Gulp file for using Gulp with Underscores theme. Place in root theme directory, saved as gulpfile.js

functions.php

/*
This is taken directly from here and modified to fit our needs: https://developer.wordpress.org/themes/basics/including-css-javascript/
*/

function add_that_css_and_js() {
 
  wp_enqueue_style( 'enqueue-that-css', get_template_directory_uri() . '/css/main.css', array(), '1.0', 'all');
 
  wp_enqueue_script( 'enqueue-that-js', get_template_directory_uri() . '/js/min/main.min.js', array ( 'jquery' ), 1.0, true);

}
add_action( 'wp_enqueue_scripts', 'add_that_css_and_js' );

gulp-for-underscores-theme-wp.js

// If you're interested in automating more control, check out gulpjs.com for more dependencies
// This is meant as a starting point. You can do a LOT more with gulpjs than this

// Requiring dependencies here, make sure to add them via the terminal
var gulp   = require('gulp'),
    sass   = require('gulp-sass'),
    concat = require('gulp-concat'),
    minify = require('gulp-minify');

// Need to create a /css folder and a /sass folder inside the /css folder
gulp.task('build-that-css', function() {
  return gulp.src('./css/sass/*.scss')
    .pipe(sass().on('error', sass.logError))
    .pipe(concat('main.css'))
    .pipe(gulp.dest('css/'));
});
// Obviously enqueue this new css file "main.css" in your functions.php

gulp.task('compress-that-js', function() {
  gulp.src('./js/*.js')
    .pipe(minify({
    	ext: {
    		src: 'main.js', // create main.js for all your extra theme JS
    		min: '.min.js'
    	} 
    }))
    .pipe(gulp.dest('js/min/'))
	// enqueue this minified file in your functions.php file 
});

// Gulp is watching you and your coding with the command: gulp watch
gulp.task('watch', function() {
  gulp.watch('./css/sass/*.scss', ['build-that-css']);
  gulp.watch('./js/*.js', ['compress-that-js']);
});

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