C# - Declaring output as a string

I have some code that removes duplicate lines from a text file, it then outputs the result (text with no duplicates) to a file. How could I also declare this output as a string as well?

private static void RemoveDuplicate(string sourceFilePath, string destinationFilePath)
{
    var readLines = File.ReadAllLines(sourceFilePath, Encoding.Default);

    File.WriteAllLines(destinationFilePath, readLines.Distinct().ToArray(), Encoding.Default);
}

You could have the method return a string value:

private static string RemoveDuplicate(string sourceFilePath, string destinationFilePath)
{
    var readLines = File.ReadAllLines(sourceFilePath, Encoding.Default);
    var result = readLines.Distinct().ToArray();
    File.WriteAllLines(destinationFilePath, result, Encoding.Default);
    return string.Join(Environment.NewLine, result);
}

and then:

string result = RemoveDuplicate("source.txt", "dest.txt");

String should be returned, not string array so,use String.join, you can use your own delimiter to seperate lines, i used comma, you could use a new line.

private static string RemoveDuplicate(string sourceFilePath, string destinationFilePath)
{
var readLines = File.ReadAllLines(sourceFilePath, Encoding.Default);
var result = readLines.Distinct().ToArray();
string resultString =  String.Join(",",ids);
File.WriteAllLines(destinationFilePath, result, Encoding.Default);
return resultString;
}