How to efficiently read only last line of the text file

Question

Need to get just last line from big log file. What is the best way to do that?

Answer 1

You want to read the file backwards using ReverseLineReader:

How to read a text file reversely with iterator in C#

Then run .Take(1) on it.

var lines = new ReverseLineReader(filename);
var last = lines.Take(1);

You'll want to use Jon Skeet's library MiscUtil directly rather than copying/pasting the code.

Answer 2

    String lastline="";
    String filedata;

    // Open file to read
    var fullfiledata = new FileStream(filepath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
    StreamReader sr = new StreamReader(fullfiledata);

    //long offset = sr.BaseStream.Length - ((sr.BaseStream.Length * lengthWeNeed) / 100);
    // Assuming a line doesnt have more than 500 characters, else use above formula
    long offset = sr.BaseStream.Length - 500;

    //directly move the last 500th position
    sr.BaseStream.Seek(offset, SeekOrigin.Begin);

    //From there read lines, not whole file
    while (!sr.EndOfStream)
    {
        filedata = sr.ReadLine();
        // Interate to see last line
        if (sr.Peek() == -1)
        {
            lastline = filedata;
        }
    }       

    return lastline;
}

Answer 3

Or you can do it two line (.Net 4 only)

var lines = File.ReadLines(path);
string line = lines.Last();