如何从C＃中的文本中提取连续的电子邮件地址

Question

I have the following three examples of strings:

string1 = "abcd@efg.com this is just some text. these are just some numbers 123456 xyz@xyz.com asdasd asdad"

string2 = "abcd@efg.com mnop@qrs.com This is just some text. these are just some numbers 123456 xyz@xyz.com asdasd asd"

string3 = "abcd@efg.com mnop@qrs.com uvw@xyz.com This is just some text. these are just some numbers 123456 xyz@xyz.com asdad"

Final output should be a List consisting of all the emails that appear consecutively at the beginning of the string.

Output for string1 - one email address

Output for string3 - three email addresses

Address "xyz@xyz.com" should be ignored as it appears between some other text. Is there any solution for this? The existing method returns all the addresses.

    private List<string> ExtractEmails(string strStringGoesHere)
    {
        List<string> lstExtractedEmails = new List<string>();
        Regex reg = new Regex(@"[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,6}", RegexOptions.IgnoreCase);
        Match match;
        for (match = reg.Match(strStringGoesHere); match.Success; match = match.NextMatch())
        {
            if (!(lstExtractedEmails.Contains(match.Value)))
            {
                lstExtractedEmails.Add(match.Value);
            }
        }
        return lstExtractedEmails;
    }

Answer 1

You may use \\G anchor that only matches at the start of the string and then at the end of each successful match:

@"(?i)\G\s*([A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,6})"

See this demo

Details

• (?i) - inline case insensitive flag
• \\G - anchor that only matches at the start of the string and at the end of each successful match
• \\s* - 0+ whitespaces
• ([A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[AZ]{2,6}) - Group 1 matching an email like substring (there are other patterns that you may use here , but generally, it is something like \\S+@\\S+\\.\\S+ ).

C# demo :

var strs = new List<string> {"abcd@efg.com this is just some text. these are just some numbers 123456 xyz@xyz.com asdasd asdad",
    "abcd@efg.com mnop@qrs.com This is just some text. these are just some numbers 123456 xyz@xyz.com asdasd asd",
    "abcd@efg.com mnop@qrs.com uvw@xyz.com This is just some text. these are just some numbers 123456 xyz@xyz.com asdad" };
foreach (var s in strs) 
{
    var results = Regex.Matches(s, @"(?i)\G\s*([A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,6})")
        .Cast<Match>()
        .Select(x => x.Groups[1].Value);
    Console.WriteLine(string.Join(", ", results));
}

Results:

abcd@efg.com
abcd@efg.com, mnop@qrs.com
abcd@efg.com, mnop@qrs.com, uvw@xyz.com