Process.start: how to get the output?


I would like to run an external command line program from my Mono/.NET app. For example, I would like to run mencoder. Is it possible:

  1. To get the command line shell output, and write it on my text box?
  2. To get the numerical value to show a progress bar with time elapsed?
9/14/2014 8:21:55 AM

Accepted Answer

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:

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.

8/8/2018 7:14:32 AM

Alright, for anyone who wants both Errors and Outputs read, but gets deadlocks with any of the solutions, provided in other answers (like me), here is a solution that I built after reading MSDN explanation for StandardOutput property.

Answer is based on T30's code:

static void runCommand()
    //* Create your Process
    Process process = new Process();
    process.StartInfo.FileName = "cmd.exe";
    process.StartInfo.Arguments = "/c DIR";
    process.StartInfo.UseShellExecute = false;
    process.StartInfo.RedirectStandardOutput = true;
    process.StartInfo.RedirectStandardError = true;
    //* Set ONLY ONE handler here.
    process.ErrorDataReceived += new DataReceivedEventHandler(ErrorOutputHandler);
    //* Start process
    //* Read one element asynchronously
    //* Read the other one synchronously
    string output = process.StandardOutput.ReadToEnd();

static void ErrorOutputHandler(object sendingProcess, DataReceivedEventArgs outLine) 
    //* Do your stuff with the output (write to console/log/StringBuilder)

The standard .NET way of doing this is to read from the Process' StandardOutput stream. There is an example in the linked MSDN docs. Similar, you can read from StandardError, and write to StandardInput.


  1. It is possible to get the command line shell output of a process as described here :

  2. This depends on mencoder. If it ouputs this status on the command line then yes :)


you can use shared memory for the 2 processes to communicate through, check out MemoryMappedFile

you'll mainly create a memory mapped file mmf in the parent process using "using" statement then create the second process till it terminates and let it write the result to the mmf using BinaryWriter, then read the result from the mmf using the parent process, you can also pass the mmf name using command line arguments or hard code it.

make sure when using the mapped file in the parent process that you make the child process write the result to the mapped file before the mapped file is released in the parent process

Example: parent process

    private static void Main(string[] args)
        using (MemoryMappedFile mmf = MemoryMappedFile.CreateNew("memfile", 128))
            using (MemoryMappedViewStream stream = mmf.CreateViewStream())
                BinaryWriter writer = new BinaryWriter(stream);

            Console.WriteLine("Starting the child process");
            // Command line args are separated by a space
            Process p = Process.Start("ChildProcess.exe", "memfile");

            Console.WriteLine("Waiting child to die");

            Console.WriteLine("Child died");

            using (MemoryMappedViewStream stream = mmf.CreateViewStream())
                BinaryReader reader = new BinaryReader(stream);
                Console.WriteLine("Result:" + reader.ReadInt32());
        Console.WriteLine("Press any key to continue...");

Child process

    private static void Main(string[] args)
        Console.WriteLine("Child process started");
        string mmfName = args[0];

        using (MemoryMappedFile mmf = MemoryMappedFile.OpenExisting(mmfName))
            int readValue;
            using (MemoryMappedViewStream stream = mmf.CreateViewStream())
                BinaryReader reader = new BinaryReader(stream);
                Console.WriteLine("child reading: " + (readValue = reader.ReadInt32()));
            using (MemoryMappedViewStream input = mmf.CreateViewStream())
                BinaryWriter writer = new BinaryWriter(input);
                writer.Write(readValue * 2);

        Console.WriteLine("Press any key to continue...");

to use this sample, you'll need to create a solution with 2 projects inside, then you take the build result of the child process from %childDir%/bin/debug and copy it to %parentDirectory%/bin/debug then run the parent project

childDir and parentDirectory are the folder names of your projects on the pc good luck :)


The solution that worked for me in win and linux is the folling

// GET api/values
        public ActionResult<IEnumerable<string>> Cifrado(String xml)
            String nombreXML = DateTime.Now.ToString("ddMMyyyyhhmmss").ToString();
            String archivo = "/app/files/"+nombreXML + ".XML";
            String comando = " --armor --recipient [email protected]  --encrypt " + archivo;
                System.IO.File.WriteAllText(archivo, xml);                
                //String comando = "C:\\GnuPG\\bin\\gpg.exe --recipient [email protected] --armor --encrypt C:\\Users\\Administrador\\Documents\\pruebas\\nuevo.xml ";
                ProcessStartInfo startInfo = new ProcessStartInfo() {FileName = "/usr/bin/gpg",  Arguments = comando }; 
                Process proc = new Process() { StartInfo = startInfo, };
                proc.StartInfo.RedirectStandardOutput = true;
                proc.StartInfo.RedirectStandardError = true;
                return new string[] { "Archivo encriptado", archivo + " - "+ comando};
            }catch (Exception exception){
                return new string[] { archivo, "exception: "+exception.ToString() + " - "+ comando };

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