How can one get an absolute or normalized file path in .NET?

How can one with minimal effort (using some already existing facility, if possible) convert paths like c:\aaa\bbb\..\ccc to c:\aaa\ccc?

I would write it like this:

public static string NormalizePath(string path)
{
    return Path.GetFullPath(new Uri(path).LocalPath)
               .TrimEnd(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar)
               .ToUpperInvariant();
}

This should handle few scenarios like

1. uri and potential escaped characters in it, like

   > file:///C:/Test%20Project.exe -> C:\TEST PROJECT.EXE

2. path segments specified by dots to denote current or parent directory

   > c:\aaa\bbb\..\ccc -> C:\AAA\CCC

3. tilde shortened (long) paths

   > C:\Progra~1\ -> C:\PROGRAM FILES

4. inconsistent directory delimiter character

   > C:/Documents\abc.txt -> C:\DOCUMENTS\ABC.TXT

Other than those, it can ignore case, trailing \ directory delimiter character etc.

Path.GetFullPath perhaps?

Canonicalization is one of the main responsibilities of the Uri class in .NET.

var path = @"c:\aaa\bbb\..\ccc";
var canonicalPath = new Uri(path).LocalPath; // c:\aaa\ccc

FileInfo objects can also help here. (https://docs.microsoft.com/en-us/dotnet/api/system.io.fileinfo?view=net-5.0)

var x = Path.Combine(@"C:\temp", "..\\def/abc");
var y = new FileInfo(x).FullName; // "C:\\def\\abc"

FileInfo vs. DirectoryInfo can also help if you want to control the file vs. directory distinction.

But Path.GetFullPath is better if you just need the string.