Opening a folder in explorer and selecting a file

// suppose that we have a test.txt at E:\
string filePath = @"E:\test.txt";
if (!File.Exists(filePath))
{
    return;
}

// combine the arguments together
// it doesn't matter if there is a space after ','
string argument = "/select, \"" + filePath +"\"";

System.Diagnostics.Process.Start("explorer.exe", argument);

If your path contains comma's, putting quotes around the path will work when using Process.Start(ProcessStartInfo).

It will NOT work when using Process.Start(string, string) however. It seems like Process.Start(string, string) actually removes the quotes inside of your args.

Here is a simple example that works for me.

string p = @"C:\tmp\this path contains spaces, and,commas\target.txt";
string args = string.Format("/e, /select, \"{0}\"", p);

ProcessStartInfo info = new ProcessStartInfo();
info.FileName = "explorer";
info.Arguments = args;
Process.Start(info);

Use this method:

Process.Start(String, String)

First argument is an application (explorer.exe), second method argument are arguments of the application you run.

For example:

in CMD:

explorer.exe -p

in C#:

Process.Start("explorer.exe", "-p")

Use "/select,c:\file.txt"

Notice there should be a comma after /select instead of space..

The most possible reason for it not to find the file is the path having spaces in. For example, it won't find "explorer /select,c:\space space\space.txt".

Just add double quotes before and after the path, like;

explorer /select,"c:\space space\space.txt"

or do the same in C# with

System.Diagnostics.Process.Start("explorer.exe","/select,\"c:\space space\space.txt\"");

You need to put the arguments to pass ("/select etc") in the second parameter of the Start method.

string windir = Environment.GetEnvironmentVariable("windir");
if (string.IsNullOrEmpty(windir.Trim())) {
    windir = "C:\\Windows\\";
}
if (!windir.EndsWith("\\")) {
    windir += "\\";
}    

FileInfo fileToLocate = null;
fileToLocate = new FileInfo("C:\\Temp\\myfile.txt");

ProcessStartInfo pi = new ProcessStartInfo(windir + "explorer.exe");
pi.Arguments = "/select, \"" + fileToLocate.FullName + "\"";
pi.WindowStyle = ProcessWindowStyle.Normal;
pi.WorkingDirectory = windir;

//Start Process
Process.Start(pi)

It might be a bit of a overkill but I like convinience functions so take this one:

    public static void ShowFileInExplorer(FileInfo file) {
        StartProcess("explorer.exe", null, "/select, "+file.FullName.Quote());
    }
    public static Process StartProcess(FileInfo file, params string[] args) => StartProcess(file.FullName, file.DirectoryName, args);
    public static Process StartProcess(string file, string workDir = null, params string[] args) {
        ProcessStartInfo proc = new ProcessStartInfo();
        proc.FileName = file;
        proc.Arguments = string.Join(" ", args);
        Logger.Debug(proc.FileName, proc.Arguments); // Replace with your logging function
        if (workDir != null) {
            proc.WorkingDirectory = workDir;
            Logger.Debug("WorkingDirectory:", proc.WorkingDirectory); // Replace with your logging function
        }
        return Process.Start(proc);
    }

This is the extension function I use as <string>.Quote():

static class Extensions
{
    public static string Quote(this string text)
    {
        return SurroundWith(text, "\"");
    }
    public static string SurroundWith(this string text, string surrounds)
    {
        return surrounds + text + surrounds;
    }
}

Simple C# 9.0 method based on Jan Croonen's answer:

private static void SelectFileInExplorer(string filePath)
{
    Process.Start(new ProcessStartInfo()
    {
        FileName = "explorer.exe",
        Arguments = @$"/select, ""{filePath}"""
    });
}