<?php
$text = "ghi ác xyz ác, jkl";
$search = "ác";
$_x_word = '/\s(' . preg_quote($search) . ')\s/i';
PD9waHAKCiR0ZXh0ID0gImdoaSDDoWMgeHl6IMOhYywgamtsIjsKJHNlYXJjaCA9ICLDoWMiOwokX3hfd29yZCA9ICcvXHMoJyAuIHByZWdfcXVvdGUoJHNlYXJjaCkgLiAnKVxzL2knOwpwcmVnX21hdGNoX2FsbCgkX3hfd29yZCwgJHRleHQsICRtYXRjaF93b3Jkcyk7CnZhcl9kdW1wKCRtYXRjaF93b3Jkcyk7