Here is a more complete program using a subcommand and with descriptions for the help. In a multi-command program, you have an action handler for each command (or stand-alone executables for the commands).
Options are defined with the `.option()` method, also serving as documentation for the options. Each option can have a short flag (single character) and a long name, separated by a comma or space or vertical bar ('|').
The parsed options can be accessed by calling `.opts()` on a `Command` object, and are passed to the action handler.
Multi-word options such as "--template-engine" are camel-cased, becoming `program.opts().templateEngine` etc.
An option and its option-argument can be separated by a space, or combined into the same argument. The option-argument can follow the short option directly or follow an `=` for a long option.
```sh
serve -p 80
serve -p80
serve --port 80
serve --port=80
```
You can use `--` to indicate the end of the options, and any remaining arguments will be used without being interpreted.
By default options on the command line are not positional, and can be specified before or after other arguments.
Multiple boolean short options may be combined together following the dash, and may be followed by a single short option taking a value.
For example `-d -s -p cheese` may be written as `-ds -p cheese` or even `-dsp cheese`.
Options with an expected option-argument are greedy and will consume the following argument whatever the value.
So `--id -xyz` reads `-xyz` as the option-argument.
`program.parse(arguments)` processes the arguments, leaving any args not consumed by the program options in the `program.args` array. The parameter is optional and defaults to `process.argv`.
### Default option value
You can specify a default value for an option.
Example file: [options-defaults.js](./examples/options-defaults.js)
```js
program
.option('-c, --cheese <type>', 'add the specified type of cheese', 'blue');
program.parse();
console.log(`cheese: ${program.opts().cheese}`);
```
```console
$ pizza-options
cheese: blue
$ pizza-options --cheese stilton
cheese: stilton
```
### Other option types, negatable boolean and boolean|value
You can define a boolean option long name with a leading `no-` to set the option value to false when used.
Defined alone this also makes the option true by default.
If you define `--foo` first, adding `--no-foo` does not change the default value from what it would
otherwise be.
Example file: [options-negatable.js](./examples/options-negatable.js)
You may specify a required (mandatory) option using `.requiredOption()`. The option must have a value after parsing, usually specified on the command line, or perhaps from a default value (say from environment). The method is otherwise the same as `.option()` in format, taking flags and description, and optional default value or custom processing.
For information about possible ambiguous cases, see [options taking varying arguments](./docs/options-taking-varying-arguments.md).
### Version option
The optional `version` method adds handling for displaying the command version. The default option flags are `-V` and `--version`, and when present the command prints the version number and exits.
```js
program.version('0.0.1');
```
```console
$ ./examples/pizza -V
0.0.1
```
You may change the flags and description by passing additional parameters to the `version` method, using
the same syntax for flags as the `option` method.
```js
program.version('0.0.1', '-v, --vers', 'output the current version');
```
### More configuration
You can add most options using the `.option()` method, but there are some additional features available
by constructing an `Option` explicitly for less common cases.
Example files: [options-extra.js](./examples/options-extra.js), [options-env.js](./examples/options-env.js), [options-conflicts.js](./examples/options-conflicts.js), [options-implies.js](./examples/options-implies.js)
Specify a required (mandatory) option using the `Option` method `.makeOptionMandatory()`. This matches the `Command` method [.requiredOption()](#required-option).
### Custom option processing
You may specify a function to do custom processing of option-arguments. The callback function receives two parameters,
the user specified option-argument and the previous value for the option. It returns the new value for the option.
This allows you to coerce the option-argument to the desired type, or accumulate values, or do entirely custom processing.
if (options.float !== undefined) console.log(`float: ${options.float}`);
if (options.integer !== undefined) console.log(`integer: ${options.integer}`);
if (options.verbose > 0) console.log(`verbosity: ${options.verbose}`);
if (options.collect.length > 0) console.log(options.collect);
if (options.list !== undefined) console.log(options.list);
```
```console
$ custom -f 1e2
float: 100
$ custom --integer 2
integer: 2
$ custom -v -v -v
verbose: 3
$ custom -c a -c b -c c
[ 'a', 'b', 'c' ]
$ custom --list x,y,z
[ 'x', 'y', 'z' ]
```
## Commands
You can specify (sub)commands using `.command()` or `.addCommand()`. There are two ways these can be implemented: using an action handler attached to the command, or as a stand-alone executable file (described in more detail later). The subcommands may be nested ([example](./examples/nestedCommands.js)).
