PHP的正则表达式 - 类似于IP模式？

Question

I need a regular expression which consist of: 1-3 digits and optional dot. It is something like IP pattern. I want my regex to allow the following:

192

192.

192.168

192.168.

and NOT the following:

192.1688

This is what I have so far:

preg_match('/^((\d{1,3})(\.?))+$/', $string);

But it still allows me to have more than 3 digits. Any suggestions how to fix the regex?

Answer 1

If you plan to match any number of 1-3 digit sequences separated with a dot (which is optional at the end), you can use

^\d{1,3}(?:\.\d{1,3})*\.?$

See demo

If you need the numbers to be in the range between 0 and 255 as in IP address, use

^(?:25[0-5]|2[0-4][0-9]|[01]?[1-9][0-9]?)(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[1-9][0-9]?))*\.?$

See another demo.

To limit to only 2 groups of numbers, use a ? quantifier with the second non-capturing group:

^(?:25[0-5]|2[0-4][0-9]|[01]?[1-9][0-9]?)(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[1-9][0-9]?))?\.?$
                                                                                       ^

See the 3rd demo