They can get ridiculously convoluted as in the case above and, according to the specification, are often too strict anyway.
If you actually check the Google query I linked above, people have been writing (or trying to write) RFC-compliant regular expressions to parse email addresses for years.
Would you like to answer one of these unanswered questions instead?
This uses the Internet Address class which has most of the RFC mail address checks implmented.
a regex alone on clientside, does not know if there is a mailserver nor if the domain itself exists.
it merly checks if the syntax of any email is valid or not.
* * @author Roedy Green, Canadian Mind Products * @version 1.0 to do: check validity of & in first part of email address.
Does not probe to see if mailserver * exists in DNS or online. See Validate Email File for * an example of how to use this class.I've recently written about using bash arrays and bash regular expressions, so here's a more useful example of using them to test IP addresses for validity.To belabor the obvious: IP addresses are 32 bit values written as four numbers (the individual bytes of the IP address) separated by dots (periods).Here’s a fairly common code sample from Rails Applications with some sort of authentication system: If you’re experienced at Regex, this seems simple. Sections 3.2.4 and 3.4.1 of the RFC go into the requirements on how an email address needs to be formatted and, well, there’s not much you can’t do in your email address when quotes or backslashes are involved.If (like me when I first saw this) you AREN’T experienced at Regex, it takes a while to parse. The local string (the part of the email address that comes before the @) can contain any of these characters: is a valid email address. For this reason, for a time I began running any email address against the following regular expression instead: Simple, right? This is often the most I do and, when paired with a confirmation field for the email address on your registration form, can alleviate most problems with user error.An is a digital signature with several key properties.