将长度验证合并到现有的电子邮件地址格式正则表达式中

Question

I am using this regex in C# for email format validation based on information from http://www.regular-expressions.info/email.html :

Regex.IsMatch("test@gmail.com", 
              @"^[A-Z0-9'._%+-]+@(?:[A-Z0-9-]+\.)+[A-Z]{2,4}$",RegexOptions.IgnoreCase);

I would also like to validate that the total length of the email is between 5 - 254 characters. How should this regex be modified to satisfy the length condition? I don't want to check the length of the string in C# explicitly.

Answer 1

I suggest you not put such restriction. if you really want the regex. As paxdiablo said many number of questions exist in SO. Email validation in regex

^.{1,254}$

http://rick.measham.id.au/paste/explain.pl?regex=%5E.%7B1%2C150%7D%24

Answer 2

尽管单独进行长度检查可能更干净一些，但是您可以通过在表达式的开头添加不捕获的前瞻来合并长度约束：

^(?=.{5,254})[A-Z0-9'._%+-]+@(?:[A-Z0-9-]+\.)+[A-Z]{2,4}$