正则表达式屏蔽 email 除了域之前的三个字符

Question

I am trying to mask email address in the following different ways.

1. Mask all characters except first three and the ones follows the @ symbol. This expression works fine.

   (?<=.{3}).(?=[^@]*?@)

   abcdefgh@gmail.com -> abc*****@gmail.com

2. Mask all characters except last three before @ symbol.

   Example: abcdefgh@gmail.com -> *****fgh@gmail.com

   I am not sure how to check for @ and do reverse match.

Can someone throw pointers on this?

Answer 1

Maybe you could do a positive lookahead:

.(?=.*...@)

See the online Demo

• . - Any character other than newline.
• (?=.*...@) - Positive lookahead for zero or more characters other than newline followed by three characters other than newline and @ .

Answer 2

You could use a negated character class [^\s@] matching a non whitespace char except an @. Then assert what is on the right is that negated character class 3 times followed by matching the @ sign.

In the replacement use *

[^\s@](?=[^@\s]*[^@\s]{3}@)

• [^\s@] Negated character class, match a non whitespace char except @
• (?= Positive lookahead, assert what is on the right is
  • [^@\s]* Match 0+ times a non whitespace char except @
  • [^@\s]{3} Match 3 times a non whitespace char except @
  • @ Match the @
• ) Close lookahead

Regex demo

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If there can be only a single @ in the email address, you could for example make use of a finite quantifier in the positive lookbehind:

(?<=(?<!\S)[^\s@]{0,1000})[^\s@](?=[^@\s]*[^@\s]{3}@[^\s@]+\.[a-z]{2,}(?!\S))

Regex demo