为什么不直接使用 修剪:

$string = trim($string, '_');

Regex 用于模式匹配 ___ 不是模式，它只是下划线.

Regex is for pattern matching ___ is not a pattern it's just underlines.

但如果我要使用正则表达式，我会这样做:

But if I was gonna use a Regex, I'd do something like this:

$string = preg_replace('/^_+|_+$/', '', $string);

对于正则表达式

• ^ 是一行的开始
• _为下划线，+为一个或多个
• | 是 OR
• _为下划线，+为一个或多个
• $ 是行尾

• ^ is the start of a line
• _ is underline, the + is one or more
• | is OR
• _ is underline, the + is one or more
• $ is the end of line

然后我们只需将其替换为 ''

Then we just replace it with ''