using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"[a-z0-9!#$%&'*+\/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+\/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?
";
string input = @"frankp@gmail.com
shannon.eee@gmail.com
franks&shannon@gmail.com
frank%ddd@gmail.com
frank@gmail$.com
frank@gmail_gmail.com
frank@gmail.research.com
joe@ggg.gg.cccc.com
joe..joe@gmail.com
/
https://stackoverflow.com/questions/5174171/fix-regular-expression-for-emails-to-not-allow-consecutive-periods/5174201#5174201
*To avoid matching two consecutive dots you can add a negative lookahead at the beginning of your regular expression:
/^(?!.*\.{2})[a-z0-9etc...
------------
It will fail to match if there are two consecutive periods anywhere in the string and it doesn't require any other modifications to your original regular expression.
However it seems a bad idea as your regular expression isn't correct in the first place. If you insist on using regular expressions to validate email addresses, try this:
*/
wilson..gmail.com
wilson.gmail.com
^(?!.*\.{2})/[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?
";
RegexOptions options = RegexOptions.Multiline;
foreach (Match m in Regex.Matches(input, pattern, options))
{
Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
}
}
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx