How To: Execute command line in C#, get STD OUT results

Question

How do I execute a command-line program from C# and get back the STD OUT results? Specifically, I want to execute DIFF on two files that are programmatically selected and write the results to a text box.

Groat

See also https://mcmap.net/q/44950/-how-to-parse-command-line-output-from-c - it shows events for output and errors. – Fabi

Related (but without capturing STDOUT): stackoverflow.com/questions/1469764 – Likewise

Answer 1

// Start the child process.
 Process p = new Process();
 // Redirect the output stream of the child process.
 p.StartInfo.UseShellExecute = false;
 p.StartInfo.RedirectStandardOutput = true;
 p.StartInfo.FileName = "YOURBATCHFILE.bat";
 p.Start();
 // Do not wait for the child process to exit before
 // reading to the end of its redirected stream.
 // p.WaitForExit();
 // Read the output stream first and then wait.
 string output = p.StandardOutput.ReadToEnd();
 p.WaitForExit();

Code is from MSDN.

Consult

Is there a way to do this without a batch file? Thing is, I need to send some parameters to the command. I'm using the xsd.exe <Assembly> /type:<ClassName>, so I need to be able to set both the Assembly and the ClassName, and then run the command. – Nert

You can add arguments to your call through the {YourProcessObject}.StartInfo.Arguments string. – Stilwell

What if you like executing and interactive app? Because you can't use ReadToEnd if you do so. – Piaffe

How to make the process run as administrator? – Gustavogustavus

I have encountered a number of problems where my process, using this code, halts completely because the process has written sufficient data to the p.StandardError stream. When the stream becomes full, it appears that the process will halt until the data is consumed, so I have to read both StandardError and StandardOutput in order to guarantee that a task executes correctly. – Heterocercal

In that case, how can you get the output of a command string (for example, ls on Unix/Linux)? – Inappetence

Quick headsup from c# compiler: The Process object must have the UseShellExecute property set to false in order to redirect IO streams. – Fernferna

It might not be the case here for the batch file but when calling a process this way it can write to a separate error stream. To access that information you need to redirect the error stream p.StartInfo.RedirectStandardError = true; and read it string error = p.StandardError.ReadToEnd(); – Screwworm

Why are they not disposing it? – Kohl

This code is very risky for the reasons stated by @TedSpence, it is dead-lock prone to processes which write to Standard Error. Some would say using this approach is not robust or risk-adverse programming. – Manutius

Don't forgot to add 'exit' to the end of your batch file! – Belamy

To run the process as administrator, add p.StartInfo.Verb = "runas"; @SaherAhwal – Limbus

How does this method update stdout in real time? Like update the stdout in the textbox immediately, instead of waiting to the end? – Buckingham

Answer 2

Here's a quick sample:

//Create process
System.Diagnostics.Process pProcess = new System.Diagnostics.Process();

//strCommand is path and file name of command to run
pProcess.StartInfo.FileName = strCommand;

//strCommandParameters are parameters to pass to program
pProcess.StartInfo.Arguments = strCommandParameters;

pProcess.StartInfo.UseShellExecute = false;

//Set output of program to be written to process output stream
pProcess.StartInfo.RedirectStandardOutput = true;   

//Optional
pProcess.StartInfo.WorkingDirectory = strWorkingDirectory;

//Start the process
pProcess.Start();

//Get program output
string strOutput = pProcess.StandardOutput.ReadToEnd();

//Wait for process to finish
pProcess.WaitForExit();

Pinzler

+1 for showing how to add arguments to running a command-line program (which the accepted answer doesn't have.) – Corrupt

Answer 3

There one other parameter I found useful, which I use to eliminate the process window

pProcess.StartInfo.CreateNoWindow = true;

this helps to hide the black console window from user completely, if that is what you desire.

