

GitHub - sindresorhus/meow: CLI app helper
source link: https://github.com/sindresorhus/meow
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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
- 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
#!/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?)
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
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
)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 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,
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',
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.
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
.
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.
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:
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
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.
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.
Tidelift helps make open source sustainable for maintainers while giving companies
assurances about security, maintenance, and licensing for their dependencies.
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