如何将环境变量设置为gulp任务？

gulp.task('set-dev-node-env', function() {    return process.env.NODE_ENV = 'development';});gulp.task('set-prod-node-env', function() {    return process.env.NODE_ENV = 'production';});

像这样使用它：

gulp.task('build_for_prod', ['set-prod-node-env'], function() {    // maybe here manipulate config object      config.paths.src.scripts = config.paths.deploy.scripts;    runSequence(        'build',        's3'    );});