Tarn Barford

I still write heaps of little console applications to do all sorts of things. Most of the console applications I write are tools for tasks like deployment, manipulating data and processing images. Usually they are for my own use, if I find one really useful I might pass it on to the rest of our development team or publish it on this blog.

For these little tools, I prefer using console applications over windows application as I feel they are more useful. Even though its easier to use a tool that has a little GUI, its not more useful if you ever want to automate it.

Ideally I would prefer to write assemblies and use them from Powershell as it would provide the greatest usage flexibility. But it also requires competence scripting with Powershell. I was very excited about Windows Powershell when it was released, but a year on, I still haven't made it the integral part of my development toolset I thought it would be. This is an area I want to improve on, but this post is about command line arguments.

Generally these little non production, internal applications are quite light weight and fit for purpose. I find I often write simple logging and command line processing that is also fit for purpose. This is fine, its usually very simple, quick to write and works. The problem is that I write this same functionality over and over again for each little application.

I was toying with the idea of writing a generic command line parsing class. I figured I could use reflection on a settings class decorated with attributes describing the specific command line syntax. I figured I could even generate the help text using reflection too. While this seemed like a great idea, I am aware of time I've previously spent (wasted?) re-writing code where a perfectly good open source solution is available.

So I did a search and found a couple of existing command line solutions. Not surprisingly, given they were both written in .NET 2.0+, they both used reflection and attributes. I ended up using the Command Line Parser Library from CodePlex. I'm not sure if it does everything, but it does everything I need for 99% of the console applications I write that require command line processing.

Anyway here is all the code from my test application:

public class Options
{
    [Option("r", "run", HelpText = "Run the export", Required = true)]
    public bool Run;

    [Option("n", "Name", HelpText = "Use a specific name")]
    public string Name = String.Empty;

    [HelpOption(HelpText = "Dispaly this help screen.")]
    public string GetUsage()
    {
        HelpText help = new HelpText(new HeadingInfo("Hello WorldExample", "1.0.0"));
        help.Copyright = new CopyrightInfo("sharpthinking", 2008);
        help.AddPreOptionsLine("Usage: Hello --run");
        help.AddOptions(this);
        return help;
    }
}

class Program
{
    static void Main(string[] args)
    {
        Options options = new Options();
        if (Parser.ParseArguments(args, options, Console.Error))
        {
            string name = string.IsNullOrEmpty(options.Name) ? "World" : options.Name;
            Console.WriteLine("Hello {0}!", name);
        }
    }
}

And we get the expected usage from the command line

image

Now I have to make sure I bundle the console applications with an external assembly, but it does make using command line arguments easy.

Command Line Arguments