envsub

What is envsub

Envsub is an application which allows you parse templated files using values from env variables or yaml file.

How it works

Envsub use go template engine to parse pointed files with values from:

• env variables
• env variable contains values in JSON format
• YAML file

If template file name contains .tmpl suffix it will be removed after parsing template.

example1.conf.tmpl => example1.conf

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You can also provide --output, -o flag to set output filename

CAVEAT: works only when parsing single file!

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Installation

MacOS Homebrew:

brew install kruc/homebrew-tap/envsub

Linux

 wget -qO- https://github.com/kruc/envsub/releases/latest/download/envsub_linux.tar.gz | tar -xvz -C /usr/local/bin && chmod +x /usr/local/bin/envsub

Usage

1. Use env variables for templates

   In template file use following placeholder {{ .ENV_VARIABLE_NAME }} to replace it with corresponding env variable

   envsub file.tmpl --envs

2. Use extra values

   Prepare json values:

   {
     "rootValue": {
       "firstLevel": {
         "secondLevel": {
           "key1": "value1",
           "key2": [
             "listel1",
             "listel2"
           ]
         }
       }
     }
   }

   Export it as env variable:

   export JSON_ENV_VARIABLE_NAME={"rootValue":{"firstLevel":{"secondLevel":{"key1":"value1","key2":["listel1","listel2"]}}}}

   In template file use following placeholder

   {{.rootValue.firstLevel.secondLevel.key1}}

   to replace it with corresponding json key (value1 in this case)

   envsub file.tmpl -e JSON_ENV_VARIABLE_NAME

3. Use yaml configuration file

   config.yaml:

   example1: value1
   example2: test-user
   example3:
     - val1
     - val2

   file.tmpl

   1. Simple example:
   {{ .example1 }}

   After execute:

   envsub file.tmpl -f config.yaml

   We will get file contains

   1. Simple example:
   value1

4. Use glob patterns to specify template filenames

   envsub file.json tpl/one.yaml wild/*.tmpl --envs

Check examples directory for more use cases