it work nice when you want change the image url in your css, and copy the image to the new path

do-change-url-in-css.js

const fs = require('fs');
const path = require('path');
const exec = require('child_process').exec;

const filename = path.resolve(__dirname, 'index.css');

fs.readFile(filename, 'utf8', (err, data) => {
    if (err) throw err;
    var reg = new RegExp(/'([a-zA-z_0-9]+(?:.jpg|.png))'/, 'g');

    //get all image url in css
    var asset_urls = data.match(reg);

    //replace with prepend string '/img/packs/$1'
    data = data.replace(reg, '\'/img/packs/$1\'');
    fs.writeFile(filename, data, (err) => {
        if (err) throw err;
        console.log('It\'s saved!');
    });

    //do mv command
    asset_urls = asset_urls.map(url => url.substring(1, url.length - 1));
    asset_urls.forEach((url) => {
    	exec('mv ' + url + ' ./img/packs', (error, stdout, stderr) => {
    		if (error) {
    			console.error(`exec error: ${error}`);
    			// return;
    		}
    		console.log(`stdout: ${stdout}`);
    		console.log(`stderr: ${stderr}`);
    	});
    });

});