https://github.com/gruntjs/grunt-contrib-concat issue

Gruntfile.js

module.exports = function(grunt) {
  // grunt.registerTask('custom', 'Add a custom task to grunt', function() {
  //   ;
  // }
  // Project configuration.
  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    cssmin: {
      compress: {
        files: {
          '<%= pkg.baseDir %>style.min.css': ['<%= pkg.baseDir %>css/shame.css', '<%= pkg.baseDir %>style.css', '<%= pkg.baseDir %>css/peer.css']
        }
      }
    },
    concat: {
      options: {
        stripBanners: true
      },
      dist: {
        src: ['<%= pkg.baseDir %>css/shame.css', '<%= pkg.baseDir %>style.css', '<%= pkg.baseDir %>css/peer.css']
      , dest: '<%= pkg.baseDir %>style.pack.css'
      }
    }
  });

  // Load plugins
  grunt.loadNpmTasks('grunt-contrib-concat');
  grunt.loadNpmTasks('grunt-contrib-cssmin');

  // Default task(s).
  grunt.registerTask('default', ['cssmin']);

  // concat
  grunt.registerTask('concat', ['concat']);  
}

package.json

{
  "name": "pragmatic",
  "private": true,
  "version": "0.1.2",
  "author": "dotnetCarpenter <jon@it-kollektivet.dk>",
  "description": "build system for the pragmatic project",
  "devDependencies": {
    "grunt": "~0.4.1",
    "grunt-contrib-concat": "~0.3.0",
    "grunt-contrib-cssmin": "~0.6.0"
  },
  "baseDir": "wordpress/wp-content/themes/pragmatic/"
}

project structure

-
|- Gruntfile.js
|- node_modules
|- package.json
|- wordpress
   |-wp-content
     |- themes
        |- pragmatic
           |- css
              |- peer.css
              |- shame.css
           |- style.css
           |- style.min.css

Back reference to issue #29 gruntjs/grunt-contrib-concat#29