I tweeted about an interesting blog post regarding Regex and email validation.

The point of the post makes is don’t even try to validate an email address because basically everything with one @ is a valid email address.

Nevertheless there are several Regexs in there that I’m not familiar with, so lets dig deeper!


\A and \z are patterns to match the beginning and end of a string.

[^@] is a character set [] for any character except ^ the character @.

+ means: match one or more of the preceding token. So in our case one or more set of characters that don’t include @.

@ simply matches @.

Recap: so far we’re matching the start part of the email address and it’s @.

([^@\.]+\.)+ deserves to be split:

  • () is a capturing group, and it groups multiple tokens together and creates a capture group for extracting a substring or using a backreference. That’s why it’s followed by +.

  • [^@\.]+ as seen before is a character set for any character except @ and \.. \. stands for is the escaped ., we need to escape it because . is a special Regex character that matches any character except line breaks. Again we have the +, which we explained already.

  • \. at the end of any number of group of characters that do not include @ or . we need to have a ..

Recap: this second part matches the second half of the email address, and says any number of groups of characters that doesn’t include @ or . and end with .. Something like mokagio42@_email.provider.that.is.nice._com.

  • [^@\.]+ we’ve already seen all the elements of this group, and it’s function is to match the “termination” of the email address.

Wrapping it up

Given an email address like moka.gio42+tech-journal@e-mail.address.com we have:

  • moka.gio42+tech-journal matched by [^@]+
  • @ matched by @
  • e-mail.address.com matched by ([^@\.]+\.)+[^@\.]+