hardwired configuration loader

1.2.8  •  Published 2 years ago  •  by Dominic Tarr  •  Unknown License

The non-configurable configuration loader for lazy people.


The only option is to pass rc the name of your app, and your default configuration.

var conf = require('rc')(appname, {
  //defaults go here.
  port: 2468,

  //defaults which are objects will be merged, not replaced
  views: {
    engine: 'jade'

rc will return your configuration options merged with the defaults you specify. If you pass in a predefined defaults object, it will be mutated:

var conf = {};
require('rc')(appname, conf);

If rc finds any config files for your app, the returned config object will have a configs array containing their paths:

var appCfg = require('rc')(appname, conf);
appCfg.configs[0] // /etc/appnamerc
appCfg.configs[1] // /home/dominictarr/.config/appname
appCfg.config // same as appCfg.configs[appCfg.configs.length - 1]


Given your application name (appname), rc will look in all the obvious places for configuration.

  • command line arguments, parsed by minimist (e.g. --foo baz, also nested: --foo.bar=baz)
  • environment variables prefixed with ${appname}_
    • or use “__” to indicate nested properties
      (e.g. appname_foo__bar__baz => foo.bar.baz)
  • if you passed an option --config file then from that file
  • a local .${appname}rc or the first found looking in ./ ../ ../../ ../../../ etc.
  • $HOME/.${appname}rc
  • $HOME/.${appname}/config
  • $HOME/.config/${appname}
  • $HOME/.config/${appname}/config
  • /etc/${appname}rc
  • /etc/${appname}/config
  • the defaults object you passed in.

All configuration sources that were found will be flattened into one object, so that sources earlier in this list override later ones.

Configuration File Formats

Configuration files (e.g. .appnamerc) may be in either json or ini format. No file extension (.json or .ini) should be used. The example configurations below are equivalent:

Formatted as ini

; You can include comments in `ini` format if you want.


; `rc` has built-in support for ini sections, see?

  www     = ./commands/www
  console = ./commands/repl

; You can even do nested sections

  engine  = ejs

  new     = generate-new
  engine  = generate-backend

Formatted as json

  // You can even comment your JSON, if you want
  "dependsOn": "0.10.0",
  "commands": {
    "www": "./commands/www",
    "console": "./commands/repl"
  "generators": {
    "options": {
      "engine": "ejs"
    "modules": {
      "new": "generate-new",
      "backend": "generate-backend"

Comments are stripped from JSON config via strip-json-comments.

Since ini, and env variables do not have a standard for types, your application needs be prepared for strings.

To ensure that string representations of booleans and numbers are always converted into their proper types (especially useful if you intend to do strict === comparisons), consider using a module such as parse-strings-in-object to wrap the config object returned from rc.

Simple example demonstrating precedence

Assume you have an application like this (notice the hard-coded defaults passed to rc):

const conf = require('rc')('myapp', {
    port: 12345,
    mode: 'test'

console.log(JSON.stringify(conf, null, 2));

You also have a file config.json, with these contents:

  "port": 9000,
  "foo": "from config json",
  "something": "else"

And a file .myapprc in the same folder, with these contents:

  "port": "3001",
  "foo": "bar"

Here is the expected output from various commands:

node .

  "port": "3001",
  "mode": "test",
  "foo": "bar",
  "_": [],
  "configs": [
  "config": "/Users/stephen/repos/conftest/.myapprc"

Default mode from hard-coded object is retained, but port is overridden by .myapprc file (automatically found based on appname match), and foo is added.

node . --foo baz

  "port": "3001",
  "mode": "test",
  "foo": "baz",
  "_": [],
  "configs": [
  "config": "/Users/stephen/repos/conftest/.myapprc"

Same result as above but foo is overridden because command-line arguments take precedence over .myapprc file.

node . --foo barbar --config config.json

  "port": 9000,
  "mode": "test",
  "foo": "barbar",
  "something": "else",
  "_": [],
  "config": "config.json",
  "configs": [

Now the port comes from the config.json file specified (overriding the value from .myapprc), and foo value is overriden by command-line despite also being specified in the config.json file.

Advanced Usage

Pass in your own argv

You may pass in your own argv as the third argument to rc. This is in case you want to use your own command-line opts parser.

require('rc')(appname, defaults, customArgvParser);

Pass in your own parser

If you have a special need to use a non-standard parser, you can do so by passing in the parser as the 4th argument. (leave the 3rd as null to get the default args parser)

require('rc')(appname, defaults, null, parser);

This may also be used to force a more strict format, such as strict, valid JSON only.

Note on Performance

rc is running fs.statSync– so make sure you don’t use it in a hot code path (e.g. a request handler)


Multi-licensed under the two-clause BSD License, MIT License, or Apache License, version 2.0

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Weekly Downloads



Last ver 2 years ago
Created 7 years ago
Last commit 2 years ago
15 days between commits


Node version: 8.11.1
17.3K unpacked


License Unknown
Not OSI Approved
0 vulnerabilities


27 contributors
Dominic Tarr
Maintainer, 104 commits, 33 merges
Works at Protozoa
Mike McNeil
13 commits, 2 PRs
Works at Sails (sailshq)
Javier Collado
4 commits, 1 PRs
Works at Javier Collado
Dane Springmeyer
4 commits
Bogdan Chadkin
3 commits, 3 PRs
Works at realadvisor
Daniel Stockman
2 commits, 2 PRs
Works at zillow


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