Phillip Trelford's Array

The .Net Framework ships with a C# code compiler that lets you generate in-memory assemblies. This can be used to run C# scripts without the need for the installation of a large application like PowerShell. The following code, which targets .Net 2.0, builds into a 7K executable, and is all that is needed to run C# source files from the command line:

using System;
using System.CodeDom.Compiler;
using System.Collections.Specialized;
using System.Diagnostics;
using System.IO;
using System.Text.RegularExpressions;
using Microsoft.CSharp;
using System.Collections.Generic;

static class Program
{
    /// <summary>
    /// Executes specified C# script file
    /// </summary>
    /// <param name="args">Path of C# script file</param>
    static void Main(string[] args)
    {
        // Check parameters
        if (args.Length == 0)
        {
            Console.WriteLine("Please specify a C# script file");
            Environment.Exit(-1);
        }
        // First parameter is source file path
        string path = args[0];
        // Check file exists 
        if (!File.Exists(path))
        {            
            Console.WriteLine("Specified file does not exist");            
            Environment.Exit(-1); 
        }
        // Read source from file
        string source = ReadFile(path);
        // Initialize compiler options
        CompilerParameters compilerParameters = 
            new CompilerParameters();      
        compilerParameters.GenerateExecutable = true;
        compilerParameters.GenerateInMemory = true;
        compilerParameters.TreatWarningsAsErrors = true;
        compilerParameters.CompilerOptions = "/nowarn:1633"; // unrecognized pragmas
        // Prepass source for #pragma reference statements        
        StringReader reader = new StringReader(source);       
        while (true)
        {
            string line = reader.ReadLine();
            if (line == null) break;            
            string pattern = 
                "\\s*#pragma\\s+reference\\s+\"(?<path>[^\"]*)\"\\s*";
            Match match = Regex.Match(line, pattern);                   
            if (match.Success)            
                compilerParameters.ReferencedAssemblies.Add
                    (match.Groups["path"].Value);            
        }
        // Specify .NET version
        Dictionary<string, string> providerOptions =
            new Dictionary<string, string>();
        providerOptions.Add("CompilerVersion", "v3.5");
        CSharpCodeProvider provider = new CSharpCodeProvider(providerOptions); 
        // Compile source           
        CompilerResults results =
                provider.CompileAssemblyFromSource(
                    compilerParameters,
                    new string[] { source });
        // Show errors
        if (results.Errors.HasErrors)
        {
            Console.WriteLine("Errors Building " + path);
            foreach (var err in results.Errors)
                Console.WriteLine(err);
            Environment.Exit(-1);
        }
        // Extract argument tail
        string[] parameters = new string[args.Length - 1];
        Array.Copy(args, 1, parameters, 0, args.Length-1);
        // Invoke compiled assembly's entry point
        results.CompiledAssembly.EntryPoint.Invoke
            (null, new object[1] { parameters });        
    }
    
    private static string ReadFile(string path)
    {
        using (StreamReader reader = File.OpenText(path))
            return reader.ReadToEnd();
    }
}

Script files look just like Console applications:

using System;

public class Class1
{
    static void Main(string[] args)
    {
        Console.WriteLine("Hello World");
    }
}

Finally additional assemblies can be referenced using #pragma directives:

#pragma warning disable 1633 // disable unrecognized pragma directive warning
#pragma reference "System.Windows.Forms.dll"

using System.Windows.Forms;

public class Class1
{
    static void Main(string[] args)
    {
        MessageBox.Show("Hello World");
    }
}