Grunt/Yeoman Multiple Gruntfile.js Files - gruntjs

Question

My goal is the be able to build my project to two separate build folders, each with its' own Grunt tasks.
I noticed the grunt-cli has the --gruntfile option which allows you to specify another Gruntfile to use. So far, I have a Gruntfile.js working perfectly (near stock from Yeoman). Also, I have another Gruntfile2.js sitting alongside.
Gruntfile.js
var yeomanConfig = {
app: 'app',
dist: '../www_browser'
};
Gruntfile2.js
var yeomanConfig = {
app: 'app',
dist: '../www'
};
grunt build is meant to run Gruntfile.js, and does so perfectly.
grunt build --gruntfile Gruntfile2.js is meant to run Gruntfile2.js, and does so with some hiccups. (supposed to build to ../www folder NOT ../www_browser folder)
The --gruntfile directive builds to the proper folder for almost every task except grunt-usemin and gunt-contrib-htmlmin. I know this because of this output to the console here:
Running "usemin:css" (usemin) task
Processing as CSS - ../www_browser/styles/22f60055.main.css
Running "concurrent:dist" (concurrent) task
Running "htmlmin:dist" (htmlmin) task
File ../www_browser/404.html created.
File ../www_browser/index.html created.
You'll notice the ../www_browser, here in console output. Every other task runs in the expected ../www folder.
Is this a usemin cache thing? Grunt cache thing? Or do some tasks simply run from the default Gruntfile.js regardless of the --gruntfile Gruntfile2.js directive?
I have given up on trying to do multiple targets from a single Gruntfile for now. There are too many dependencies in Yeoman's Gruntfile.js that don't yet support multiple build targets, and I spent 12 hours to no avail with that approach.
Version Info
$: grunt --version
grunt-cli v0.1.9
grunt v0.4.1
$: npm --version
1.2.25
$: yo --version
1.0.3
package.json
{
"name": "myapp",
"version": "0.0.0",
"dependencies": {},
"devDependencies": {
"grunt": "~0.4.1",
"grunt-contrib-copy": "~0.4.1",
"grunt-contrib-concat": "~0.1.3",
"grunt-contrib-coffee": "~0.6.5",
"grunt-contrib-uglify": "~0.2.0",
"grunt-contrib-compass": "~0.2.0",
"grunt-contrib-jshint": "~0.4.1",
"grunt-contrib-cssmin": "~0.6.0",
"grunt-contrib-connect": "~0.2.0",
"grunt-contrib-clean": "~0.4.0",
"grunt-contrib-htmlmin": "~0.1.3",
"grunt-bower-requirejs": "~0.4.1",
"grunt-contrib-requirejs": "~0.4.0",
"grunt-contrib-imagemin": "~0.1.3",
"grunt-contrib-watch": "~0.4.0",
"grunt-rev": "~0.1.0",
"grunt-usemin": "~0.1.10",
"grunt-mocha": "~0.3.0",
"grunt-open": "~0.2.0",
"grunt-svgmin": "~0.1.0",
"grunt-concurrent": "~0.1.0",
"matchdep": "~0.1.1",
"connect-livereload": "~0.2.0"
},
"engines": {
"node": ">=0.8.0"
}
}

Answer 1

It looks like you're using an older version of grunt-concurrent, which doesn't seem to be passing the grunt flags through to the child-processes.
See here: https://github.com/sindresorhus/grunt-concurrent/blob/v0.1.0/tasks/concurrent.js#L11
On the current version of the plugin, the flags are passed, see here: https://github.com/sindresorhus/grunt-concurrent/blob/v0.3.1/tasks/concurrent.js#L22
So, I suggest updating your version of grunt-concurrent:
npm install grunt-concurrent#latest --save-dev