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

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. Yes, I could figure this out for myself, but surely someone else has done something like it and I'm lazy...

Answer 1

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]

Answer 2

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.

Answer 3

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();
   

Answer 4

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();
        }

Answer 5

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.

Answer 6

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.