meow
CLI app helper
I would recommend reading this guide on how to make user-friendly command-line tools.
Features
- 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 - Sets the process title to the binary name defined in package.json
- No dependencies!
Install
npm install meowUsage
./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, // This is required
flags: {
rainbow: {
type: 'boolean',
shortFlag: 'r'
}
}
});
/*
{
input: ['unicorns'],
flags: {rainbow: true},
...
}
*/
foo(cli.input.at(0), cli.flags);API
meow(helpText, options)
meow(options)
Returns an object with:
input(Array) - Non-flag argumentsflags(Object) - Flags converted to camelCase excluding aliasesunnormalizedFlags(Object) - Flags converted to camelCase including aliasespkg(Object) - Thepackage.jsonobjecthelp(string) - The help text used with--helpshowHelp([exitCode=2])(Function) - Show the help text and exit withexitCodeshowVersion()(Function) - Show the version text and exit
helpText
Type: string
Shortcut for the help option.
options
Type: object
importMeta
Required
Type: object
Pass in 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:stringbooleannumber)choices: Limit valid values to a predefined set of choices.default: Default value when the flag is not specified.shortFlag: A short flag alias.aliases: Other names for the flag.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.
- Multiple values are provided by specifying the flag multiple times, for example,
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
Functioninstead of aboolean, 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.
- If it's only known at runtime whether the flag is required or not, you can pass a
Note that flags are always defined using a camel-case key (myKey), but will match arguments in kebab-case (--my-key).
Example:
flags: {
unicorn: {
type: 'string',
choices: ['rainbow', 'cat', 'unicorn'],
default: ['rainbow', 'cat'],
shortFlag: 'u',
aliases: ['unicorns'],
isMultiple: true,
isRequired: (flags, input) => {
if (flags.otherFlag) {
return true;
}
return false;
}
}
}description
Type: string | false
Default: The package.json "description" property
Description to show above the help text.
Set it to false to disable it altogether.
help
Type: string | false
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.
Set it to false to disable it altogether.
version
Type: string
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.
Note: Setting this stops meow from finding a package.json.
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 | 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:
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,
shortFlag: 'r'
},
unicorn: {
type: 'boolean',
default: false,
shortFlag: 'u'
},
cake: {
type: 'boolean',
shortFlag: 'c'
},
sparkles: {
type: 'boolean',
default: true
}
}
});
/*
{
flags: {
rainbow: true,
unicorn: false,
sparkles: true
},
unnormalizedFlags: {
rainbow: true,
r: true,
unicorn: false,
u: false,
sparkles: true
},
…
}
*/allowUnknownFlags
Type boolean
Default: true
Whether to allow unknown flags or not.
helpIndent
Type number
Default: 2
The number of spaces to use for indenting the help text.
Tips
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.