Process.Start: How to Get the Output

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.

C# Process.Start: how to read output?

Firstly, you are checking for process.HasExited in a while loop.
This, of course will be false by default, and then your code will just skip this. That is why I suggest using an asynchronous method or an event-based aproach.

If you choose asynchronous, you can do this:

using (var process = Process.Start(psi))
{
    errors = await process.StandardError.ReadToEndAsync();
    results = await process.StandardOutput.ReadToEndAsync();
}

here, psi is an instance of ProcessStartInfo.

You set them after creating the process, but you can create an object and pass that in the constructor.

If you cannot make it asynchronous, you can do:

using (var process = Process.Start(psi))
{
    errors = process.StandardError.ReadToEndAsync().Result;
    results = process.StandardOutput.ReadToEndAsync().Result;
}

How to get the output of a System.Diagnostics.Process?

What you need to do is capture the Standard Output stream:

p.StartInfo.RedirectStandardOutput = true;
p.StartInfo.UseShellExecute = false;
// instead of p.WaitForExit(), do
string q = "";
while ( ! p.HasExited ) {
    q += p.StandardOutput.ReadToEnd();
}

You may also need to do something similar with StandardError. You can then do what you wish with q.

It is a bit finicky, as I discovered in one of my questions

As Jon Skeet has pointed out, it is not smart performance-wise to use string concatenation like this; you should instead use a StringBuilder:

p.StartInfo.RedirectStandardOutput = true;
p.StartInfo.UseShellExecute = false;
// instead of p.WaitForExit(), do
StringBuilder q = new StringBuilder();
while ( ! p.HasExited ) {
    q.Append(p.StandardOutput.ReadToEnd());
}
string r = q.ToString();

Capturing standard out and error with Start-Process

That's how Start-Process was designed for some reason. Here's a way to get it without sending to file:

$pinfo = New-Object System.Diagnostics.ProcessStartInfo
$pinfo.FileName = "ping.exe"
$pinfo.RedirectStandardError = $true
$pinfo.RedirectStandardOutput = $true
$pinfo.UseShellExecute = $false
$pinfo.Arguments = "localhost"
$p = New-Object System.Diagnostics.Process
$p.StartInfo = $pinfo
$p.Start() | Out-Null
$p.WaitForExit()
$stdout = $p.StandardOutput.ReadToEnd()
$stderr = $p.StandardError.ReadToEnd()
Write-Host "stdout: $stdout"
Write-Host "stderr: $stderr"
Write-Host "exit code: " + $p.ExitCode

Process.Start does not output the full output

It seems the issue was with PsExec itself (a Sysinternal utility) as I have tried an alternative called PAExec and the same command works fine, so I am using this one in my code instead.

How to get log from Process.Start

Set your ProcessStartInfo.RedirectStandardOutput to true - this will redirect all output to Process.StandardOutput, which is a stream that you can read to find all output messages:

ProcessStartInfo process = new ProcessStartInfo 
{ 
   CreateNoWindow = false,
   UseShellExecute = false,
   WorkingDirectory = msPath,
   RedirectStandardOutput = true,
   FileName = msCompiler,
   Arguments = "-p {0} -v / {1}"
            .StrFormat(
              CurrentSetting.CodeSource, 
              CurrentSetting.CompileTarget)
};

Process p = Process.Start(process);
string output = p.StandardOutput.ReadToEnd();

You can also use the OutputDataReceived event in a similar way to what @Bharath K describes in his answer.

There are similar properties/events for StandardError - you will need to set RedirectStandardError to true as well.

Using Process.Start to capture console output

Given the description:

you would remove the event subscription and the call to process.BeginOutputReadLine()

he is talking about those two lines:

process.OutputDataReceived += (o, e) => { if (e.Data == null) mreOut.Set(); else output(e.Data); };
process.BeginOutputReadLine();

Note that the code you substitute to this should be just:

new ReadOutput(process.StandardInput, mreOut);

ReadOutput class would be outside the Run method (since in C#, methods cannot contain classes).

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