Grunt pattern to name dest after source

gistfile1.js

'sass': {
    dist: {
		// this pattern will recurse through Grunt project directory and look for folders called 'sass'
		// it then looks inside the 'sass' folder for any files with extensive '*.scss' and converts them
		// to a CSS file named the same except located in '../css/*.css'
		files: grunt.file.expandMapping(['**/sass/*.scss'], 'css', {
			rename: function (dest, matched) {
				return matched.replace(/\/sass\//, '/' + dest + '/').replace(/\.scss$/, '.css');
			}
		})
	}
}