title: C# need regular expression to capture the second occurence after a underscore
body: <p>I am using the regular expression below to capture all numbers/letters after a underscore but I need to capture only the second occurence i.e "00500" as you see below:</p>
  
  <pre><code>regular expresion: (?&lt;=_)[a-zA-Z0-9]+
  
  string:
  "-rw-rw-rw- 1 rats rats 31K Sep 17 13:33 /opt/data/automation_sent/20180918/labc/0/20180918_00500.itx"
  </code></pre>
  
  <p>I am doing in C# and I thought the value would be in the second group[1] but it is not; it only captures the string "_sent":</p>
  
  <pre><code>        string temp2 = "";
          Regex getValueAfterUnderscore = new Regex(@"(?&lt;=_)[a-zA-Z0-9]+");
          Match match2 = getValueAfterUnderscore.Match(line);
          if (match2.Success)
          {
              temp2 = match2.Groups[1].Value;
              Console.WriteLine(temp2); 
          }
  </code></pre>
  
  <p>Any ideas? Thank you!</p>