Search string for {{custom_field}} and return the post meta

gistfile1.txt

if ( strpos( $content, '{{custom_field' ) !== false ) {
  $data = preg_match_all('/{{custom_field="([^"]*)"}}/', $content, $matches);
  foreach ( $matches[1] as $match ) {
    if ( null !== get_post_meta( get_the_ID(), $match, true ) && '' !== get_post_meta( get_the_ID(), $match, true ) ) {
      $search[] = '{{custom_field="' . $match . '"}}';
      $replace[] = get_post_meta( get_the_ID(), $match, true );
    }
  }
}