如何限制字符串中的“/”数

Question

How do I use lookahead assertion to limit by range the number of "/"

I have tired the following

^(?=/{1,3})$

but it doesn't work

Answer 1

The easiest solution is to use a negative lookahead:

^(?!(?:[^/]*/){4})

That basically means the string cannot contain 4 slashes.

This assumes you allow other characters between slashes, but a maximum of 3 slashes.

A positive version would be ^(?=[^/]*(?:/[^/]*){0,3}$) or ^[^/]*(?:/[^/]*){0,3}$ , without the lookahead. Of course, the problem is trivial without regular expressions, if possible.

Lets try to break that last one down:

• ^ - Start of the string.
• [^/]* - Some characters that are not slashes (or none)
• (?: ) - A logical group. Similar to () , but does not capture the result (we do not need it after validation)
• /[^/]* - Slash, followed by non-slash characters.
• {0,3} - From 0 to 3 times.
• $ - End of the string.

Answer 2

您可以尝试以下（您必须说应该没有/之后）：

^(?=/{1,3}([^/]|$))