Using Gulp and Node to change file content based on a string pattern

gulp.js

gulp.task('update-content-file', function () {
	"use strict";
	var fs = fs || require('fs');
	var path = 'path/to/folder';
	// example of CSS path change and adding new css
	var oldContent = /<link href="(.*)dev\/css\/main.css" rel="stylesheet">/;
	var newContent = '<link href="/dev/css/main.css" rel="stylesheet"><link href="/dev/css/specific.css" rel="stylesheet">';

	fs.readdir(path, function(err, files)  {

		files.forEach(function (file) {
			// testing if has 'html' string in file name, not testing images, xml etc
			if(/html/.test(file) ) {
				// remove files based on some name
				if (/someString/.test(file)) {
					// remove all backup files
					fs.unlink(path + '/' + file, (err) => {
						if (err) throw err;
				});
				} else {
					// Read file
					fs.readFile(path + '/' + file, 'utf8', function (err, data) {
						if (err) {
							return console.log(err);
						}
						// looking for string pattern and replacing old -> new
						var result = data.replace(CSSOldPath, CSSNewPath);

						// writing back
						fs.writeFile(path + '/' + file, result, 'utf8', function (err) {
							if (err) return console.log(err);
						});

						// Writing in terminal changed files
						console.log('File name: ', file);
					})
				}
			}
		});
	});

});