Question

I want to write a console application that have a different behavior depending if the input is coming from keyboard or from, say, a file.

Is it possible? What’s the most elegant way to do it in C#?

Answer 1

You can find out by p/invoking the Windows FileType() API function. Here’s a helper class:

using System;
using System.Runtime.InteropServices;

public static class ConsoleEx {
    public static bool IsOutputRedirected {
        get { return FileType.Char != GetFileType(GetStdHandle(StdHandle.Stdout)); }
    }
    public static bool IsInputRedirected {
        get { return FileType.Char != GetFileType(GetStdHandle(StdHandle.Stdin)); }
    }
    public static bool IsErrorRedirected {
        get { return FileType.Char != GetFileType(GetStdHandle(StdHandle.Stderr)); }
    }

    // P/Invoke:
    private enum FileType { Unknown, Disk, Char, Pipe };
    private enum StdHandle { Stdin = -10, Stdout = -11, Stderr = -12 };
    [DllImport("kernel32.dll")]
    private static extern FileType GetFileType(IntPtr hdl);
    [DllImport("kernel32.dll")]
    private static extern IntPtr GetStdHandle(StdHandle std);
}

Usage:

bool inputRedirected = ConsoleEx.IsInputRedirected;

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UPDATE: these methods were added to the Console class in .NET 4.5. Without attribution I might add 🙁 Simply use the corresponding method instead of this helper class.

https://msdn.microsoft.com/en-us/library/system.console.isoutputredirected.aspx
https://msdn.microsoft.com/en-us/library/system.console.isinputredirected.aspx
https://msdn.microsoft.com/en-us/library/system.console.iserrorredirected.aspx