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I have the following Regular Expression which matches an email address format:

^[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+$

This is used for validation with a form using JavaScript. However, this is an optional field. Therefore how can I change this regex to match an email address format, or an empty string?

From my limited regex knowledge, I think \b matches an empty string, and | means "Or", so I tried to do the following, but it didn't work:

^[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+$|\b

I have the following Regular Expression which matches an email address format:

^[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+$

This is used for validation with a form using JavaScript. However, this is an optional field. Therefore how can I change this regex to match an email address format, or an empty string?

From my limited regex knowledge, I think \b matches an empty string, and | means "Or", so I tried to do the following, but it didn't work:

^[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+$|\b

• javascript
• regex
• email-validation
• string

Share Improve this question Follow edited Jul 27, 2012 at 9:55 Teun Zengerink 4,39355 gold badges3232 silver badges3232 bronze badges asked Jul 26, 2010 at 9:04 CurtisCurtis 103k6868 gold badges276276 silver badges357357 bronze badges 4

• 6 If you must validate an email, be as permissive as possible. You'd be surprised how easy it is to miss real, valid and functional email addresses with home-baked regexes. Your regex, for instance, will fail on these valid addresses: [email protected], [email protected], root@localhost, [email protected]. – Zano Commented Jul 26, 2010 at 9:23
• 1 Agreeing with Zano, just take a look at this regex ex-parrot.com/pdw/Mail-RFC822-Address.html – Anders Commented Jul 26, 2010 at 9:36
• @Anders wow, thats a very complex regex! I think I've misunderestimated the complexity of regex – Curtis Commented Jul 26, 2010 at 9:50
• 5 No, I think you've misunderestimated the complexity of email validation :-) – Zano Commented Jul 26, 2010 at 9:55

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5 Answers 5

Sorted by: Reset to default 286

To match pattern or an empty string, use

^$|pattern

Explanation

• ^ and $ are the beginning and end of the string anchors respectively.
• | is used to denote alternates, e.g. this|that.

References

• regular-expressions.info/Anchors and Alternation

---

On \b

\b in most flavor is a "word boundary" anchor. It is a zero-width match, i.e. an empty string, but it only matches those strings at very specific places, namely at the boundaries of a word.

That is, \b is located:

• Between consecutive \w and \W (either order):
  • i.e. between a word character and a non-word character
• Between ^ and \w
  • i.e. at the beginning of the string if it starts with \w
• Between \w and $
  • i.e. at the end of the string if it ends with \w

References

• regular-expressions.info/Word Boundaries

---

On using regex to match e-mail addresses

This is not trivial depending on specification.

Related questions

• What is the best regular expression for validating email addresses?
• Regexp recognition of email address hard?
• How far should one take e-mail address validation?

An alternative would be to place your regexp in non-capturing parentheses. Then make that expression optional using the ? qualifier, which will look for 0 (i.e. empty string) or 1 instances of the non-captured group.

For example:

/(?: some regexp )?/

In your case the regular expression would look something like this:

/^(?:[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+)?$/

No | "or" operator necessary!

Here is the Mozilla documentation for JavaScript Regular Expression syntax.

I'm not sure why you'd want to validate an optional email address, but I'd suggest you use

^$|^[^@\s]+@[^@\s]+$

meaning

^$        empty string
|         or
^         beginning of string
[^@\s]+   any character but @ or whitespace
@         
[^@\s]+
$         end of string

You won't stop fake emails anyway, and this way you won't stop valid addresses.

\b matches a word boundary. I think you can use ^$ for empty string.

^$ did not work for me if there were multiple patterns in regex.

Another solution:

/(pattern1)(pattern2)?/g

"pattern2" is optional. If empty, not matched.

? matches (pattern2) between zero and one times.

Tested here ("m" is there for multi-line example purposes): https://regex101.com/r/mezfvx/1

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