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yargs the modern, pirate-themed successor to optimist.
node.js command-line interfaces made easy
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Quick Overview
Meow is a command-line interface (CLI) helper for Node.js. It simplifies the process of creating CLI applications by providing an easy-to-use API for parsing arguments, handling flags, and managing configuration. Meow is designed to be lightweight and straightforward, making it ideal for small to medium-sized CLI projects.
Pros
- Simple and intuitive API for parsing command-line arguments
- Supports both long and short option flags
- Automatically generates help text based on the provided options
- Lightweight with minimal dependencies
Cons
- Limited advanced features compared to more comprehensive CLI frameworks
- May require additional libraries for complex command structures
- Not suitable for large-scale CLI applications with extensive subcommands
- Limited built-in validation for command-line inputs
Code Examples
- Basic usage:
import meow from 'meow';
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'
}
}
});
console.log(cli.input[0], cli.flags);
- Handling default values:
import meow from 'meow';
const cli = meow(`
Usage
$ bar [options]
Options
--name, -n Specify a name
--age, -a Specify an age
Examples
$ bar --name John --age 30
`, {
importMeta: import.meta,
flags: {
name: {
type: 'string',
alias: 'n',
default: 'Anonymous'
},
age: {
type: 'number',
alias: 'a',
default: 0
}
}
});
console.log(`Name: ${cli.flags.name}, Age: ${cli.flags.age}`);
- Using boolean flags:
import meow from 'meow';
const cli = meow(`
Usage
$ baz [options]
Options
--verbose, -v Enable verbose output
--quiet, -q Disable all output
Examples
$ baz --verbose
`, {
importMeta: import.meta,
flags: {
verbose: {
type: 'boolean',
alias: 'v'
},
quiet: {
type: 'boolean',
alias: 'q'
}
}
});
if (cli.flags.verbose) console.log('Verbose mode enabled');
if (cli.flags.quiet) console.log('Quiet mode enabled');
Getting Started
To use Meow in your project, follow these steps:
-
Install Meow:
npm install meow
-
Create a new JavaScript file (e.g.,
cli.js
) and import Meow:import meow from 'meow';
-
Define your CLI structure using the Meow API:
const cli = meow(` Usage $ your-cli-name [options] Options --option, -o Description of the option Examples $ your-cli-name --option value `, { importMeta: import.meta, flags: { option: { type: 'string', alias: 'o' } } });
-
Access parsed arguments and flags:
console.log(cli.input); console.log(cli.flags);
Competitor Comparisons
yargs the modern, pirate-themed successor to optimist.
Pros of yargs
- More feature-rich with advanced options like command grouping and nested commands
- Extensive documentation and examples for complex use cases
- Larger community and ecosystem with plugins and extensions
Cons of yargs
- Steeper learning curve due to more complex API
- Potentially overkill for simple CLI applications
- Larger package size and more dependencies
Code Comparison
meow:
import meow from 'meow';
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'
}
}
});
yargs:
import yargs from 'yargs';
import { hideBin } from 'yargs/helpers';
const argv = yargs(hideBin(process.argv))
.command('$0 <input>', 'the default command', (yargs) => {
yargs.positional('input', {
describe: 'the input to process'
})
})
.option('rainbow', {
alias: 'r',
type: 'boolean',
description: 'Include a rainbow'
})
.example('$0 unicorns --rainbow', '🌈 unicorns 🌈')
.parse();
node.js command-line interfaces made easy
Pros of Commander.js
- More feature-rich with built-in options for version, help, and custom commands
- Supports both declarative and programmatic command-line interfaces
- Extensive documentation and a large community for support
Cons of Commander.js
- Steeper learning curve due to more complex API
- Larger package size, which may impact performance in some scenarios
- Less focused on simplicity compared to Meow
Code Comparison
Meow:
import meow from 'meow';
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'
}
}
});
Commander.js:
import { program } from 'commander';
program
.version('0.1.0')
.argument('<input>')
.option('-r, --rainbow', 'Include a rainbow')
.action((input, options) => {
const message = options.rainbow ? `🌈 ${input} 🌈` : input;
console.log(message);
});
program.parse(process.argv);
Both libraries offer efficient ways to create command-line interfaces, with Meow focusing on simplicity and Commander.js providing more advanced features. The choice between them depends on the specific requirements of your project and your preferred coding style.
Smooth (CLI) Operator 🎶
Pros of sade
- Lightweight and minimal dependencies, resulting in faster installation and smaller package size
- Supports both synchronous and asynchronous command handlers
- Built-in support for command aliases and default commands
Cons of sade
- Less extensive documentation compared to meow
- Fewer built-in features for advanced CLI options and configurations
- Smaller community and ecosystem around the project
Code Comparison
sade:
const sade = require('sade');
sade('my-cli')
.version('1.0.0')
.option('-d, --debug', 'Enable debugging')
.action((opts) => {
console.log('Hello, world!');
})
.parse(process.argv);
meow:
const meow = require('meow');
const cli = meow(`
Usage
$ my-cli [options]
Options
--debug Enable debugging
Examples
$ my-cli --debug
`, {
flags: {
debug: {
type: 'boolean',
alias: 'd'
}
}
});
console.log('Hello, world!');
Both sade and meow are popular CLI argument parsing libraries for Node.js. sade offers a more lightweight approach with a focus on simplicity, while meow provides a more feature-rich experience with extensive documentation and a larger ecosystem. The choice between the two depends on the specific requirements of your CLI application and personal preferences.
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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 meow
Usage
./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
ð unicorns ð
`, {
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.json
objecthelp
(string) - The help text used with--help
showHelp([exitCode=2])
(Function) - Show the help text and exit withexitCode
showVersion()
(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:string
boolean
number
)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
Function
instead 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
ð unicornsâ¨ð
`, {
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
},
â¦
}
*/
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.
Top Related Projects
yargs the modern, pirate-themed successor to optimist.
node.js command-line interfaces made easy
Smooth (CLI) Operator 🎶
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Introducing Visual Copilot: A new AI model to turn Figma designs to high quality code using your components.
Try Visual Copilot