Extracts a shortcode tag from a post content and returns the content with target shortcode tag stripped out.

extract_shortcode.php

<?php
/**
 * Based on:
 * https://codex.wordpress.org/Function_Reference/get_shortcode_regex 
 */
function extract_shortcode($content, $tag) {
  
  $shortcode_match = false;
  
  
  $pattern = get_shortcode_regex();

  if (   preg_match_all( '/'. $pattern .'/s', $content, $matches )
      && array_key_exists( 2, $matches )
      && in_array( $tag, $matches[2] ) )
  {
      $tag_index = array_search($tag, $matches[2]);
      $complete_shortcode = $matches[0][$tag_index];
      return $complete_shortcode;
  }
}

/**
 * @param string $code name of the shortcode
 * @param string $content
 * @return string content with shortcode striped
 * @usage $content = strip_shortcode('gallery', $content);
 */
function strip_shortcode($code, $content)
{
    global $shortcode_tags;

    $stack = $shortcode_tags;
    $shortcode_tags = array($code => 1);

    $content = strip_shortcodes($content);

    $shortcode_tags = $stack;
    return $content;
}