gistfile1.js

less: {
     compile: {
        options: {
            paths: ["bower_components/bootstrap/less"]
        },
        files: {
            "app/styles/style.css": "app/styles/style.less"
        }
    }
 }

gistfile2.js

less: {
		  files: ['<%= config.app %>/styles/{,*/}*.less'],
    tasks: ['less']
},
styles: {
    files: ['<%= config.app %>/styles/{,*/}*.css'],
    tasks: ['newer:copy:styles', 'autoprefixer']
}

gistfile3.txt

 grunt.loadNpmTasks('grunt-contrib-less');