您可以为其使用正则表达式:

You can use a regular expression for it:

preg_match_all('/\b([A-Z]+)\b/', $str, $matches);

要匹配小写字母，请使用以下命令:

To match the lowercase words, use this:

preg_match_all('/\b([a-z]+)\b/', $str, $matches2);

然后，您可以使用implode()之类的功能来构建字符串.

Then you can use functions such as implode() to build the strings.