$str = '张三和李四出去玩';
$keywordRegex = '张三|李四|王五';
$keywordRegex = '/'.$keywordRegex.'/';
preg_match_all($keywordRegex,$str,$matches);
var_dump($matches);exit;

返回结果:

array(1) { [0]=> array(2) { [0]=> string(6) "张三" [1]=> string(6) "李四" } }