How to create text file based on date in c#

Question

I have a text file which is getting populated continuously from the server data.Here is the sample data present in the text file..

1/1/2014   234  34  456788889989 23 
1/1/2014   234  34  456788889989 23 
1/1/2014   234  34  456788889989 23 
2/1/2014   234  34  456788889989 23 
2/1/2014   234  34  456788889989 23 
2/1/2014   234  34  456788889989 23 
3/1/2014   234  34  456788889989 23 
3/1/2014   234  34  456788889989 23 
3/1/2014   234  34  456788889989 23 

Here is my code to create text file..

System.IO.File.WriteAllText(@"D:\datewise.txt", "");

Here for every date there is lot of data present as row.Now as soon as date changes i have to create a text file and copy all the data from sample text file to the newly created text file.How to achieve this?

Answer 1

    using System.Text.RegularExpressions;
    using System.IO;
    using System.Text;

    string pattern = "^3/1/2014.*"; 
    string strPath = new string("c:\\"); 
    string strDateTime = DateTime.Now.ToString("yyyyMMdd"); 
    string FileToCopy = "c:\\regexTest.txt"; 
    string NewCopy = strPath + strDateTime + ".txt"; 
    StringBuilder sb = new StringBuilder(""); 
    if (System.IO.File.Exists(FileToCopy) == true) { 
    string[] lines = File.ReadAllLines(FileToCopy); 
    foreach (string line in lines) { 
    if (Regex.IsMatch(line, pattern)) { 
    sb.Append(line + System.Environment.NewLine); 
    } 
    } 
    } 

    if (sb.Length > 0) { 
    System.IO.File.WriteAllText(NewCopy, sb.ToString); 
    }