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https://github.com/Yord/shargs
🦈 shargs is a combinator library for building command-line argument parsers.
https://github.com/Yord/shargs
command-line parser shargs
Last synced: 12 days ago
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🦈 shargs is a combinator library for building command-line argument parsers.
- Host: GitHub
- URL: https://github.com/Yord/shargs
- Owner: Yord
- License: mit
- Created: 2020-01-14T07:53:31.000Z (over 4 years ago)
- Default Branch: master
- Last Pushed: 2021-01-31T21:22:22.000Z (over 3 years ago)
- Last Synced: 2024-05-20T21:35:54.020Z (about 1 month ago)
- Topics: command-line, parser, shargs
- Language: JavaScript
- Homepage:
- Size: 3.7 MB
- Stars: 86
- Watchers: 2
- Forks: 0
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
Lists
- awesome-stars - shargs - line argument parsers. | Yord | 86 | (JavaScript)
README
🦈 shargs (**sh**ell **args**) is a library for building command-line argument parsers.
[![node version][shield-node]][node]
[![npm version][shield-npm]][npm-package]
[![license][shield-license]][license]
[![PRs Welcome][shield-prs]][contribute]
[![linux unit tests status][shield-unit-tests-linux]][actions]
[![macos unit tests status][shield-unit-tests-macos]][actions]
[![windows unit tests status][shield-unit-tests-windows]][actions]
## Features
+ Compose functions to build [highly customizable](#command-line-parsers) command-line argument [parsers](#the-parsersync-function).
+ 35+ opt-in features, e.g. ([multiple](#multiple-subcommands)) [subcommands](#subcommand),
[spelling mistake detection](#suggestOpts), [default values](#setDefaultValues),
and ([best guess](#bestGuessCast)) [casting](#cast).
+ [Synchronous](#the-parsersync-function) and Promise-based [asynchronous](#async-parsers) modes
with async/await support.
+ [Automatic usage documentation generation](#automatic-usage-documentation-generation) with fine-grained control over
[layouts](#automatic-usage-documentation-generation) and [styles](#style).
+ Easily extensible with your own [custom parser stages](#custom-checks-and-stages)
and [custom usage layouts](#custom-usage-functions).
+ [Extensively documented](#documentation) and very well tested (800+ unit and integration tests).
+ [Modular library layout](#installation) with zero runtime dependencies.
## Installation
Install as a bundle (recommended):
npm install --save shargs
Install as modules:
npm install --save shargs-core # core functions like parserSync (in bundle: shargs/core or shargs)
npm install --save shargs-opts # a DSL for command-line options (in bundle: shargs/opts)
npm install --save shargs-parser # collection of parser functions (in bundle: shargs/parser)
npm install --save shargs-usage # collection of usage functions (in bundle: shargs/usage)
npm install --save shargs-repl # build REPLs powered by shargs (not in bundle)
The documentation assumes the bundle is installed,
but the only difference between the bundle and modules installation is how functions are imported:
The bundle uses `require('shargs/opts')`, while `require('shargs-opts')` is used by modules
(note the use of `/` vs. `-`).
Read [installing as bundle or modules](#installing-as-bundle-or-modules) for more details.
## Getting Started
Describe your command and its options:
```js
const opts = [
stringPos('question', {desc: 'Ask a question.', required: true}),
number('answer', ['-a', '--answer'], {desc: 'The answer.', defaultValues: [42]}),
flag('help', ['-h', '--help'], {desc: 'Print this help message and exit.'})
]
const deepThought = command('deepThought', opts, {desc: 'Ask the Ultimate Question.'})
```
The `deepThought` command has three command-line options:
1. A `required` string positional argument named `question`.
2. An `answer` number option specified with `-a` or `--answer` that should default to `42` if not given.
3. A `help` command-line flag given by `-h` or `--help`.
You may use the `shargs-opts` module to get a nice DSL for describing our options.
However, you could have also written them out as objects yourself or could have used a different DSL.
Read up on the details in the [command-line options](#command-line-options) section.
Declare your own command-line parser:
```js
const parser = parserSync({
argv: [splitShortOpts],
opts: [setDefaultValues, requireOpts, cast],
args: [flagsAsBools]
})
```
Shargs gives you fine-grained control over how the options are parsed.
By using the `shargs-core` and `shargs-parser` modules, we have build the following `parser`:
1. `splitShortOpts`: Short option groups like `-cvzf` are transformed to `-c -v -z -f`.
2. `setDefaultValues`: Options with default values that were not provided are set.
3. `requireOpts`: It is verified that all required options have been given.
4. `cast`: Strings are cast to other types, like numbers or booleans.
5. `flagsAsBools`: Command-line flags are transformed to booleans.
Note that you did not tell `parser` how exactly to do those things.
Everything is nice and declarative, and the details are hidden away in the parser stages.
The [parserSync function](#the-parserSync-function)
and [command-line parsers](#command-line-parsers) sections have all the details.
Layout a usage documentation:
```js
const docs = usage([synopsis, space, optsList, space, desc])
const style = {
line: [{width: 80}],
cols: [{width: 25}, {width: 55}]
}
```
You may use `shargs-usage` to automatically generate a usage documentation based on a command definition
(e.g. `deepThought` from before).
The module provides all components generally found in usage documentations, like:
1. A `synopsis`, summarizing available options: e.g. `deepThought () [-a|--answer] [-h|--help]`.
2. An options list (`optsList`), describing option details in a tabular format.
Note that `shargs-usage` is declarative:
You only specify what components our usage documentation should have.
The details on how exactly those components transform command-line options into text is hidden away.
See the [automatic usage documentation generation](#automatic-usage-documentation-generation)
and [style](#style) sections.
Use the parser and the usage documentation in your program:
```js
const argv = process.argv.slice(2)
const {errs, args} = parser(deepThought)(argv)
errs.forEach(err => console.log(err.msg))
const help = docs(deepThought)(style)
if (args.help) console.log(help)
```
The command-line option DSL, the parser DSL, and the usage documentation DSL combined
give you a very flexible way to write command-line programs.
Find out more in the [building command-line parsers with shargs](#building-command-line-parsers-with-shargs) section.
Run your command with node ./deepThought --help:
```bash
deepThought () [-a|--answer] [-h|--help]
Ask a question. [required]
-a, --answer= The answer. [default: 42]
-h, --help Print this help message and exit.
Ask the Ultimate Question.
```
The [automatic usage documentation generation](#automatic-usage-documentation-generation)
and [building command-line parsers with shargs](#building-command-line-parsers-with-shargs) sections have more.
### Tutorials
+ [Beginners: Implementing a `git`-like interface.][shargs-tutorial-git]
### Examples
+ [An asynchronous version of deepThought.][shargs-example-async-deepthought]
+ [A synchronous version of deepThought.][shargs-example-sync-deepthought]
+ [deepThought with three layers of configuration: A config file, environment variables, and command-line arguments.][shargs-example-sync-deepthought-config-env-argv]
+ [A command-line arguments SQL parser.][shargs-example-sync-sql]
+ [A REPL (Real Eval Print Loop) build with `shargs-repl`.][shargs-example-repl]
## Documentation
This documentation encompasses the following shargs modules:
1. [`shargs-opts`][shargs-opts] is documented in [command-line options](#command-line-options).
2. [`shargs-core`][shargs-core] is documented in [the `parserSync` function](#the-parserSync-function).
3. [`shargs-parser`][shargs-parser] is documented in [command-line parsers](#command-line-parsers).
4. [`shargs-usage`][shargs-usage] is documented in [automatic usage documentation generation](#automatic-usage-documentation-generation).
5. [`shargs-repl`][shargs-repl] is documented in [building REPLs with shargs](#building-repls-with-shargs).
### Command-line Options
Command-line options are the most important concept in shargs.
They are the basis for its two main features:
[Command-line parsers](#command-line-parsers)
and [automatic usage documentation generation](#automatic-usage-documentation-generation).
Shargs defines many different types of command-line options represented by objects with the following interfaces:
Type
Interface
Description
Flag Option
{key, args, types: []}
A present or absent value.
Primitive Option
{key, args, types: [_]}
A unary value given by argument.
Array Option
{key, args, types: [_, _, ...]}
An array of length n given by argument.
Variadic Option
{key, args}
A variable length array given by argument.
Subcommand Option
{key, args, opts}
An option group given by argument.
Primitive Positional Argument
{key, types: [_]}
A unary value given by position.
Array Positional Argument
{key, types: [_, _, ...]}
An array of length n given by position.
Variadic Positional Argument
{key}
A variable length array given by position.
Command Positional Argument
{key, opts}
An option group given by position.
Rest
{values}
An argument value of unknown type.
Since writing objects following these interfaces by hand can be tedious,
[`shargs-opts`][shargs-opts] gives you a simple type-based DSL for defining valid command-line options:
```js
const {command, flag, number, subcommand} = require('shargs/opts')
const opts = [
subcommand(askOpts)('ask', ['ask'], {required: true, desc: 'Ask a question.'}),
number('answer', ['-a', '--answer'], {defaultValues: [42], desc: 'The answer.'}),
flag('help', ['-h', '--help'], {desc: 'Print this help message and exit.'})
]
const deepThought = command('deepThought', opts, {
desc: 'Deep Thought was created to come up with the Answer to ' +
'The Ultimate Question of Life, the Universe, and Everything.'
})
```
In the example, using the type functions [`subcommand`](#subcommand), [`number`](#number), [`flag`](#flag),
and [`command`](#command) guarantees the generation of valid objects.
#### Type Functions
The following type functions are available:
Type Function
Description
array(types)(key, args, fields)
arrayPos(types)(key, fields)
array generates an array option,
while arrayPos generates an array positional argument,
representing arrays whose length is known in advance.
The closely related variadic
and variadicPos represent arrays with unknown lengths.
`array` returns the following object:
```js
const array = types => (key, args, fields) => ({
key, args, types, ...fields
})
```
`arrayPos` returns the following object:
```js
const arrayPos = types => (key, fields) => ({
key, types, ...fields
})
```
bool(key, args, fields)
boolPos(key, fields)
bool generates a primitive option,
while boolPos generates a primitive positional argument,
representing the boolean values 'true' and 'false'.
Note that the values are represented as strings and you may want to cast them.
If you need more values representing 'true' (e.g. 't', 'yes')
or 'false' (e.g. 'F', 'no'),
have a look at broadenBools.
If you want to treat a value as its reverse,
see reverseBools.
If you need flags instead of bools, have a look at the
boolAsFlag and boolsAsFlags
parser stages.
`bool` returns the following object:
```js
const bool = (key, args, fields) => ({
key, args, types: ['bool'], ...fields
})
```
`boolPos` returns the following object:
```js
const boolPos = (key, fields) => ({
key, types: ['bool'], ...fields
})
```
subcommand(opts)(key, args, fields)
command(key, opts, fields)
subcommand generates a subcommand option,
while command generates a command positional argument.
Combined, they enable commands to do multiple things like git init, git commit, and git push.
subcommand's and command's opts fields
are arrays of command-line options used to parse their values.
Subcommands may have their own command-specific parsers
or are parsed by command's parser.
command or subcommand values are either terminated by the end of the input
or by --.
`subcommand` returns the following object:
```js
const subcommand = opts => (key, args, fields) => ({
key, args, opts, ...fields
})
```
`command` returns the following object:
```js
const command = (key, opts, fields) => ({
key, opts, ...fields
})
```
flag(key, args, fields)
flag generates a flag option,
representing command-line options that take no value.
Shargs counts the number of times a flag occurs, so a flag may be amplified by repeating it.
If you don't need counts and prefer numbers or boolean values, have a look at the
flagAsBool, flagAsNumber,
flagsAsBools and flagsAsNumbers
parser stages.
If you need the presence of a flag to imply negativity (e.g. --no-fun),
see complement,
reverse and reverseFlags.
`flag` returns the following object:
```js
const flag = (key, args, fields) => ({
key, args, types: [], ...fields
})
```
number(key, args, fields)
numberPos(key, fields)
number generates a primitive option,
while numberPos generates a primitive positional argument,
representing JavaScript numbers.
Numbers are represented as strings and you may want to cast them.
If you need flags instead of numbers, have a look at the
numberAsFlag and numbersAsFlags
parser stages.
`number` returns the following object:
```js
const number = (key, args, fields) => ({
key, args, types: ['number'], ...fields
})
```
`numberPos` returns the following object:
```js
const numberPos = (key, fields) => ({
key, types: ['number'], ...fields
})
```
string(key, args, fields)
stringPos(key, fields)
string generates a primitive option,
while stringPos generates a primitive positional argument,
representing strings.
`string` returns the following object:
```js
const string = (key, args, fields) => ({
key, args, types: ['string'], ...fields
})
```
`stringPos` returns the following object:
```js
const stringPos = (key, fields) => ({
key, types: ['string'], ...fields
})
```
variadic(key, args, fields)
variadicPos(key, fields)
variadic generates a variadic option,
while variadicPos generates a variadic positional argument.
These types represent arrays whose length is not known in advance.
An opts array can have at most one variadic positional argument
and no other positional arguments (*Pos) may be defined after it.
The closely related array
and arrayPos represent arrays with known lengths, while
command and subcommand are
variadicPos and variadic with opts fields.
A variadic's or variadicPos' values are either terminated by the end of the input
or by --.
`variadic` returns the following object:
```js
const variadic = (key, args, fields) => ({
key, args, ...fields
})
```
`variadicPos` returns the following object:
```js
const variadicPos = (key, fields) => ({
key, ...fields
})
```
You may write out command-line options by hand, or write your own DSLs for creating them, they are just JavaScript objects:
```js
const askOpts = [
{key: 'format', args: ['--format'], types: ['string'], only: ['json', 'xml'], defaultValues: ['json'],
desc: 'Respond either with json or xml.'},
{key: 'html', args: ['--no-html'], types: [], reverse: true, desc: 'Remove HTML tags.'},
{key: 'help', args: ['-h', '--help'], types: [], desc: 'Print this help message and exit.'},
{key: 'question', types: ['string'], required: true, desc: 'State your question.'}
]
```
Apart from [`key`](#key), [`args`](#args), [`types`](#types), [`opts`](#opts), and [`values`](#values)
that we have already seen and that determine an option's type,
command-line option objects may be given any other fields,
that may be used to provide information to parser stages
(e.g. [`defaultValues`](#defaultValues), [`only`](#only)),
or to provide descriptions for usage documentation generation
(e.g. desc, descArg).
If you write your own parser stages, you may also define your own fields.
#### Option Fields
The following fields are used by [`shargs-core`][shargs-core], [`shargs-parser`][shargs-parser] stages
or [`shargs-usage`][shargs-usage] functions:
Field
Type
Description
args
string[]
args defines argument names for command-line options (e.g. ['-h', '--help']).
Argument names have no restrictions and can be any string.
E.g. ['-h', '--help'] could be used for a help flag
or ['ask'] could be used for a command.
Positional arguments must not have an args field,
as they are not given by argument, but by their position.
contradicts defines what keys an option is incompatible with.
This information is used by the contradictOpts parser stage
to report errors if incompatible options are used together.
Note that contradicts is unidirectional and not transitive
(e.g. if a contradicts b and b contradicts c,
a does not contradict c, and thus a and c are compatible).
Only two keys that each contradict the other key
are mutually exclusive.
defaultValues defines default values for command-line options.
They are used by the setDefaultValues parser stage
that sets the values field if no values are supplied.
The defaultValues' type depends on the command-line option type:
Subcommands takes the same array of options as opts.
Flag options' values have to be a number.
All other options take an array of values,
that must have the same length as their types field.
desc
string
desc defines an option description used by various usage functions.
