WP Provide first sentence only for the excerpt

gistfile1.txt

add_filter(
  'get_the_excerpt',
  function ($excerpt) {
    // Split the except into sentances
    $re = '/(?<=[.!?]|[.!?][\'"])\s+/';
    $sentences = preg_split($re, $excerpt, -1, PREG_SPLIT_NO_EMPTY);
    return $sentences[0];
  }
);