How to create a parser?

Question

PHP

I've been suffering for a long time, trying to compose a parser, but I'm stuck on regular expressions...
I'm trying to get a link to the background image of the VK group (let's say from the group https://vk.com/officialpages) in order to put it on the site and it was updated when the admin will update the background image in the group
.... it is in style, I want to get at least the entire block and remove the unnecessary part from there using substr, but if you tell me how to pull out the link directly, I will be grateful.
The parser itself produces an empty page:

$content = file_get_contents('https://vk.com/officialpages');
preg_match_all ('|<div class="page_block"><[^>]+>(.*)</[^>]+></div>|isU', $content, $content2, PREG_SET_ORDER);
echo $content2['0']['1'];

PS: sorry for the stupid question, maybe this is the first time I'm poking a parser...

Answer 1

DOM is generally better,
but you can start with a parse saved on disk