Clippard

When calling "sc" I had to also set StartInfo.WindowStyle = ProcessWindowStyle.Hidden. – Roseannroseanna

Answer 4

// usage
const string ToolFileName = "example.exe";
string output = RunExternalExe(ToolFileName);

public string RunExternalExe(string filename, string arguments = null)
{
    var process = new Process();

    process.StartInfo.FileName = filename;
    if (!string.IsNullOrEmpty(arguments))
    {
        process.StartInfo.Arguments = arguments;
    }

    process.StartInfo.CreateNoWindow = true;
    process.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
    process.StartInfo.UseShellExecute = false;

    process.StartInfo.RedirectStandardError = true;
    process.StartInfo.RedirectStandardOutput = true;
    var stdOutput = new StringBuilder();
    process.OutputDataReceived += (sender, args) => stdOutput.AppendLine(args.Data); // Use AppendLine rather than Append since args.Data is one line of output, not including the newline character.

    string stdError = null;
    try
    {
        process.Start();
        process.BeginOutputReadLine();
        stdError = process.StandardError.ReadToEnd();
        process.WaitForExit();
    }
    catch (Exception e)
    {
        throw new Exception("OS error while executing " + Format(filename, arguments)+ ": " + e.Message, e);
    }

    if (process.ExitCode == 0)
    {
        return stdOutput.ToString();
    }
    else
    {
        var message = new StringBuilder();

        if (!string.IsNullOrEmpty(stdError))
        {
            message.AppendLine(stdError);
        }

        if (stdOutput.Length != 0)
        {
            message.AppendLine("Std output:");
            message.AppendLine(stdOutput.ToString());
        }

        throw new Exception(Format(filename, arguments) + " finished with exit code = " + process.ExitCode + ": " + message);
    }
}

private string Format(string filename, string arguments)
{
    return "'" + filename + 
        ((string.IsNullOrEmpty(arguments)) ? string.Empty : " " + arguments) +
        "'";
}

Langland

Might want to change OutputDataReceived handler to stdOut.AppendLine() – Hothead

In my opinion, this is a much more comprehensive solution than the accepted answer. I am using it now, and haven't used the accepted one, but that one really looks lacking. – Breast

Thanks for process.StartInfo.RedirectStandardError = true; and if (process.ExitCode == 0) which accepted answer doesn't have. – Afrikaner

Thanks, It works on Ubuntu 20 LTS. (just for the record) – Satanism

To run an arbitrary command and terminate, add "/c" before the arguments. For example, filename = "cmd.exe" and arguments = "/c python --version". – Little

Answer 5

The accepted answer on this page has a weakness that is troublesome in rare situations. There are two file handles which programs write to by convention, stdout, and stderr. If you just read a single file handle such as the answer from Ray, and the program you are starting writes enough output to stderr, it will fill up the output stderr buffer and block. Then your two processes are deadlocked. The buffer size may be 4K. This is extremely rare on short-lived programs, but if you have a long running program which repeatedly outputs to stderr, it will happen eventually. This is tricky to debug and track down.

There are a couple good ways to deal with this.

1. One way is to execute cmd.exe instead of your program and use the /c argument to cmd.exe to invoke your program along with the "2>&1" argument to cmd.exe to tell it to merge stdout and stderr.

           var p = new Process();
           p.StartInfo.FileName = "cmd.exe";
           p.StartInfo.Arguments = "/c mycmd.exe 2>&1";
   

2. Another way is to use a programming model which reads both handles at the same time.

           var p = new Process();
           p.StartInfo.FileName = "cmd.exe";
           p.StartInfo.Arguments = @"/c dir \windows";
           p.StartInfo.CreateNoWindow = true;
           p.StartInfo.RedirectStandardError = true;
           p.StartInfo.RedirectStandardOutput = true;
           p.StartInfo.RedirectStandardInput = false;
           p.OutputDataReceived += (a, b) => Console.WriteLine(b.Data);
           p.ErrorDataReceived += (a, b) => Console.WriteLine(b.Data);
           p.Start();
           p.BeginErrorReadLine();
           p.BeginOutputReadLine();
           p.WaitForExit();
   

