This library helps you create professional command-line tools using TypeScript. By "professional", we mean:

• no gotchas for users: Seems obvious, but try typing "npm install --save-dex" instead of "npm install --save-dev" sometime. The command seems to execute successfully, but it doesn't save anything! The misspelled flag was silently ignored. This lack of rigor plagues many familiar Node.js tools and can be confusing and frustrating. For a great user experience, a command line tool should always be strict about its syntax.

• no gotchas for developers: Many command-line libraries store their parsed data in a simple JavaScript object. This is convenient for small projects. But suppose a large project has many different source files that define and read parameters. If you try to readdata['output-dir'] when it wasn't defined, or if you misspell the key name, your tool will silently behave as if the parameter was omitted. And isdata['max-count'] a string or a number? Hard to tell! We solve this by modeling each parameter kind as a real TypeScript class.

• simple by design: Making a CLI is similar to making a graphical UI -- some people have a knack for clean and intuitive designs, but your average developer... needs some help. :-) Keeping things simple is the best help.ts-command-line intentionally provides a minimalist set of CLI building blocks that encourage simple designs. If your app has lots of knobs and switches, we recommend NOT to design a complex CLI with hundreds of parameters. Move those options into a commented config file with a published JSON schema.

• automatic documentation: Some command-line libraries treat the--help docs as someone else's job.ts-command-line requires each every parameter to follow a standardized naming pattern and have a documentation string. It will automatically generate the--help docs for you. If you like to write long paragraphs, no problem -- they will be word-wrapped correctly.[golf clap]

• structure and extensibility: Instead of a simple function chain,ts-command-line provides a "scaffold" pattern that makes it easy to find and understand the command-line implementation for any tool project. The scaffold model is generally recommended, but there's also a "dynamic" model if you need it. See below for examples.

• environment variable mappings: Any CLI parameter can be associated with an environment variable. If the parameter is not explicitly provided, the value from the environment will be used. The associated environment variables are automatically documented in the--help.

Internally, the implementation is based onargparse and the Python approach to command-lines.

Compared to other libraries,ts-command-line doesn't provide zillions of custom syntaxes and bells and whistles. Instead it aims to be a simple, consistent, and professional solution for your command-line tool. Give it a try!

Suppose that we want to parse a command-line like this:

widget --verbose push --force --max-count 123

In this example, we can identify the following components:

• Thetool name in this example iswidget. This is the name of your Node.js bin script.
• Theparameters are--verbose,--force, and--max-count.
• The value "123" is theargument for the--max-count integer parameter. (Flags don't have arguments, because their value is determined by whether the flag was provided or not.)
• Similar to Git's command-line, thepush token is called anaction. It acts as sub-command with its own unique set of parameters.
• The--verbose flag is aglobal parameter because it precedes the action name. It affects all actions.
• The--force flag is anaction parameter because it comes after the action name. It only applies to that action.

Several different kinds of parameters are supported:

Other parameter kinds could be implemented if requested. That said, keeping your CLI grammar simple and systematic makes it easier for users to learn.

If your tool uses the scaffold model, you will create subclasses of two abstract base classes:CommandLineParser for the overall command-line, andCommandLineAction for each action.

Continuing our example from above, suppose we want to start with a couple simple flags like this:

widget --verbose push --force

We could define our subclass for the "push" action like this:

exportclassPushActionextendsCommandLineAction{private_force:CommandLineFlagParameter;private_protocol:CommandLineChoiceParameter;publicconstructor(){super({actionName:'push',summary:'Pushes a widget to the service',documentation:'Here we provide a longer description of how our action works.'});this._force=this.defineFlagParameter({parameterLongName:'--force',parameterShortName:'-f',description:'Push and overwrite any existing state'});this._protocol=this.defineChoiceParameter({parameterLongName:'--protocol',description:'Specify the protocol to use',alternatives:['ftp','webdav','scp'],environmentVariable:'WIDGET_PROTOCOL',defaultValue:'scp'});}protectedoverrideasynconExecuteAsync():Promise<void>{// abstractawaitBusinessLogic.doTheWork(this._force.value,this._protocol.value||"(none)");}}

