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Opposite of regex.matches?

Posted on 2011-03-08

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Last Modified: 2012-05-11

Right now I'm using reg expressions to locate only valid email addresses within a long string. This string is a bunch of email addresses separated by a comma.

mc = Regex.Matches(strEmailAddresses, "([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5})")

How can I find out only the ones that do NOT match? ie that FAIL the regular expression?

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Question by:RobertNZana

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9 Comments

LVL 19

Expert Comment

by:daveamour

ID: 350708572011-03-08

How is your string structured - ie how are email addresses split up within the string?

LVL 9

Author Comment

by:RobertNZana

ID: 350708752011-03-08

Simple string. All email addresses separated by comma. Purpose of this function is to report back those email addresses which are invalid.

Example: "myaddress1@mail.com, myaddress2@mail.com, INVALID_EMAIL@, myaddress3@mail.com"

The function should return "INVALID_EMAIL@".

LVL 23

Expert Comment

by:wdosanjos

ID: 350710672011-03-08

Try this:

Dim strEmailAddresses As String = "myaddress1@mail.com, myaddress2@mail.com, INVALID_EMAIL@, myaddress3@mail.com"
Dim emailAddr As String

For Each emailAddr in strEmailAddresses.Split(",")
	emailAddr = emailAddr.Trim()
	If Not Regex.IsMatch(emailAddr, "([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5})") Then
		Console.WriteLine("'{0}' invalid email address", emailAddr)
	End If
Next

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LVL 9

Author Comment

by:RobertNZana

ID: 350715452011-03-08

For some reason this email address is passing when it should not: myemail.@mail.net

LVL 23

Accepted Solution

by:wdosanjos

wdosanjos earned 500 total points

ID: 350719312011-03-08

Please change the regular expression to:

^[a-zA-Z0-9_\-]+([_\-\.]?[a-zA-Z0-9]+)*?@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5})$

This one better handles the dot, so the following email addresses are not valid:

my.email.@address.com
.my.email@address.com
my..email@address.com

Dim strEmailAddresses As String = "my.email.@address.com, .my.email@address.com, my..email@address.com, myaddress1@mail.com, myaddress2@mail.com, INVALID_EMAIL@, myaddress3@mail.com, a@address.com"
Dim emailAddr As String

For Each emailAddr in strEmailAddresses.Split(",")
        emailAddr = emailAddr.Trim()
        If Not Regex.IsMatch(emailAddr, "^[a-zA-Z0-9_\-]+([_\-\.]?[a-zA-Z0-9]+)*?@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5})$") Then
                Console.WriteLine("'{0}' invalid email address", emailAddr)
        End If
Next

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LVL 9

Author Comment

by:RobertNZana

ID: 350719572011-03-08

But will john.smith@att.net work? This is valid.

LVL 23

Expert Comment

by:wdosanjos

ID: 350723012011-03-08

Yes, that works. I mean is a valid email, so Regex.IsMatch returns true.

LVL 9

Author Comment

by:RobertNZana

ID: 350735622011-03-08

Thanks. What is the reg ex statement to check if an email is valid?

LVL 23

Expert Comment

by:wdosanjos

ID: 350742102011-03-08

Regex.IsMatch just returns true if the string provided matches the regular expression. In this case the regular expression is to validate the email address format.

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