Manutius

I think this answers the original question better, as it shows how to run a CMD command through C# (not a file). – Belamy

Answer 6

 System.Diagnostics.ProcessStartInfo psi =
   new System.Diagnostics.ProcessStartInfo(@"program_to_call.exe");
 psi.RedirectStandardOutput = true;
 psi.WindowStyle = System.Diagnostics.ProcessWindowStyle.Hidden;
 psi.UseShellExecute = false;
 System.Diagnostics.Process proc = System.Diagnostics.Process.Start(psi); ////
 System.IO.StreamReader myOutput = proc.StandardOutput;
 proc.WaitForExit(2000);
 if (proc.HasExited)
  {
      string output = myOutput.ReadToEnd();
 }

Renz

May deadlock when the process writes a lot of data. It's better to start reading data while the process still runs. – Mckinzie

Answer 7

You will need to use ProcessStartInfo with RedirectStandardOutput enabled - then you can read the output stream. You might find it easier to use ">" to redirect the output to a file (via the OS), and then simply read the file.

[edit: like what Ray did: +1]

Ovenware

That forces you to write a file somewhere that you need permission for, need to find a location and a name for and mustn't forget to delete when you're done with it. Easier to use RedirectStandardOutput actually. – Conciseness

Answer 8

Since the most answers here dont implement the using statemant for IDisposable and some other stuff wich I think could be nessecary I will add this answer.

For C# 8.0

// Start a process with the filename or path with filename e.g. "cmd". Please note the 
//using statemant
using myProcess.StartInfo.FileName = "cmd";
// add the arguments - Note add "/c" if you want to carry out tge  argument in cmd and  
// terminate
myProcess.StartInfo.Arguments = "/c dir";
// Allows to raise events
myProcess.EnableRaisingEvents = true;
//hosted by the application itself to not open a black cmd window
myProcess.StartInfo.UseShellExecute = false;
myProcess.StartInfo.CreateNoWindow = true;
// Eventhander for data
myProcess.Exited += OnOutputDataRecived;
// Eventhandler for error
myProcess.ErrorDataReceived += OnErrorDataReceived;
// Eventhandler wich fires when exited
myProcess.Exited += OnExited;
// Starts the process
myProcess.Start();
//read the output before you wait for exit
myProcess.BeginOutputReadLine();
// wait for the finish - this will block (leave this out if you dont want to wait for 
// it, so it runs without blocking)
process.WaitForExit();

// Handle the dataevent
private void OnOutputDataRecived(object sender, DataReceivedEventArgs e)
{
    //do something with your data
    Trace.WriteLine(e.Data);
}

//Handle the error
private void OnErrorDataReceived(object sender, DataReceivedEventArgs e)
{        
    Trace.WriteLine(e.Data);
    //do something with your exception
    throw new Exception();
}    

// Handle Exited event and display process information.
private void OnExited(object sender, System.EventArgs e)
{
     Trace.WriteLine("Process exited");
}

Estafette

Answer 9

Here is small example:

using System;
using System.Diagnostics;

class Program
{
    static void Main(string[] args)
    {
        var p = Process.Start(
            new ProcessStartInfo("git", "branch --show-current")
            {
                CreateNoWindow = true,
                UseShellExecute = false,
                RedirectStandardError = true,
                RedirectStandardOutput = true,
                WorkingDirectory = Environment.CurrentDirectory
            }
        );

        p.WaitForExit();
        string branchName =p.StandardOutput.ReadToEnd().TrimEnd();
        string errorInfoIfAny =p.StandardError.ReadToEnd().TrimEnd();

        if (errorInfoIfAny.Length != 0)
        {
            Console.WriteLine($"error: {errorInfoIfAny}");
        }
        else { 
            Console.WriteLine($"branch: {branchName}");
        }

    }
}

I believe this is shortest form.

Please notice that most of command line tools easily confuse standard output and standard error, sometimes it makes sense just to clue those together into single string.

Also p.ExitCode might be sometimes useful.