More specifically, desc is used by
desc, optsList,
optsLists, optsDef,
and optsDefs and their *With versions.
descArg
string
descArg defines a description for an argument value
(e.g. {descArg: 'format'} would print --format=<format>
instead of --format=<string>).
It is used by the optsList, optsLists,
optsDef, and optsDefs usage functions
and their *With versions.
only, types, and key
are other fields that change the argument value description.
These fields are applied in the following order (highest priority first):
descArg, only, types,
and key.
If descArg is an empty string, no argument value description is displayed.
descDefault
string
descDefault overrides the default shield (e.g. [default: 42]) displayed in several usage commands.
It is used by the optsList, optsLists,
optsDef, and optsDefs usage functions
and their *With versions.
If descDefault is an empty string, the default shield is hidden.
implies defines what keys an option must be defined with.
This information is used by the implyOpts parser stage
to report errors if mandatory options are missing.
Note that implies is unidirectional
(e.g. if a implies b and a is present, b must be present as well,
but if b is present, a does not have to be present)
and transitive
(e.g. if a implies b and b implies c,
a also implies c,
and thus if a is present, c must also be present).
Only two keys that each imply the other key
are mutually inclusive.
key
string
key defines the name of a command-line option.
It is used by the parser function
as a field name for the parsed values in the resulting args object.
Most command-line options should have a unique key to avoid collisions with other options.
However, if two different options describe the same result field, it may make sense to give them a shared key.
See complement for an example.
A key must not be named _.
It is also used by the
optsList, optsLists,
optsDef, optsDefs,
synopses, and synopsis usage functions
and their *With versions to describe argument values (e.g. --format=<format>).
descArg, only,
and types are other fields that change the argument value description.
These fields are applied in the following order (highest priority first):
descArg, only,
types, and key.
only
any[]
only defines valid values of an option.
It is used by the restrictToOnly parser stage to validate user input.
only may be used to implement enumerations.
It is also used by the optsList, optsLists,
optsDef, and optsDefs usage functions
and their *With versions to describe argument values (e.g. --format=<json|xml>).
descArg, types,
and key are other fields that change the argument value description.
These fields are applied in the following order (highest priority first):
descArg, only, types,
and key.
opts defines the command-line options of commands
and subcommands.
required
boolean
required defines whether a command-line option has to be present or not.
It is used by the requireOpts stage that reports an error
if a required option does not have values.
A positional argument (*Pos) can only be required,
if all previously defined positional arguments are required as well.
The synopsis, synopses,
optsList, optsLists,
optsDef, and optsDefs usage functions
and their *With versions mark required options.
reverse
boolean
reverse defines whether the values of a given option should be reversed by
the reverseBools or reverseFlags
parser stages.
types
string[]
types defines what user input a command-line option takes.
Flag options' types must be [].
Primitive options' and primitive positional arguments'
types must be [\_],
and array options' and array positional arguments'
types must be [\_, \_, ...],
where _ is the name of a type given as a string.
Variadic options, variadic positional arguments,
subcommand options, and command positional arguments
must not have a types field.
types is also used by the
optsList, optsLists,
optsDef, and optsDefs usage functions
and their *With versions to describe argument values
(e.g. --format=<bool> for a bool option).
descArg, only,
and key are other fields that change the argument value description.
These fields are applied in the following order (highest priority first):
descArg, only, types,
and key.
values
any[]
This field should only be set by parser stages and never manually.
values are assigned by the parser.
You may want to use defaultValues.
The length of a values' array depends on the command-line option type:
Flag options, primitive options,
primitive positional arguments, and rest
must each have values of length 1.
Array options' and array positional arguments'
values field must match their types in length.
subcommand option's, command positional argument's,
variadic option's, and variadic positional argument's
values may have any number of entries.
#### Option Decorators
Certain changes to options are so frequent, that [`shargs-opts`][shargs-opts] provides decorators for them.
You may think of decorators as recurring patterns that are provided as functions.
[`shargs-opts`][shargs-opts] provides the following decorators:
Decorator
Description
complement(prefix)(opt)
complement transforms a bool or flag
option into a complementary option prefixed with a given string
(e.g. --no-html if used on --html).
The complementary option has the same key as the original option,
but reverses its value.
If complement is used,
you most probably want to also use the reverseBools
or reverseFlags parser stage.
Example:
```js
const {flag, complement} = require('shargs/opts')
const no = complement('--no-')
const html = flag('html', ['-H', '--html'], {defaultValues: ['false']})
const noHtml = no(html)
```
Is the same as:
```js
const {flag} = require('shargs/opts')
const html = flag('html', ['-H', '--html'], {defaultValues: ['false']})
const noHtml = flag('html', ['--no-H', '--no-html'], {reverse: true})
```
Note the differences in `defaultValues` and `reverse`.
posArgToOpt(args)(opt)
posArgToOpt transforms a positional argument into an option
by adding args.
Example:
```js
const {command, stringPos} = require('shargs/opts')
const opts = [stringPos('question')]
const deepThought = command('deepThought', opts)
const args = ['deepThought', 'D']
posArgToOpt(args)(deepThought)
```
Is the same as:
```js
const {subcommand} = require('shargs/opts')
subcommand(opts)('deepThought', args)
```
#### Verify Commands
Shargs provides a function for verifying that commands have the correct structure:
```js
const {verifyCommand} = require('shargs')
const {errs, opt} = verifyCommand(deepThought)
```
In the example, it would return a list of `errs` if `deepThought` was invalid.
If the command is valid, the `errs` list is empty.
`verifyCommand` is used internally by `parserSync` and `parser`, but may be used independently.
### The `parserSync` Function
The `parserSync` function is [`shargs`][shargs]' core abstraction.
It generates a command-line parser from a collection of parser stages
and is usually used alongside [`shargs-parser`][shargs-parser]:
```js
const {parserSync} = require('shargs')
const {cast, flagsAsBools, requireOpts, restrictToOnly} = require('shargs/parser')
const {reverseFlags, setDefaultValues, splitShortOpts} = require('shargs/parser')
const stages = {
argv: [splitShortOpts],
opts: [setDefaultValues, requireOpts, reverseFlags, cast],
args: [flagsAsBools]
}
const substages = {
ask: [...stages.opts, restrictToOnly]
}
const parser = parserSync(stages, substages)
```
`parserSync` takes two parameters:
1. A [`stages`](#stages) object that takes [parser stages](#command-line-parsers)
and defines what transformations should be applied in which order.
2. An optional [`substages`](#substages) object that defines subcommand-specific `opts` parser stages.
`parserSync` has a twin function called [`parser`](#async-parsers) that does the same, but works asynchronously.
#### `stages`
Shargs has seven different processing steps called stages that are applied in a predefined order
and transform argument values (`process.argv`) via command-line options (`opts`) to arguments (`args`):
Stage
Field
Type
1
toArgv
any => {errs, argv}
Transforms a value into command-line argument values syntax, e.g.
```js
"-p commit -am 'First commit'"
```
could be transformed to
```js
['-p', 'commit', '-am', 'First commit']
```
2
argv
Array<{errs, argv} => {errs, argv}>
Several stages that modify command-line argument values, e.g.
```js
['-p', 'commit', '-am', 'First commit']
```
could be transformed to
```js
['-p', 'commit', '-a', '-m', 'First commit']
```
3
toOpts
command => {errs, argv} => {errs, opts}
Transforms argument values into command-line options, e.g.
```js
['-p', 'commit', '-a', '-m', 'First commit']
```
could be transformed to
```js
[
{key: 'paginate', args: ['-p'], types: [], values: [1]},
{key: 'commit', args: ['commit'], opts: [...], values: [
{key: 'all', args: ['-a'], types: [], values: [1]},
{key: 'message', args: ['-m'], types: ['string'], values: ['First commit']},
...
]},
...
]
```
4
opts
Array<{errs, opts} => {errs, opts}>
Several stages that modify command-line options, e.g.
```js
[
{key: 'paginate', args: ['-p'], types: [], values: [1]},
{key: 'commit', args: ['commit'], opts: [...], values: [
{key: 'all', args: ['-a'], types: [], values: [1]},
{key: 'message', args: ['-m'], types: ['string'], values: ['First commit']},
...
]},
...
]
```
could be transformed to
```js
[
{key: 'paginate', args: ['-p'], types: [], values: [1]},
{key: 'commit', args: ['commit'], opts: [...], values: [
{key: 'all', args: ['-a'], types: ['bool'], values: ['true']},
{key: 'message', args: ['-m'], types: ['string'], values: ['First commit']},
...
]},
...
]
```
5
toArgs
{errs, opts} => {errs, args}
Transforms command-line options into arguments object arrays, e.g.
```js
[
{key: 'paginate', args: ['-p'], types: [], values: [1]},
{key: 'commit', args: ['commit'], opts: [...], values: [
{key: 'all', args: ['-a'], types: ['bool'], values: ['true']},
{key: 'message', args: ['-m'], types: ['string'], values: ['First commit']},
...
]},
...
]
```
could be transformed to
```js
[
{_: [], paginate: {type: 'flag', count: 1}},
{commit: [
{_: [], all: 'true', message: 'First commit'}
]}
]
```
6
args
Array<{errs, args} => {errs, args}>
Several stages that modify arguments object arrays, e.g.
```js
[
{_: [], paginate: {type: 'flag', count: 1}},
{commit: [
{_: [], all: 'true', message: 'First commit'}
]}
]
```
could be transformed to
```js
[
{_: [], paginate: {type: 'flag', count: 1}},
{commit: {
{_: [], all: true, message: 'First commit'}
}}
]
```
7
fromArgs
{errs, args} => any
Transforms argument object arrays into any result value:
```js
[
{_: [], paginate: {type: 'flag', count: 1}},
{commit: [
{_: [], all: true, message: 'First commit'}
]}
]
```
could be transformed to
```js
{
_: [],
paginate: {type: 'flag', count: 1},
commit: {
_: [],
all: true,
message: 'First commit'
}
}
```
The [`argv`](#argv-field), [`opts`](#opts-field), and [`args`](#args-field) stages
are the user-facing API to declare a parser's behavior.
The [`toOps`](#toOpts-field) and [`toArgs`](#toArgs-field) stages
define the core behavior of [`parserSync`](#the-parserSync-function) (and [`parser`](#async-parsers))
and shargs defines sensible defaults that should not have to be changed in most use cases.
However, if you do have a use case that needs adjustments to those stages, you may carefully swap them out.
If you read the types from top to bottom, you get a good impression of how `parserSync` works.
#### `substages`
`substages` define custom `opts` stages for subcommands.
That means, while most subcommands are parsed using the `opts` defined in `stages`,
those whose [`key`](#key) matches a key in the `substages` object are parsed using the `opts` defined under that key.
Keys may be deeply nested to account for [`subcommand`](#subcommand)s of [`subcommand`](#subcommand)s:
E.g. if `ask` had a subcommand with the `question` [`key`](#key), `{ask: {question: [...stages.opts, restrictToOnly]}}` would assign custom `opts` to `question`.
The `_` [`key`](#key) is special in `substages`:
It is a wildcard that is used by any [`subcommand`](#subcommand) that is not given explicitly by [`key`](#key).
E.g. `{ask: {_: [...stages.opts, restrictToOnly]}}` and `{_: {_: [...stages.opts, restrictToOnly]}}` both work for `question`.
#### Async Parsers
The [`parserSync`](#the-parsersync-function) function has an asynchronous alternative called `parser`.
It is used exactly like `parserSync`, but also works with stages returning
[JavaScript Promises](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise)
and returns a Promise itself:
```js
// stages, substages, deepThought, argv are taken from the Getting Started section
const {parser} = require('shargs')
const asyncParser = parser(stages, substages)
const parse = asyncParser(deepThought)
const {errs, args} = await parse(argv)
```
In addition to `parserSync`'s parameters,
`parser`'s [`stages`](#stages) and [`substages`](#substages) parameters also take parser stages that return Promises:
Stage
Field
Type
1
toArgv
any => {errs, argv}
any => Promise<{errs, argv}>
Transforms a value into command-line argument values syntax, e.g.
```js
"-p commit -am 'First commit'"
```
could be transformed to
```js
['-p', 'commit', '-am', 'First commit']
```
2
argv
Array<{errs, argv} => {errs, argv}>
Array<{errs, argv} => Promise<{errs, argv}>>
Several stages that modify command-line argument values, e.g.
```js
['-p', 'commit', '-am', 'First commit']
```
could be transformed to
```js
['-p', 'commit', '-a', '-m', 'First commit']
```
3
toOpts
command => {errs, argv} => {errs, opts}
command => {errs, argv} => Promise<{errs, opts}>
Transforms argument values into command-line options, e.g.
```js
['-p', 'commit', '-a', '-m', 'First commit']
```
could be transformed to
```js
[
{key: 'paginate', args: ['-p'], types: [], values: [1]},
{key: 'commit', args: ['commit'], opts: [...], values: [
{key: 'all', args: ['-a'], types: [], values: [1]},
{key: 'message', args: ['-m'], types: ['string'], values: ['First commit']},
...
]},
...
]
```
4
opts
Array<{errs, opts} => {errs, opts}>
Array<{errs, opts} => Promise<{errs, opts}>>
Several stages that modify command-line options, e.g.
```js
[
{key: 'paginate', args: ['-p'], types: [], values: [1]},
{key: 'commit', args: ['commit'], opts: [...], values: [
{key: 'all', args: ['-a'], types: [], values: [1]},
{key: 'message', args: ['-m'], types: ['string'], values: ['First commit']},
...
]},
...
]
```
could be transformed to
```js
[
{key: 'paginate', args: ['-p'], types: [], values: [1]},
{key: 'commit', args: ['commit'], opts: [...], values: [
{key: 'all', args: ['-a'], types: ['bool'], values: ['true']},
{key: 'message', args: ['-m'], types: ['string'], values: ['First commit']},
...
]},
...
]
```
5
toArgs
{errs, opts} => {errs, args}
{errs, opts} => Promise<{errs, args}>
Transforms command-line options into arguments object arrays, e.g.
```js
[
{key: 'paginate', args: ['-p'], types: [], values: [1]},
{key: 'commit', args: ['commit'], opts: [...], values: [
{key: 'all', args: ['-a'], types: ['bool'], values: ['true']},
{key: 'message', args: ['-m'], types: ['string'], values: ['First commit']},
...
]},
...
]
```
could be transformed to
```js
[
{_: [], paginate: {type: 'flag', count: 1}},
{commit: [
{_: [], all: 'true', message: 'First commit'}
]}
]
```
6
args
Array<{errs, args} => {errs, args}>
Array<{errs, args} => Promise<{errs, args}>>
Several stages that modify arguments object arrays, e.g.
```js
[
{_: [], paginate: {type: 'flag', count: 1}},
{commit: [
{_: [], all: 'true', message: 'First commit'}
]}
]
```
could be transformed to
```js
[
{_: [], paginate: {type: 'flag', count: 1}},
{commit: {
{_: [], all: true, message: 'First commit'}
}}
]
```
7
fromArgs
{errs, args} => any
{errs, args} => Promise<any>
Transforms argument object arrays into any result value:
```js
[
{_: [], paginate: {type: 'flag', count: 1}},
{commit: [
{_: [], all: true, message: 'First commit'}
]}
]
```
could be transformed to
```js
{
_: [],
paginate: {type: 'flag', count: 1},
commit: {
_: [],
all: true,
message: 'First commit'
}
}
```
If you read the stages' field types from top to bottom, you get a good impression of what an asynchronous parser does.
Internally, an asynchronous shargs parser really differs only in one major way from a synchronous parser:
Instead of using function composition, it uses [Promise.prototype.then][then] to chain parser stages.
#### Advanced Parsers
+ [Multiple subcommands](#multiple-subcommands)
### Command-line Parsers
You do not have to write all parser stages yourself.
