c# Check if an executable exists in the windows path

Question

If I run a process with ShellExecute (or in .net with System.Diagnostics.Process.Start()) the filename process to start doesn't need to be a full path.

If I want to start notepad, I can use

Process.Start("notepad.exe");

instead of

Process.Start(@"c:\windows\system32\notepad.exe");

because the direcotry c:\windows\system32 folder is part of the PATH environment variable.

how can I check if a file exists on the PATH without executing the process and without parsing the PATH variable?

System.IO.File.Exists("notepad.exe"); // returns false
(new System.IO.FileInfo("notepad.exe")).Exists; // returns false

but I need something like this:

System.IO.File.ExistsOnPath("notepad.exe"); // should return true

and

System.IO.File.GetFullPath("notepad.exe"); // (like unix which cmd) should return
                                           // c:\windows\system32\notepad.exe

Is there a predefined class to do this task available in the BCL?

Answer 1

I think there's nothing built-in, but you could do something like this:

public static bool ExistsOnPath(string fileName)
{
    if (GetFullPath(fileName) != null)
        return true;
    return false;
}

public static string GetFullPath(string fileName)
{
    if (File.Exists(fileName))
        return Path.GetFullPath(fileName);

    var values = Environment.GetEnvironmentVariable("PATH");
    foreach (var path in values.Split(';'))
    {
        var fullPath = Path.Combine(path, fileName);
        if (File.Exists(fullPath))
            return fullPath;
    }
    return null;
}

Answer 2

This is risky, there's a lot more to it than just searching the directories in the PATH. Try this:

 Process.Start("wordpad.exe");

The executable is stored in c:\Program Files\Windows NT\Accessories on my machine, that directory is not on the path. The HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths key plays a role in finding executables. I'm fairly sure there are additional land-mines like this around, directory virtualization in 64-bit versions of Windows could trip you up for example.

To make this more reliable, I think you need to pinvoke AssocQueryString(). Not sure, never had the need. The better approach is certainly to not have to ask the question.