In the first parameter to `.command()` you specify the command name. You may append the command-arguments after the command name, or specify them separately using `.argument()`. The arguments may be `<required>` or `[optional]`, and the last argument may also be `variadic...`.
You can use `.addCommand()` to add an already configured subcommand to the program.
For safety, `.addCommand()` does not automatically copy the inherited settings from the parent command. There is a helper routine `.copyInheritedSettings()` for copying the settings when they are wanted.
If you prefer, you can work with the command directly and skip declaring the parameters for the action handler. The `this` keyword is set to the running command and can be used from a function expression (but not from an arrow function).
A command's options and arguments on the command line are validated when the command is used. Any unknown options or missing arguments will be reported as an error. You can suppress the unknown option checks with `.allowUnknownOption()`. By default it is not an error to
pass more arguments than declared, but you can make this an error with `.allowExcessArguments(false)`.
When `.command()` is invoked with a description argument, this tells Commander that you're going to use stand-alone executables for subcommands.
Commander will search the files in the directory of the entry script for a file with the name combination `command-subcommand`, like `pm-install` or `pm-search` in the example below. The search includes trying common file extensions, like `.js`.
You may specify a custom name (and path) with the `executableFile` configuration option.
You may specify a custom search directory for subcommands with `.executableDir()`.
You handle the options for an executable (sub)command in the executable, and don't declare them at the top-level.
Long descriptions are wrapped to fit the available width. (However, a description that includes a line-break followed by whitespace is assumed to be pre-formatted and not wrapped.)
-`beforeAll`: add to the program for a global banner or header
-`before`: display extra information before built-in help
-`after`: display extra information after built-in help
-`afterAll`: add to the program for a global footer (epilog)
The positions "beforeAll" and "afterAll" apply to the command and all its subcommands.
The second parameter can be a string, or a function returning a string. The function is passed a context object for your convenience. The properties are:
- error: a boolean for whether the help is being displayed due to a usage error
- command: the Command which is displaying the help
The default behaviour is to suggest correct spelling after an error for an unknown command or option. You
can disable this.
```js
program.showSuggestionAfterError(false);
```
```console
$ pizza --hepl
error: unknown option '--hepl'
(Did you mean --help?)
```
### Display help from code
`.help()`: display help information and exit immediately. You can optionally pass `{ error: true }` to display on stderr and exit with an error status.
`.outputHelp()`: output help information without exiting. You can optionally pass `{ error: true }` to display on stderr.
`.helpInformation()`: get the built-in command help information as a string for processing or displaying yourself.
### .name
The command name appears in the help, and is also used for locating stand-alone executable subcommands.
You may specify the program name using `.name()` or in the Command constructor. For the program, Commander will
fallback to using the script name from the full arguments passed into `.parse()`. However, the script name varies
depending on how your program is launched so you may wish to specify it explicitly.
```js
program.name('pizza');
const pm = new Command('pm');
```
Subcommands get a name when specified using `.command()`. If you create the subcommand yourself to use with `.addCommand()`,
then set the name using `.name()` or in the Command constructor.
### .usage
This allows you to customise the usage description in the first line of the help. Given:
.helpOption('-e, --HELP', 'read more information');
```
### .addHelpCommand()
A help command is added by default if your command has subcommands. You can explicitly turn on or off the implicit help command with `.addHelpCommand()` and `.addHelpCommand(false)`.
You can both turn on and customise the help command by supplying the name and description:
The built-in help is formatted using the Help class.
You can configure the Help behaviour by modifying data properties and methods using `.configureHelp()`, or by subclassing using `.createHelp()` if you prefer.
The data properties are:
-`helpWidth`: specify the wrap width, useful for unit tests
-`sortSubcommands`: sort the subcommands alphabetically
-`sortOptions`: sort the options alphabetically
-`showGlobalOptions`: show a section with the global options from the parent command(s)
You can override any method on the [Help](./lib/help.js) class. There are methods getting the visible lists of arguments, options, and subcommands. There are methods for formatting the items in the lists, with each item having a _term_ and _description_. Take a look at `.formatHelp()` to see how they are used.
