.NET Run Files

Run C# code directly without creating project files using .NET 10's dotnet run file.cs feature.

When to Use This Skill

Use this skill when the user wants to:

• Execute C# code quickly without creating a project

• Write one-liner scripts via stdin (ideal for Claude Code)

• Learn about run file directives (#:package , #:sdk , #:property )

• Create executable shell scripts in C#

• Convert a run file to a full project

Guide

For detailed examples and directives reference, load references/guide.md .

Quick Reference

Basic Execution

Run a .cs file

dotnet run app.cs

Run from stdin

echo 'Console.WriteLine("Hello");' | dotnet run -

Multi-line via heredoc

dotnet run - << 'EOF' var now = DateTime.Now; Console.WriteLine($"Time: {now}"); EOF

Directives

#:package Humanizer@* // NuGet package (version required, wildcards ok) #:sdk Microsoft.NET.Sdk.Web // SDK selection #:property LangVersion preview // MSBuild property #:project ../src/MyLib // Project reference

Convert to Project

dotnet project convert app.cs

Core Operations

1. Run a C# File

Steps:

• Create a .cs file with your code (top-level statements supported)

• Add directives at the top if needed (packages, SDK, properties)

• Execute: dotnet run filename.cs

Example:

// hello.cs Console.WriteLine("Hello from .NET!");

dotnet run hello.cs

2. Execute via Stdin

Purpose: Run C# code without creating files - ideal for quick scripts and AI-assisted workflows.

Patterns:

Simple one-liner

echo 'Console.WriteLine(Math.PI);' | dotnet run -

With package

dotnet run - << 'EOF' #:package Humanizer@* using Humanizer; Console.WriteLine(TimeSpan.FromMinutes(90).Humanize()); EOF

Heredoc for multi-line

dotnet run - << 'EOF' using System.Text.Json;

var obj = new { Name = "Test", Value = 42 }; Console.WriteLine(JsonSerializer.Serialize(obj)); EOF

Interactive Flow

When user asks to run C# code without specifics:

• Ask what they want to accomplish

• Determine if stdin one-liner or file-based is better

• For simple tasks → use stdin pattern

• For complex tasks → create a .cs file

• Add necessary directives based on requirements

• Execute and show results

Claude Code Integration Tips

For AI-assisted workflows:

• Prefer stdin for quick calculations, data transformations, API calls

• Use heredoc syntax for multi-line code

• Output JSON for easy parsing: dotnet run script.cs | jq .