using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"^(.*)_[12]?\d{1,2}\.[12]?\d{1,2}\.[12]?\d{1,2}\.[12]?\d{1,2}_\d+\.([a-z]{3,4})$";
string substitution = @"\1.\2";
string input = @"pdf_of_filename_53613785621.183761237_127.10.10.0_8726347.xls";
RegexOptions options = RegexOptions.IgnoreCase;
Regex regex = new Regex(pattern, options);
string result = regex.Replace(input, substitution, 1);
}
}
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