optimist-config-file  

Extends optimist npm module with support for JSON/YAML config file and Docker's inspired environment variables handling.

How to use it

> Refer to examples/example.js

``
npm install --save optimist-config-file
`

`js
const program = require('optimist-config-file');

program
.usage('...')
// ...
.describe('config', 'uses JSON or YAML-formatted config file to set parameters').string('config');

// handle --config option for passing YAML/JSON config files
program.setConfigFile('config');

// allow env variables to be passed
program.setReplacementVars(process.env);

// parse options
const options = program.parse(process.argv);

console.log(options);
`

$3

YAML config file:

`yaml
banner: Hello, ${USERNAME}! Greetings from ${HOSTNAME:-The Unknown Machine}.
`

Invocations with environment variables and options:

`sh
./example.js --config config.yaml
Hello, macbre! Greetings from The Unknown Machine.

HOSTNAME=hostname ./example.js --config config.yaml
Hello, macbre! Greetings from debian.

./example.js --config config.yaml --banner='foo'
Hello, macbre! Greetings from The Unknown Machine.
``

As you can see config file values have precedence over command line ones.