Remove unwanted content from posts

functions.php

<?php

/**
 * Remove unwanted content from posts
 *
 * When your site get hacked you can have some unwanted content in database like
 * links or script tags. This script will mass update all your posts to remove
 * this kind of content. Take a look to $regex variable and remove or add pattern
 * to fit your needs. To test regex you can use tool like https://regex101.com/
 *
 * Script will not trigger automatically you must add "update" parameter to your
 * site url e.g. http://example.org?update=1
 *
 * If you have many posts disable creating revision posts by adding
 * WP_POST_REVISIONS constant to wp-config.php. It will speed up script
 * and reduce the demand for memory usage. define( 'WP_POST_REVISIONS', false );
 *
 * For 1000 posts script executes about 30s and use 45mb memory
 * on 1 CPU and 512mb machine.
 */
function motivast_remove_unwanted_content() {

    $update = filter_input(INPUT_GET, 'update', FILTER_SANITIZE_NUMBER_INT);

    if( $update === '1' ) {

        // Get all posts
        $query = new WP_Query(array(
            'post_type' => 'post',
            'posts_per_page' => -1,
            'order' => 'ASC',
        ));

        $posts = $query->get_posts();

        foreach ($posts as $post) {

            // Get content
            $content = $post->post_content;

            // Regex and replacement
            $regex = array(
                '/^\<script\>.+\<\/script\>$/mg',                         // Any script tag
                '/^\<a.+>.+\<\/a\>$/mg',                                  // Any link in the post
                '/^\<a.*href=\"http:\/\/example\.org\".*\>.+\<\/a\>$/mg', // Link with http://example.org in the href
            );

            $replacement = '';

            // Replace content
            $new_content = preg_replace($regex, $replacement, $content);

            // Prepare arguments
            $args = array(
                'ID' => $post->ID,
                'post_content' => $new_content,
            );

            // Update post
            wp_update_post( $args );
        }
    }
}

add_action('init', 'motivast_remove_unwanted_content');