Example file: [configure-help.js](./examples/configure-help.js)
```js
program.configureHelp({
sortSubcommands: true,
subcommandTerm: (cmd) => cmd.name() // Just show the name, instead of short usage.
If the default parsing does not suit your needs, there are some behaviours to support other usage patterns.
By default program options are recognised before and after subcommands. To only look for program options before subcommands, use `.enablePositionalOptions()`. This lets you use
an option for a different purpose in subcommands.
Example file: [positional-options.js](./examples/positional-options.js)
With positional options, the `-b` is a program option in the first line and a subcommand option in the second line:
By default options are recognised before and after command-arguments. To only process options that come
before the command-arguments, use `.passThroughOptions()`. This lets you pass the arguments and following options through to another program
without needing to use `--` to end the option processing.
To use pass through options in a subcommand, the program needs to enable positional options.
Example file: [pass-through-options.js](./examples/pass-through-options.js)
With pass through options, the `--port=80` is a program option in the first line and passed through as a command-argument in the second line:
```sh
program --port=80 arg
program arg --port=80
```
By default the option processing shows an error for an unknown option. To have an unknown option treated as an ordinary command-argument and continue looking for options, use `.allowUnknownOption()`. This lets you mix known and unknown options.
By default the argument processing does not display an error for more command-arguments than expected.
To display an error for excess arguments, use`.allowExcessArguments(false)`.
### Legacy options as properties
Before Commander 7, the option values were stored as properties on the command.
This was convenient to code but the downside was possible clashes with
existing properties of `Command`. You can revert to the old behaviour to run unmodified legacy code by using `.storeOptionsAsProperties()`.
extra-typings: There is an optional project to infer extra type information from the option and argument definitions.
This adds strong typing to the options returned by `.opts()` and the parameters to `.action()`.
See [commander-js/extra-typings](https://github.com/commander-js/extra-typings) for more.
```
import { Command } from '@commander-js/extra-typings';
```
ts-node: If you use `ts-node` and stand-alone executable subcommands written as `.ts` files, you need to call your program through node to get the subcommands called correctly. e.g.
```sh
node -r ts-node/register pm.ts
```
### createCommand()
This factory function creates a new command. It is exported and may be used instead of using `new`, like:
```js
const { createCommand } = require('commander');
const program = createCommand();
```
`createCommand` is also a method of the Command object, and creates a new command rather than a subcommand. This gets used internally
when creating subcommands using `.command()`, and you may override it to
customise the new subcommand (example file [custom-command-class.js](./examples/custom-command-class.js)).
### Node options such as `--harmony`
You can enable `--harmony` option in two ways:
- Use `#! /usr/bin/env node --harmony` in the subcommands scripts. (Note Windows does not support this pattern.)
- Use the `--harmony` option when call the command, like `node --harmony examples/pm publish`. The `--harmony` option will be preserved when spawning subcommand process.
### Debugging stand-alone executable subcommands
An executable subcommand is launched as a separate child process.
If you are using the node inspector for [debugging](https://nodejs.org/en/docs/guides/debugging-getting-started/) executable subcommands using `node --inspect` et al,
the inspector port is incremented by 1 for the spawned subcommand.
If you are using VSCode to debug executable subcommands you need to set the `"autoAttachChildProcesses": true` flag in your launch.json configuration.
### Display error
This routine is available to invoke the Commander error handling for your own error conditions. (See also the next section about exit handling.)
As well as the error message, you can optionally specify the `exitCode` (used with `process.exit`)
and `code` (used with `CommanderError`).
```js
program.error('Password must be longer than four characters');
program.error('Custom processing has failed', { exitCode: 2, code: 'my.custom.error' });
```
### Override exit and output handling
By default Commander calls `process.exit` when it detects errors, or after displaying the help or version. You can override
this behaviour and optionally supply a callback. The default override throws a `CommanderError`.
The override callback is passed a `CommanderError` with properties `exitCode` number, `code` string, and `message`. The default override behaviour is to throw the error, except for async handling of executable subcommand completion which carries on. The normal display of error messages or version or help
is not affected by the override which is called after the display.
```js
program.exitOverride();
try {
program.parse(process.argv);
} catch (err) {
// custom processing...
}
```
By default Commander is configured for a command-line application and writes to stdout and stderr.
You can modify this behaviour for custom applications. In addition, you can modify the display of error messages.
Example file: [configure-output.js](./examples/configure-output.js)
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