The [`shargs-parser`][shargs-parser] library offers a large collection of common parser stages, you can use.
The parser stages presented here are split into *checks* and *stages*.
While *checks* only report errors, *stages* also transform their `argv`, `opts`, or `args`.
Usually, it makes sense to declare *checks* before *stages*.
#### `argv` Checks
Description
verifyArgv(rules)
Reports a FalseArgvRules error
if the passed rules predicate returns false for an argument value.
If `rules` is not a function, reports a [`WrongArgvRulesType`](#WrongArgvRulesType) error.
Example:
```js
const {verifyArgv} = require('shargs/parser')
const rules = argv => (
argv.some(_ => _ === '--question') &&
argv.some(_ => _ === '--answer')
)
const argv = ['--answer', '42']
verifyArgv(rules)({argv})
```
Result:
```js
{
errs: [
{
code: 'FalseArgvRules',
msg: 'Your argv rules returned false...',
info: {...}
}
]
}
```
#### `argv` Stages
Description
Allows arguments of the form --answer=42 to be interpreted like --answer 42.
It only removes the first `=`,
so `['--question=1+2=3?']` is transformed into `['--question', '1+2=3?']`.
Example:
```js
const {equalsSignAsSpace} = require('shargs/parser')
const argv = ['--answer=42']
equalsSignAsSpace({argv})
```
Result:
```js
{
argv: ['--answer', '42']
}
```
Allows to omit whitespaces between short arguments and their values.
Passing -a42 would be the same as passing -a 42.
Cannot be used together with splitShortOpts.
Example:
```js
const {shortOptsNoSpace} = require('shargs/parser')
const argv = ['-a42']
shortOptsNoSpace({argv})
```
Result:
```js
{
argv: ['-a', '42']
}
```
Allows using short option groups.
The group -xvzf would be interpreted as -x -v -z -f.
Cannot be used together with shortOptsNoSpace.
Example:
```js
const {splitShortOpts} = require('shargs/parser')
const argv = ['-ha', '42']
splitShortOpts({argv})
```
Result:
```js
{
argv: ['-h', '-a', '42']
}
```
traverseArgv(p)(f)
Transforms arguments by applying a function f to each argument satisfying a predicate p.
While `p`'s signature is `arg => true|false`,
`f`'s signature must be `(arg, index, argv) => ({errs = [], argv = []})`.
Many other `argv` checks and stages are defined in terms of `traverseArgv`
and it is of great help for writing custom `argv` stages.
Example:
```js
const {traverseArgv} = require('shargs/parser')
const argv = [
'--answer=42',
'--help'
]
const hasEqualsSign = arg => arg.indexOf('=') > -1
const replaceFirstEqualsSign = arg => ({
argv: [
arg.slice(0, arg.indexOf('=')),
arg.slice(arg.indexOf('=') + 1)
]
})
traverseArgv(hasEqualsSign)(replaceFirstEqualsSign)({argv})
```
Result:
```js
{
argv: [
'--answer', '42',
'--help'
]
}
```
#### `opts` Checks
Description
Reports a ContradictionDetected error if options with a contradicts list violate their constraints.
This is the case, if both, the option and an option from its [`contradicts`](#contradicts) list, have [`values`](#values).
If [`contradicts`](#contradicts) is not a list, it reports a [`WrongContradictsType`](#WrongContradictsType) error.
Example:
```js
const {contradictOpts} = require('shargs/parser')
const {number, string} = require('shargs/opts')
const opts = [
number('age', ['-a'], {
values: ['27']
}),
string('birthday', ['-b'], {
contradicts: ['age'],
values: ['27.7.1927']
})
]
contradictOpts({opts})
```
Result:
```js
{
errs: [
{
code: 'ContradictionDetected',
msg: 'Some given keys contradict each other.',
info: {...}
}
]
}
```
Reports a SubcommandRequired
unless at least one subcommand has values.
Example:
```js
const {demandASubcommand} = require('shargs/parser')
const {flag, number, subcommand} = require('shargs/opts')
const opts = [
subcommand([])('ask', ['ask'], {desc: 'Ask a question.'}),
number('answer', ['-a', '--answer'], {
values: ['42'],
desc: 'The answer.'
}),
flag('help', ['-h', '--help'], {
desc: 'Print this help message and exit.'
})
]
demandASubcommand({opts})
```
Result:
```js
{
errs: [
{
code: 'SubcommandRequired',
msg: 'No subcommand found. Please use at least one subcommand!',
info: {...}
}
]
}
```
Reports an ImplicationViolated error
if options with an implies list violate their constraints.
This is the case, if the option has [`values`](#values), but an option from its [`implies`](#implies) list has not.
If [`implies`](#implies) is not a list, it reports a [`WrongImpliesType`](#WrongImpliesType) error.
Example:
```js
const {implyOpts} = require('shargs/parser')
const {number, string} = require('shargs/opts')
const opts = [
number('answer', ['-a']),
string('question', ['-q'], {
implies: ['answer'],
values: ['How much is the fish?']
})
]
implyOpts({opts})
```
Result:
```js
{
errs: [
{
code: 'ImplicationViolated',
msg: 'Some given keys that imply...',
info: {...}
}
]
}
```
Reports a RequiredOptionMissing error
if an option whose required field is true is missing.
If [`values`](#values) is not an array,
it reports a [`WrongFormatForRequiredOption`](#WrongFormatForRequiredOption) error.
Example:
```js
const {requireOpts} = require('shargs/parser')
const {string} = require('shargs/opts')
const opts = [
string('question', ['--question'], {required: true})
]
requireOpts({opts})
```
Result:
```js
{
errs: [
{
code: 'RequiredOptionIsMissing',
msg: 'A required option has not been provided.',
info: {...}
}
]
}
```
Corrects spelling mistakes by suggesting existing command-line arguments for all unknown provided arguments.
E.g. if --asnwer was provided, the --answer argument would be suggested.
It checks all [rest](#rest) [`values`](#values),
assuming they are in the [rest](#rest) category because of spelling mistakes.
It collects all command-line options' [`args`](#args)
and computes a distance metric (currently Levenshtein distance) between each arg and each [`rest`](#rest).
It reports the results in a [`DidYouMean`](#DidYouMean) error,
suggesting probable [`args`](#args) replacements for spelling mistakes.
Example:
```js
const {suggestOpts} = require('shargs/parser')
const {number} = require('shargs/opts')
const opts = [
number('answer', ['-a', '--ans']),
{values: ['--asn']}
]
suggestOpts({opts})
```
Result:
```js
{
errs: [
{
code: 'DidYouMean',
msg: 'An unknown command-line argument...',
info: {
argv: '--asn',
options: [
[],
[],
[{'--ans': number('answer', ['-a', '--ans'])}],
[{'-a': number('answer', ['-a', '--ans'])}]
]
}
}
]
}
```
The `options` array looks a little bit strange, so an explanation is in order.
The array's index is the cost necessary to transform the unknown option in the arguments, represented as keys.
Because of this, you can conveniently work with the results, e.g. by only using the most probable ones:
```js
'Did you mean: ' + (
options
.slice(0, 3)
.reduce((a, b) => a.concat(b))
.flatMap(Object.keys)
.join(', ')
)
```
Results in:
```bash
Did you mean: --age
```
Reports an InvalidRequiredPositionalArgument error
if defined positional arguments (*Pos) violate their rules for the
required field
or the position of variadicPos.
If a positional argument is [`required`](#required),
all previously defined positional arguments must be [`required`](#required), as well,
and no other positional arguments can be defined after a [`variadicPos`](#variadicPos).
In case of a violation of the second rule, `validatePosArgs` reports an
[`InvalidVariadicPositionalArgument`](#InvalidVariadicPositionalArgument) error.
Example:
```js
const {validatePosArgs} = require('shargs/parser')
const {stringPos, variadicPos} = require('shargs/opts')
const opts = [
stringPos('name1', {required: true, values: ['Arthur']}),
stringPos('name2', {required: false, values: ['Ford']}),
stringPos('name3', {required: true, values: ['Trillian']}),
variadicPos('names', {values: ['Zaphod', 'Marvin']}),
stringPos('name4', {values: ['Douglas']})
]
validatePosArgs({opts})
```
Result:
```js
{
errs: [
{
code: 'InvalidRequiredPositionalArgument',
msg: 'If a positional argument is required, all prev...',
info: {...}
},
{
code: 'InvalidVariadicPositionalArgument',
msg: 'Only the last positional argument may be variadic.',
info: {...}
}
]
}
```
verifyOpts(rules)
Reports a FalseOptsRules error
if the opts array does not adhere to the rules predicate.
rules must have the following function signature: opt => true|false.
If `rules` is not a function, `verifyOpts` reports a [`WrongOptsRulesType`](#WrongOptsRulesType) error.
Example:
```js
const {verifyOpts} = require('shargs/parser')
const {string} = require('shargs/opts')
const implies = (p, q) => !p || q
const rules = opts => implies(
opts.some(_ => _.key === 'question' && _.values),
opts.some(_ => _.key === 'answer' && _.values)
)
const opts = [
string('question', ['--question'], {
values: ['How much is the fish?']
}),
number('answer', ['-a'])
]
verifyOpts(rules)({opts})
```
Result:
```js
{
errs: [
{
code: 'FalseOptsRules',
msg: 'Your opts rules returned false...',
info: {...}
}
]
}
```
Reports an error if an option's
values do not fit its types.
See the [`values`](#values) documentations for the exact rules.
If the lengths of [`values`](#values) and [`types`](#types) do not match,
an [`InvalidArity`](#InvalidArity) error is reported.
If the [`types`](#types) field has an invalid value, an [`InvalidTypes`](#InvalidTypes) error is reported
and `verifyValuesArity` reports an [`InvalidValues`](#InvalidValues) error in case of invalid [`values`](#values).
Example:
```js
const {verifyValuesArity} = require('shargs/parser')
const {number} = require('shargs/opts')
const opts = [
number('answer', ['--answer'], {values: ['42', '23']})
]
verifyValuesArity({opts})
```
Result:
```js
{
errs: [
{
code: 'InvalidArity',
msg: "An option's types arity does not match...",
info: {...}
}
]
}
```
#### `opts` Stages
Description
Collects all repeated keys in an array,
instead of keeping only the first mention of a key.
Example:
```js
const {arrayOnRepeat} = require('shargs/parser')
const {number, string} = require('shargs/opts')
const opts = [
string('answer', ['-a'], {values: ['42']}),
number('answer', ['-a'], {values: [42]})
]
arrayOnRepeat({opts})
```
Result:
```js
{
opts: [
array(['string', 'number'])('answer', ['-a'], {
values: ['42', 42]
})
]
}
```
Takes a best guess approach to transform rest values that did not match a command-line option
into new command-line options.
E.g. {values: ['--version']} becomes {key: 'version', types: [], values: [1]} and
[{values: ['--not']}, {values: ['panic']}]
becomes {key: 'not', types: ['string'], args: ['--not'], values: ['panic']}.
Single [`rest`](#rest) options are interpreted as [`flag`](#flag)s
while two consecutive [`rest`](#rest) options are interpreted as [`string`](#string)s
if the first [`rest`](#rest) is in short option format
(one minus with a single character, e.g. `-n`, `-a`)
or in long option format (two minuses with any more characters, e.g. `--name`, `--answer`).
[`bestGuessArgs`](#bestGuessArgs) is very similar to `bestGuessOpts`,
but also considers non-consecutive rest [`values`](#values).
Example:
```js
const {bestGuessOpts} = require('shargs/parser')
const {flag, string} = require('shargs/opts')
const opts = [
string('age', ['--age'], {values: ['unknown']}),
{values: ['--paranoid']},
{values: ['--name']},
{values: ['Marvin']},
{values: ['foo']}
]
bestGuessOpts({opts})
```
Result:
```js
{
opts: [
string('age', ['--age'], {values: ['unknown']}),
flag('paranoid', [], {values: [1]}),
string('name', [], {values: ['Marvin']}),
{values: ['foo']}
]
}
```
broadenBools(alt)
Transforms bools with
values like 'yes' or 'no' into
bools with 'true' or 'false'
values based on an alt mapping
(e.g. {true: ['yes'], false: ['no']}).
Example:
```js
const {broadenBools} = require('shargs/parser')
const {bool, number} = require('shargs/opts')
const opts = [
number('answer', ['-a', '--answer'], {values: ['42']}),
bool('verbose', ['--verbose'], {values: ['no']})
]
const alt = {
true: ['yes'],
false: ['no', 'f']
}
broadenBools(alt)({opts})
```
Result:
```js
{
opts: [
number('answer', ['-a', '--answer'], {values: ['42']}),
bool('verbose', ['--verbose'], {values: ['false']})
]
}
```
Casts string values
into other JavaScript types (e.g. numbers, booleans)
according to the command-line options' types
(e.g. {key: 'answer', types: ['number'], values: ['42']} is transformed to
{key: 'answer', types: ['number'], values: [42]}).
If [`types`](#types) contains `'number'`, but [`values`](#values)
cannot be cast into a number, an [`ArgumentIsNotANumber`](#ArgumentIsNotANumber) error is reported.
If [`types`](#types) contains `'bool'`, but [`values`](#values)
is not `['true']` or `['false']`, an [`ArgumentIsNotABool`](#ArgumentIsNotABool) error is reported.
Example:
```js
const {cast} = require('shargs/parser')
const {bool, number} = require('shargs/opts')
const opts = [
number('answer', ['-a', '--answer'], {values: ['42']}),
bool('verbose', ['--verbose'], {defaultValues: ['false']})
]
cast({opts})
```
Result:
```js
{
opts: [
number('answer', ['-a', '--answer'], {values: [42]}),
bool('verbose', ['--verbose'], {defaultValues: [false]})
]
}
```
Validates all command-line options with both, only
and values fields,
by making sure that all values in values
are also contained in only.
If values are not found in [`only`](#only),
a [`ValueRestrictionsViolated`](#ValueRestrictionsViolated) error is reported for each value.
Example:
```js
const {restrictToOnly} = require('shargs/parser')
const {number} = require('shargs/opts')
const opts = [
number('answer', ['--answer'], {only: ['42'], values: ['23']})
]
restrictToOnly({opts})
```
Result:
```js
{
errs: [
{
code: 'ValueRestrictionViolated',
msg: 'A value lies outside the allowed values...',
info: {...}
}
],
opts
}
```
Transforms
values of
primitive options and
array options
whose types contain 'bool' and whose
reverse field is true
by replacing 'true'/true with 'false'/false and vice versa.
Example:
```js
const {reverseBools} = require('shargs/parser')
const {bool} = require('shargs/opts')
const opts = [
bool('verbose', ['-v'], {reverse: true, values: [true]}),
bool('verbose', ['-v'], {reverse: true, values: ['true']})
]
reverseBools({opts})
```
Result:
```js
{
opts: [
bool('verbose', ['-v'], {reverse: true, values: [false]}),
bool('verbose', ['-v'], {reverse: true, values: ['false']})
]
}
```
Transforms
values of
flag options whose reverse field is true
by inverting the flag's value (e.g. 1 becomes -1).
Example:
```js
const {reverseFlags} = require('shargs/parser')
const {flag} = require('shargs/opts')
const opts = [
flag('help', ['-h'], {reverse: true, values: [1]})
]
reverseFlags({opts})
```
Result:
```js
{
opts: [
flag('help', ['-h'], {reverse: true, values: [-1]})
]
}
```
Transforms all options that have no
values, but defaultValues,
by setting the values field
to the defaultValues' value.
Example:
```js
const opts = [
flag(['-f'], {defaultValues: [1]}),
bool(['-b'], {defaultValues: ['true']})
]
setDefaultValues({opts})
```
Result:
```js
{
opts: [
flag(['-f'], {values: [1]}),
bool(['-b'], {values: ['true']})
]
}
```
traverseOpts(p)(f)
Transforms opts by applying a function f
to each option satisfying a predicate p.
