使用正则表达式替换 email 字符串中倒数第二个字符（点）

Question

Please i would love to replace the second last occurrence of a char in a, the length of the strings can vary but the delimiter is always same I will give some examples below and what I have tried Input 1: james.sam.uri.stackoverflow.com

Output 1: james.sam.uri@stackoverflow.com

Input 2: noman.stackoverflow.com

Output 2: noman@stackoverflow.com

Input 3: queen.elizabeth.empire.co.uk

Output 3: queen.elizabeth@empire.co.uk

My solution

//This works but I don't want this as its not a regex solution
const e = "noman.stackoverflow.com"
var index = e.lastIndexOf(".", email.lastIndexOf(".")-1)
return ${e.substring(0,index)}@${e.substring(index+1)}

Regex
e.replace(/\.(\.*)/, @$1)
//this works for Input 2 not Input 1, i need regex that would work for both, it only matches the first dot

Answer 1

The issue in the example data for the second last dot, is that the last example ends on .co.uk

One option for these specific examples could be using a pattern to exclude that specific part.

(\S+)\.(?!co\.uk$)(\S*?\.[^\s.]+)$

• (\S+) Capture group 1 , match 1+ non whitespace chars
• \.(?.co\.uk$) Match a . followed by a negative lookahead asserting directly to the right is not co.uk
• ( Capture group 2
  • \S*?\. Match 0+ times a non whitspace char non greedy and then a .
  • [^\s.]+ Match 1+ times a non whitespace char except a .
• ) Close group 2
• $ End of string

See a regex demo .

 [ "james.sam.uri.stackoverflow.com", "noman.stackoverflow.com", "queen.elizabeth.empire.co.uk" ].forEach(s => console.log(s.replace(/(\S+)\.(?.co\?uk$)(\S*.\.[^\s,]+)$/; "$1@$2")) );

Answer 2

Here's another approach:

(\S+)\.(\S+\.\S{3,}?)$
       (            )$  At the end of the string, capture by
             \S{3,}?    lazily matching 3+ non-whitespace characters
        \S+\.           and any non-whitespace characters with period in front.
(\S+)\.                 Also capture anything before the separating period.

Notably, it would fail for an email like test.stackoverflow.co.net . If that format is a requirement, I'd recommend a different approach.

 [ "james.sam.uri.stackoverflow.com", "noman.stackoverflow.com", "queen.elizabeth.empire.co.uk", "test.stackoverflow.co.net" ].forEach(s => console.log(s.replace(/(\S+)\.(\S+\.\S{3,}?)$/, "$1@$2")) );