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Using ENV in Ruby is like using raw SQL statements - it feels wrong, because it is.

If you agree, this gem is for you.

The benefits over using ENV directly:

  • much friendlier stubbing in tests
  • you no longer have to care whether false is "0" or "false" or whatever
  • keys become methods
  • namespaces which can be passed around as objects
  • you can subclass!
  • you can marshal/unmarshal your own types automatically!
  • strict mode saves you from doing validation yourself
  • and there's more to come...

Other benefits (and compared to other solutions):

  • should still work with Ruby 1.8 (in case anyone is still stuck with it)
  • it's designed to be as lightweight and as fast as possible compared to ENV
  • designed to be both hackable and convenient


Add this line to your application's Gemfile:

gem 'nenv', '~> 0.1'

And then execute:

$ bundle

Or install it yourself as:

$ gem install nenv

Examples !!!

Automatic booleans

You no longer have to care whether the value is "0" or "false" or "no" or "FALSE" or ... whatever

# Without Nenv
t.verbose = (ENV['CI'] == 'true')
ENV['DEBUG'] = "true"

now becomes:

t.verbose =
gemdeps = Nenv.rubygems_gemdeps? || Nenv.bundle_gemfile?
Nenv.debug = true


# Without Nenv

now becomes:

git = Nenv :git
puts git.browser
puts git.pager
puts git.editor

Or in block form

Nenv :git do |git|
  puts git.browser
  puts git.pager
  puts git.editor

Custom type handling

# Code without Nenv
paths = [ENV['GEM_HOME`]] + ENV['GEM_PATH'].split(':')
enable_logging if Integer(ENV['WEB_CONCURRENCY']) > 1
mydata = YAML.load(ENV['MY_DATA'])
ENV['VERBOSE'] = debug ? "1" : nil

can become:

# setup
gem = Nenv :gem
gem.instance.create_method(:path) { |p| p.split(':') }

web = Nenv :web
web.instance.create_method(:concurrency) { |c| Integer(c) }

my = Nenv :my
my.instance.create_method(:data) { |d| YAML.load(d) }

Nenv.instance.create_method(:verbose=) { |v| v ? 1 : nil }

# and then you can simply do:

paths = [gem.home] + gem.path
enable_logging if web.concurrency > 1
mydata =
Nenv.verbose = debug

Automatic conversion to string

ENV['RUBYGEMS_GEMDEPS'] = 1  # TypeError: no implicit conversion of Fixnum (...)

Nenv automatically uses to_s:

Nenv.rubygems_gemdeps = 1  # no problem here

Custom assignment

data = YAML.load(ENV['MY_DATA'])
data[:foo] = :bar
ENV['MY_DATA'] = YAML.dump(data)

can now become:

my = Nenv :my
my.instance.create_method(:data) { |d| YAML.load(d) }
my.instance.create_method(:data=) { |d| YAML.dump(d) }

data =
data[:foo] = :bar = data

Strict mode

# Without Nenv
fail 'home not allowed' if ENV['HOME'] = Dir.pwd  # BUG! Assignment instead of comparing!
puts ENV['HOME'] # Now contains clobbered value

Now, clobbering can be prevented:

env =

fail 'home not allowed' if env.home = Dir.pwd  # Fails with NoMethodError
puts env.home # works

Mashup mode

You can first define all the load/dump logic globally in one place

Nenv.instance.create_method(:web_concurrency) { |d| Integer(d) }
Nenv.instance.create_method(:path) { |p| Pathname(p.split(File::PATH_SEPARATOR)) }
Nenv.instance.create_method(:path=) { |array| }

# And now, anywhere in your app:

Nenv.web_concurrency += 3
Nenv.path += Pathname.pwd + "foo"

MyEnv = do
end'my').foo? # same as ENV['MY_FOO'][/^(?:false|no|n|0)/i,1].nil?

class MyEnv < Nenv::Environment
  def initialize
end # same as ENV['MY_FOO'][/^(?:false|no|n|0)/i,1].nil?


Still, avoid using environment variables if you can.

At least, avoid actually setting them - especially in multithreaded apps.

As for Nenv, while you can access the same variable with or without namespaces, filters are tied to instances, e.g.:

Nenv.instance.create_method(:foo_bar) { |d| Integer(d) }
Nenv('foo').instance.create_method(:bar) { |d| Float(d) }
env = { |e| e.create_method(:bar) }

all work on the same variable, but each uses a different filter for reading the value.

Documentation / SemVer / API

Any behavior not mentioned here (in this README) is subject to change. This includes module names, class names, file names, method names, etc.

If you are relying on behavior not documented here, please open a ticket.

What's wrong with ENV?

Well sure, having ENV act like a Hash is much better than calling "getenv".

Unfortunately, the advantages of using ENV make no sense:

  • it's faster but ... environment variables are rarely used thousands of times in tight loops
  • it's already an object ... but there's not much you can do with it (try ENV.class)
  • it's globally available ... but you can't isolate it in tests (you need to reset it every time)
  • you can use it to set variables ... but it's named like a const
  • it allows you to use keys regardless of case ... but by convention lowercase shouldn't be used except for local variables (which are only really used by shell scripts)
  • it's supposed to look ugly to discourage use ... but often your app/gem is forced to use 3rd party environment variables anyway
  • it's a simple Hash-like class ... but either you encapsulate it in your own classes - or all the value mapping/validation happens everywhere you want the data (yuck!)

But the BIGGEST disadvantage is in specs, e.g.:

allow(ENV).to receive(:[]).with('MY_VARIABLE').and_return("foo")
allow(ENV).to receive(:[]=).with('MY_VARIABLE', "foo bar")
# (and if you get the above wrong, you may be debugging for a long, long time...)

which could instead be completely isolated as (and without side effects):

allow(env).to receive(:variable).and_return("foo")
expect(env).to receive(:variable=).with("foo bar")
# (with verifying doubles it's hard to get it wrong and get stuck)

Here's a full example:

# In your implementation
MyEnv = do

class Foo
  def foo += "bar"

# Stubbing the class in your specs
RSpec.describe Foo do
  let(:env) { instance_double(MyEnv) }
  before { allow(MyEnv).to receive(:new).with(:my).and_return(env) }

  describe "#foo" do
    before { allow(env).to receive(:variable).and_return("foo") }

    it "appends a value" do
      expect(env).to receive(:variable=).with("foo bar")


  1. Fork it ([my-github-username]/nenv/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request