Javascript regex negation - Negate period on email regex

Question

I want an existing email regex to fail when entering a period (".") before the @.

This is the regex I have right now:

^[a-zA-Z]+[a-zA-Z0-9.][email protected]$

These should pass:

[email protected]
[email protected]

But these shouldn't:

[email protected]
[email protected]

The first case starting with period is handled but second case is not.

@dan08 not if it's square brackets - then it loses its special meaning. — VLAZ, Nov 29 '16 at 22:48
@dan08 yeah - most characters lose theirs special meaning in square brackets. The ones that most notably don't are `[]` (you still need to escape those), as well as `-` which indicates a character range. However, if placed in the beginning or the end, then it's treated as a dash. — VLAZ, Nov 29 '16 at 22:52

Matthew Crumley · Answer 1 · 2016-11-30T01:11:33.913

This should work without requiring two or more characters before the @ sign.

^[a-zA-Z][a-zA-Z0-9]*(?:\.+[a-zA-Z0-9]+)*@domain\.com$

Here's how it breaks down:

^                  Make sure we start at the beginning of the string
[a-zA-Z]           First character needs to be a letter
[a-zA-Z0-9]*       ...possibly followed by any number of letters or numbers.
(?:                Start a non-capturing group
    \.+            Match any periods...
    [a-zA-Z0-9]+   ...followed by at least one letter or number
)*                 The whole group can appear zero or more times, to
                     offset the + quantifiers inside. Otherwise the
                     period would be required
@domain\.com$      Match the rest of the string. At this point, the
                     only periods we've allowed are followed by at
                     least one number or letter

score 0 · Answer 2 · answered Nov 29 '16 at 22:51

0

I would try: ^[a-zA-Z]+[a-zA-Z0-9.]*[a-zA-Z0-9][email protected]$

answered Nov 29 '16 at 22:51

theTrueMikeBrown

125
4

Note that this requires at least two characters before the @, so `[email protected]`, for example, would fail. That might or might not be what you want. – Matthew Crumley Nov 29 '16 at 23:07
True - I was trying to keep this close to his original regex because it seemed that he wanted it to start with a letter. – theTrueMikeBrown Nov 29 '16 at 23:55
Oops, I didn't notice that it couldn't start with a number either. Anyway, that wasn't really a criticism, just a note about the exact meaning/implication of the expression. – Matthew Crumley Nov 30 '16 at 00:46

score 0 · Answer 3 · edited May 23 '17 at 12:33

Try this regex: ^[\w.+-]*[^\W.]@domain\.com$.

[\w.+-]* matches any number of alphanumerical characters, +, - and .
[^\W.] matches any character that is not a non-alphanumerical character or a . (which means any accepted character but .)
@domain\.com matches the rest of the email, change the domain as you wish or use @\w\.\w+ for matching most domains. (matching all domains is more complex, see more complete examples of email matching regex here)

Javascript regex negation - Negate period on email regex

3 Answers3