Then we might define the parser subclass like this:

exportclassWidgetCommandLineextendsCommandLineParser{private_verbose:CommandLineFlagParameter;publicconstructor(){super({toolFilename:'widget',toolDescription:'The "widget" tool is a code sample for using the @rushstack/ts-command-line library.'});this.addAction(newPushAction());this._verbose=this.defineFlagParameter({parameterLongName:'--verbose',parameterShortName:'-v',description:'Show extra logging detail'});}protectedoverrideasynconExecuteAsync():Promise<void>{BusinessLogic.configureLogger(this._verbose.value);awaitsuper.onExecuteAsync();}}

To invoke the parser, the application entry point will do something like this:

constcommandLine:WidgetCommandLine=newWidgetCommandLine();commandLine.executeAsync();

When we runwidget --verbose push --force, thePushAction.onExecute() method will get invoked and then your business logic takes over.

For a more complete example, take a look at thets-command-line-test sample project.

If you invoke the tool as "widget --help", the docs are automatically generated:

usage: widget [-h] [-v] <command> ...The "widget" tool is a code sample for using the @rushstack/ts-command-linelibrary.Positional arguments:  <command>    push         Pushes a widget to the serviceOptional arguments:  -h, --help     Show this help message and exit.  -v, --verbose  Show extra logging detailFor detailed help about a specific command, use: widget <command> -h

For help about thepush action, the user can type "widget push --help", which shows this output:

usage: widget push [-h] [-f] [--protocol {ftp,webdav,scp}]Here we provide a longer description of how our action works.Optional arguments:  -h, --help            Show this help message and exit.  -f, --force           Push and overwrite any existing state  --protocol {ftp,webdav,scp}                        Specify the protocol to use. This parameter may                        alternatively specified via the WIDGET_PROTOCOL                        environment variable. The default value is "scp".

The action subclasses provide a simple, recognizable pattern that you can use across all your tooling projects. It's the generally recommended approach. However, there are some cases where we need to break out of the scaffold. For example:

• Actions or parameters may be discovered at runtime, e.g. from a config file
• The actions and their implementations may sometimes have very different structures

In this case, you can use theDynamicCommandLineAction andDynamicCommandLineParser classes which are not abstract (and not intended to be subclassed). Here's our above example rewritten for this model:

// Define the parserconstcommandLineParser:DynamicCommandLineParser=newDynamicCommandLineParser({toolFilename:'widget',toolDescription:'The "widget" tool is a code sample for using the @rushstack/ts-command-line library.'});commandLineParser.defineFlagParameter({parameterLongName:'--verbose',parameterShortName:'-v',description:'Show extra logging detail'});// Define the actionconstaction:DynamicCommandLineAction=newDynamicCommandLineAction({actionName:'push',summary:'Pushes a widget to the service',documentation:'Here we provide a longer description of how our action works.'});commandLineParser.addAction(action);action.defineFlagParameter({parameterLongName:'--force',parameterShortName:'-f',description:'Push and overwrite any existing state'});action.defineChoiceParameter({parameterLongName:'--protocol',description:'Specify the protocol to use',alternatives:['ftp','webdav','scp'],environmentVariable:'WIDGET_PROTOCOL',defaultValue:'scp'});// Parse the command linecommandLineParser.executeAsync().then(()=>{console.log('The action is: '+commandLineParser.selectedAction!.actionName);console.log('The force flag is: '+action.getFlagParameter('--force').value);});

You can also mix the two models. For example, we could augment theWidgetCommandLine from the original model by addingDynamicAction objects to it.

• CHANGELOG.md - Findout what's new in the latest version
• API Reference

Here are some real world GitHub projects that illustrate different use cases forts-command-line:

• @microsoft/rush
• @microsoft/api-extractor
• @microsoft/api-documenter

@rushstack/ts-command-line is part of theRush Stack family of projects.