Question

I have to write a checker which uses regular expressions to exclude things that end with a certain email ending like @tag5.com and @tagfive.com. Not really sure how to do this since I haven’t really worked a lot with regular expressions hope someone can show me how or point me in the right direction.

Only need to know what regular expression to use to be more specific.

—edit—

nm I found a better solution to the problem I was having and don’t have to deal with regular expressions.

Answer 1

It appears the only way to promulgate a negative and positive assertion is something like this:

Regex: '(?=^(?:(?!@tag5\.com).)*$)(?=.*@tagfive\.com)'

Target: '22$[e-mail]@tagfive.comasdf!'

Since, using (?!.*@tag5\.com) will match anything.

  (?= ^              # Positive lookahead at start of line
       (?:                # Group
            (?!               # Negative lookahead assertion
                @tag5\.com        # Can't be @tag5.com at this position
            )                 # End assertion
            .                 # This character is ok, take it
       )*                 # End group, do many times until ..
     $               # End of line
  )                  # End of positive lookahead assertion
  (?=                # Meanwhile, back at the start of line, positive lookahead 
     .*                   # Keep going until we find:
     @tagfive\.com        # this (and it MUST be here)
  )                 # End of positive lookahead