Executing CURL statement in C#

Set a variable to the above command + then call system($command)... or...

You can refer to the CURL site for details about how to do all this programmatically.

Unless you deeply understand using libcurl primitives, best to stick with executing the curl command via system().

Please rephrase your question. What do you like to do really?

I'm not sure I know how to rephrase it? I want to run that command from an application developed in C#.

So like this...

            var sb = new StringBuilder();
            sb.Append("curl -X POST \\");
            sb.Append("-H \"Authorization:Signature myAuthStringHere=\" \\");
            sb.Append("--data-urlencode key_attribute=email \\");
            sb.Append("--data-urlencode key_value='" + email + "' \\");
            sb.Append("--data-urlencode value='{\"externalID\":\" " + externalid + " \"}' \\");
            sb.Append("https://my-app.blahblah.com/entity.update");
            //System.Diagnostics.Process.Start("CMD.exe", sb.ToString());

            System.Diagnostics.Process process = new System.Diagnostics.Process();
            System.Diagnostics.ProcessStartInfo startInfo = new System.Diagnostics.ProcessStartInfo();
            startInfo.WindowStyle = System.Diagnostics.ProcessWindowStyle.Hidden;
            startInfo.FileName = "cmd.exe";
            startInfo.Arguments = sb.ToString();
            process.StartInfo = startInfo;
            process.Start();;

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??
Not working for me. Am I approaching this the correct way?

Well, it looks like you want to call a web service. The question is, why relying on an external program and doing the request using WebClient?

As requested but you should also look into using WebClient as ste5an says:

namespace ConsoleApplication1
{
    using System.Diagnostics;
    using System.Text;

    class Program
    {
        static void Main(string[] args)
        {
            var sb = new StringBuilder();
            sb.Append(" -H \"Authorization: Basic aW1fYV...NfbXk=\"");
            sb.Append(" --data-urlencode key_attribute=email");
            sb.Append(" --data-urlencode key_value='\"test@example.com\"'");
            sb.Append(" --data-urlencode value='{\"externalID\":\"123456\"}'");
            sb.Append(" https://my-app.blahblah.com/entity.update");

            //sb.Append(" -o google.html");
            //sb.Append(" https://google.com");

            var psi = new ProcessStartInfo("curl.exe", sb.ToString());
            var p = new Process();
            p.StartInfo = psi;
            p.Start();
            p.WaitForExit();
        }
    }
}

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This is perfect. Got it. Thanks so much!