While `p`'s signature is `opt => true|false`,
`f`'s signature must be `(opt, index, opts) => ({errs = [], opts = []})`.
Many other `opts` checks and stages are defined in terms of `traverseOpts`
and it is of great help for writing custom `opts` stages.
Example:
```js
const {traverseOpts} = require('shargs/parser')
const {flag, number} = require('shargs/opts')
const opts = [
number('answer', ['-a'], {values: ['42']}),
flag('verbose', ['-v'], {values: [1]}),
flag('help', ['-h'], {values: [1]})
]
const isFlag = _ => Array.isArray(_.types) && _.types.length === 0
const reverseFlags = opt => ({
opts: [
{...opt, values: [-opt.values[0]]}
]
})
traverseOpts(isFlag)(reverseFlags)({opts})
```
Result:
```js
{
opts: [
number('answer', ['-a'], {values: ['42']}),
flag('verbose', ['-v'], {values: [-1]}),
flag('help', ['-h'], {values: [-1]})
]
}
```
#### `args` Checks
Description
Reports an UnexpectedArgument error
for each value in the rest field _.
Example:
```js
const {failRest} = require('shargs/parser')
const args = {
_: ['--help']
}
failRest({args})
```
Result:
```js
{
errs: [
{
code: 'UnexpectedArgument',
msg: 'An unexpected argument was used...',
info: {...}
}
]
}
```
verifyArgs(rules)
Reports a FalseArgsRules error for each args object
that does not adhere to the rules predicate (with the signature arg => true|false).
Reports a [`WrongArgsRulesType`](#WrongArgsRulesType) error if `rules` is not a function.
Example:
```js
const {verifyArgs} = require('shargs/parser')
const rules = args => (
typeof args.question !== 'undefined' &&
typeof args.answer !== 'undefined'
)
const args = {
question: 'How much is the fish?'
}
verifyArgs(rules)({args})
```
Result:
```js
{
errs: [
{
code: 'FalseArgsRules',
msg: 'Your args rules returned false...',
info: {...}
}
]
}
```
#### `args` Stages
Description
Introduces new arguments by best guess based on rest field values
(e.g. {_: ['--version']} becomes {version: {type: 'flag', count: 1}}
and {_: ['--not', 'panic']} becomes {not: 'panic'}).
Transforms single rest field values into a flag and two consecutive rest options into a string.
It only assumes rest field values to be strings if the first rest is in short option format
(one minus with a single character, e.g. `-h`, `-v`)
or in long option format (two minuses with any more characters, e.g. `--help`, `--verbose`).
`bestGuessArgs` is very similar to [`bestGuessOpts`](#bestGuessOpts),
but also considers rest fields that originally did not directly follow each other.
E.g. assuming `--help` to be a known argument, `--not --help panic` would produce `{not: 'panic'}`,
although its components were not in tandem.
Example:
```js
const {bestGuessArgs} = require('shargs/parser')
const obj = {
args: {
_: ['--answer', '42', 'foo', '-h'],
command: {
_: ['bar', '-v', '--question', 'What is answer?', '-v']
}
}
}
bestGuessArgs(obj)
```
Result:
```js
{
args: {
_: ['foo'],
answer: '42',
h: {type: 'flag', count: 1},
command: {
_: ['bar'],
v: {type: 'flag', count: 2},
question: 'What is answer?'
}
}
}
```
Casts string args into other JavaScript types
using a best guess approach based on their values (e.g. {answer: '42'} becomes {answer: 42}
and {all: 'true'} becomes {all: true}).
It supports numbers and booleans (e.g. `{help: 'true'}` becomes `{help: true}`).
Example:
```js
const {bestGuessCast} = require('shargs/parser')
const args = {
_: ['--name', 'Marvin'],
str1: 'yay',
num1: '42.3',
num2: '123e-1',
num3: '0x11',
num4: '0b11',
bool1: 'true',
arr1: ['-42', 'true', 'yay'],
obj: {
num5: '0o11',
num6: '-Infinity',
num7: '',
num8: null,
bool2: 'false',
bool3: undefined
}
}
bestGuessCast({args})
```
Result:
```js
{
args: {
_: ['--name', 'Marvin'],
str1: 'yay',
num1: 42.3,
num2: 12.3,
num3: 17,
num4: 3,
bool1: true,
arr1: [-42, true, 'yay'],
obj: {
num5: 9,
num6: -Infinity,
num7: '',
num8: null,
bool2: false,
bool3: undefined
}
}
}
```
boolAsFlag(key)
Transforms bool arguments with key in args to a flag object.
E.g., assuming the all key,
{all: true} is transformed to {all: {type: 'flag', count: 1}} and
{all: false} to {all: {type: 'flag', count: -1}}.
Example:
```js
const args = {
_: [],
version: true
}
boolAsFlag('version')({args})
```
Result:
```js
{
_: [],
version: {type: 'flag', count: 1}
}
```
Transforms all bool arguments in args to flag objects
using boolAsFlag.
Example:
```js
const args = {
_: [],
html: false,
version: true
}
boolsAsFlags({args})
```
Result:
```js
{
_: [],
html: {type: 'flag', count: -1},
version: {type: 'flag', count: 1}
}
```
Sets rest values to an empty array (i.e. {_: []}).
Example:
```js
const {clearRest} = require('shargs/parser')
const args = {_: ['--verbose']}
clearRest({args})
```
Result:
```js
{
args: {_: []}
}
```
flagAsBool(key)
Transforms flags with key in args to a bool value.
E.g., assuming the all key,
{all: {type: 'flag', count: 1}} is transformed to {all: true} and
{all: {type: 'flag', count: -1}} to {all: false}.
If its `count` is greater than `0` it is considered `true`, otherwise it is considered `false`.
Example:
```js
const {flagAsBool} = require('shargs/parser')
const args = {
verbose: {type: 'flag', count: 1}
}
flagAsBool('verbose')({args})
```
Result:
```js
{
args: {
verbose: true
}
}
```
flagAsNumber(key)
Transforms flags with key in args to a number using its count.
E.g., assuming the verbose key,
{verbose: {type: 'flag', count: 3}} becomes {verbose: 3}.
Example:
```js
const {flagAsNumber} = require('shargs/parser')
const args = {
verbose: {type: 'flag', count: 2}
}
flagAsNumber('version')({args})
```
Result:
```js
{
args: {
verbose: 2
}
}
```
Transforms all flag arguments in args to bool values
using flagAsBool.
Example:
```js
const {flagsAsBools} = require('shargs/parser')
const args = {
verbose: {type: 'flag', count: 1}
}
flagsAsBools({args})
```
Result:
```js
{
args: {
verbose: true
}
}
```
Transforms all flag arguments in args to numbers using their count
like flagAsNumber.
Example:
```js
const {flagsAsNumbers} = require('shargs/parser')
const args = {
verbose: {type: 'flag', count: 2}
}
flagsAsNumbers({args})
```
Result:
```js
{
args: {
verbose: 2
}
}
```
mergeArgs(merge)
Transforms args by flattening them
by recursively merging nested objects into their parent object
(e.g. {ask: {question: '42?'}, answer: 42} becomes {question: '42?', answer: 42}).
A custom `merge` function may be passed with the following function signature:
`(obj1 = {}, obj2 = {}) => {}`.
The default `merge` function (if `merge` is `undefined`)
prefers keys from the parent object over keys from nested objects,
but concatenates rest values (`_`) from both objects
(e.g. `{_: ['foo'], answer: 42, ask: {_: ['bar'], answer: 23}}` becomes
`{_: ['foo', 'bar'], answer: 42}`).
Example:
```js
const {mergeArgs} = require('shargs/parser')
const args = {
_: ['--help'],
version: {type: 'flag', count: 2},
name: 'Arthur',
command: {
_: ['-v'],
version: {type: 'flag', count: 1},
name: 'Trillian',
help: true
},
verbose: true
}
const mergeLeft = (outer, inner) => ({
...inner,
...outer,
_: [
...(outer._ || []),
...(inner._ || [])
]
})
mergeArgs(mergeLeft)({args})
```
Result:
```js
{
args: {
_: ['--help', '-v'],
version: {type: 'flag', count: 2},
name: 'Arthur',
help: true,
verbose: true
}
}
```
numberAsFlag(key)
Transforms numbers with key in args to flag objects.
The number becomes the flag's count.
E.g. {answer: 42} becomes {answer: {type: 'flag', count: 42}}.
Example:
```js
const args = {
_: [],
answer: 42
}
numberAsFlag('answer')({args})
```
Result:
```js
{
_: [],
answer: {type: 'flag', count: 42}
}
```
Transforms all numbers in args to flag objects using numberAsFlag.
Example:
```js
const args = {
_: [],
answer: 42
}
numbersAsFlags({args})
```
Result:
```js
{
_: [],
answer: {type: 'flag', count: 42}
}
```
traverseArgs(fs)
Transforms args by applying functions fs to each key/value pair based on the value's type.
`fs` supports the following types:
`array`, `boolean`, `flag`, `function`, `null`, `number`, `object`, `string`, `undefined`, and `otherwise`.
The default behavior for most types is to not change the value, with three notable exceptions:
`function`s and `otherwise`s key/value pairs are removed from args,
while `object`'s default function applies `fs` to nested objects.
`{flag: ({key, val, errs, args}) => ({errs, args})}`
is the signature for `fs` with fields for each type.
Many other `args` checks and stages are defined in terms of `traverseArgs`
and it is of great help for writing custom `args` stages.
Example:
```js
const {traverseArgs} = require('shargs/parser')
const args = {
verbose: {type: 'flag', count: 2},
answer: 23
}
const fs = {
flag: ({key, val, errs, args}) => ({
errs,
args: {...args, [key]: val.count}
}),
number: ({key, val, errs, args}) => ({
errs,
args: {...args, [key]: val + 19}
})
}
traverseArgs(fs)({args})
```
Result:
```js
{
args: {
verbose: 2,
answer: 42
}
}
```
Allowed fs fields:
```js
const fs = {
array: ({key, val, errs, args}) => ({errs, args}),
boolean: ({key, val, errs, args}) => ({errs, args}),
flag: ({key, val, errs, args}) => ({errs, args}),
function: ({key, val, errs, args}) => ({errs, args}),
null: ({key, val, errs, args}) => ({errs, args}),
number: ({key, val, errs, args}) => ({errs, args}),
otherwise: ({key, val, errs, args}) => ({errs, args}),
object: ({key, val, errs, args}) => ({errs, args}),
string: ({key, val, errs, args}) => ({errs, args}),
undefined: ({key, val, errs, args}) => ({errs, args})
}
```
#### Advanced Parser Stages
+ [Custom checks and stages](#custom-checks-and-stages)
### Automatic Usage Documentation Generation
Shargs strictly separates the concerns of parsing command-line arguments and generating usage documentation.
The [`shargs-usage`][shargs-usage] module specializes on
generating terminal-based usage documentation for `--help` flags
from [command-line options](#command-line-options):
```js
const {desc, optsLists, space, synopses, usage} = require('shargs/usage')
const docs = usage([
synopses,
space,
optsLists,
space,
desc
])
```
[`shargs-usage`][shargs-usage] lets you define how your usage documentation should look like in a declarative way.
In the example, we tell our `docs` to start with [`synopses`](#synopses), have [`optsLists`](#optsLists) in the body,
and close with a [`desc`](#usage-desc)ription.
We separate these three parts with [`space`](#space)s and enclose everything in a [`usage`](#usage) function.
Note that we did not mention any command-line options, yet:
```js
const {command, flag, number, stringPos} = require('shargs/opts')
const opts = [
stringPos('question', {desc: 'Ask a question.', required: true}),
number('answer', ['-a', '--answer'], {desc: 'The answer.', defaultValues: [42]}),
flag('help', ['-h', '--help'], {desc: 'Print this help message and exit.'})
]
const deepThought = command('deepThought', opts, {
desc: 'Deep Thought was created to come up with the Answer to ' +
'The Ultimate Question of Life, the Universe, and Everything.'
})
const optsDocs = docs(deepThought)
```
`optsDocs` now knows what to layout (`deepThought`), and how to layout it (`docs`).
Finally, we `style` the different parts (lines and columns) of the documentation:
```js
const style = {
line: [{width: 60}],
cols: [{width: 25}, {width: 35}]
}
const text = optsDocs(style)
```
Now, if we `console.log(text)`, the following `text` is printed to the console:
```bash
deepThought () [-a|--answer] [-h|--help]
Ask a question. [required]
-a, --answer= The answer. [default: 42]
-h, --help Print this help message and exit.
Deep Thought was created to come up with the Answer to The
Ultimate Question of Life, the Universe, and Everything.
```
`deepThought`, `docs`, and [`style`](#style)
are the moving parts of [automatic usage documentation generation](#automatic-usage-documentation-generation)
and are defined independently.
We have already talked about [command-line options](#command-line-options) before
and will talk about [`style`](#style) in an upcoming section.
#### Usage Functions
[`shargs-usage`][shargs-usage] provides the following usage functions to declare layouts:
Usage Function
Description
desc takes a command-line option's desc field
and formats it according to a style.
If the description is too long to fit one line, it is split and spread over several lines.
`desc` is defined as `descWith({id: 'line'})`.
Example:
```bash
Deep Thought should answer the Ultimate
Question
```
Code:
```js
const {desc, usage} = require('shargs/usage')
const opt = {
opts: [],
desc: 'Deep Thought should answer the Ultimate Question'
}
const style = {
line: [{width: 40}]
}
usage([
desc
])(opt)(style)
```
note(string)
noteWith({id})(string)
note takes a string and formats it according to a style,
ignoring its second parameter.
If the string is too long to fit one line, it is split and spread over several lines.
`note` is defined as `noteWith({id: 'line'})`.
Example:
```bash
Deep Thought was created to come up with
the Answer
```
Code:
```js
const {note, usage} = require('shargs/usage')
const style = {
line: [{width: 40}]
}
usage([
note('Deep Thought was created to come up with the Answer')
])()(style)
```
notes(strings)
notesWith({id})(strings)
notes takes a list of strings and formats it
according to a style,
ignoring its second parameter.
If a string is too long to fit one line, it is split and spread over several lines.
`notes` is defined as `notesWith({id: 'line'})`.
Example:
```bash
Deep Thought was created to come up with
the Answer
to The Ultimate Question.
```
Code:
```js
const {notes, usage} = require('shargs/usage')
const style = {
line: [{width: 40}]
}
usage([
notes([
'Deep Thought was created to come up with the Answer',
'to The Ultimate Question.'
])
])()(style)
```
optsDef
optsDefWith({id, pad})
optsDef layouts its opts as a definition list
and formats it according to its style.
The term part comprises of an opt's [`args`](#args), [`descArg`](#descArg),
[`only`](#only), [`types`](#types), and [`key`](#key) fields, followed by the
[`contradicts`](#contradicts), [`defaultValues`](#defaultValues),
[`implies`](#implies), and [`required`](#required) fields.
The [`desc`](#desc) field is given in the definition part.
`optsDef` is defined as `optsDefWith({id: 'line', pad: 4})`.
Example:
```bash
-a, --answer= [default: 42]
The answer.
-h, --help
Prints help.
--version
The version.
```
Code:
```js
const {optsDef, usage} = require('shargs/usage')
const {flag, number} = require('shargs/opts')
const opt = {
opts: [
number('answer', ['-a', '--answer'], {
desc: 'The answer.', defaultValues: ['42']
}),
flag('help', ['-h', '--help'], {desc: 'Prints help.'}),
flag('version', ['--version'], {desc: 'The version.'})
]
}
const style = {
line: [{width: 40}]
}
usage([
optsDef
])(opt)(style)
```
optsDefs
optsDefsWith({id, pad})
optsDefs first layouts its opts and then the opts
of all its subcommands recursively,
using optsDefs,
indenting each optsDef layer by pad spaces.
