Executing C# code in Linux

The .NET ecosystem was traditionally limited to Windows, but Microsoft's introduction of Mono changed this landscape. Mono enables the execution of .NET applications on Linux systems, making them run as if they were native Linux packages rather than Windows executable files.

What is Mono?

Mono is an open-source, cross-platform implementation of Microsoft's .NET Framework. It allows developers to run .NET applications on various platforms including Linux and macOS. Mono provides a complete development stack that supports Windows Forms, LINQ, XML web services, ADO.NET, and ASP.NET using the same CLR namespaces.

Installing Mono on Linux

To install Mono on a Linux system, you can use the package manager. For Ubuntu/Debian-based systems −

sudo apt update
sudo apt install mono-complete

Alternatively, you can install just the compiler using −

sudo apt-get install mono-mcs

Verify the installation by checking the version −

mono --version
mcs --version

Writing and Compiling C# Code

The structure of a Mono-based console application is identical to a traditional .NET console application. Create a simple C# program to test the setup −

Example

using System;

namespace HelloLinux {
    class Program {
        public static void Main(string[] args) {
            Console.WriteLine("Hello from C# running on Linux!");
            Console.WriteLine("Current Platform: " + Environment.OSVersion);
            Console.WriteLine("Runtime Version: " + Environment.Version);
        }
    }
}

Save this code as Program.cs. To compile and run the program −

# Compile the C# code
mcs Program.cs

# Run the compiled executable
mono Program.exe

The output of the above code is −

Hello from C# running on Linux!
Current Platform: Unix 5.4.0.74
Runtime Version: 4.0.30319.42000

Working with .NET Libraries

Mono supports most .NET libraries and namespaces. Here's an example using common .NET features −

Example

using System;
using System.Collections.Generic;
using System.Linq;

namespace LinuxDemo {
    class Program {
        public static void Main(string[] args) {
            List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
            
            var evenNumbers = numbers.Where(n => n % 2 == 0).ToList();
            
            Console.WriteLine("Even numbers:");
            foreach (int num in evenNumbers) {
                Console.Write(num + " ");
            }
            Console.WriteLine();
            
            Console.WriteLine("Sum of even numbers: " + evenNumbers.Sum());
        }
    }
}

Compile and run using the same commands −

mcs LinuxDemo.cs
mono LinuxDemo.exe

The output of the above code is −

Even numbers:
2 4 6 8 10 
Sum of even numbers: 30

Compilation Options

The Mono compiler (mcs) supports various compilation options −

Example with Custom Output Name

mcs -out:MyApp.exe Program.cs
mono MyApp.exe

Conclusion

Mono enables seamless execution of C# applications on Linux systems, providing full compatibility with .NET libraries and frameworks. With simple installation and familiar compilation commands, developers can easily deploy .NET applications across multiple platforms without modifying their existing codebase.