Question

After following this topic I am able to create
the new row but my question is how do
I save or write the new line to the file?

I tried ‘StreamWriter’ but it only writes the newly
created line.

Any suggestions please?

Here is my code so far:

string path = @"C:/CSV.txt";

string[] lines = File.ReadAllLines(path);

var splitlines = lines.Select(l => l.Split(','));

foreach (var line in splitlines)
{
   if(line[1].Contains("34"))
   {                                        
     line[1] = "100";
     var newline = string.Join(",", line);
     StreamWriter sr = new StreamWriter(path);    
     sr.WriteLine(newline);
     sr.Close();                                      
   }
 }

Answer 1

Here is your solution using StreamReader class:

String path = @"C:\CSV.txt";
List<String> lines = new List<String>();

if (File.Exists(path));
{
    using (StreamReader reader = new StreamReader(path))
    {
        String line;

        while ((line = reader.ReadLine()) != null)
        {
            if (line.Contains(","))
            {
                String[] split = line.Split(',');

                if (split[1].Contains("34"))
                {
                    split[1] = "100";
                    line = String.Join(",", split);
                }
            }

            lines.Add(line);
        }
    }

    using (StreamWriter writer = new StreamWriter(path, false))
    {
        foreach (String line in lines)
            writer.WriteLine(line);
    }
}

If you want to overwrite the file, use this StreamWriter constructor with append = false.