Process.start: how to get the output?

When you create your Process object set StartInfo appropriately:

var proc = new Process 
{
    StartInfo = new ProcessStartInfo
    {
        FileName = "program.exe",
        Arguments = "command line arguments to your executable",
        UseShellExecute = false,
        RedirectStandardOutput = true,
        CreateNoWindow = true
    }
};

then start the process and read from it:

proc.Start();
while (!proc.StandardOutput.EndOfStream)
{
    string line = proc.StandardOutput.ReadLine();
    // do something with line
}

You can use int.Parse() or int.TryParse() to convert the strings to numeric values. You may have to do some string manipulation first if there are invalid numeric characters in the strings you read.

You can set RedirectStandardError = true and access any errors from process.StandardError

    public static void ExecutePowershellScript()
    {
        var file = @"C:\Path\filename.ps1";

        var start = new ProcessStartInfo()
        {
            FileName = "powershell.exe",
            Arguments = $"-NoProfile -ExecutionPolicy unrestricted -file \"{file}\"",
            UseShellExecute = false,
            RedirectStandardOutput = true,
            RedirectStandardError = true
        };
        using Process process = Process.Start(start);
        string output = process.StandardOutput.ReadToEnd();
        string errors = process.StandardError.ReadToEnd();
    }

Okay, scratch the above suggestion. After being corrected by mklement0,

This is a perfectly reasonable attempt, but, unfortunately, it can lead to hangs (while waiting for one's stream end, the other, when exceeding the buffer size, may cause process execution to block). If you need to capture both streams, you must collect the output from one of them via events. – mklement0

I changed the solution to use the ErrorDataReceived event

        public static async Task ExecutePowershellScript()
        {
            var file = @"C:\Path\filename.ps1";

            var start = new ProcessStartInfo
            {
                FileName = "powershell.exe",
                Arguments = $"-NoProfile -ExecutionPolicy unrestricted -file \"{file}\"",
                UseShellExecute = false,
                // redirect standard error stream to process.StandardError
                RedirectStandardError = true
            };

            using var process = new Process
            {
                StartInfo = start
            };

            // Subscribe to ErrorDataReceived event
            process.ErrorDataReceived += (sender, e) =>
            {
                //  code to process the error lines in e.Data
            };

            process.Start();

            // Necessary to start redirecting errors to StandardError
            process.BeginErrorReadLine();

            // Wait for process to exit
            await process.WaitForExitAsync();

        }

start.Start();
while (!start.StandardOutput.EndOfStream)
{
    string line = start.StandardOutput.ReadLine();
}