Duck punching Gulp into waiting for something asynchronous. Example: Varying pipelines / tasks based on the contents of an external file.

duckPunchingGulpStart.js

/*
 * Example: productionMode.txt contains either 0 or 1
 */


var productionMode = true; //defaults to production, don't change this
var gulp = require('gulp');
var gutil = require('gulp-util');
var concat = require('gulp-concat');
var uglify = require('gulp-uglify');


// duck punching

var originalGulpStart = gulp.start;
gulp.start = function(args){
	var startArgs = arguments,
		self = this;

	fs.readFile('./productionMode.txt', function(err, data){
		if(err) throw new Error('error reading dev mode file');
		
		productionMode = data.toString() === '1';

		originalGulpStart.apply(self, startArgs);
	});
};


// tasks

gulp.task('default', 'scripts');

gulp.task('scripts', function(){
	gulp.src('./src/*.js')
		.pipe(concat('script.js'))
		.pipe(productionMode ? uglify() : gutil.noop()) // only minifies in production mode
		.pipe(gulp.dest('./output');
});

Why wouldn't you just do this?

var gulp = require('gulp');
var gutil = require('gulp-util');
var concat = require('gulp-concat');
var uglify = require('gulp-concat');
var fs = require('fs');

var productionTxt = fs.readFileSync('./productionMode.txt', 'utf8');
var productionMode = productionTxt === '1';


// tasks

gulp.task('default', ['scripts']);

gulp.task('scripts', function(){
    return gulp.src('./src/*.js')
        .pipe(concat('script.js'))
        .pipe(productionMode ? uglify() : gutil.noop()) // only minifies in production mode
        .pipe(gulp.dest('./output');
});

Thanks @contra. I guess because I never heard of readFileSync :). I've only began to really get into Node lately. Even my use case for this was to read a file written in a different server-side language. This would still stand though for async stuff in general though, right?