Regular expression, how to add an exception?

Question

PHP

I use this code in WordPress. Determines the first image from the article and uses it as the post image. But in some articles there is an information block, and there is a picture "info.png" or "warning.png" in it. How to modify the script to skip this picture ("info.png" or "warning.png"), if it exists.

function get_first_post_image()
{
    global $post, $posts;
    $first_img = "";
    ob_start();
    ob_end_clean();
    if (
        preg_match_all(
            '/<img.+src=[\'"]([^\'"]+)[\'"].*>/i',
            $post->post_content,
            $matches
        )
    ) {
        $first_img = $matches[1][0];
        return $first_img;
    } else {
        $first_img = "https://sample.com/images/post-default.png";
        return $first_img;
    }
}

Here's what I got but it doesn't work

function get_post_image()
{
    global $post, $posts;
    $first_img = "";
    ob_start();
    ob_end_clean();
    if (
        preg_match_all(
            '/<img.+src=[\'"]([^\'"]+)[\'"].*>/i',
            $post->post_content,
            $matches
        )
    ) {
        if ($matches[1][0] === "info.png" || $matches[1][0] === "warning.png") {
            $first_img =
                $matches[2][0] ?? "https://sample.com/media/post-default.png";
            return $first_img;
        } else {
            $first_img = $matches[1][0];
            return $first_img;
        }
    }
}

PHP Version 7.1.11

Answer 1

Parsing arbitrary html through regular expressions is already a thankless task, and if you also try to complicate this regular expression, it's even easier to shoot yourself in the foot.
Don't be smart:

if ($matches[1][0] === 'info.png' || $matches[1][0] === 'warning.png') {
  return $matches[2][0] ?? 'https://sample.com/images/post-default.png';
} else {
  return $matches[1][0];
}