Deleting Text In Between Two Lines

Question

I'm trying to remove lines that are in between two different lines. Currently, I have:

string s = "";
String path = @"C:\TextFile";
StreamWriter sw = new StreamWriter(path, true);
StreamReader sr = new StreamReader(path, true);

s = sr.ReadLine();

if (s=="#Start")
{
    while (s != "#End")
    {
        sw.WriteLine(s);
        //need something here to overwrite existing data with s not just add s
    }
}  

sr.Close();
sw.Close();  

The content of my text file looks like this:

#Start
facebook.com
google.com
youtube.com
#End     

I tried to follow Efficient way to delete a line from a text file however it deletes any file containing a certain character, whereas there are other lines outside of the range containing .com that I don't want to remove

I want to delete all the contents in between start and end so after the method runs the remains of the text file is

#Start
#End

Answer 1

You have two problems:

1. You're only reading the first line, and then you're using that one value everywhere. Clearly if s == "#Start", it can't also satisfy the condition s == "#End", etc.
2. Even if you were reading each line, you expect that after #End there will be no more data - you don't loop through the rest of the lines, you just stop writing. Based on your question, I think you want to write all lines from the file and only change those between #Start and #End.

-

Perhaps a constant loop as below would be better?:

string s;
bool inRewriteBlock = false;
while ((s = sr.ReadLine()) != null)
{
    if (s == "#Start")
    {
        inRewriteBlock = true;
    }
    else if (s == "#End")
    {
        inRewriteBlock = false;
    }
    else if (inRewriteBlock)
    {
        sw.WriteLine(s);
        //need something here to overwrite existing data with s not just add s
    }
    else
    {
        sw.WriteLine(s);
    }
}

By default, the code will output every line it reads verbatim. However, if it reads #Start it will enter a special mode (inRewriteBlock == true) where you can rewrite those lines however you want. Once it reaches #End it will transition back into the default mode (inRewriteBlock == false).

Answer 2

You should check and rewrite every thing between #Start and #End instead of file is start with "#Start" only.

You can try this:

            //Read all text lines first
        string[] readText = File.ReadAllLines(path);

        //Open the text file to write
        var oStream = new FileStream(path, FileMode.Truncate, FileAccess.Write, FileShare.Read);
        StreamWriter sw = new System.IO.StreamWriter(oStream);


        bool inRewriteBlock = false;

        foreach (var s in readText)
        {
            if (s.Trim() == "#Start")
            {
                inRewriteBlock = true;
                sw.WriteLine(s);
            }
            else if (s.Trim() == "#End")
            {
                inRewriteBlock = false;
                sw.WriteLine(s);
            }
            else if (inRewriteBlock)
            {
                //REWRITE DATA HERE (IN THIS CASE IS DELETE LINE THEN DO NOTHING)
            }
            else
            {
                sw.WriteLine(s);
            }
        }

        sw.Close();

Answer 3

You can simply do this: (This assumes file can be stored in memory)

string path = @"C:\\Users\\test\\Desktop\\Test.txt";

List<string> fileData = File.ReadAllLines(path).ToList();
// File.ReadAllLines(path).ToList().Select(y => y.Trim()).ToArray().ToList(); will remove all trailing/preceding spaces in data
int startsWith = fileData.IndexOf("#Start");
int endsWith = fileData.IndexOf("#End");

if(startsWith != -1 && endsWith != -1)
  fileData.RemoveRange(startsWith+1, endsWith-1);

File.WriteAllLines("C:\\Test\\Test1.txt", fileData.ToArray());

It doesnt account for special scenarios like startsWith is at the end of the file with no endswith.