`optsDefs` is defined as `optsDefsWith({id: 'line', pad: 4})`.
Example:
```bash
-a, --answer= [default: 42]
The answer.
-h, --help
Show the usage docs.
ask [required]
Ask questions.
-h
Usage docs.
... [required]
Questions.
```
Code:
```js
const {optsDefs, usage} = require('shargs/usage')
const {flag, subcommand} = require('shargs/opts')
const {number, variadicPos} = require('shargs/opts')
const required = true
const askOpts = [
flag('help', ['-h'], {desc: 'Show the usage docs.'}),
variadicPos('questions', {required, desc: 'Questions.'})
]
const ask = subcommand(askOpts)
const opt = {
opts: [
ask('ask', ['ask'], {desc: 'Ask questions.', required}),
number('answer', ['-a', '--answer'], {
desc: 'The answer.', defaultValues: ['42']
}),
flag('help', ['-h', '--help'], {desc: 'Usage docs.'})
]
}
const style = {
line: [{width: 40}]
}
usage([
optsDefs
])(opt)(style)
```
optsList
optsListWith({id})
optsList layouts its opts as a table with two columns
and formats it according to its style.
The first column comprises of an opt's [`args`](#args), [`descArg`](#descArg),
[`only`](#only), [`types`](#types), and [`key`](#key) fields.
The [`desc`](#desc) field is given in the second column, followed by the
[`contradicts`](#contradicts), [`defaultValues`](#defaultValues),
[`implies`](#implies), and [`required`](#required) fields.
`optsList` is defined as `optsListWith({id: 'cols'})`.
Example:
```bash
-a, --answer= The answer. [default: 42]
-h, --help Prints help.
--version The version.
```
Code:
```js
const {optsList, usage} = require('shargs/usage')
const {flag, number} = require('shargs/opts')
const opt = {
opts: [
number('answer', ['-a', '--answer'], {
desc: 'The answer.', defaultValues: ['42']
}),
flag('help', ['-h', '--help'], {desc: 'Prints help.'}),
flag('version', ['--version'], {desc: 'The version.'})
]
}
const style = {
cols: [{width: 25}, {width: 25}]
}
usage([
optsList
])(opt)(style)
```
optsLists
optsListsWith({id, pad})
optsLists first layouts its opts and then the opts
of all its subcommands recursively,
using optsLists,
indenting the first column of each optsList layer by four spaces.
`optsLists` is defined as `optsListsWith({id: 'cols', pad: 4})`.
Example:
```bash
-a, --answer= The answer. [default: 42]
-h, --help Usage docs.
ask Ask questions. [required]
-h Show the usage docs.
... Questions. [required]
```
Code:
```js
const {optsLists, usage} = require('shargs/usage')
const {flag, subcommand} = require('shargs/opts')
const {number, variadicPos} = require('shargs/opts')
const required = true
const askOpts = [
flag('help', ['-h'], {desc: 'Show the usage docs.'}),
variadicPos('questions', {required, desc: 'Questions.'})
]
const ask = subcommand(askOpts)
const opt = {
opts: [
ask('ask', ['ask'], {desc: 'Ask questions.', required}),
number('answer', ['-a', '--answer'], {
desc: 'The answer.', defaultValues: ['42']
}),
flag('help', ['-h', '--help'], {desc: 'Usage docs.'})
]
}
const style = {
cols: [{width: 25}, {width: 25}]
}
usage([
optsLists
])(opt)(style)
```
space ignores its first argument and returns a line consisting entirely of spaces,
with a width according to style.
`space` is defined as `spaceWith({id: 'line', lines: 1})`.
Example:
```bash
Deep Thought was created to come up with
the Answer to The Ultimate Question.
```
Code:
```js
const {note, space, usage} = require('shargs/usage')
const style = {
line: [{width: 40}]
}
usage([
note('Deep Thought was created to come up with'),
space,
note('the Answer to The Ultimate Question.')
])()(style)
```
synopses
synopsesWith({id})
synopses first layouts its opts and then the opts
of all its subcommands,
using a synopsis each.
`synopses` is defined as `synopsesWith({id: 'line'})`.
Example:
```bash
deepThought (-a|--answer) [-h|--help]
deepThought (ask) [-h] (...)
```
Code:
```js
const {synopses, usage} = require('shargs/usage')
const {command, flag, number} = require('shargs/opts')
const {subcommand, variadicPos} = require('shargs/opts')
const required = true
const askOpts = [
flag('help', ['-h']),
variadicPos('questions', {required})
]
const ask = subcommand(askOpts)
const opts = [
ask('ask', ['ask'], {required}),
number('answer', ['-a', '--answer'], {required}),
flag('help', ['-h', '--help'])
]
const deepThought = command('deepThought', opts)
const style = {
line: [{width: 40}]
}
usage([
synopses
])(deepThought)(style)
```
synopsis
synopsisWith({id})
synopsis layouts the program's name in the first and its opts
in the second column of a table
and formats it according to its style.
For each opt, the [`args`](#args), [`descArg`](#descArg), [`only`](#only), [`required`](#required), [`types`](#types),
and [`key`](#key) fields are used for a brief overview.
`synopsis` is defined as `synopsisWith({id: 'line'})`.
Example:
```bash
deepThought (-a|--answer) [-h|--help]
[--version] ...
```
Code:
```js
const {synopsis, usage} = require('shargs/usage')
const {command, flag} = require('shargs/opts')
const {number, variadicPos} = require('shargs/opts')
const opts = [
number('answer', ['-a', '--answer'], {
desc: 'The answer.', required: true
}),
flag('help', ['-h', '--help'], {desc: 'Prints help.'}),
flag('version', ['--version'], {desc: 'The version.'}),
variadicPos('questions')
]
const deepThought = command('deepThought', opts)
const style = {
line: [{width: 40}]
}
usage([
synopsis
])(deepThought)(style)
```
#### Usage Combinators
While [usage functions](#usage-functions) taken for themselves are useful,
they really begin to shine if they are combined by usage combinators.
Usage combinators are higher-order usage functions that take other usage functions as parameters,
combine them in various ways, and return a new usage function.
Let's see how usage combinators may be used to implement [`synopses`](#synopses):
```js
const {decorate, noSubcommands, onlySubcommands} = require('shargs/usage')
const {optsMap, synopsis, usage, usageMap} = require('shargs/usage')
const prefixKey = prefix => optsMap(opts => ({...opts, key: prefix + ' ' + opts.key}))
function synopses (opt) {
return usage([
noSubcommands(synopsis),
decorate(prefixKey(opt.key), onlySubcommands)(
usageMap(synopses)
)
])(opt)
}
```
This example uses [usage decorators](#usage-decorators), that are only introduced in the next section.
The implementation of `synopses` uses two usage combinators:
[`usage`](#usage) and [`usageMap`](#usageMap).
[`usage`](#usage) is used to combine two usage functions:
A [`synopsis`](#synopsis) of all `opts`, but subcommands, and the usage function returned by [`usageMap`](#usageMap).
[`usageMap`](#usageMap) iterates over all [`subcommand`](#subcommand)s
and recursively calls `synopses` on each [`subcommand`](#subcommand)'s [`opts`](#opts).
The recursion stops, if `opt`'s `opts` has no more [`subcommand`](#subcommand)s,
since usage functions with empty `opts` return an empty string.
Combinators are a powerful feature, as they let you build more complex things from smaller parts.
[`shargs-usage`][shargs-usage] provides the following usage combinators:
Usage Combinator
Description
usage(functions)(opt)(style)
usage takes a list of usage functions
that each take an opt, a style and return a string.
It then applies its own opt and style to each function,
and concatenates the resulting strings.
Example:
```bash
deepThought [-a|--answer] [-h|--help] [--version]
-a, --answer= The answer.
-h, --help Prints help.
--version Prints version.
Deep Thought was created to come up with the
Answer.
```
Code:
```js
const {note, optsList, space} = require('shargs/usage')
const {synopsis, usage} = require('shargs/usage')
const {command, flag, number} = require('shargs/opts')
const opts = [
number('answer', ['-a', '--answer'], {desc: 'The answer.'}),
flag('help', ['-h', '--help'], {desc: 'Prints help.'}),
flag('version', ['--version'], {desc: 'Prints version.'})
]
const deepThought = command('deepThought', opts, {
desc: 'Deep Thought was created to come up with the Answer.'
})
const style = {
line: [{width: 50}],
cols: [{width: 25}, {width: 25}]
}
usage([synopsis, space, optsList, space, desc])(deepThought)(style)
```
usageMap(f)({opts})(style)
usageMap takes a function f that takes an option
and returns a layout function.
It maps f over the option's opts
and applies its style to each resulting layout function.
Finally, it concatenates the resulting strings and returns the result.
Example:
```bash
-a, --answer
The answer.
-h, --help
Prints help.
--version
Prints version.
```
Code:
```js
const {text, textWith, usageMap} = require('shargs/usage')
const {flag, number} = require('shargs/opts')
const opt = {
opts: [
number('answer', ['-a', '--answer'], {desc: 'The answer.'}),
flag('help', ['-h', '--help'], {desc: 'Prints help.'}),
flag('version', ['--version'], {desc: 'Prints version.'})
]
}
const style = {
line: [{width: 40}]
}
usageMap(({args, desc}) => layout([
text(args.join(', ')),
textWith({id: 'desc'})(desc)
]))(opt)(style)
```
#### Usage Decorators
When defining layouts, we may want to feature some `opts` in one place,
and the remaining in a different place of our documentation.
Maybe the [`subcommand`](#subcommand)s should be presented in a definition list,
while the other options are layed out as a table.
Usage decorators enable these use cases by modifying inputs of [usage functions](#usage-functions):
```js
const {desc, optsDef, optsList, space, synopsis, usage} = require('shargs/usage')
const {decorate, noSubcommands, onlyFirstArg, onlySubcommands} = require('shargs/usage')
const decoratedDocs = usage([
noSubcommands(onlyFirstArg(synopsis)),
space,
onlySubcommands(optsDef),
space,
noSubcommands(optsList),
space,
desc
])
```
The example uses three different decorators:
[`noSubcommands`](#noSubcommands), [`onlySubcommands`](#onlySubcommands), and [`onlyFirstArg`](#onlyFirstArg).
Each of these decorators modifies the `opts` array in some way,
before passing it on to their wrapped [usage function](#usage-functions).
The first two focus on filtering `opts`:
[`noSubcommands`](#noSubcommands) removes all [`subcommand`](#subcommand)s,
while [`onlySubcommands`](#onlySubcommands) keeps only [`subcommand`](#subcommand)s.
[`onlyFirstArg`](#onlyFirstArg) goes one step further and modifies each option in `opts`,
removing all but the first argument in their [`args`](#args) fields.
[`shargs-usage`](#shargs-usage) has the following usage decorators:
Usage Decorator
Description
justArgs(args)(usageFunction)
justArgs modifies its opt
by removing all opts that have no args field
or whose args do not contain any argument
given in the args list.
Example:
```js
const {justArgs, usage} = require('shargs/usage')
const {flag, number, subcommand} = require('shargs/opts')
const style = {
cols: [{width: 25}, {width: 25}]
}
const opt = {
opts: [
number('answer', ['-a', '--answer'], {
desc: 'The answer'
}),
subcommand([])('ask', ['ask'], {desc: 'Asks a question'}),
flag('version', ['--version'], {desc: 'Prints version'})
]
}
usage([
justArgs(['-a'])(optsList)
])(opt)(style)
```
Result:
```bash
-a, --answer= The answer
```
noSubcommands(usageFunction)
noSubcommands modifies its opt
by removing all subcommands from its opts.
Example:
```js
const {noSubcommands, usage} = require('shargs/usage')
const {flag, number, subcommand} = require('shargs/opts')
const style = {
cols: [{width: 25}, {width: 25}]
}
const opt = {
opts: [
number('answer', ['-a', '--answer'], {
desc: 'The answer'
}),
subcommand([])('ask', ['ask'], {desc: 'Asks a question'}),
flag('version', ['--version'], {desc: 'Prints version'})
]
}
usage([
noSubcommands(optsList)
])(opt)(style)
```
Result:
```bash
-a, --answer= The answer
--version Prints version
```
onlySubcommands(usageFunction)
onlySubcommands modifies its opt
by keeping only subcommands in its opts.
Example:
```js
const {onlySubcommands, usage} = require('shargs/usage')
const {flag, number, subcommand} = require('shargs/opts')
const style = {
cols: [{width: 25}, {width: 25}]
}
const opt = {
opts: [
number('answer', ['-a', '--answer'], {
desc: 'The answer'
}),
subcommand([])('ask', ['ask'], {desc: 'Asks a question'}),
flag('version', ['--version'], {desc: 'Prints version'})
]
}
usage([
onlySubcommands(optsList)
])(opt)(style)
```
Result:
```bash
ask Asks a question
```
onlyFirstArg(usageFunction)
onlyFirstArg modifies its opt
by first keeping only opts that have args
and by then removing all args but the first.
Example:
```js
const {onlyFirstArg, usage} = require('shargs/usage')
const {flag, number, subcommand} = require('shargs/opts')
const style = {
cols: [{width: 25}, {width: 25}]
}
const opt = {
opts: [
number('answer', ['-a', '--answer'], {
desc: 'The answer'
}),
subcommand([])('ask', ['ask'], {desc: 'Asks a question'}),
flag('version', ['--version'], {desc: 'Prints version'})
]
}
usage([
onlyFirstArg(optsList)
])(opt)(style)
```
Result:
```bash
-a The answer
ask Asks a question
--version Prints version
```
optsFilter(p)(usageFunction)
optsFilter modifies its opt by applying a filter with the predicate p,
whose function signature must be opt => true|false to its opts.
Many other usage decorators are defined in terms of optsFilter
and it is of great help for writing custom ones.
Example:
```js
const {optsFilter, usage} = require('shargs/usage')
const {flag, number, subcommand} = require('shargs/opts')
const style = {
cols: [{width: 25}, {width: 25}]
}
const opt = {
opts: [
number('answer', ['-a', '--answer'], {
desc: 'The answer'
}),
subcommand([])('ask', ['ask'], {desc: 'Asks a question'}),
flag('version', ['--version'], {desc: 'Prints version'})
]
}
usage([
optsFilter(({types}) => types !== null)(optsList)
])(opt)(style)
```
Result:
```bash
-a, --answer= The answer
ask Asks a question
--version Prints version
```
optsMap(f)(usageFunction)
optsMap modifies its opt by applying a function f
to each option in opts,
whose function signature must be opt => opt.
Many other usage decorators are defined in terms of optsMap
and it is of great help for writing custom ones.
Example:
```js
const {optsMap, usage} = require('shargs/usage')
const {flag, number, subcommand} = require('shargs/opts')
const style = {
cols: [{width: 25}, {width: 25}]
}
const opt = {
opts: [
number('answer', ['-a', '--answer'], {
desc: 'The answer'
}),
subcommand([])('ask', ['ask'], {desc: 'Asks a question'}),
flag('version', ['--version'], {desc: 'Prints version'})
]
}
usage([
optsMap(opt => ({...opt, args: opt.args.slice(0, 1)}))(optsList)
])(opt)(style)
```
Result:
```bash
-a The answer
ask Asks a question
--version Prints version
```
#### Usage Decorator Combinators
If many usage decorators are applied to a usage function, things get unwieldy, fast:
```js
const {justArgs, noSubcommands, onlyFirstArg, synopsis} = require('shargs/usage')
const briefSynopsis = noSubcommands(onlyFirstArg(justArgs(['--help'])(synopsis)))
```
In the example, `briefSynopsis` is decorated three times and the code is not very readable.
