使用正则表达式测试IP地址

Question

Im trying to test the following strings of ip addresses for validity, such as:

1.1.1.1/8
15.10.30.100/16
100.10.10.44/24
198.30.20.30/32

and I have the following regex that tests whether each item of ip:

 !/^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]\/\/(/^\d+)/ig?)$/.test(item.trim())

But im not sure how about the part where there is a forward slash followed by a number such as /24 , /32 ... which is \\/\\/(/^\\d+)/ig . Could anybody point what i did wrong here?

Answer 1

I did not check the error in your regex but I here's a working one

(?:(?:25[0-5]|[0-2]?[0-4]?[0-9]|[0-1]?[0-9]?[0-9])\.){3}(?:(?:25[0-5]|[0-2]?[0-4]?[0-9]|[0-1]?[0-9]?[0-9]))(?:\/(?:3[0-2]|[1-2]?[0-9])|$)$

Test it here

The regex should check allocation blocks from 0 to 32 and IP4 without it.

If you want to check specific allocation blocks you should use this one

(?:(?:25[0-5]|[0-2]?[0-4]?[0-9]|[0-1]?[0-9]?[0-9])\.){3}(?:(?:25[0-5]|[0-2]?[0-4]?[0-9]|[0-1]?[0-9]?[0-9]))(?:\/(?:8|16|24|32)|$)

and filtering blocks inside the last nested non-capturing group (?:8|16|24|32)

Test it here

Answer 2

You must have had trouble pasting the regex from an online regex tester to the JS code. However, there are issues here: 1) you have \\/\\/ that requires // to appear in the string, 2) you added ^ anchor close to the end of the pattern (and since it requires the start of string position, it prevented your regex from matching). Besides, no need for g and i modifiers, you only test the whole string against the pattern that has no letters in it.

Use

/^(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}\/(?:[12]?\d|3[0-2])$/

See the regex demo .

In JS, you may build the pattern dynamically for better readability:

 var octet = "(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)"; var rx = new RegExp("^" + octet + "(?:\\\\." + octet + "){3}/(?:[12]?\\\\d|3[0-2])$"); var strs = [ "1.1.1.1/8", "15.10.30.100/16", "100.10.10.44/24", "198.30.20.30/32", "1.1.1.1/0", "1.1.1.1/32", "1.1.1.1/33"]; for (var s of strs) { console.log(s, "=>", rx.test(s)); } 

Pattern details

• ^ - start of string
• (?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?) - an octet pattern, 0 to 255
• (?:\\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3} - 3 occurrences of:
  • \\. - a dot
  • (?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?) - an octet pattern
• \\/ - a slash
• (?:[12]?\\d|3[0-2]) - an opptional 1 or 2 followed with any digit ( 0 to 29 , matched with [12]?\\d ), or 3 followed with digits from 0 to 2 ( 30 to 32 )
• $ - end of string.