用于空字符串的PHP最短正则表达式[关闭]

I want to find the shortest possible regular expression pattern to match an empty string(no whitespacer or anything at all)

I have found

 /(\d|)/    (7chars)
and '^[\s]*$' (9 chars)

till now.

Technically /(\d|)/ is 5 characters, the slashes are just delimiters.

The shortest regex I know of that would match an empty string is ^$.

Why do you need a regex if you can use empty() ? i.e.:

$emptyStr = "";

if(empty($emptyStr)){
   echo "I'm empty";
}

you guessed, it outputs "I'm empty".