![]() ![]() The help output generated for you by System.CommandLine is customized to suit your needs. This command is simply the top-level command that is the name of the application, which in this case with be “LiveFile.”Ī visual representation of this configuration is visible in the application’s help output. Finally, each of the options is added to the rootCommand. These options all contain a type (the generic parameter specified on the Option class), which defines the argument type for that option. We declare the options for our root command. The full code for this example is available on GitHub. RootCommand rootCommand = new(description: "A countdown timer application")Īsync (DateTime countdownTo, FileInfo outputFile, Verbosity verbosity, IConsole console) => GetDefaultValue: () => new FileInfo( "output.txt"),ĭescription: "The output file to write to") ĭescription: "The verbosity of the output") Option countdownToOption = new(ĭescription: "The target time to count down to") It runs a countdown timer and outputs the remaining time to a file (this can be useful for running a countdown timer in OBS).įirst, we will configure the command-line syntax for our simple app using C# top-level statements. In this example, we build a simple console application called LiveFile. In addition, the command-line interface supports more advanced concepts, including option argument delimiters, bundling, and directives. It only accepts a single value therefore, it has an arity of one. In this example, -configuration is an option to the publish command that accepts Release as an argument. ![]() Arguments may have an arity, indicating how many values they can hold. In this example, -no-build is an option for the publish command.Īrgument: A value passed to either a command or an option. Option: An optional named parameter for a command. In this example, dotnet is the root command, and publish is the executed subcommand. Using the dotnet CLI as an example: > dotnet publish When running a CLI application, only a single command executes. The very top-level command, the name of your executable (also referred to as arg0), is the root command. Key Terms to Understand the System.CommandLine APIĬommand: A command is an action or verb that the command-line app performs. Though there is quite a lot of information in the specification, three key terms help clarify the System.CommandLine API. Among other things, POSIX defines the syntax for command-line applications. Underlying many command-line interfaces is the Portable Operating System Interface (POSIX). Providing a universal experience can be quite difficult as many users are familiar with a mix of Bash, batch scripting, PowerShell, and others. System.CommandLine strives to ensure the parsing of the command line is consistent and provides both a good developer experience and a good end-user experience. You need to install pre-release NuGet packages because the library is still in beta. As of writing this article, the latest version posted on is 2.0.0-beta3.22114.1 (posted on Feb 18 th, 2022). It is worth mentioning that the public API of the project has been under constant development and improvement. It is an amazing library with many features, including tab completion and trim compatibility, while still being very performant. ![]() With the Beta 3 release and the official documentation now added, the library is getting much closer to the full General Availability (GA) release. I have had the privilege of working on the System.CommandLine library for the last several years. It is possible to invoke apps from the command line, but many apps do not leverage this interface. It took me a while to wrap my head around Jon’s statement, but the longer I have thought about it, the more I agree. "All apps are command-line apps" – Jon Sequeria, Principle Software Engineer on System.CommandLine. Overviewing the System.CommandLine Library ![]()
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