Altering Regex to allow apostrophe in email address

Question

At work, our current ValidationExpression looks horrible and very confusing for me. We are using the WebForms <asp:RegularExpressionValidator> user control which looks like this:

<asp:RegularExpressionValidator ID="regEmail" runat="server" 
    ValidationGroup="EditEmails"
    Text="*" ErrorMessage="Invalid email address." 
    ControlToValidate="txtAdd" 
    Display="Dynamic" 
    ValidationExpression="^(([A-Za-z0-9]+_+)|([A-Za-z0-9]+\-+)|([A-Za-z0-9]+\.+)|([A-Za-z0-9]+\++))*[A-Za-z0-9]+@((\w+\-+)|(\w+\.))*\w{1,63}\.[a-zA-Z]{2,6}$"/>

I need to somehow alter this to allow apostrophes ( ' ) inside an email because at the moment this expression is failing.

Example of an email that needs to pass this validation: Test.O'neill@example.co.uk

I am unsure what the expression does but I'm sure this could be made shorter (maybe not simpler but that does not matter as long as it works).

Anyone know of a better regular expression I could use which works against valid emails and takes this into consideration? Thank you!

EDIT: My question is different because the proposed duplicate question does not work for VB.Net RegularExpression Validator user control.

Possible duplicate of [How to validate an email address using a regular expression?](https://stackoverflow.com/questions/201323/how-to-validate-an-email-address-using-a-regular-expression) — Jason, Mar 16 '18 at 16:06
https://stackoverflow.com/questions/201323/how-to-validate-an-email-address-using-a-regular-expression — Jason, Mar 16 '18 at 16:06
Try [`^([a-z\d]+[_+.-])*[a-z\d']+@(\w+[.-])*\w{1,63}\.[a-z]+$`](https://regex101.com/r/CKffa0/1). It's **much** shorter than your current version and greatly simplifies it. — ctwheels, Mar 16 '18 at 16:07
That possible duplication question refers to PHP and I think ASP.NET would vary slightly and not work, especially considering the length of it. — Mayron, Mar 16 '18 at 16:08
@ctwheels Thank you. I'll test that out now :) I was really hoping to find a far more simplified one because the old looks like a terrible hack job. — Mayron, Mar 16 '18 at 16:13
@ctwheels no offense taken, it's not my code lol. I've only been asked to change it to provide apostrophe support. It hurts my eyes! — Mayron, Mar 16 '18 at 16:15
@Mayron it should work in vb. Have you added the `i` flag (case-insensitive)? It's a regex option — ctwheels, Mar 16 '18 at 16:27
@ctwheels Thanks! I followed this stackoverflow question to add that option: https://stackoverflow.com/questions/2641236/make-regular-expression-case-insensitive-in-asp-net-regularexpressionvalidator and it worked! — Mayron, Mar 16 '18 at 16:32

score 3 · Accepted Answer · answered Mar 16 '18 at 16:37

See regex in use here

^([a-z\d]+[_+.-])*[a-z\d']+@(\w+[.-])*\w{1,63}\.[a-z]+$

^ Assert position at the start of the line
([a-z\d]+[_+.-])* Capture the following any number of times
- [a-z\d]+ Match any ASCII letter or digit one or more times (also matches uppercase variants with i flag enabled)
- [_+.-] Match any character in the set
[a-z\d']+ Match any ASCII letter, digit, or apostrophe one or more times
@ Match this literally
(\w+[.-])* Capture the following any number of times
- \w+ Match any word character one or more times
- [.-] Match any character in the set
\w{1,63} Match any word character between one and 63 times
\. Match a literaly dot .
[a-z]+ Match any ASCII letter one or more times
$ Assert position at the end of the line

To implement the above pattern in a case-insensitive manner, add the RegexOptions.IgnoreCase flag. For more information see this post.

Thanks a bunch for the breakdown! Very useful. Much appreciated :) — Mayron, Mar 16 '18 at 16:39

Altering Regex to allow apostrophe in email address

1 Answers1