Gulp file change into a concat stream
<p>I have a multiple build set up with my gulp file(dev,uat etc) and I need to define certain variables in my app.js file then concat them into my main bundle file. </p>

<p>I dont want to have to create the edited file then concat that file. Is it possible to make the variable change then take the file changed in memory and use that in the concat?</p>

<pre><code>gulp.src('_app.js').pipe(replace("'baseURL':", "'baseURL':'www.test.com'"))
            .pipe(concat(['list of files','file in memory']));
</code></pre>