CLI utilities in C#: from idea to ready-made tool in one evening

Why C# is ideal for CLI tools, and why this matters for a Python developer

When we talk about creating console utilities, the first things that come to mind are Python, Bash, or Go. But what if I told you that C# is one of the most underrated languages for writing fast, cross-platform, and beautiful CLI tools? Yes, that same C# that many associate with web forms and corporate monsters.

With the release of .NET 6/8, C# has gained minimal API, native compilation (AOT), and the incredibly convenient System.CommandLine library. Now you can create a utility that works on Windows, Linux, and macOS in literally 15 minutes. For students and developers learning Python, this is a great way to expand your toolkit and understand how CLI utilities work in other languages.

In this article, we won't just write "Hello World". We will create a full-fledged file utility that can parse arguments, output colored text, handle errors, and even show a progress bar. Let's go!

Project setup: minimal effort

The first thing to do is make sure you have the .NET SDK installed (version 6.0 or higher). Check it simply:

dotnet --version

If everything is fine, create a new console project:

dotnet new console -n FileGuardian\ncd FileGuardian

At this stage, we already have a ready-made skeleton. But for a real CLI utility, we need a library for argument parsing. Add it:

dotnet add package System.CommandLine --version 2.0.0-beta4.22272.1

Done. Now we have everything to create a professional console application in C#.

Why System.CommandLine instead of manual parsing?

Many beginners write args[0], args[1] and catch IndexOutOfRangeException. This is the path of pain. System.CommandLine gives you:

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• Automatic parsing of flags (--output, -o)
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• Hints on incorrect input
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• Built-in --help generation
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• Support for subcommands (like in git)
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This is a must-have for any serious C# console utility.

Writing the utility core: the first command

Imagine we are creating a file monitoring tool — FileGuardian. It will check file sizes and warn if they exceed a limit. Sounds useful, right?

Open Program.cs and write the following:

using System.CommandLine;\n\nvar rootCommand = new RootCommand("FileGuardian — file monitoring utility");\n\nvar fileOption = new Option<FileInfo?>(\n    name: "--file",\n    description: "Path to the file for analysis"\n);\nrootCommand.AddOption(fileOption);\n\nrootCommand.SetHandler((file) =>\n{\n    if (file is null || !file.Exists)\n    {\n        Console.Error.WriteLine("❌ File not found!");\n        return;\n    }\n    \n    long sizeInBytes = file.Length;\n    double sizeInMb = sizeInBytes / (1024.0 * 1024.0);\n    \n    Console.WriteLine($"📄 File: {file.Name}");\n    Console.WriteLine($"📏 Size: {sizeInMb:F2} MB");\n    \n    if (sizeInMb > 100)\n        Console.WriteLine("⚠️ Warning: file exceeds 100 MB!");\n}, fileOption);\n\nawait rootCommand.InvokeAsync(args);

Run it:

dotnet run -- --file somefile.txt

It already works. But this is just the beginning. Let's add some flair — colored output and a progress bar.

Beautiful output: adding colors and emojis

The console doesn't have to be black and white. C# makes it easy to change text colors. Let's create a helper class:

public static class ConsoleHelper\n{\n    public static void WriteSuccess(string message)\n    {\n        Console.ForegroundColor = ConsoleColor.Green;\n        Console.WriteLine($"✅ {message}"