In this article, an overview of MRI package is provided with a usage example picked from Changesets source code.

MRI package:

You can use MRI package to quickly scan for flags and arguments. It is an alternative to yargs-parser.

Install

npm install - save mri

Usage

// Example CLI with options 
$ demo-cli - foo - bar=baz -mtv - hello world

The following code is picked from MRI npm package documentation.

const mri = require('mri');
const argv = process.argv.slice(2);
mri(argv);
//=> { _: ['hello', 'world'], foo:true, bar:'baz', m:true, t:true, v:true }
mri(argv, { boolean:['bar'] });
//=> { _: ['baz', 'hello', 'world'], foo:true, bar:true, m:true, t:true, v:true }
mri(argv, {
 alias: {
 b: 'bar',
 foo: ['f', 'fuz']
 }
});
//=> { _: ['hello', 'world'], foo:true, f:true, fuz:true, b:'baz', bar:'baz', m:true, t:true, v:true }

MRI usage in Changesets:

MRI is found to be imported in Changesets CLI package

When you add a changeset using the command npx changeset add or npx changeset, these are accessed in the CLI package as shown below.

const args = process.argv.slice(2);

Parsing CLI args in changeset

The below code shows how mri used in Changeset CLI package

const parsed = mri(args, {
 boolean: ["sinceMaster", "verbose", "empty", "open", "gitTag", "snapshot"],
 string: [
 "output",
 "otp",
 "since",
 "ignore",
 "tag",
 "snapshot",
 "snapshotPrereleaseTemplate",
 ],
 alias: {
 // Short flags
 v: "verbose",
 o: "output",
 // Support kebab-case flags
 "since-master": "sinceMaster",
 "git-tag": "gitTag",
 "snapshot-prerelease-template": "snapshotPrereleaseTemplate",
 // Deprecated flags
 "update-changelog": "updateChangelog",
 "is-public": "isPublic",
 "skip-c-i": "skipCI",
 },
 default: {
 gitTag: true,
 },
});

parsed value will look like below, I deduced this based on the documentation:

{
 // string value (if you have used 'add' in npx changeset add)
 ['add'],
// boolean values
 "sinceMaster": true, 
 "verbose": true, 
 "empty": true, 
 "open": true, 
 "gitTag": true, 
 "snapshot": true
// string values
 // Note: if you have passed these options in your CLI, these keys will be parsed as string, no matter the what you pass in
 // example: if you pass in - otp=123, 123 here, even though is a number, gets parsed as string since otp is configured to be parsed as
 // string in the above code
 "output",
 "otp",
 "since",
 "ignore",
 "tag",
 "snapshot",
 "snapshotPrereleaseTemplate",
// The alias option in mri allows you to define alternative names (aliases) for CLI arguments.
 // This is particularly useful for supporting:
// Short flags: Such as -v for - verbose.
 // Kebab-case flags: Allowing flags like - since-master to map to camelCase variables in JavaScript (e.g., sinceMaster).
 // Deprecated flags: If you want to support older names for backward compatibility but still map them to the current property names.
}

parsed variable is used in a function named run imported from /run.ts

// run function call
run(parsed._, parsed, cwd).catch((err)

The first parameter is pared._ because in the documentation, it is provided that parsed commands like ‘add’ looks like { _: [‘add’]}

// run function definition
export async function run(
 input: string[],
 flags: { [name: string]: any },
 cwd: string
) {

parsed contains mri parsed object based on the CLI args and the configuration set for booleans, strings, defaults, aliases.

cwd is a current working directory, you can get this with process.cwd()

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Scan for CLI flags and arguments using MRI package