As a general rule of thumb, you must avoid parsing HTML/XML content with regular expressions. Here's why:
Entire HTML parsing is not possible with regular expressions, since it depends on matching the opening and the closing tag which is not possible with regexps.
Regular expressions can only match regular languages but HTML is a context-free language. The only thing you can do with regexps on HTML is heuristics but that will not work on every condition. It should be possible to present a HTML file that will be matched wrongly by any regular expression.
— https://stackoverflow.com/a/590789/65732
Use a DOM parser instead which is specifically designed for the purpose of parsing HTML/XML documents. Here's an example:
# Installing Symfony's dom parser using Composer
composer require symfony/dom-crawler symfony/css-selector
<?php
require 'vendor/autoload.php';
use Symfony\Component\DomCrawler\Crawler;
$html = file_get_contents('https://kithnyc.com/collections/footwear/products/kith-x-adidas-consortium-response-trail-boost?variant=35276776455');
$crawler = new Crawler($html);
$price = $crawler->filter('.product-header-title[itemprop="price"]')->text();
// UPDATE: Does not work! as the page updates the button text
// later with javascript. Read more for another solution.
$in_stock = $crawler->filter('#AddToCartText')->text();
if ($in_stock == 'Sold Out') {
$in_stock = 0; // or `false`, if you will
}
echo "Price: $price - Availability: $in_stock";
// Outputs:
// Price: $220.00 - Availability: Buy Now
// We'll fix "Availability" later...
Using such parsers, you have the ability to extract elements using XPath as well.
But if you want to parse the javascript code included in that page, you'd better use a browser emulator like Selenium. Then you have programmatic access to all the globally available javascript vars/functions in that page.
Update
Getting the price
So you were getting this error running the above code:
PHP Fatal error:
Uncaught Symfony\Component\CssSelector\Exception\SyntaxErrorException: Expected identifier, but found.
That's because the target page uses an invalid class name for the price element (.-price) and this Symfony's CSS selector component cannot parse it correctly, hence the exception. Here's the element:
<span id="ProductPrice" class="product-header-title -price" itemprop="price" content="220">$220.00</span>
To workaround it, let's use the itemprop attribute instead. Here's the selector that can match it:
.product-header-title[itemprop="price"]
I updated the above code accordingly to reflect it. I tested it and it's working for the price part.
Getting the stock status
Now that I actually tested the code, I see that the stock status of products is set later using javascript. It's not there when you fetch the page using file_get_contents(). You can see it for yourself, refresh the page, the button appears as Buy Now, then a second later it changes to Sold Out.
But fortunately, the quantity of the product variant is buried deep somewhere in the page. Here's a pretty printed copy of the huge object Shopify uses to render the product pages.
So now the problem is parsing javascript code with PHP. There are a few general approaches to tackle the problem:
Feel free to skip these approaches as they are not specific to your problem. Jump straight to number 6, if you just want a solution to your question.
The most reliable and common approach is to scrape data from such sites (that heavily rely on javascript) is to use a browser emulator like Selenium which are able to execute javascript code. Have a look at Facebook's PHP WebDriver package which is the most sophisticated PHP binding for Selenium WebDriver available. It provides you with an API to remotely control web browsers and execute javascript against them.
Also, see Behat's Mink that comes with various drivers for both headless browsers as well as full-fledged browser controllers. The drivers include Goutte, BrowserKit, Selenium1/2, Zombie.js, Sahi and WUnit.
See V8js, the PHP extension; which embeds V8 javascript engine into PHP. It allows you to evaluate javascript code right from your PHP script. But it's a little bit overkill to install a PHP extension if you're not heavily using the feature. But if you want to extract the relevant script using the DOM parser:
$script = $crawler->filterXPath('//head/following-sibling::script[2]')->text();
Use HtmlUnit to parse the page and then feed the final HTML to PHP. You gonna need a small Java wrapper. Right, overkill for your case.
Extract the javascript code and parse it using a JS parser/tokenizer library like hiltonjanfield/js4php5 or squizlabs/PHP_CodeSniffer which has a JS tokenizer.
In case that the application is making ajax calls to manipulate the DOM. You might be able to re-dispatch those requests and parse the response for your own application's sake. An example is the ajax call the page is making to cart.js to retrieve the data related to the cart items. But it's not the case for reading the product variant quantity here.
You may recall that I told you that it's a bad idea to utilize regular expressions to parse entire HTML/XML documents. But it's OK to use them partially to extract strings from an HTML/XML document when other approaches are even harder. Read the SO answer I quoted at the top of this post if you have any confusions about when to use it.
This approach is about matching the inventory_quantity of the product variant by running a simple regex against the whole page source (or you can only execute it against the script tag regarding a better performance):
<?php
require 'vendor/autoload.php';
use Symfony\Component\DomCrawler\Crawler;
$html = file_get_contents('https://kithnyc.com/collections/footwear/products/kith-x-adidas-consortium-response-trail-boost?variant=35276776455');
$crawler = new Crawler($html);
$price = trim($crawler->filter('.product-header-title[itemprop="price"]')->text());
preg_match('/35276776455,.+?inventory_quantity":(\d)/', $html, $in_stock);
$in_stock = $in_stock[1];
echo "Price: $price - Availability: $in_stock";
// Outputs:
// Price: $220.00 - Availability: 0
This regex needs a variant ID (35276776455 in this case) to work, as the quantity of each product comes with a variant. You can extract it from the URL's query string: ?variant=35276776455.
Now that we're done with the stock status and we've done it with regex, you might want to do the same with the price and drop the DOM parser dependency:
<?php
$html = file_get_contents('https://kithnyc.com/collections/footwear/products/kith-x-adidas-consortium-response-trail-boost?variant=35276776455');
// You need to check if it's matched before assigning
// $price[1]. Anyway, this is just an example.
preg_match('/itemprop="price".+?>\s*\$(.+?)\s*<\/span>/s', $html, $price);
$price = $price[1];
preg_match('/35276776455,.+?inventory_quantity":(\d)/', $html, $in_stock);
$in_stock = $in_stock[1];
echo "Price: $price - Availability: $in_stock";
// Outputs:
// Price: $220.00 - Availability: 0
Conclusion
Even though that I still believe that it's a bad idea to parse HTML/XML documents with regex, I must admit that available DOM parsers are not able to parse embedded javascript code (and probably will never be), which is your case. We can partially utilize regular expressions to extract strings from HTML/XML; the parts which are not parsable using DOM parsers. So, all in all:
- Use DOM parsers to parse/scrape the HTML code that initially exists in the page.
- Intercept ajax calls that may include information you want. Re-call them in a separate http request to get the data.
- Use browser emulators for parsing/scraping JS-heavy sites that populate their pages using ajax calls and such.
- Partially use regex to extract what is not extractable using DOM parsers.
If you just want these two fields, you're fine to go with regex. Otherwise, consider other approaches.
