gruntjs - How to set the environment for Grunt? -

i defined task section of gruntfile.js 2 environments -- development , production. don't understand, how grunt decides, wheter use environment section.

gruntfile.js

module.exports = function(grunt) {    // project configuration.   grunt.initconfig({     pkg: grunt.file.readjson('package.json'),     less: {       development: {         options: {           paths: ["public/css"]         },         files: {           "public/css/style.css": "public/css/style.less"         }       },       production: {         options: {           paths: ["public/css"],           plugins: [           ],           modifyvars: {           }         },         files: {           "public/css/style.css": "public/css/style.less"         }       }     },     watch: {       css: {         files: 'public/css/*.less',         tasks: ['less'],         options: {           livereload: true,         },       },     }   });    // load plugin provides "less" task.   grunt.loadnpmtasks('grunt-contrib-less');   // load plugin provides "watch" task.   grunt.loadnpmtasks('grunt-contrib-watch');    // default task(s).   grunt.registertask('default', ['less', 'watch']);  }; 

how let grunt know, environment active?

to alternate suggest create development task , run grunt development

// default task(s). grunt.registertask('default', ['less:production', 'watch']);  // development task grunt.registertask('development', ['less:development', 'watch']);