⑂🐚 yzx

yzx is a fork of zx that can be executed concurrently (in web servers for example). See zx issue 252 for the reason of the fork. It is called yzx because 'Y' looks like both the symbol of a fork and the symbol of concurrency.

#!/usr/bin/env yzx

await $`cat package.json | grep name`

let branch = await $`git branch --show-current`
await $`dep deploy --branch=${branch}`

await Promise.all([
  $`sleep 1; echo 1`,
  $`sleep 2; echo 2`,
  $`sleep 3; echo 3`,
])

let name = 'foo bar'
await $`mkdir /tmp/${name}`

Bash is great, but when it comes to writing scripts, people usually choose a more convenient programming language. JavaScript is a perfect choice, but standard Node.js library requires additional hassle before using. The yzx package provides useful wrappers around child_process, escapes arguments and gives sensible defaults.

Install

npm i -g yzx

Requirement

Node.js >= 14.13.1

Documentation

Write your scripts in a file with .mjs extension in order to be able to use await on top level. If you prefer the .js extension, wrap your scripts in something like void async function () {...}().

Add the following shebang to the beginning of your yzx scripts:

#!/usr/bin/env yzx

Now you will be able to run your script like so:

chmod +x ./script.mjs
./script.mjs

Or via the yzx executable:

yzx ./script.mjs

All functions ($, sleep, etc) are available straight away without any imports.

Or import globals explicitly (for better autocomplete in VS Code).

import 'yzx/globals'

$`command`

Executes a given string using the spawn function from the child_process package and returns ProcessPromise<ProcessOutput>.

Everything passed through ${...} will be automatically escaped and quoted.

let name = 'foo & bar'
await $`mkdir ${name}`

There is no need to add extra quotes. Read more about it in quotes.

You can pass an array of arguments if needed:

let flags = [
  '--oneline',
  '--decorate',
  '--color',
]
await $`git log ${flags}`

If the executed program returns a non-zero exit code, ProcessOutput will be thrown.

try {
  await $`exit 1`
} catch (p) {
  console.log(`Exit code: ${p.exitCode}`)
  console.log(`Error: ${p.stderr}`)
}

ProcessPromise

class ProcessPromise<T> extends Promise<T> {
  readonly stdin: Writable
  readonly stdout: Readable
  readonly stderr: Readable
  readonly exitCode: Promise<number>
  pipe(dest): ProcessPromise<T>
  kill(signal = 'SIGTERM'): Promise<void>
}

The pipe() method can be used to redirect stdout:

await $`cat file.txt`.pipe(process.stdout)

Read more about pipelines.

ProcessOutput

class ProcessOutput {
  readonly stdout: string
  readonly stderr: string
  readonly exitCode: number
  toString(): string
}

Methods

$.cd()

Changes the current working directory.

$.cd('/tmp')
await $`pwd` // outputs /tmp

Functions

question()

A wrapper around the readline package.

Usage:

let bear = await question('What kind of bear is best? ')
let token = await question('Choose env variable: ', {
  choices: Object.keys(process.env)
})

In second argument, array of choices for Tab autocompletion can be specified.

function question(query?: string, options?: QuestionOptions): Promise<string>
type QuestionOptions = { choices: string[] }

sleep()

A wrapper around the setTimeout function.

await sleep(1000)

nothrow()

Changes behavior of $ to not throw an exception on non-zero exit codes.

function nothrow<P>(p: P): P

Usage:

await nothrow($`grep something from-file`)

// Inside a pipe():

await $`find ./examples -type f -print0`
  .pipe(nothrow($`xargs -0 grep something`))
  .pipe($`wc -l`)

If only the exitCode is needed, you can use the next code instead:

if (await $`[[ -d path ]]`.exitCode == 0) {
  ...
}

// Equivalent of:

if ((await nothrow($`[[ -d path ]]`)).exitCode == 0) {
  ...
}

Configuration

$.shell

Specifies what shell is used. Default is which bash.

$.shell = '/usr/bin/bash'

Or use a CLI argument: --shell=/bin/bash

$.prefix

Specifies the command that will be prefixed to all commands run.

Default is set -euo pipefail;.

Or use a CLI argument: --prefix='set -e;'

$.quote

Specifies a function for escaping special characters during command substitution.

$.verbose

Specifies verbosity. Default is true.

In verbose mode, the yzx prints all executed commands alongside with their outputs.

Or use a CLI argument --quiet to set $.verbose = false.

Polyfills

__filename & __dirname

In ESM modules, Node.js does not provide __filename and __dirname globals. As such globals are really handy in scripts, yzx provides these for use in .mjs files (when using the yzx executable).

FAQ

Passing env variables

process.env.FOO = 'bar'
await $`echo $FOO`

Passing array of values

If array of values passed as argument to $, items of the array will be escaped individually and concatenated via space.

Example:

let files = [...]
await $`tar cz ${files}`

Importing from other scripts

It is possible to make use of $ and other functions via explicit imports:

#!/usr/bin/env node
import {$} from 'yzx'
await $`date`

Scripts without extensions

If script does not have a file extension (like .git/hooks/pre-commit), yzx assumes that it is an ESM module.

Markdown scripts

The yzx can execute scripts written in markdown (docs/markdown.md):

yzx docs/markdown.md

TypeScript scripts

import {$} from 'yzx'
// Or
import 'yzx/globals'

void async function () {
  await $`ls -la`
}()

Compile the TypeScript to JS and run it. Or use something like ts-node.

ts-node script.ts

Executing remote scripts

If the argument to the yzx executable starts with https://, the file will be downloaded and executed.

yzx https://medv.io/example-script.mjs

yzx https://medv.io/game-of-life.mjs

Executing scripts from stdin

The yzx supports executing scripts from stdin.

yzx <<'EOF'
await $`pwd`
EOF

Using in a concurrent environnement (web servers, etc)

To be able to yzx in a web server, the $ object must not be a global shared object, because each request may need its own current working directory (for example). So yzx exports a global function YZX to create new instances of $.

import { YZX } from 'yzx'

const $ = YZX()
await $`pwd`
...

License

Apache-2.0