Cross-platform file name handling in .NET Core

How to handle file name in System.IO classes in a cross-platform manner to make it work on Windows and Linux?

For example, I write this code that works perfectly on Windows, however it doesn't create a file on Ubuntu Linux:

var tempFilename = $@"..\Data\uploads\{filename}";
using (FileStream fs = System.IO.File.Create(tempFilename))
{
    file.CopyTo(fs);
    fs.Flush();                    
}

Solution 1:

You can also use Path.DirectorySeparatorChar as below:

 Console.WriteLine("..{0}Data{0}uploads{0}{{filename}}", Path.DirectorySeparatorChar);

Reference: MSDN

Solution 2:

Windows using Backslash. Linux using Slash. Path.Combine set the right symbol :
Path.Combine Method - MSDN

Solution 3:

Lots of good answers. I would just like to add that one can avoid having to specify the directory separator character by using Path.Combine

Example with the file relatively located at ".\..\toto\app.config":

Path.Combine("..", "toto", "app.config");

Unfortunately, Path.Combine does not resolve a relative path to an absolute Path in .Net Core. Path.GetFullPath is here for that:

Path.GetFullPath(Path.Combine("..", "toto", "app.config"))

Solution 4:

You can simply use slashes. Relative paths will work identically, and absolute paths can only be relative to the root of the main drive (as absolute paths starting with "c:" are not portable)