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 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 with System.IO.File.Exists:

public static bool ExistsOnPath(string fileName) {     return GetFullPath(fileName) != null; }  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(Path.PathSeparator))     {         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 HKCR\Applications and HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths keys also play 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.