Add a new line at a specific position in a text file.

Question

I am trying to add a specific line of text in a file. Specifically between two boundaries.

An example of what it would look like if I wanted to add a line in between

Answer 1

try this method

using System.IO;
using System.Linq;

    /// 

    /// Add a new line at a specific position in a simple file        
    /// 
    /// Complete file path
    /// Line to search in the file (first occurrence)
    /// Line to be added
    /// insert above(false) or below(true) of the search line. Default: above 
    internal static void insertLineToSimpleFile(string fileName, string lineToSearch, string lineToAdd, bool aboveBelow = false)
    {          
        var txtLines = File.ReadAllLines(fileName).ToList();
        int index = aboveBelow?txtLines.IndexOf(lineToSearch)+1: txtLines.IndexOf(lineToSearch);
        if (index > 0)
        {
            txtLines.Insert(index, lineToAdd);
            File.WriteAllLines(fileName, txtLines);
        }
    }