installation

Dependencies

envproc is written in python and tested with python 2.7 so you will nee a configured python interpreter

Get the file

Download envproc from github or clone the entire repository. Only the envproc file is needed. You might need to add the extension .py on windows based systems to the downloaded file.

wget https://raw.githubusercontent.com/behringer24/envproc/master/envproc

Usage

Getting help

Call envproc -h or envproc --help to get the standard commandline help

usage: envproc [-h] [-c CHAR] [-f] [-v] [infile] [outfile]

Preprocess configuration files and fille with environment variables.

positional arguments:
  infile                the input file to preprocess. Or use pipe for stdin
  outfile               the output file to write the parsed result to. Or use
                        pipe for stdout

optional arguments:
  -h, --help            show this help message and exit
  -c CHAR, --char CHAR  character that is used as an variable indicator
  -f, --force           do not stop execution if environment variable is not
                        found
  -v, --version         show program's version number and exit

Adding variables to config files

Before you can parse your configuration files you need to add markers that can be replaced by envproc.

[...]
variable_name = ${env:ENVNAME}
[...]

In this example the placeholder ${env:ENVNAME} will be replaced with the value of the environment variable ENVNAME. If the variable is not set, envproc will stop execution and display an error.

So if you would like to put the value of the common PATH variable into your configuration file you would write:

[...]
app_path_var = ${env:PATH}
[...]

Parsing your config files

envproc can be used in different ways, with the simple use of input- and output file or with streams/pipes stdin and stdout.

Simple filenames for in and out

envproc your_config_template.conf your_config.conf

This will read your_config_template.conf as an input file template and write the processed results to your_config.conf.

Using pipes for in and out

envproc < your_config_template.conf > your_config.conf

Changing the prefix character

As default envproc uses $ as the prefix character in the pattern it searches your configs for, like ${env:PATH}. In some cases you might want to change it to another character. For this you can use the --char or -c option.

envproc -c% infile.conf outfile.conf

This changes the pattern it looks for to %{env:PATH}.