Example above serves for purpose of writing command line utility like tools if you want to do it by yourself. Please note that for cli automation it's also possible to use Cake Frosten and Cake Git extension.

Cykana

Answer 10

One-liner run command:

new Process() { StartInfo = new ProcessStartInfo("echo", "Hello, World") }.Start();

Read output of command in shortest amount of reable code:

    var cliProcess = new Process() {
        StartInfo = new ProcessStartInfo("echo", "Hello, World") {
            UseShellExecute = false,
            RedirectStandardOutput = true
        }
    };
    cliProcess.Start();
    string cliOut = cliProcess.StandardOutput.ReadToEnd();
    cliProcess.WaitForExit();
    cliProcess.Close();

Cutler

Answer 11

In case you also need to execute some command in the cmd.exe, you can do the following:

// Start the child process.
Process p = new Process();
// Redirect the output stream of the child process.
p.StartInfo.UseShellExecute = false;
p.StartInfo.RedirectStandardOutput = true;
p.StartInfo.FileName = "cmd.exe";
p.StartInfo.Arguments = "/C vol";
p.Start();
// Read the output stream first and then wait.
string output = p.StandardOutput.ReadToEnd();
p.WaitForExit();
Console.WriteLine(output);

This returns just the output of the command itself:

You can also use StandardInput instead of StartInfo.Arguments:

// Start the child process.
Process p = new Process();
// Redirect the output stream of the child process.
p.StartInfo.UseShellExecute = false;
p.StartInfo.RedirectStandardInput = true;
p.StartInfo.RedirectStandardOutput = true;
p.StartInfo.FileName = "cmd.exe";
p.Start();
// Read the output stream first and then wait.
p.StandardInput.WriteLine("vol");
p.StandardInput.WriteLine("exit");
string output = p.StandardOutput.ReadToEnd();
p.WaitForExit();
Console.WriteLine(output);

The result looks like this:

Selfregulated

Answer 12

You can launch any command line program using the Process class, and set the StandardOutput property of the Process instance with a stream reader you create (either based on a string or a memory location). After the process completes, you can then do whatever diff you need to on that stream.

Rossini

Answer 13

This might be useful for someone if your attempting to query the local ARP cache on a PC/Server.

List<string[]> results = new List<string[]>();

        using (Process p = new Process())
        {
            p.StartInfo.CreateNoWindow = true;
            p.StartInfo.RedirectStandardOutput = true;
            p.StartInfo.UseShellExecute = false;
            p.StartInfo.Arguments = "/c arp -a";
            p.StartInfo.FileName = @"C:\Windows\System32\cmd.exe";
            p.Start();

            string line;

            while ((line = p.StandardOutput.ReadLine()) != null)
            {
                if (line != "" && !line.Contains("Interface") && !line.Contains("Physical Address"))
                {
                    var lineArr = line.Trim().Split(' ').Select(n => n).Where(n => !string.IsNullOrEmpty(n)).ToArray();
                    var arrResult = new string[]
                {
                   lineArr[0],
                   lineArr[1],
                   lineArr[2]
                };
                    results.Add(arrResult);
                }
            }

            p.WaitForExit();
        }

Febrile

Answer 14

This may not be the best/easiest way, but may be an option:

When you execute from your code, add " > output.txt" and then read in the output.txt file.

Haller

You are assuming you have write permissions, that might not be true – Porkpie

Answer 15

There is a ProcessHelper Class in PublicDomain open source code which might interest you.

