public enum FileMode
{
// Creates a new file. An exception is raised if the file already exists.
CreateNew = 1,
// Creates a new file. If the file already exists, it is overwritten.
Create = 2,
// Opens an existing file. An exception is raised if the file does not exist.
Open = 3,
// Opens the file if it exists. Otherwise, creates a new file.
OpenOrCreate = 4,
// Opens an existing file. Once opened, the file is truncated so that its
// size is zero bytes. The calling process must open the file with at least
// WRITE access. An exception is raised if the file does not exist.
Truncate = 5,
// Opens the file if it exists and seeks to the end. Otherwise,
// creates a new file.
Append = 6,
}
using (FileStream stream = new FileStream(Path, FileMode.Append, FileAccess.Write, FileShare.ReadWrite))
using (TextWriter writer = new StreamWriter(stream))
{
writer.WriteLine("Blablabla");
writer.Flush();
}