Delete specific line from a text file?

Question

I need to delete an exact line from a text file but I cannot for the life of me workout how to go about doing this.

Any suggestions or examples would be greatly appr

Answer 1

I cared about the file's original end line characters ("\n" or "\r\n") and wanted to maintain them in the output file (not overwrite them with what ever the current environment's char(s) are like the other answers appear to do). So I wrote my own method to read a line without removing the end line chars then used it in my DeleteLines method (I wanted the option to delete multiple lines, hence the use of a collection of line numbers to delete).

DeleteLines was implemented as a FileInfo extension and ReadLineKeepNewLineChars a StreamReader extension (but obviously you don't have to keep it that way).

public static class FileInfoExtensions
{
    public static FileInfo DeleteLines(this FileInfo source, ICollection<int> lineNumbers, string targetFilePath)
    {
        var lineCount = 1;

        using (var streamReader = new StreamReader(source.FullName))
        {
            using (var streamWriter = new StreamWriter(targetFilePath))
            {
                string line;

                while ((line = streamReader.ReadLineKeepNewLineChars()) != null)
                {
                    if (!lineNumbers.Contains(lineCount))
                    {
                        streamWriter.Write(line);
                    }

                    lineCount++;
                }
            }
        }

        return new FileInfo(targetFilePath);
    }
}

public static class StreamReaderExtensions
{
    private const char EndOfFile = '\uffff';

    /// <summary>
    /// Reads a line, similar to ReadLine method, but keeps any
    /// new line characters (e.g. "\r\n" or "\n").
    /// </summary>
    public static string ReadLineKeepNewLineChars(this StreamReader source)
    {
        if (source == null)
            throw new ArgumentNullException(nameof(source));

        char ch = (char)source.Read();

        if (ch == EndOfFile)
            return null;

        var sb = new StringBuilder();

        while (ch !=  EndOfFile)
        {
            sb.Append(ch);

            if (ch == '\n')
                break;

            ch = (char) source.Read();
        }

        return sb.ToString();
    }
}

Answer 2

One way to do it if the file is not very big is to load all the lines into an array:

string[] lines = File.ReadAllLines("filename.txt");
string[] newLines = RemoveUnnecessaryLine(lines);
File.WriteAllLines("filename.txt", newLines);

Answer 3

The best way to do this is to open the file in text mode, read each line with ReadLine(), and then write it to a new file with WriteLine(), skipping the one line you want to delete.

There is no generic delete-a-line-from-file function, as far as I know.

Answer 4

No rocket scien code require .Hope this simple and short code will help.

List linesList = File.ReadAllLines("myFile.txt").ToList();            
linesList.RemoveAt(0);
File.WriteAllLines("myFile.txt"), linesList.ToArray());

OR use this

public void DeleteLinesFromFile(string strLineToDelete)
    {
        string strFilePath = "Provide the path of the text file";
        string strSearchText = strLineToDelete;
        string strOldText;
        string n = "";
        StreamReader sr = File.OpenText(strFilePath);
        while ((strOldText = sr.ReadLine()) != null)
        {
            if (!strOldText.Contains(strSearchText))
            {
                n += strOldText + Environment.NewLine;
            }
        }
        sr.Close();
        File.WriteAllText(strFilePath, n);
    }