Usage decorator combinators facilitate a cleaner code layout:
```js
const {decorate, justArgs, noSubcommands, onlyFirstArg, synopsis} = require('shargs/usage')
const decorated = decorate(noSubcommands, onlyFirstArg, justArgs(['--help']))
const briefSynopsis = decorated(synopsis)
```
This version of `briefSynopsis` is much more readable.
Note, that [`decorate`](#decorate-usage) applies its usage decorators from right to left.
As is apparent from the example, usage decorator combinators are usage decorators, themselves.
[`shargs-usage`][shargs-usage] has the following usage decorator combinators:
Usage Decorator Combinator
Description
decorate(decorators)(usageFunction)
decorate takes many usage function decorators
and applies them to its usageFunction from right to left.
#### Style
[Layout functions](#layout-functions) are transformed to strings by applying `style`s:
```js
const style = {
line: [{width: 80}],
cols: [{width: 25}, {width: 55}]
}
```
In the example, `style` provides the details for how many columns a usage documentation text should be wide,
and whether it should have padding.
A `style` is an object whose values are arrays of *style objects*, that must have a [`width`](#width) key,
and may have [`padEnd`](#padEnd) and [`padStart`](#padStart) keys:
Parameter
Type
Description
padEnd
number
padEnd defines a padding to the right.
It is filled with spaces.
padStart
number
padStart defines a padding to the left.
It is filled with spaces.
width
number
width defines the length of text.
The full length of the string is the width
plus padEnd and padStart.
#### Advanced Usage Documentation
+ [Layout functions](#layout-functions)
+ [Layout combinators](#layout-combinators)
+ [Layout decorators](#layout-decorators)
+ [Layout decorator combinators](#layout-decorator-combinators)
+ [Custom layout functions](#custom-layout-functions)
+ [Custom usage functions](#custom-usage-functions)
### Building Command-line Parsers with Shargs
This section reuses code snippets from earlier sections:
Snippets
askOpts from the type functions section.
```js
const askOpts = [
{key: 'format', args: ['--format'], types: ['string'], only: ['json', 'xml'],
defaultValues: ['json'], desc: 'Respond either with json or xml.'},
{key: 'html', args: ['--no-html'], types: [], reverse: true, desc: 'Remove HTML tags.'},
{key: 'help', args: ['-h', '--help'], types: [], desc: 'Print this help message and exit.'},
{key: 'question', types: ['string'], required: true, desc: 'State your question.'}
]
```
deepThought from the command-line options section.
```js
const {command, flag, number, subcommand} = require('shargs/opts')
const opts = [
subcommand(askOpts)('ask', ['ask'], {required: true, desc: 'Ask a question.'}),
number('answer', ['-a', '--answer'], {defaultValues: [42], desc: 'The answer.'}),
flag('help', ['-h', '--help'], {desc: 'Print this help message and exit.'})
]
const deepThought = command('deepThought', opts, {
desc: 'Deep Thought was created to come up with the Answer to ' +
'The Ultimate Question of Life, the Universe, and Everything.'
})
```
parser from the parserSync function section.
```js
const {parserSync} = require('shargs')
const {cast, flagsAsBools, requireOpts, restrictToOnly} = require('shargs/parser')
const {reverseFlags, setDefaultValues, splitShortOpts} = require('shargs/parser')
const stages = {
argv: [splitShortOpts],
opts: [setDefaultValues, requireOpts, reverseFlags, cast],
args: [flagsAsBools]
}
const substages = {
ask: [...stages.opts, restrictToOnly]
}
const parser = parserSync(stages, substages)
```
docs from the
automatic usage documentation generation section.
```js
const {desc, optsLists, space, synopses, usage} = require('shargs/usage')
const docs = usage([
synopses,
space,
optsLists,
space,
desc
])
```
style from the style section.
```js
const style = {
line: [{width: 80}],
cols: [{width: 25}, {width: 55}]
}
```
Imagine these snippets were located in their own modules and were imported earlier.
Then, a sample command-line program written with shargs could be:
```js
const argv = process.argv.slice(2)
const {errs, args} = parser(deepThought)(argv)
if (args.help) {
const help = docs(deepThought)(style)
console.log(help)
process.exit(0)
}
if (errs.length > 0) {
errs.forEach(({code, msg}) => console.log(`${code}: ${msg}`))
process.exit(1)
}
console.log(`The answer is: ${args.answer}`)
process.exit(0)
```
First, we skip the first two values of `process.argv`.
They are `node` and the file name and can be ignored.
We then parse the remaining `argv` with our `deepThought` parser and get two results:
A list of `errs`, and an `args` object with parsed argument values.
Based on those two results, we build our program.
If the `args.help` field is set, we print a `help` text generated from `docs` by applying `deepThought` and `style`.
Then, we `exit` with exit code `0`.
If we run the program with `node ./deepThought --help`, the following text is printed:
```bash
deepThought [-a|--answer] [-h|--help]
deepThought (ask) [--format] [--no-html] [-h|--help] ()
-a, --answer= The answer. [default: 42]
-h, --help Print this help message and exit.
ask Ask a question. [required]
--format= Respond either with json or xml. [default: json]
--no-html Remove HTML tags.
-h, --help Print this help message and exit.
State your question. [required]
Deep Thought was created to come up with the Answer to The Ultimate Question of
Life, the Universe, and Everything.
```
If the `errs` array has errors, we print all errors and `exit` with exit code `1`.
E.g. if we execute `node ./deepThought --answer 5`, without specifying the required `ask` subcommand,
the following text appears:
```bash
Required option is missing: An option that is marked as required has not been provided.
```
Otherwise, we print the `args.answer`.
E.g. if we run it with `node ./deepThought ask "What is the meaning of Life, the Universe, and Everything?"`,
it prints:
```bash
The answer is: 42
```
## More In-depth Documentation
Feel free to skip this section if you are new to Shargs.
It introduces more advanced topics:
+ [Installing as Bundle or Modules](#installing-as-bundle-or-modules)
+ [Multiple Subcommands](#multiple-subcommands)
+ [Custom Checks and Stages](#custom-checks-and-stages)
+ [Layout Functions](#layout-functions)
+ [Layout Combinators](#layout-combinators)
+ [Layout Decorators](#layout-decorators)
+ [Layout Decorator Combinators](#layout-decorator-combinators)
+ [Custom Layout Functions](#custom-layout-functions)
+ [Custom Usage Functions](#custom-usage-functions)
+ [Building REPLs with Shargs](#building-repls-with-shargs)
+ [Error Codes](#error-codes)
### Installing as Bundle or Modules
Since version 0.26.0, shargs may be installed in two different ways:
Either as a bundle (recommended), or individually as modules.
npm install --save shargs # bundle installation (core, opts, parser, and usage)
npm install --save shargs-core # module (in bundle: shargs/core or shargs)
npm install --save shargs-opts # module (in bundle: shargs/opts)
npm install --save shargs-parser # module (in bundle: shargs/parser)
npm install --save shargs-usage # module (in bundle: shargs/usage)
npm install --save shargs-repl # module (not in bundle)
The [`shargs`][shargs] bundle combines several modules in one distribution with its own version number.
The advantage for the user is that the module versions are guaranteed to be compatible and updates are simpler.
Installing individual modules is more flexible,
e.g. if you want to use a specific set of module versions,
if one module of the bundle is not needed
or if one of the modules is replaced with a different implementation.
It is recommended to start with the bundle installation
and import modules like `require('shargs/opts')` or `import 'shargs/core'`.
If you want to switch to a module installation later, you may simply replace your imports with module imports:
E.g. `require('shargs-opts')` and `import 'shargs-core'`.
If you are using modules and need to know which versions are compatible,
you may refer to the module versions used by the [`shargs`][shargs] bundle.
### Multiple Subcommands
Shargs supports specifying multiple [`subcommand`](#subcommand)s.
E.g. you could use both, the `ask` and `design` [`subcommand`](#subcommand)s in the same command
in the following version of `deepThought`:
```js
const {command, flag, number, stringPos, subcommand} = require('shargs/opts')
const ask = subcommand([stringPos('question')])
const design = subcommand([stringPos('name')])
const opts = [
ask('ask', ['ask'], {desc: 'Ask a question.'}),
design('design', ['design'], {desc: 'Design a more powerful computer.'}),
flag('help', ['-h', '--help'], {desc: 'Print this help message and exit.'})
]
const deepThought = command('deepThought', opts, {desc: 'Ask the Ultimate Question.'})
```
If you provide both subcommands in your `argv`, both are parsed:
```js
const argv = ['design', 'Earth', 'ask', 'What is the answer to the Ultimate Question?']
const parse = parserSync()(deepThought)
const {argv, errs} = parse(argv)
console.log(argv)
/*
{
_: [],
ask: {
_: [],
question: 'What is the answer to the Ultimate Question?'
},
design: {
_: [],
name: 'Earth'
}
}
*/
```
Note that the subcommand order is not preserved.
This is due to the default behavior of [`fromArgs`](#fromArgs-field),
that keeps only the first mention of a subcommand and merges all subcommands into an (unordered) object.
The input to [`fromArgs`](#fromArgs-field) is still ordered and has duplicates,
so if your program needs the [subcommand](#subcommand) order or duplicates,
just write a custom [`fromArgs`](#fromArgs-field) stage:
```js
const merge = (obj1, obj2) => ({
...obj1,
subcommands: [
...(obj1.subcommands || []),
obj2
]
})
const fromArgs = ({errs, args}) => ({
errs,
args: args.slice(1).reduce(merge, args[0])
})
```
This demonstration implementation of [`fromArgs`](#fromArgs-field) is very simple
and lacks some features like e.g. subcommands of subcommands.
Please improve it before using it in your production programs.
### Building REPLs with Shargs
> :construction: **Work in progress:** This feature is currently worked on and its API is not yet stable.
[`Shargs-repl`][shargs-repl] lets you build REPLs with actions defined by shargs [`commands`](#command).
### Custom Checks and Stages
Shargs makes writing and using custom checks and stages very simple.
The only thing you have to do is to follow the correct function signatures for your check or stage,
as given in the [`stages`](#stages) and [`substages`](#substages) sections.
The following code snippets showcase very simple examples with the correct signatures.
Regardless of whether you implement a check or a stage, the most important thing to remember is:
Always pass on errors!
Custom `argv` stage example:
```js
function splitShortOpts ({errs = [], argv = []} = {}) {
const argv2 = argv.flatMap(arg =>
arg.length > 2 && arg[0] === '-' && arg[1] !== '-'
? arg.slice(1).split('').map(c => '-' + c)
: arg
)
return {errs, argv: argv2}
}
```
If you write a custom `argv` stage, have a look at [`traverseArgv`](#traverseArgv)!
Custom `opts` stage example:
```js
function demandACommand ({errs = [], opts = []} = {}) {
const errs2 = []
const aCommand = opts.some(
({key, args, types, opts}) => (
typeof key !== 'undefined' &&
typeof types === 'undefined' &&
Array.isArray(args) && Array.isArray(opts)
)
)
if (!aCommand) {
errs2.push({
code: 'CommandRequired',
msg: 'No command found. Please use at least one command!',
info: {options: opts}
})
}
return {errs: errs.concat(errs2), opts}
}
```
If you write a custom `opts` stage, have a look at [`traverseOpts`](#traverseOpts)!
Custom `args` stage example:
```js
const {traverseArgs} = require('shargs/parser')
function flagsAsBools ({errs = [], args = {}} = {}) {
const fs = {
flag: ({key, val, errs, args}) => ({
errs,
args: {...args, [key]: val.count > 0}
})
}
const {errs: errs2, args: args2} = traverseArgs(fs)({args})
return {errs: errs.concat(errs2), args: args2}
}
```
If you write a custom `args` stage, have a look at [`traverseArgs`](#traverseArgs)!
### Layout Functions
[Usage functions](#usage-functions) that are applied to an `opt` yield so called `layout functions`.
If we take a closer look at the signatures of usage and layout functions,
the connection between the two becomes apparent:
Type
Function Signature
Description
Layout Function
style => string
Layout functions take a style and return a string.
Usage Function
opt => style => string
Usage functions take an opt and return a layout function.
In [`shargs-usage`][shargs-usage], an `opt`'s purpose is to provide the textual contents of layout functions
and the [usage functions](#usage-functions)' only job is to specify how this textual content is extracted from the `opt`.
The layout functions do the actual work of formatting strings.
Let's have a look at an example:
```js
const {br, defs, layout, table, text} = require('shargs/usage')
const askDocs = layout([
table([
['deepThought (ask)', '[--format] [--no-html] [-h|--help] ()']
]),
br,
defs([
['--format= [default: json]', 'Respond either with json or xml.'],
['--no-html', 'Remove HTML tags.'],
['-h, --help', 'Print this help message and exit.'],
[' [required]', 'State your question.']
]),
br,
text(
'Deep Thought was created to come up with the Answer to ' +
'The Ultimate Question of Life, the Universe, and Everything.'
)
])
```
In the example, `askDocs` is a [`layout`](#layout) that comprises four different layout functions:
[`table`](#table), [`br`](#br), [`defs`](#defs), and [`text`](#text).
Depending on how we [`style`](#style) the [`layout`](#layout), we get different strings:
```js
const style = {
line: [{width: 80}],
cols: [{width: 16}, {width: 64}]
}
const string = askDocs(style)
```
If we `console.log(string)`, the following text is printed to the console:
```bash
deepThought (ask) [--format] [--no-html] [-h|--help] ()
--format= [default: json]
Respond either with json or xml.
--no-html
Remove HTML tags.
-h, --help
Print this help message and exit.
[required]
State your question.
Deep Thought was created to come up with the Answer to The Ultimate Question of
Life, the Universe, and Everything.
```
Experiment with [`style`](#style) to get different layouts!
[`shargs-usage`][shargs-usage] gives you the following layout functions:
Layout Function
Description
br returns a line filled with spaces,
with a width according to style.
`br` is defined as `brWith({id: 'line', lines: 1})`.
Example:
```bash
Deep Thought was created to come up with
the Answer
to The Ultimate Question.
```
Code:
```js
const {br, layout, text} = require('shargs/usage')
const style = {
line: [{width: 40}]
}
layout([
text('Deep Thought was created to come up with the Answer'),
br,
text('to The Ultimate Question.')
])(style)
```
cols(columns)
colsWith({id})(columns)
cols takes a list of columns,
where each column is a list of strings corresponding to lines.
It formats the `columns` according to their [`width`](#width)s
and cuts off strings that are too long.
`cols` is defined as `colsWith({id: 'cols'})`.
Example:
```bash
-a, --answer= The answer. [default: 42]
-h, --help Prints help.
--version Prints version.
```
Code:
```js
const {cols, layout} = require('shargs/usage')
const style = {
cols: [{width: 25}, {width: 25}]
}
layout([
cols([
[
'-a, --answer=',
'-h, --help',
'--version'
],
[
'The answer. [default: 42]',
'Prints help.',
'Prints version.'
]
])
])(style)
```
defs(tuples)
defsWith({id, pad})(tuples)
defs takes a list of tuples,
where each entry is a tuple of strings,
with a term at the first and a definition at the second position.
It formats its `tuples` as a definition list over two [`line`](#line)s,
with the term in the first, and the definition in the second [`line`](#line).
If a term or definition extends its [`line`](#line),
it is continued in another [`line`](#line).
`defs` is defined as `defsWith({id: 'line', pad: 4})`.
Example:
```bash
-a, --answer= [default: 42]
The answer.
-h, --help
Prints help.
--version
Prints version.
