How to search the environment’s path for an exe or dll

I’d love it if there was a nice clean way to do this; however, there isn’t. When running a process via the Process.Start(…) call one must provide a fully qualified path to an executable. The problem is that hard-coding the full path to the exe isn’t always the best option. This is why there is a “PATH” environment variable. The following expands the provided file name to the full qualified path by looking in the current directory and environment path variable:

    /// <summary>
    /// Expands environment variables and, if unqualified, locates the exe in the working directory
    /// or the evironment's path.
    /// </summary>
    /// <param name="exe">The name of the executable file</param>
    /// <returns>The fully-qualified path to the file</returns>
    /// <exception cref="System.IO.FileNotFoundException">Raised when the exe was not found</exception>
    public static string FindExePath(string exe)
    {
        exe = Environment.ExpandEnvironmentVariables(exe);
        if (!File.Exists(exe))
        {
            if (Path.GetDirectoryName(exe) == String.Empty)
            {
                foreach (string test in (Environment.GetEnvironmentVariable("PATH") ?? "").Split(';'))
                {
                    string path = test.Trim();
                    if (!String.IsNullOrEmpty(path) && File.Exists(path = Path.Combine(path, exe)))
                        return Path.GetFullPath(path);
                }
            }
            throw new FileNotFoundException(new FileNotFoundException().Message, exe);
        }
        return Path.GetFullPath(exe);
    }

Most of this method is self-explanatory except the second if condition “Path.GetDirectoryName(exe) == String.Empty”. The reason for this is to determine if the name provided contains a ‘/’, ‘\’, ‘:’ or other path information. You might be able to replace it with an IndexOfAny(Path.GetInvalidFileNameChars()) or similar expression, but I thought this would produce more accurate results.