Add support for dotenv

.env

@@ -0,0 +1 @@
+MESSAGE_FROM_DOTENV=Hello, World!

.npmignore

@@ -1,2 +1,3 @@
 test.js
 .travis.yml
+.env

README.md

@@ -135,6 +135,27 @@ b.transform(envify({
 }))
 ```
 
+## Loading `.env` file ##
+
+Envify can load a `.env` file for you using the
+[dotenv](https://github.com/motdotla/dotenv) package. To enable this
+functionallity, simply use the subarg syntax and include `dotenv` after
+`envify`, e.g.:
+
+``` bash
+browserify index.js -t [ envify dotenv --NODE_ENV development ]
+```
+
+Or if you're using the module API, you can pass `_: "dotenv"` into your
+arguments like so:
+
+``` javascript
+b.transform(envify({
+    _: 'dotenv'
+  , NODE_ENV: 'development'
+}))
+```
+
 ## Contributors ##
 
 * [hughsk](http://github.com/hughsk)

custom.js

@@ -1,8 +1,27 @@
-var esprima = require('esprima')
+var dotenv = require('dotenv')
+  , esprima = require('esprima')
+  , fs = require('fs')
   , through = require('through')
 
 var processEnvPattern = /\bprocess\.env\b/
 
+var dotenvCache
+function getDotenv() {
+  if (dotenvCache === undefined) {
+    try {
+      dotenvCache = dotenv.parse(fs.readFileSync('.env'))
+    } catch (err) {
+      if (err.code === 'ENOENT') {
+        dotenvCache = {}
+      } else {
+        throw err
+      }
+    }
+  }
+
+  return dotenvCache
+}
+
 module.exports = function(rootEnv) {
   rootEnv = rootEnv || process.env || {}
 
@@ -24,6 +43,10 @@ module.exports = function(rootEnv) {
       var purge = args.indexOf('purge') !== -1
       var replacements = []
 
+      if (args.indexOf('dotenv') !== -1) {
+        envs.push(getDotenv())
+      }
+
       function match(node) {
         return (
           node.type === Syntax.MemberExpression

package.json

@@ -20,6 +20,7 @@
     "tape": "^4.6.0"
   },
   "dependencies": {
+    "dotenv": "^4.0.0",
     "esprima": "^4.0.0",
     "through": "~2.3.4"
   },

test.js

@@ -183,3 +183,29 @@ test('-t [ envify purge --argument ]', function(t) {
       , 'var y = process.env.argument'
     ].join('\n'))
 })
+
+test('-t [ envify dotenv ]', function(t) {
+  var stream = envify({ argument: 'not purged' })
+  var buffer = ''
+
+  stream(__filename, { _: ['dotenv'] })
+    .on('data', function(d) { buffer += d })
+    .on('end', function() {
+      t.notEqual(-1, buffer.indexOf('var x = "Hello, World!"'), 'replaces with value from dotenv file')
+      t.end()
+    })
+    .end('var x = process.env.MESSAGE_FROM_DOTENV')
+})
+
+test('-t [ envify dotenv --MESSAGE_FROM_DOTENV intercepted ]', function(t) {
+  var stream = envify({ argument: 'not purged' })
+  var buffer = ''
+
+  stream(__filename, { _: ['dotenv'], MESSAGE_FROM_DOTENV: 'intercepted' })
+    .on('data', function(d) { buffer += d })
+    .on('end', function() {
+      t.notEqual(-1, buffer.indexOf('var x = "intercepted"'), 'uses arguments before dotenv file')
+      t.end()
+    })
+    .end('var x = process.env.MESSAGE_FROM_DOTENV')
+})