Negate characters for email Regex

Question

I am trying to write a basic regex to validate an email address. For this specific case I am trying to make sure the string inputted only includes letters, numbers, "." and "@". Or in other words I am making sure it doesnt include characters like £&¬! etc.

I tried getting the NOT version of this [[:alnum:].@]+ so that it would highlight a character not in that set but I couldnt get it to work. I also tried characters not in [\W.@]+ (the . is meant to be escaped but stackoverflow is removing the \ from this post) but the \W is still picking up the . and @ symbols.

If I understood you correctly, you're saying `\W` is picking up `.` and `@`? That just means you can't use `\W` then, right? I would think, if you want a string that only has letters, numbers, . and @, you would want `[\w.@]`, note the lower-case `w`, and don't do any negation. Sidenote, I'm pretty sure (not positive) that you don't need to escape `.` inside brackets — dwanderson, May 04 '16 at 16:19
Is there a reason why `[\w.@]` or `[a-zA-Z0-9.@]` does not meet your needs? — Steven Doggart, May 04 '16 at 16:20
I should have been clearer in saying that I want characters that do not match [\w.@] or [a-zA-Z0-9.@] to be highlighted — Mufasatheking, May 04 '16 at 16:26
Sounds like you can just use `[^\w@.]` to find bad characters. — coffee-converter, May 04 '16 at 16:29
`[\W.@]+ (the . is meant to be escaped` - Put back ticks around it `[\W\.@]+` But, the dot `.` does not need to be escaped inside character classes. — , May 04 '16 at 16:33
But, what I would use is `(?:[^\w@.]|_)+` to find invalid chars. — , May 04 '16 at 16:46

score 0 · Answer 1 · answered May 04 '16 at 16:20

There are lots of examples of regex patterns for email addresses out there. Here is a very basic/naive one that allows only alphanumeric and periods (and a single @). This one does not care if the domain part is in a valid format (i.e. things like "abc@gmail......com" would pass):

^[A-Za-z0-9.]+@[A-Za-z0-9.]+$

score 0 · Accepted Answer · answered May 04 '16 at 16:20

You can ...

... match for positives (your regex plus anchors to make sure it matches the complete test string)
( ^[[:alnum:].@]+$ )
... match for negatives which means that at some point an illegal character occurs
( [^[:alnum:].@] )

... and check whether there has been a match. n the first case that means 'ok', in the second 'fail'.

Theer are regex dialects that do not support posix character classes, in this case replace [:alnum:] with 0-9a-zA-Z.

Negate characters for email Regex

2 Answers2