```
Code:
```js
const {defs, layout} = require('shargs/usage')
const style = {
line: [{width: 40}]
}
layout([
defs([
['-a, --answer= [default: 42]', 'The answer.'],
['-h, --help', 'Prints help.'],
['--version', 'Prints version.']
])
])(style)
```
line(string)
lineWith({id})(string)
line takes a string
and formats it according to a style's width.
If a `string` exceeds its [`width`](#width), it is cut off, otherwise, the [`width`](#width) is filled up with spaces.
It ends with a line break. `line` is defined as `lineWith({id: 'line'})`.
Example:
```bash
Deep Thought was created to come up with
the Answer
```
Code:
```js
const {layout, line} = require('shargs/usage')
const style = {
line: [{width: 40}]
}
layout([
line('Deep Thought was created to come up with'),
line('the Answer')
])(style)
```
lines(strings)
linesWith({id})(strings)
lines takes a list of strings
and layouts each string with line.
`lines` is defined as `linesWith({id: 'line'})`.
Example:
```bash
Deep Thought was created to come up with
the Answer
to The Ultimate Question.
```
Code:
```js
const {layout, lines} = require('shargs/usage')
const style = {
line: [{width: 40}]
}
layout([
lines([
'Deep Thought was created to come up with',
'the Answer',
'to The Ultimate Question.'
])
])(style)
```
table(rows)
tableWith({id})(rows)
table takes a list of rows, lays it out as a borderless table,
and formats it according to a style.
If an entry exceeds the length of a column, it breaks into the next row.
`table` is defined as `tableWith({id: 'cols'})`.
Example:
```bash
-a, --answer= The answer. [default: 42]
-h, --help Prints help.
--version Prints version.
```
Code:
```js
const {layout, table} = require('shargs/usage')
const style = {
cols: [{width: 25}, {width: 25}]
}
layout([
table([
['-a, --answer=', 'The answer. [default: 42]'],
['-h, --help', 'Prints help.'],
['--version', 'Prints version.']
])
])(style)
```
text(string)
textWith({id})(string)
text takes a string and formats it according to a style.
If the `string` exceeds a line, it continues on the next.
`text` is defined as `textWith({id: 'line'})`.
Example:
```bash
Deep Thought was created to come up with
the Answer
```
Code:
```js
const {layout, text} = require('shargs/usage')
const style = {
line: [{width: 40}]
}
layout([
text('Deep Thought was created to come up with the Answer')
])(style)
```
texts(strings)
textsWith({id})(strings)
texts takes a list of strings
and layouts each string with text.
`texts` is defined as `textsWith({id: 'line'})`.
Example:
```bash
Deep Thought was created to come up with
the Answer
to The Ultimate Question.
```
Code:
```js
const {layout, texts} = require('shargs/usage')
const style = {
line: [{width: 40}]
}
layout([
texts([
'Deep Thought was created to come up with the Answer',
'to The Ultimate Question.'
])
])(style)
```
### Layout Combinators
Layout combinators are functions that take [layout functions](#layout-functions) as parameters
and return new [layout functions](#layout-functions).
They are the primary way of building more complex constructs from simpler components.
The following examples demonstrate the use of layout combinators:
```js
const {layout, layoutMap, textWith} = require('shargs/usage')
const defsWith = ({id}) => layoutMap(
([term, definition] = []) => layout([
textWith({id})(term),
textWith({id})(definition)
])
)
```
[`defsWith`](#defsWith) is implemented in terms of [`layout`](#layout), [`layoutMap`](#layoutMap),
and [`textWith`](#textWith).
It [`maps`](#layoutMap) over a list of `term` and `definition` pairs and `layout`s them as [`text`](#text)s.
[`shargs-usage`][shargs-usage] has the following layout combinators:
Layout Combinator
Description
layout(functions)(style)
layout takes a list of layout functions
that each take a style and return a string.
It then applies its own style to each function,
and concatenates the resulting strings.
Example:
```js
const {layout, line} = require('shargs/usage')
const style = {
line: [{width: 40}]
}
layout([
line('Deep Thought was created to come up with'),
line('the Answer')
])(style)
```
Result:
```bash
Deep Thought was created to come up with
the Answer
```
layoutMap(f)(list)(style)
layoutMap takes a function f that takes any value
and returns a layout function.
It maps f over the list
and applies its style to each resulting layout function.
Finally, it concatenates the resulting strings and returns the result.
Example:
```js
const {layout, layoutMap, textWith} = require('shargs/usage')
const defsWith = ({id}) => layoutMap(
([term, definition] = []) => layout([
textWith({id})(term),
textWith({id})(definition)
])
)
const defs = defsWith({id: 'line'})
const style = {
line: [{width: 40}]
}
defs([
['-a, --answer= [default: 42]', 'The answer.'],
['-h, --help', 'Prints help.'],
['--version', 'Prints version.']
])(style)
```
Result:
```bash
-a, --answer= [default: 42]
The answer.
-h, --help
Prints help.
--version
Prints version.
```
### Layout Decorators
When working with [layout functions](#layout-functions) that take a [`style`](#style) as input,
you sometimes want to modify this [`style`](#style) just before it is passed to the function,
and only for this function call.
This is what layout decorators are for:
```js
const {layout, layoutMap, pad, text} = require('shargs/usage')
const defs = layoutMap(
([term, definition] = []) => layout([
text(term),
pad(['line', 0], 4)(text(definition))
])
)
```
The example shows a sample implementation of [`defs`](#defs) using the [`pad`](#pad) layout decorator.
Here, the `term`, as well as the `definition` have the same id, [`text`](#text)s default id `'line'`.
However, we want to add a padding of `4` spaces to the `definition`.
So we use [`pad`](#pad) to add `4` spaces to the id at the `['line', 0]` path of [`style`](#style).
[`shargs-usage`][shargs-usage] ships with the following layout decorators:
Layout Decorator
Description
pad(path, spaces)(layoutFunction)
pad looks up the style object at the path in its style
and modifies it, by adding a number of spaces to its padStart
and subtracting the same number from its width.
It then passes the modified style to its layoutFunction.
Example:
```js
const {layout, pad, table} = require('shargs/usage')
const style = {
cols: [{width: 20}, {width: 20}]
}
layout([
pad(['cols', 0], 4)(table([['--answer', '42']]))
])(style)
```
Result:
```js
--answer 42
```
stylePath(path, f)(layoutFunction)
stylePath looks up the style object at the path in its style
and modifies it by applying the function f to it.
It then passes the modified style to its layoutFunction.
```js
const {layout, stylePath, table} = require('shargs/usage')
const pad4 = obj => ({
...obj,
padStart: (obj.padStart || 0) + 4,
width: obj.width - 4
})
const style = {
cols: [{width: 20}, {width: 20}]
}
layout([
stylePath(['cols', 0], pad4)(table([['--answer', '42']]))
])(style)
```
Result:
```js
--answer 42
```
### Layout Decorator Combinators
If many decorators are applied to a [layout function](#layout-functions), the resulting code can get deeply nested:
```js
const {layout, pad, table} = require('shargs/usage')
const style = {
cols: [{width: 25}, {width: 30}]
}
layout([
pad(['cols', 0], 4)(
pad(['cols', 1], 4)(
table([
['-a, --answer=', 'The answer. [default: 42]']
])
)
)
])(style)
```
Layout decorator combinators avoid nesting deeply, by first collecting layout decorators and applying them all at once:
```js
const {decorate, layout, pad, table} = require('shargs/usage')
const style = {
cols: [{width: 25}, {width: 30}]
}
const decorated = decorate(pad(['cols', 0], 4), pad(['cols', 1], 4))
layout([
decorated(
table([
['-a, --answer=', 'The answer. [default: 42]']
])
)
])(style)
```
Note, that [`decorate`](#decorate-layout) applies layout decorators from right to left.
[`shargs-usage`][shargs-usage] contains the following layout decorator combinators:
Layout Decorator Combinator
Description
decorate(decorators)(layoutFunction)
decorate takes many layout function decorators
and applies them to its layoutFunction from right to left.
### Custom Layout Functions
Using your own [layout function](#layout-function) is straightforward:
Your function only has to have the correct signature and it is ready to be used as a [layout function](#layout-function):
It must take a [`style` object](#style) and return a `string`.
The following example showcases the custom `table2` layout function that takes `columns` instead of `rows` as input:
```js
const {table} = require('shargs/usage')
const table2 = (columns = []) => style => {
const rows = []
for (let i = 0; i < columns[0].length; i++) {
const row = []
for (let j = 0; j < columns.length; j++) {
row.push(columns[j][i])
}
rows.push(row)
}
return table(rows)(style)
}
```
You may use `table2` as a [layout function](#layout-function) if you apply it to a `columns` array,
since that returns a function that takes a `style` argument and returns a `string`.
This is of course a very simplified example that makes many assumptions that are often not valid
and should not be made in real projects.
Your own function would most probably need much more validations and handling of edge cases.
### Custom Usage Functions
Writing and using custom [usage functions](#usage-functions) in shargs is very simple:
You only have to write a function with the correct signature and it can be used as a [usage function](#usage-function).
It must take an [`opt`](#command-line-options) object and a [`style` object](#style) and return a `string`.
The following example shows the custom `descs` function that displays the options' descriptions:
```js
const {text} = require('shargs/usage')
const desc = ({desc = ''} = {}) => text(desc)
```
Using [`usageMap`](#usageMap) simplifies the process of defining your own functions:
```js
const {table, usageMap} = require('shargs/usage')
const optsTable = usageMap(
({key, args, required, desc}) => table([
[(required ? '*' : '') + key, args.join(', '), desc]
])
)
```
### Error Codes
[`shargs-core`][shargs-core] and [`shargs-parser`][shargs-parser] report errors if a
[command-line option](#command-line-options)'s syntax is invalid, or if `checks` fail.
The following table contains all error codes currently in use and where they are thrown:
Code
Message
Thrown by
ArgumentIsNotABool
The passed command line argument must either be 'true' or 'false'.
ArgumentIsNotANumber
The passed command line argument must be a number.
CommandExpected
Expected a command with a string "key" field and an "opts" array.
ContradictionDetected
Some given keys contradict each other.
DidYouMean
An unknown command-line argument was passed. Did you mean any of the following options?
FalseArgsRules
Your args rules returned false. Please abide to the rules defined in verifyArgs.
FalseArgvRules
Your argv rules returned false. Please abide to the rules defined in verifyArgv.
FalseOptsRules
Your opts rules returned false. Please abide to the rules defined in verifyOpts.
ImplicationViolated
Some given keys that imply each other are not all defined.
IncompatibleTypes
Repeated options must either both be variadic or both not.
InvalidArgs
The "args" field has an invalid value: "args" must be a non-empty array of strings.
InvalidArity
An option's types arity does not match its values arity.
InvalidBoolMapping
The mapping provided to broadenBools must only map from 'true' or 'false' to a list of alternatives.
The "key" field has an invalid value: "key" must be a string, cannot be "_" or "--", and must not include whitespaces.
InvalidNestedCommand
Commands cannot be nested inside commands. Did you forget an "args" field for your subcommand?
InvalidOptionsListInCombine
Options list in combine was undefined, null or empty.
InvalidOpts
The "opts" field has an invalid value: "opts" must be an array of command-line options and positional arguments.
InvalidRequiredPositionalArgument
If a positional argument is required, all previous positional arguments must be required as well.
The required field must either be undefined, true or false.
InvalidTypes
Each argument must have a types key that must be null or an array.
verifyCommand
verifyValuesArity
InvalidValues
An option's values field has an invalid type.
InvalidVariadicPositionalArgument
Only the last positional argument may be variadic.
OptionExpected
A command-line option was expected, but something else was received.
PosArgExpected
A positional argument was expected, but something else was received.
RequiredOptionMissing
An option that is marked as required has not been provided.
SubcommandExpected
A subcommand was expected, but something else was received.
SubcommandRequired
No subcommand found. Please use at least one subcommand!
UnexpectedArgument
An unexpected argument was used that has no option defined.
UnknownCommandLineOptionType
The command-line option or positional argument given is of an unknown type.
ValueRestrictionsViolated
A value lies outside the allowed values of an option.
WrongArgsRulesType
The args rules are of a wrong type, please provide a predicate with the following signature: (args) => boolean.
WrongArgvRulesType
The argv rules are of a wrong type, please provide a predicate with the following signature: (argv) => boolean.
WrongContradictsType
The contradicts field has the wrong type, please provide an array of command-line option keys.
A required option has values or defaultValues in the wrong format.
Default values are different depending on the command-line option type:
Commands take objects, flags take counts, and other options take arrays of the correct length.
WrongImpliesType
The implies field has the wrong type, please provide an array of command-line option keys.
The opts rules are of a wrong type, please provide a predicate with the following signature: (options) => boolean.
## FAQ
Question
Answer
How can I use config objects with shargs?
A config object in this question denotes an object that is used to read in default values from a file or a URI.
Shargs does not include reading and merging config objects because there are other specialized libraries for this task
that are easy to use alongside shargs.
There are several simple ways to combine shargs' args objects with config objects:
If you just want to have default values, you may want to check out the [`defaultValues`](#defaultValues) options field.
If this does not suffice or you have a different problem, read on.
Say we have read in a `config` object from somewhere:
```js
const config = {
question: 'How can I use config objects with shargs?',
answer: 'Read the FAQ section!'
}
```
And we have run a shargs parser and have obtained the following `args` object:
```js
const args = {
_: [],
question: 'What is the meaning of life, the universe, and everything?'
}
```
Then *using* the config object would just mean merging the two objects:
```js
const preferArgs = {
...config,
...args
}
const preferConfig = {
...args,
...config
}
```
Of course these example merges are simple cases, because the objects are *flat*.
In case of [`subcommand`](#subcommand)s, the `args` object would have (deeply) nested objects.
Such cases are common and there are specialized libraries for merging deeply nested objects,
like [ramda][ramda] or [lodash][lodash]:
```js
const {mergeDeepLeft, mergeDeepRight} = require('ramda')
const preferArgs = mergeDeepLeft(args, config)
const preferConfig = mergeDeepRight(args, config)
```
Why do command-line options have a key field?
The key field is an apparent difference between shargs and other command-line parsers.
So one might ask, why shargs uses it, while other parsers do not need it.
But as is mostly the case, shargs has good reasons:
Command-line parsers read arguments and assign them to variables that are passed as inputs to programs.
So we are dealing with two different sets of names, here: Names of arguments and names of variables.
Those two sets are connected by a unidirectional mapping, where arguments map to variable names.
If a single argument would only ever map to a single variable, the two could just as well have the same name.
But for more complex mappings, things start to get complex, too:
Say we have two arguments, `-v` and `--version`, that can be used interchangeably.
If they would map to two variables, `-v` and `--version`,
the program would have to have knowledge about the arguments being interchangeable,
in order to correctly interpret its inputs.
As leaking this knowledge to the program would be undesirable,
parsers usually work around this by assigning the value of one argument to both variables.
But now we are in a situation where we have two dependant variables that always have the same value.
A less verbose solution is just letting both arguments map to the same variable (the [`key`](#key) field):
```js
const {string} = require('shargs/opts')
const opts = [
string('version', ['-v', '--version'])
]
```
A special situation of two arguments mapping to the same variable is, when the arguments belong to separate options.
This frequently occurs for [`flag`](#flag) and [`bool`](#bool) options that have a [`complement`](#complement):
```js
const {flag} = require('shargs/opts')
const opts = [
flag('fun', ['--fun']),
flag('fun', ['--no-fun'], {reverse: true})
]
```
In the example, `--fun` adds `1` to the flag count, while `--no-fun` adds `-1` due to [`reverse`](#reverse)
(assuming the parser has the [`reverseFlags`](#reverseFlags) stage).
But we have other possible mappings yet to explore:
Situations, where one argument maps to two different variable names.
