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CLI app helper


Version published
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  • Require Node.js 14 01cf2a5


  • Improve TypeScript types (#218) 6c57fc8




CLI app helper

I would recommend reading this guide on how to make user-friendly command-line tools.


  • Parses arguments
  • Converts flags to 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 instead of the default silent fail
  • Sets the process title to the binary name defined in package.json


$ npm install meow


$ ./foo-app.js unicorns --rainbow #!/usr/bin/env node import meow from 'meow'; import foo from './lib/index.js'; const cli = meow(` Usage $ foo <input> 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);


meow(helpText, 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

Type: string

Shortcut for the help option.


Type: object


Type: object

Pass in import.meta. This is used to find the correct package.json file.


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.

Note that flags are always defined using a camel-case key (myKey), but will match arguments in kebab-case (--my-key).


flags: { unicorn: { type: 'string', alias: 'u', default: ['rainbow', 'cat'], isMultiple: true, isRequired: (flags, input) => { if (flags.otherFlag) { return true; } return false; } } }

Type: string | boolean
Default: The package.json "description" property

Description to show above the help text.

Set it to false to disable it altogether.


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 without having to care about using the correct amount of indent.

The description will be shown above your help text automatically.


Type: string | boolean
Default: The package.json "version" property

Set a custom version output.


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.


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.


Type: object
Default: Closest package.json upwards

package.json as an object.

You most likely don't need this option.


Type: string[]
Default: process.argv.slice(2)

Custom arguments object.


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.


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.


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 }, } */

Type: boolean
Default: true

Whether to use hard-rejection or not. Disabling this can be useful if you need to handle process.on('unhandledRejection') yourself.


Type boolean
Default: true

Whether to allow unknown flags or not.


Meow will make unhandled rejected promises fail hard instead of the default silent fail. Meaning you don't have to manually .catch() promises used in your CLI.


See chalk if you want to colorize the terminal output.

See get-stdin if you want to accept input from stdin.

See conf if you need to persist some data.

See update-notifier if you want update notifications.

More useful CLI utilities…

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What is meow?

CLI app helper

Is meow popular?

The npm package meow receives a total of 15,278,953 weekly downloads. As such, meow popularity was classified as popular.

Is meow well maintained?

We found that meow demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago.It has 1 open source maintainer collaborating on the project.

Last updated on 11 Oct 2022

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