# meow
> CLI app helper
*I would recommend reading this [guide](https://clig.dev) on how to make user-friendly command-line tools.*
## Features
- Parses arguments
- Converts flags to [camelCase](https://github.com/sindresorhus/camelcase)
- Negates flags when using the `--no-` prefix
- Outputs version when `--version`
- Outputs description and supplied help text when `--help`
- Makes unhandled rejected promises [fail hard](https://github.com/sindresorhus/hard-rejection) instead of the default silent fail
- Sets the process title to the binary name defined in package.json
## Install
```
$ npm install meow
```
## Usage
```
$ ./foo-app.js unicorns --rainbow
```
```js
#!/usr/bin/env node
import meow from 'meow';
import foo from './lib/index.js';
const cli = meow(`
Usage
$ foo
Options
--rainbow, -r Include a rainbow
Examples
$ foo unicorns --rainbow
🌈 unicorns 🌈
`, {
importMeta: import.meta,
flags: {
rainbow: {
type: 'boolean',
alias: 'r'
}
}
});
/*
{
input: ['unicorns'],
flags: {rainbow: true},
...
}
*/
foo(cli.input[0], cli.flags);
```
## API
### meow(helpText, options?)
### meow(options)
Returns an `object` with:
- `input` *(Array)* - Non-flag arguments
- `flags` *(Object)* - Flags converted to camelCase excluding aliases
- `unnormalizedFlags` *(Object)* - Flags converted to camelCase including aliases
- `pkg` *(Object)* - The `package.json` object
- `help` *(string)* - The help text used with `--help`
- `showHelp([exitCode=2])` *(Function)* - Show the help text and exit with `exitCode`
- `showVersion()` *(Function)* - Show the version text and exit
#### helpText
Type: `string`
Shortcut for the `help` option.
#### options
Type: `object`
##### importMeta
Type: `object`
Pass in [`import.meta`](https://nodejs.org/dist/latest/docs/api/esm.html#esm_import_meta). This is used to find the correct package.json file.
##### flags
Type: `object`
Define argument flags.
The key is the flag name in camel-case and the value is an object with any of:
- `type`: Type of value. (Possible values: `string` `boolean` `number`)
- `alias`: Usually used to define a short flag alias.
- `default`: Default value when the flag is not specified.
- `isRequired`: Determine if the flag is required. (Default: false)
- If it's only known at runtime whether the flag is required or not, you can pass a `Function` instead of a `boolean`, which based on the given flags and other non-flag arguments, should decide if the flag is required. Two arguments are passed to the function:
- The first argument is the **flags** object, which contains the flags converted to camel-case excluding aliases.
- The second argument is the **input** string array, which contains the non-flag arguments.
- The function should return a `boolean`, true if the flag is required, otherwise false.
- `isMultiple`: Indicates a flag can be set multiple times. Values are turned into an array. (Default: false)
- Multiple values are provided by specifying the flag multiple times, for example, `$ foo -u rainbow -u cat`. Space- or comma-separated values are [currently *not* supported](https://github.com/sindresorhus/meow/issues/164).
Note that flags are always defined using a camel-case key (`myKey`), but will match arguments in kebab-case (`--my-key`).
Example:
```js
flags: {
unicorn: {
type: 'string',
alias: 'u',
default: ['rainbow', 'cat'],
isMultiple: true,
isRequired: (flags, input) => {
if (flags.otherFlag) {
return true;
}
return false;
}
}
}
```
##### description
Type: `string | boolean`\
Default: The package.json `"description"` property
Description to show above the help text.
Set it to `false` to disable it altogether.
##### help
Type: `string | boolean`
The help text you want shown.
The input is reindented and starting/ending newlines are trimmed which means you can use a [template literal](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/template_strings) without having to care about using the correct amount of indent.
The description will be shown above your help text automatically.
##### version
Type: `string | boolean`\
Default: The package.json `"version"` property
Set a custom version output.
##### autoHelp
Type: `boolean`\
Default: `true`
Automatically show the help text when the `--help` flag is present. Useful to set this value to `false` when a CLI manages child CLIs with their own help text.
This option is only considered when there is only one argument in `process.argv`.
##### autoVersion
Type: `boolean`\
Default: `true`
Automatically show the version text when the `--version` flag is present. Useful to set this value to `false` when a CLI manages child CLIs with their own version text.
This option is only considered when there is only one argument in `process.argv`.
##### pkg
Type: `object`\
Default: Closest package.json upwards
package.json as an `object`.
*You most likely don't need this option.*
##### argv
Type: `string[]`\
Default: `process.argv.slice(2)`
Custom arguments object.
##### inferType
Type: `boolean`\
Default: `false`
Infer the argument type.
By default, the argument `5` in `$ foo 5` becomes a string. Enabling this would infer it as a number.
##### booleanDefault
Type: `boolean | null | undefined`\
Default: `false`
Value of `boolean` flags not defined in `argv`.
If set to `undefined`, the flags not defined in `argv` will be excluded from the result.
The `default` value set in `boolean` flags take precedence over `booleanDefault`.
_Note: If used in conjunction with `isMultiple`, the default flag value is set to `[]`._
__Caution: Explicitly specifying `undefined` for `booleanDefault` has different meaning from omitting key itself.__
Example:
```js
import meow from 'meow';
const cli = meow(`
Usage
$ foo
Options
--rainbow, -r Include a rainbow
--unicorn, -u Include a unicorn
--no-sparkles Exclude sparkles
Examples
$ foo
🌈 unicorns✨🌈
`, {
importMeta: import.meta,
booleanDefault: undefined,
flags: {
rainbow: {
type: 'boolean',
default: true,
alias: 'r'
},
unicorn: {
type: 'boolean',
default: false,
alias: 'u'
},
cake: {
type: 'boolean',
alias: 'c'
},
sparkles: {
type: 'boolean',
default: true
}
}
});
/*
{
flags: {
rainbow: true,
unicorn: false,
sparkles: true
},
unnormalizedFlags: {
rainbow: true,
r: true,
unicorn: false,
u: false,
sparkles: true
},
…
}
*/
```
##### hardRejection
Type: `boolean`\
Default: `true`
Whether to use [`hard-rejection`](https://github.com/sindresorhus/hard-rejection) or not. Disabling this can be useful if you need to handle `process.on('unhandledRejection')` yourself.
#### allowUnknownFlags
Type `boolean`\
Default: `true`
Whether to allow unknown flags or not.
## Promises
Meow will make unhandled rejected promises [fail hard](https://github.com/sindresorhus/hard-rejection) instead of the default silent fail. Meaning you don't have to manually `.catch()` promises used in your CLI.
## Tips
See [`chalk`](https://github.com/chalk/chalk) if you want to colorize the terminal output.
See [`get-stdin`](https://github.com/sindresorhus/get-stdin) if you want to accept input from stdin.
See [`conf`](https://github.com/sindresorhus/conf) if you need to persist some data.
See [`update-notifier`](https://github.com/yeoman/update-notifier) if you want update notifications.
[More useful CLI utilities…](https://github.com/sindresorhus/awesome-nodejs#command-line-utilities)
---