Say we have a `--birthday` argument and the `birthday` and `age` variables.
`birthday` is a string in date format, while `age` is a number holding the current age,
transformed by the custom `ageAsNumber` stage.
This kind of mapping is only possible if the parser's arguments are independent of the program's variables.
So, command-line options have a `key` field, because:
1. Separating internal variable names from external argument names is a good practice.
2. Separating argument and variable names enables functionality that would otherwise not be possible.
3. Separating arguments and variables makes interpreting variables less verbose for programs.
If you really do not need `key` fields and wish to use just argument names instead,
it is straight forward to adjust the type function syntax accordingly:
```js
const array2 = types => (args = [], fields = {}) => ({
key: args.length > 0 ? args[0] : undefined,
args,
types,
...fields
})
const number2 = array2(['number'])
// ...
```
Can I use custom command-line option types like date?
Yes, you can add and use your own option types.
Both, the command-line options DSL and the parser functions have been designed with this in mind:
Say you want to add your own custom `date` type.
First, you need to add a [command-line option](#command-line-options) of that type:
```js
const {array} = require('shargs/opts')
const date = array(['date'])
```
A `date` is an option that takes exactly one argument, whose type is described as `'date'`.
Now we have an option, we may want to write parser stages that work with `dates`.
How about a stage that transforms dates to their millisecond representation:
```js
const {traverseOpts} = require('shargs/parser')
function dateToMillis ({errs = [], opts = []} = {}) {
const isDate = ({types}) => (
Array.isArray(types) &&
types.length === 1 &&
types[0] === 'date'
)
const toMillis = string => new Date(string).getTime()
const dateToMillis = opt => ({
opts: [{
...opt,
...(Array.isArray(opt.values)
? {values: opt.values.map(toMillis)}
: {}
)
}]
})
return traverseOpts(isDate)(dateToMillis)({errs, opts})
}
```
This parser stage works alongside the other parser stages.
Note, that a real implementation would test much more edge cases, like dates that occur in arrays.
Can I use comma-separated values to define arrays?
shargs-parser does not include a parser stage
to split comma-separated values into arrays.
But it is easy enough to write a stage yourself:
We are inventing a new option type for this FAQ: `commas`:
```js
const {array} = require('shargs/opts')
const commas = array(['commas'])
```
The `commas` type function is used to mark options we want to split.
We then write a custom [`opts` stage](#opts-stages) to perform the splitting:
```js
const {traverseOpts} = require('shargs/parser')
const isCommas = ({key, types, values}) => (
typeof key !== 'undefined' &&
Array.isArray(types) && types.indexOf('commas') > -1 &&
Array.isArray(values) && values.length === types.length
)
const transformCommaArray = opt => {
let values = []
let types = []
for (let i = 0; i < opt.values.length; i++) {
const value = opt.values[i]
const type = opt.types[i]
if (type === 'commas') {
const elements = value.split(',')
values = [...values, ...elements]
types = [...types, ...Array.from({length: elements.length}, () => 'string')]
} else {
values.push(value)
types.push(type)
}
}
return {opts: [{...opt, types, values}]}
}
const splitCommas = traverseOpts(isCommas)(transformCommaArray)
```
`splitCommas` may now be used with options of type `commas`!
So why doesn't `shargs-parser` support comma-separated values by default?
The reason is that using comma-separated values is just not that common.
And if you nonetheless need comma-separated values, it is simple enough to implement yourself.
Why are --no-* arguments not reversed by the bestGuess* stages?
The reason is because there is no simple way to opt-out of this functionality, once it is employed.
You could add an optOutReverse parameter to each bestGuess* stage, I guess,
but that would clutter the stages' signatures.
So shargs decided to leave interpreting these arguments to the individual programs.
Can I have command-line options with 0..1 values?
An example for such an option would be ternary logics types,
like true, false, unknown,
that could be represented as a mixture of flags
and bools.
Shargs does not support such options out of the box, but you can implement them with some gotchas:
We generally recommend against using options with 0..1 cardinalities in programs.
This is also why shargs does not support it.
A better approach is using an enumeration, implemented with the [`only`](#only) options field
and the [`restrictToOnly`](#restrictToOnly) parser stage.
If you want to use it anyway, here is how you could do it in shargs:
Flags give you only two cases, the presence of the flag (`true` if [`flagsAsBools`](#flagsAsBools) is used),
and its absence (`unknown`):
```js
const {flag} = require('shargs/opts')
const fun = flag('fun', ['--fun'])
```
You could add a third case by using only `flags` by defining a complement:
```js
const {complement} = require('shargs/opts')
const noFun = complement('--no-')(fun)
```
Which is the same as writing:
```js
const noFun = flag('fun', ['--no-fun'], {reverse: true})
```
If you provide `--fun`, the `fun` variable is set to `true`, on `--no-fun` it is set to `false`,
and providing neither `--fun`, nor `--no-fun` would mean `unknown`.
You could implement the same behavior with an option that takes none or one argument,
by using a combination of variable length arrays,
aka [`subcommands`](#subcommand) and a custom command-line options field.
The general idea is to mark a `subcommand` as `threeValued` with a field,
and then transform it to a custom type in the opts stage.
First, let us define an option:
```js
const {stringPos, subcommand} = require('shargs/opts')
const funOpts = [
stringPos('threeValues')
]
const fun = subcommand(funOpts)('fun', ['--fun'], {threeValued: true})
```
Now, let us define an [`opts`](#opts-stages) stage that transforms the `subcommand`:
```js
const {traverseOpts} = require('shargs/parser')
const isThreeValued = ({threeValued}) => threeValued === true
const toThreeValued = opt => {
const types = ['threeValued']
let values = ['unknown']
if (Array.isArray(opt.values)) {
const threeValues = opt.values.find(opt => opt.key === 'threeValues')
values = threeValues.values || ['true']
}
return {
opts: [
{...opt, types, values: values.slice(0, 1), opts: undefined}
]
}
}
const subcommandsToThreeValued = traverseOpts(isThreeValued)(toThreeValued)
```
`subcommandsToThreeValued` only transforms `subcommands` that have the `threeValued` field.
For each `subcommand`, it checks, whether the `subcommand` is not present (`unknown`),
it is present but has no values (`true`), or if it is present and has at least one value,
(`true` if the value is `true`, `false` if it is `false`, otherwise `unknown`).
Note that this sample implementation is very brittle and should not be used as presented in a program.
Can I use enums?
Yes, you can use enums with a combination of string command-line options,
the only options field,
and the restrictToOnly parser stage:
```js
const {string} = require('shargs/opts')
const answers = string('answers', ['-a'], {only: ['yes', 'no', 'maybe']})
```
Can I use keys like 'a.b', indicating object fields?
Some command-line parsers allow arguments of the form --a.b 42,
whose values are stored in nested objects {a: {b: 42}}.
Shargs does not provide this functionality.
However, it is very easy to write your own parser stage for it:
First, let us write a helper function for traversing `args` objects:
```js
function traverseKeys (p) {
return f => ({errs, args}) => Object.keys(args).reduce(
({errs, args: obj}, key) => {
const val = args[key]
if (!Array.isArray(val) && typeof val === 'object') {
obj[key] = traverseKeys(p)(f)(val)
}
if (p(key)) {
const {[key]: _, ...rest} = obj
obj = {...rest, ...f(key, val)}
}
return {errs, args: obj}
},
{errs, args}
)
}
```
Using `traverseKeys`, we can implement a `nestKeys` [`args` stage](#args-stages):
```js
const _ = require('lodash')
const hasDots = key => key.indexOf('.') > -1
const nestValue = (key, val) => {
const obj = {}
_.set(obj, key, val)
return obj
}
const nestKeys = traverseKeys(hasDots)(nestValue)
```
The `nestKeys` args stage should now nest the values into an object.
The reason why shargs does not include such a stage by default is,
that this is a niche case that can be either implemented after parsing,
or is easy enough to implement yourself.
Why do shargs' functions have several parameter lists?
Many functions have an unusual signature, like text(string)(style)
and the question arises, why it is not text(string, style), instead.
The reason has to do with function composition
and tacit programming:
[`shargs`][shargs] builds command-line parsers and usage documentation by composing parser
and usage functions with functions it calls *combinators*.
An exemplary combinator function is layout(functions)(style).
`layout` takes a list of `functions` that have a common signature:
They take a [`style`](#style), and return a string.
Next, it takes its own `style` parameter and feeds it to each function, getting a list of strings.
Then it concatenates all strings together, which results in a string:
```js
const {layout, text} = require('shargs/usage')
const style = {line: [{width: 10}]}
const string = layout([
text('First.'),
text('Second.')
])(style)
// string === 'First. \nSecond. \n'
```
What [`layout`](#layout) basically gives us is a way to provide only one `style` parameter to a list of functions,
instead of one parameter per function.
But why does [`layout`](#layout) have to have such a weird signature?
Let us assume we had the following `layout2` and `text2` functions, instead:
```js
const {layout, text} = require('shargs/usage')
const layout2 = (functions, style) => layout(functions)(style)
const text2 = (string, style) => text(string)(style)
```
How could we concatenate strings only using `text2`?
```js
const style = {line: [{width: 10}]}
const string = text2('First.', style) + text2('Second.', style)
// string === 'First. \nSecond. \n'
```
Do you see how the `style` parameter is repeated for every function?
It gets worse if you have more functions.
Now let us use `layout2`:
```js
const style = {line: [{width: 10}]}
const string = layout2([
style => text2('First.', style),
style => text2('Second.', style)
], style)
// string === 'First. \nSecond. \n'
```
See how `style` is still repeated and we do not have the advantage of only providing it once?
Actually, using `layout2` looks worse than using just `text2`!
But we can do better and rewrite the same example with `text` and two parameter lists:
```js
const {text} = require('shargs/usage')
const style = {line: [{width: 10}]}
const string = layout2([
style => text('First.')(style),
style => text('Second.')(style)
], style)
// string === 'First. \nSecond. \n'
```
And then we can apply an optimization:
See how we define a function that takes a `style` and feed it to a function `text('First.')` that takes a `style`?
This is redundant, and we can just leave out `style` altogether:
```js
const {text} = require('shargs/usage')
const style = {line: [{width: 10}]}
const string = layout2([
text('First.'),
text('Second.')
], style)
// string === 'First. \nSecond. \n'
```
Now we do not repeat `style` for every function!
The code is much shorter and is easier to read.
And we can do even better by using a signature like `layout`.
Because then `layout` is also a function that takes a `style` and returns a string,
like `text`, and can be used inside other `layout` functions!
```js
const {layout, text} = require('shargs/usage')
const style = {line: [{width: 10}]}
const firstSecond = layout([
text('First.'),
text('Second.')
])
const andThird = layout([
firstSecond,
text('Third.')
])
const string = andThird(style)
// string === 'First. \nSecond. \nThird. \n'
```
And although we have five functions that each take a `style` parameter, we only have to apply it once.
Shargs employs tacit programming techniques to reduce boilerplate in its DSLs.
A side-effect is that function signatures are weird (the technical term is *curried*).
Some JavaScript libraries like [Ramda][ramda] and [lodash/fp][lodash-fp] use a technique called *auto-currying*.
If `layout` would be auto-curried, it would have the signatures of `layout`
and `layout2` at the same time and you could choose which one to use.
Shargs decided against auto-currying its functions,
since it is simple enough to [`curry`](https://ramdajs.com/docs/#curry) your functions yourself if you wanted:
```js
const {curry} = require('ramda')
const {layout} = require('shargs/usage')
const curriedLayout = curry((fs, style) => layout(fs)(style))
```
`curriedLayout` can now be used like `layout` and like `layout2`.
## Comparison to Related Libraries
shargs
yargs
commander.js
minimist
Self-description
Shargs turns command-line arguments parsing inside out
and gives you fine-grained control over parser stages and usage docs.
Yargs helps you build interactive command line tools, by parsing arguments and generating an elegant user interface.
The complete solution for node.js command-line interfaces, inspired by Ruby's commander.
Minimist is the guts of optimist's argument parser without all the fanciful decoration.
Focus
A command-line parser library with a focus on enabling developers to easily
and quickly build their own parsers of just the right size.
A large parser with lots of features with a focus on providing the options out of the box.
A medium parser with a strong focus on a textual DSL that makes it easy to define options.
A tiny parser, mostly without an options schema, with a strong focus on optimistic parsing.
First Commit
January 14th 2020
September 10th 2010
August 14th 2011
June 25th 2013
Customize Parsing
Pick and choose your parser checks and stages,
write and use custom checks and stages,
and optionally define command-specific parsers.
You can
turn on and off
some of yargs' parsing features,
and use a kind of middleware
similar to shargs' args stages.
You may specify a function to do
custom processing of option values.
None that I am aware of.
Customize Usage Docs
Use a DSL with many options to build
custom usage documentation layouts
with fine-grained control over styles.
Allows specifying the scriptName,
a usage
string,
an epilogue,
examples as strings,
and the number of columns after which to
wrap.
Display extra information by
listening to the --help event,
customize program name and usage description,
and add custom description text.
None that I am aware of.
## Reporting Issues
Please report issues [in the tracker][issues]!
## Contributing
We are open to, and grateful for, any contributions made by the community.
By contributing to shargs, you agree to abide by the [code of conduct][code].
Please read the [contributing guide][contribute].
## License
Shargs is [MIT licensed][license].
Logo created by brgfx (www.freepik.com).
[actions]: https://github.com/Yord/shargs/actions
[code]: https://github.com/Yord/shargs/blob/master/CODE_OF_CONDUCT.md
[contribute]: https://github.com/Yord/shargs/blob/master/CONTRIBUTING.md
[issues]: https://github.com/Yord/shargs/issues
[license]: https://github.com/Yord/shargs/blob/master/LICENSE
[lodash]: https://github.com/lodash/lodash
[lodash-fp]: https://github.com/lodash/lodash/wiki/FP-Guide
[node]: https://nodejs.org/
[npm-package]: https://www.npmjs.com/package/shargs
[ramda]: https://ramdajs.com/docs/#mergeDeepLeft
[shargs]: https://github.com/Yord/shargs
[shargs-core]: https://github.com/Yord/shargs-core
[shargs-example-async-deepthought]: https://github.com/Yord/shargs-example-async-deepthought
[shargs-example-repl]: https://github.com/Yord/shargs-example-repl
[shargs-example-sync-deepthought]: https://github.com/Yord/shargs-example-sync-deepthought
[shargs-example-sync-deepthought-config-env-argv]: https://github.com/Yord/shargs-example-sync-deepthought-config-env-argv
[shargs-example-sync-sql]: https://github.com/Yord/shargs-example-sync-sql
[shargs-opts]: https://github.com/Yord/shargs-opts
[shargs-parser]: https://github.com/Yord/shargs-parser
[shargs-repl]: https://github.com/Yord/shargs-repl
[shargs-tutorial-git]: https://github.com/Yord/shargs-tutorial-git
[shargs-usage]: https://github.com/Yord/shargs-usage
[shield-license]: https://img.shields.io/npm/l/shargs?color=yellow&labelColor=313A42
[shield-node]: https://img.shields.io/node/v/shargs?color=red&labelColor=313A42
[shield-npm]: https://img.shields.io/npm/v/shargs.svg?color=orange&labelColor=313A42
[shield-prs]: https://img.shields.io/badge/PRs-welcome-green.svg?labelColor=313A42
[shield-unit-tests-linux]: https://github.com/Yord/shargs/workflows/linux/badge.svg?branch=master
[shield-unit-tests-macos]: https://github.com/Yord/shargs/workflows/macos/badge.svg?branch=master
[shield-unit-tests-windows]: https://github.com/Yord/shargs/workflows/windows/badge.svg?branch=master
[then]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise/then