JarCastingmeow
CLI app helper
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 - Makes unhandled rejected promises fail hard 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
CommonJS
#!/usr/bin/env node
'use strict';
const meow = require('meow');
const foo = require('.');
const cli = meow(`
Usage
$ foo <input>
Options
--rainbow, -r Include a rainbow
Examples
$ foo unicorns --rainbow
🌈 unicorns 🌈
`, {
flags: {
rainbow: {
type: 'boolean',
alias: 'r'
}
}
});
/*
{
input: ['unicorns'],
flags: {rainbow: true},
...
}
*/
foo(cli.input[0], cli.flags);
ES Modules
#!/usr/bin/env node
import {createRequire} from 'module';
import foo from './lib/index.js';
const meow = createRequire(import.meta.url)('meow');
const cli = meow(`
Usage
$ foo <input>
Options
--rainbow, -r Include a rainbow
Examples
$ foo unicorns --rainbow
🌈 unicorns 🌈
`, {
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 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
flags
Type: object
Define argument flags.
The key is the flag name and the value is an object with any of:
type: Type of value. (Possible values:stringbooleannumber)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
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
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,
Example:
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 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:
const meow = require('meow');
const cli = meow(`
Usage
$ foo
Options
--rainbow, -r Include a rainbow
--unicorn, -u Include a unicorn
--no-sparkles Exclude sparkles
Examples
$ foo
🌈 unicorns✨🌈
`, {
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 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 instead of the default silent fail. Meaning you don't have to manually .catch() promises used in your CLI.
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.
See update-notifier if you want update notifications.
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