.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:

1. Create a .cs file with your code (top-level statements supported)
2. Add directives at the top if needed (packages, SDK, properties)
3. 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:

1. Ask what they want to accomplish
2. Determine if stdin one-liner or file-based is better
3. For simple tasks → use stdin pattern
4. For complex tasks → create a .cs file
5. Add necessary directives based on requirements
6. 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 .