Prelatism

Answer 16

Julian's solution is tested working with some minor corrections. The following is an example that also used https://sourceforge.net/projects/bat-to-exe/ GenericConsole.cs and https://www.codeproject.com/Articles/19225/Bat-file-compiler program.txt for args part:

using System;
using System.Text;  //StringBuilder
using System.Diagnostics;
using System.IO;


class Program
{
    private static bool redirectStandardOutput = true;

    private static string buildargument(string[] args)
    {
        StringBuilder arg = new StringBuilder();
        for (int i = 0; i < args.Length; i++)
        {
            arg.Append("\"" + args[i] + "\" ");
        }

        return arg.ToString();
    }

    static void Main(string[] args)
    {
        Process prc = new Process();
        prc.StartInfo = //new ProcessStartInfo("cmd.exe", String.Format("/c \"\"{0}\" {1}", Path.Combine(Environment.CurrentDirectory, "mapTargetIDToTargetNameA3.bat"), buildargument(args)));
        //new ProcessStartInfo(Path.Combine(Environment.CurrentDirectory, "mapTargetIDToTargetNameA3.bat"), buildargument(args));
        new ProcessStartInfo("mapTargetIDToTargetNameA3.bat");
        prc.StartInfo.Arguments = buildargument(args);

        prc.EnableRaisingEvents = true;

        if (redirectStandardOutput == true)
        {
            prc.StartInfo.UseShellExecute = false;
        }
        else
        {
            prc.StartInfo.UseShellExecute = true;
        }

        prc.StartInfo.CreateNoWindow = true;

        prc.OutputDataReceived += OnOutputDataRecived;
        prc.ErrorDataReceived += OnErrorDataReceived;
        //prc.Exited += OnExited;

        prc.StartInfo.RedirectStandardOutput = redirectStandardOutput;
        prc.StartInfo.RedirectStandardError = redirectStandardOutput;

        try
        {
            prc.Start();
            prc.BeginOutputReadLine();
            prc.BeginErrorReadLine();
            prc.WaitForExit();
        }
        catch (Exception e)
        {
            Console.WriteLine("OS error: " + e.Message);
        }

        prc.Close();
    }

    // Handle the dataevent
    private static void OnOutputDataRecived(object sender, DataReceivedEventArgs e)
    {
        //do something with your data
        Console.WriteLine(e.Data);
    }

    //Handle the error
    private static void OnErrorDataReceived(object sender, DataReceivedEventArgs e)
    {
        Console.WriteLine(e.Data);
    }

    // Handle Exited event and display process information.
    //private static void OnExited(object sender, System.EventArgs e)
    //{
    //    var process = sender as Process;
    //    if (process != null)
    //    {
    //        Console.WriteLine("ExitCode: " + process.ExitCode);
    //    }
    //    else
    //    {
    //        Console.WriteLine("Process exited");
    //    }
    //}
}

The code need to compile inside VS2007, using commandline csc.exe generated executable will not show console output correctly, or even crash with CLR20r3 error. Comment out the OnExited event process, the console output of the bat to exe will be more like the original bat console output.

Steffen

Answer 17

Just for fun, here's my completed solution for getting PYTHON output - under a button click - with error reporting. Just add a button called "butPython" and a label called "llHello"...

    private void butPython(object sender, EventArgs e)
    {
        llHello.Text = "Calling Python...";
        this.Refresh();
        Tuple<String,String> python = GoPython(@"C:\Users\BLAH\Desktop\Code\Python\BLAH.py");
        llHello.Text = python.Item1; // Show result.
        if (python.Item2.Length > 0) MessageBox.Show("Sorry, there was an error:" + Environment.NewLine + python.Item2);
    }

    public Tuple<String,String> GoPython(string pythonFile, string moreArgs = "")
    {
        ProcessStartInfo PSI = new ProcessStartInfo();
        PSI.FileName = "py.exe";
        PSI.Arguments = string.Format("\"{0}\" {1}", pythonFile, moreArgs);
        PSI.CreateNoWindow = true;
        PSI.UseShellExecute = false;
        PSI.RedirectStandardError = true;
        PSI.RedirectStandardOutput = true;
        using (Process process = Process.Start(PSI))
            using (StreamReader reader = process.StandardOutput)
            {
                string stderr = process.StandardError.ReadToEnd(); // Error(s)!!
                string result = reader.ReadToEnd(); // What we want.
                return new Tuple<String,String> (result,stderr); 
            }
    }

Charliecharline