Example of a dev flag for gulp

gistfile1.js

// Define your plugins here, make sure you have `gulp-util`...
var gutil = require('gulp-util');

/**
 * Define dev CLI flag
 * Run `gulp --dev`
 */
var isDev = gutil.env.dev;

gulp.task('scripts', function() {
    return gulp.src('src/scripts/*/**.js')
        .pipe(concat('main.js'))
        .pipe(gulpif(!isDev, $.uglify())) // If we use the `--dev` flag, uglify will not take place.
        .pipe(gulp.dest('dist/scripts'))
});