Change or rename a file.(upper case to loer)

fileNameChanger.js

const fs = require('fs');
const path = require('path');

if (process.argv.length <= 2) {
	console.log('Usage: ' + __filename + ' path/to/directory');
	process.exit(-1);
}

var directoryPath = process.argv[2];
fs.readdir(directoryPath, (err, files) => {
	files.forEach(file => {
		var fileName = file.replace(/(.*)\.[^.]+$/, '$1');
		var newFileName =
			fileName.replace(/([A-Z]+)/g, function(match1) {
				return '_' + match1.toLowerCase();
			}) + path.extname(file);
		fs.rename(directoryPath + '/' + file, directoryPath + '/' + newFileName, function() {});
		console.log(directoryPath + file);
	});
});