[regex] Regex empty string or email

I found a lot of Regex email validation in SO but I did not find any that will accept an empty string. Is this possible through Regex only? Accepting either empty string or email only? I want to have this on Regex only.

If you are using it within rails - activerecord validation you can set allow_blank: true

As:

validates :email, allow_blank: true, format: { with: EMAIL_REGEX }

The answers above work ($ for empty), but I just tried this and it also works to just leave empty like so:

/\A(INTENSE_EMAIL_REGEX|)\z/i

Same thing in reverse order

/\A(|INTENSE_EMAIL_REGEX)\z/i

this will solve, it will accept empty string or exact an email id

"^$|^([\w\.\-]+)@([\w\-]+)((\.(\w){2,3})+)$"

matching empty string or email

(^$|^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.(?:[a-zA-Z]{2}|com|org|net|edu|gov|mil|biz|info|mobi|name|aero|asia|jobs|museum)$)

matching empty string or email but also matching any amount of whitespace

(^\s*$|^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.(?:[a-zA-Z]{2}|com|org|net|edu|gov|mil|biz|info|mobi|name|aero|asia|jobs|museum)$)

see more about the email matching regex itself:

http://www.regular-expressions.info/email.html

I prefer /^\s+$|^$/gi to match empty and empty spaces.

console.log("  ".match(/^\s+$|^$/gi));_x000D_
console.log("".match(/^\s+$|^$/gi));

Don't match an email with a regex. It's extremely ugly and long and complicated and your regex parser probably can't handle it anyway. Try to find a library routine for matching them. If you only want to solve the practical problem of matching an email address (that is, if you want wrong code that happens to (usually) work), use the regular-expressions.info link someone else submitted.

As for the empty string, ^$ is mentioned by multiple people and will work fine.